US9270385B2  System and method for quantum based information transfer  Google Patents
System and method for quantum based information transfer Download PDFInfo
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 US9270385B2 US9270385B2 US14/510,464 US201414510464A US9270385B2 US 9270385 B2 US9270385 B2 US 9270385B2 US 201414510464 A US201414510464 A US 201414510464A US 9270385 B2 US9270385 B2 US 9270385B2
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 H—ELECTRICITY
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 H04B10/00—Transmission systems employing electromagnetic waves other than radiowaves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
 H04B10/70—Photonic quantum communication

 B—PERFORMING OPERATIONS; TRANSPORTING
 B82—NANOTECHNOLOGY
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 B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic

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 G06N10/00—Quantum computers, i.e. computer systems based on quantummechanical phenomena

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 H—ELECTRICITY
 H04—ELECTRIC COMMUNICATION TECHNIQUE
 H04B—TRANSMISSION
 H04B10/00—Transmission systems employing electromagnetic waves other than radiowaves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
 H04B10/50—Transmitters

 H—ELECTRICITY
 H04—ELECTRIC COMMUNICATION TECHNIQUE
 H04B—TRANSMISSION
 H04B10/00—Transmission systems employing electromagnetic waves other than radiowaves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
 H04B10/60—Receivers

 B—PERFORMING OPERATIONS; TRANSPORTING
 B82—NANOTECHNOLOGY
 B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
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 Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSSSECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSSREFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract
Description
This application claims priority to and the benefit of U.S. patent application Ser. No. 13/948,660, filed Jul. 23, 2013 by Ronald E. Meyers and Keith S. Deacon, entitled Quantum Based Information Transfer System And Method,” which is a continuationinpart of and claims priority to application Ser. No. 12/705,566, entitled “Quantum Based Information Transmission System and Method,” filed Feb. 12, 2010, which issued as U.S. Pat. No. 8,503,885 on Aug. 6, 2013, by Ronald E. Meyers and Keith S. Deacon the inventors herein, which in turn claims priority to U.S. application Ser. No. 11/196,738, filed Aug. 4, 2005, which issued as U.S. Pat. No. 7,660,533 on Feb. 9, 2010, by Ronald E. Meyers and Keith S. Deacon, and U.S. Provisional Patent Application Ser. No. 60/598,537 filed Aug. 4, 2004, all four of which are incorporated herein by reference.
The invention described herein may be manufactured, used, and licensed by or for the United States Government without the payment of a royalty.
This invention relates in general to methods and apparatus for processing, compression, and/or transmission of data based upon quantum properties. Quantum properties include quantum entanglement and quantum teleportation of information, which is linked to the property of quantum entanglement. Quantum entanglement can exist between any two quantum systems such as between two photons, two atomic/ionic systems, or between a photon and an atom/ion based quantum system. The prior art system depicted in
Quantum communications may sometimes be used in conjunction with compression techniques involving the usage of qubits, as shown in
The present invention is directed to a preferred embodiment system for communicating data comprising a sender subsystem; a receiver subsystem; at least one data input configured to input data into the sender subsystem; at least one entangled photon source configured to output entangled photon pairs; first photons of the pairs of entangled photons outputted by the at least one photon source being processed by one of the sender or receiver subsystem; second photons of the pairs of entangled photons being processed by the other of the sender or receiver subsystem; a photonic element configured to receive the first photons of the pairs of entangled photons and enable interference therebetween; at least one absorber configured to absorb the first photons of the pairs of entangled photons after passage through the beam splitter, the absorbance of the first photons of the pairs of entangled photons operating to transfer the properties of the entanglement to the second photons of the pairs of entangled photons; and a Bell state measurement element operatively associated with the receiver subsystem; the Bell state measurement element configured to measure the second photons of the pairs of entangled photons.
Optionally, either the at least one entangled photon source or the reception of first photons of the pairs of entangled photons by the first beam splitter may be controlled by an operator or computer to enable the transmission of a message. Optionally, the photonic element may take the form of a beam splitter and the at least absorber may be at least one detector that is configured to measure the Bell state of the first photons of the pairs of entangled photons passing through the first beam splitter. This measurement would correlate to the Bell state measured by the Bell state measurement element operatively associated with the receiver.
As a further option, the system may comprise an interrupt, such as a shutter, for example, controlled by the operator or a computer configured to prevent one or more of the first photons of the pairs of entangled photons from being inputted into the first beam splitter thereby operating to transmit an encoded message. The sender subsystem may further comprise at least one processor operatively associated with the interrupt and the at least one detector and at least one delay element, the at least one delay element configured to delay photons such that photons emitted from the at least one entangled photon source at different times are inputted synchronously into the first beam splitter operatively associated with the sender and the Bell state measurement element operatively associated with the receiver.
Optionally, the at least one entangled photon source comprises first and second entangled photon sources, the first entangled photon source being operatively associated with the sender subsystem and the second entangled photon source being operatively associated with the receiver subsystem. In addition, the at least one absorber may comprise at least one detector configured to measure the Bell state, such that the measurement of the Bell state of the first photons of the pairs of entangled photons occurs at substantially the same time as the measurement by the Bell state measurement element operatively associated with the receiver subsystem. Optionally, delay elements may be positioned within at least one of the sender or receiver subsystems to ensure coincidence of measurements of the Bell states. Optionally, sender subsystem further comprises a second beam splitter operatively associated with the at least one entangled photon source, the second beam splitter configured to split the first photons into first and second paths, the first and second paths operating to pass photons from the second beam splitter to the first beam splitter, the second path comprising a first delay element, the first delay element being configured such that first photons from the first and second paths enter the first beam splitter synchronously. Optionally, the receiver subsystem may further comprise a third beam splitter operatively associated with the at least one entangled photon source the third beam splitter configured to split the second photons into third and fourth paths, the third and fourth paths operating to pass photons from the third beam splitter to the Bell state measurement element operatively associated with the receiver subsystem, the fourth path comprising a second delay element, the second delay element being configured such that second photons from the third and fourth paths enter the Bell State measurement element synchronously.
The present invention is also directed to an alternate preferred embodiment system for communicating data comprising a transmitter subsystem; a receiver subsystem; at least one data input configured to input data into the transmitter subsystem; first, second and third entangled photon sources configured to output entangled photon pairs; first photons of the pairs of entangled photons outputted by the first, second and third entangled photon sources being processed by one of the transmitter or receiver subsystems; second photons of the pairs of entangled photons outputted by the first, second and third entangled photon sources being processed by the other of the transmitter or receiver subsystems; a first Bell state measurement element operatively associated with the transmitter; the first Bell state measurement element configured to measure the first photons of the pairs of entangled photons from the first and second entangled photon sources; a second Bell state measurement element operatively associated with the receiver system; the Bell state measurement element configured to measure the second photons of the pairs of entangled photons from the first and second entangled photon sources; a data source for the input of information; a third Bell state measurement element operatively associated with the transmitter, receiver and the data source, the third Bell state measurement element operative to measure photons representing data from the data source in conjunction with the one of pairs of photons from the third photon source; a unitary transform device operatively associated with the receiver subsystem, the unitary transform device configured to receive the other of the pairs of photons from the third entangled photon source and to output photons representing data from the data source; and an output measurement element operatively associated with the receiver; the output measurement element configured to measure the outputted photons from the unitary transform device representing data from the data source.
As an option, the alternate preferred embodiment may comprise at least one processor operatively connected to the unitary transform device and the second Bell state measurement element wherein upon being measured at the Bell state measurement element the entanglement is transferred from the first of the first photons of the pairs of entangled photons from the first and second photon sources to the second photons of the pairs of entangled photons from the first and second photon sources, and wherein the second Bell state measurement element measures the results of the swapped entanglement and transfers the results to the at least one processor which supplies the Bell state measured by the second Bell state measurement element to the unitary transform device which is used to output data from the data source. As a further option, the first, second and third entangled photon sources may be synchronously emitted. Optionally, the alternate preferred embodiment comprises an interrupt configured to prevent one or more of the first photons of the pairs of entangled photons from being measured by the first Bell state measurement device, the interrupt being operable to send an encoded message from the sender subsystem to the receiver subsystem.
The present invention is also directed to an alternate preferred embodiment system for communicating data comprising a transmitter subsystem; a receiver subsystem; a data source configured to input information in the form of qubits; the information to be transmitted from the transmitter to the receiver subsystem; at least one entangled photon source configured to output entangled photon pairs; first photons of the at least one entangled photon sources being inputted into the transmitter subsystem and second photons of the at least one entangled photon source being inputted into to the receiver subsystem; a first photonic element having two inputs; one input configured for input of a qubit from the data source and one input configured for input of a first photons of pairs of entangled photons from the at least one entangled photon source; the first photonic element having two outputs; first and second Bell state measurement elements operatively associated with the transmitter subsystem, each having first and second inputs and each of the first inputs operatively connected to one of the output ports of the first photonic element; the second inputs of the first and second Bell state measurement elements configured to receive first photons from the at least one entangled photon source; at least one processor operatively associated with the receiver subsystem; and at least one receiver Bell state measurement element operatively associated with the receiver subsystem; the at least one receiver Bell state measurement element configured to receive as an input at least one of the second photons of the pairs of photons from the at least one entangled photon source and provide a measurement to the at least one processor; whereby through the process of entanglement swapping, information is transferred from the first photons to the second photons of the pairs of photons from the at least one entangled photon source, and though measurement by the at least one receiver Bell state measurement element, information is transferred from the transmitter to the receiver subsystem.
Optionally, the first photonic element is a beam splitter and the first and second Bell state measurement devices each comprise at least one beam splitter and at least two detectors. The receiver subsystem may comprise a unitary transform device operatively associated with the at least one processor that is configured to receive as input second photons of the pairs of photons from the at least one entangled photon source; the second photons having swapped entanglement from the first photons of the pairs of photons from the at least one entangled photon source, such that qubits of data are transferred from the transmitter subsystem to the receiver subsystem through the process of swapped entanglement. When measurement is undertaken at the second Bell state measurement element, entanglement is swapped to the second photons of the first entangled photon source at the unitary transform device and the second photons of the second and third entangled photon sources inputted into the receiver Bell state measurement element; and the unitary transform device processes the information contained in the second photons from the first entangled photon source in conjunction with information outputted from the receiver Bell state measurement device to derive the information contained in the qubits.
As a further option, the alternate preferred embodiment comprises at least one delay element controlled by the at least one processor, the first, second and receiver Bell state measurement devices are synchronously operated, and the at least one processor comprises a first processor operatively associated with the transmitter subsystem and a second processor operatively associated with the receiver subsystem and wherein the first and second processors operate to control the at least one delay element.
The embodiments of the invention and the various features and advantageous details thereof are explained more fully with reference to the nonlimiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale. Descriptions of wellknown components and processing techniques are omitted so as to not unnecessarily obscure the embodiments of the invention. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments of the invention may be practiced and to further enable those of skilled in the art to practice the embodiments of the invention. Accordingly, the examples should not be construed as limiting the scope of the embodiments of the invention.
This description and the accompanying drawings that illustrate inventive aspects and embodiments should not be taken as limitingthe claims define the protected invention. Various changes may be made without departing from the spirit and scope of this description and the claims. In some instances, wellknown structures and techniques have not been shown or described in detail in order not to obscure the invention. Additionally, the drawings are not to scale. Relative sizes of components are for illustrative purposes only and do not reflect the actual sizes that may occur in any actual embodiment of the invention. Like numbers in two or more figures represent the same or similar elements. Elements and their associated aspects that are described in detail with reference to one embodiment may, whenever practical, be included in other embodiments in which they are not specifically shown or described. For example, if an element is described in detail with reference to one embodiment and is not described with reference to a second embodiment, the element may nevertheless be claimed as included in the second embodiment.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the full scope of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. For example, when referring first and second entangled photon regions, these terms are only used to distinguish one entangled photon source, region, element, component, layer or section from another source, region, element, component, layer or section. Thus, a first source, region, element, component, layer or section discussed below could be termed a second source, region, element, component, layer or section without departing from the teachings of the present invention.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
A quantum tree for the communication of information using qubits is depicted in
In preferred embodiments shown in
Due to the properties of the qubits, the systems of
In terms of data flow, a preferred methodology comprises splitting a wave function representative of an input data set into an arbitrarily oriented elliptical polarization state and a comparator wave function state, the comparator wave function state being transmitted to a detector. In the embodiments of
A data communication system operating on quantum computation principles includes a light source having a photon output coding an input data set. A TypeI or TypeII nonlinear crystal converts the photon output into an entangled photon output. An arbitrarily oriented polarization state is assured by passing the entangled photon output through a polarization modulator 44 and a phase modulator 46. A polarization interferometer 122 (
By way of background, Long, G., et al. “Efficient scheme for initializing a quantum register with an arbitrary superposed state,” Physical Review A, vol. 64, Issue 1, 014303 (2001) (hereinafter Long, et al. (hereby incorporated by reference)) discloses a scheme that can most generally initialize a quantum register with an arbitrary superposition of basis states as a step in quantum computation and quantum information processing. Long, et al. went beyond a simple quantum state such as i_{1}, i_{2}, i_{3}, . . . i_{n}> with i_{j }being either 0 or 1, to construct an arbitrary superposed quantum state. Long, et al. utilized the implementation of O(Nn^{2}) standard 1 and 2bit gate operations, without introducing additional quantum bits. Long, et al. presents a general scheme that initializes a quantum register without introducing additional qubits wherein the quantum circuit of a 3qubit system transforms the state 1000> to an arbitrary superposed state with N=2^{3 }basis states. The terminology arbitrary superposed quantum state as used herein correlates to the construction of an arbitrary superposed quantum state as described, inter alia, in Long, et al.
As depicted in
A wave function in quantum mechanics describes the quantum state of a particle as a function of space and time. The laws of quantum mechanics (such as, for example, the Schrödinger equation) describe how the wave function evolves over time. The symbol for a wave function Ψ is a complex valued function; however Ψ^{2 }is real, and corresponds to the probability density of finding a particle in a given place at a given time, if the particle's position is measured.
In conjunction with the present invention, the wave function may be coded into qubits of quantum particles. Preferably, the quantum particles are photons, but trapped ions or magnetic spin states can also be utilized to practice the principles of the present invention.
A preferred method of the present invention may utilize qubits in a quantum computer setting or the simulation of qubits in a classical computer. Qubits comprise superpositions of ones and zeros where both simultaneously exist. Photons that define the wave function may be subjected to a quantum Fourier transform operation. In the process, the photons are measured thereby destroying the quantum state, but providing the measured probability in terms of wave function and its complex conjugate
P=ψψ* (1)
In the embodiments of
Communication between remote locations can be accomplished utilizing a comparatively small number of qubits of quantum particles relative to the data exchanged. Photons are amenable to transit in an environment exposed to climactic weather between the locations. It is appreciated that colinear transmission of a comparator wave function state and an information carrying state facilitates longrange data transmission.
State Preparation
A data set is modeled by, or in the form of, a wave function. Using sound transmission as an example, the sound is characterized by intensity amplitudes at uniformly spaced intervals
A superimposed quantum form is applied to the sound data set to facilitate quantum computer manipulation. To accomplish the quantification, data amplitudes are equated to a wave function in the form of a series
is the quantum state key. The qubits are characterized as the quantum state superpositions
q _{k} =A _{k}0
A quantum probability conservation condition is imposed such that
A _{n} ^{2} +B _{n} ^{2}=1. (7)
To account for the quantum superposition, the quantum data is organized in terms of a conventional quantum binary tree. A prior art quantum binary tree is depicted as a branching between 0 and 1 outcomes for successive steps in
The outcomes of the successive steps sum to the values 0 through 2^{n}−1, where n is the number of qubits. The means of obtaining the 0 or 1 depends on the specific experimental and corresponding simulation implementation. There are several conventional rules that are possible for determining the 0 or 1 value. For example, a 0 state may correspond to a horizontal measurement and the 1 may correspond to a vertical measurement, or the reverse may be true. In general, the series of qubit measurements are prepared such that each value of the state preparation is conditioned to determine the 0 or 1 at each branch. An alternate qubit architecture operative herein is termed “winner takes all.” In the simulation depicted in
The 2^{n}, where n is the number of qubits, are divided into two parts, lower 0 to ((2^{n})/2)−1 and higher indices ((2^{n})/2) to 2^{n}−1. The side with the greatest sum of the indices measured determines the path of the first branch. The second level branch has one half the number of indices of the first branch. Consecutive indices assigned are from the selected half from the first branch. The same process is used for the second branch level as from the first branch, but with half of the indices. This process repeats until all the branching is determined and the selected single index is determined. The quantum binary tree depicted in prior art
The quantum superposition amplitudes at any qubit level in the binary tree may be constructed from, for example, sound amplitudes
where the summation is over the number of states
n _{k} (9)
at each level of the quantum binary tree. Similarly
The amplitudes α are approximated in the quantum computation by identification with probabilities which can then be sampled. For one realization, it is noted that and
α_{0}=ø_{i=0} ^{i=n} ^{ 2 } ^{k1} A _{i} (11)
and
α_{k}=ø_{i=0} ^{i=n} ^{ 2 } ^{k1j}Π_{j=0} ^{j=i} A _{i} B _{j} (12)
where Π is the product of a sequence operator. The classical index k is given in terms of the quantum qubit indices n of the quantum binary tree made of n qubits
The term
Quantum Data Simulation
Superpositions of qubits are used to store and process data such as sound. The amplitude of the “data” can be stored as the amplitudes of a superposed quantum state
ω=Σα_{i} k
where k is the eigenstate of the wavefunction Ψ. The term Ψ can be decomposed as a direct product of qubits
q _{1} q _{2} . . . q _{n} (16)
which compacts storage requirements by a factor of log 2 relative to a classical computation. A data set of size 2^{n }can be stored and operated on in n quantum bits. Mathematical transforms can also be performed on the quantum stored signal with the associated computational savings.
Quantum Computational System
Preferred embodiments for the system for quantum data compression and transmission that are preferably performed using photons as quantum particle qubits will now be described. In the preferred embodiments of the present invention depicted in
Referring now to
The process that computes the Quantum Fourier Transform (QFT) of a signal may be described as follows. First, the computer or device that holds the signal divides the signal into a series of sections. Each section contains N samples of the signal. This section of N samples is then used to prepare the first qubit. As shown in
In the Quantum Fourier Transform a number of photons, each with prepared qubit states, are sent sequentially through quantum controlled phase transforms followed by quantum Hadamard transforms associated with the half wave plate 78. The state preparation is accomplished by setting the values of the phase and setting the photons to particular elliptical polarization values.
The Hadamard transform is a quantum transform operating on one qubit at a time. The Hadamard transform in connection with the embodiments of
The qubits are operated on by the Hadamard transform as
q′ _{n} _{ k }
where n_{k }is the index of the current qubit state.
Hadamard transforms in the order of the most significant qubit to the least significant qubit. The initial state of each photon qubit is conditioned on the previously measured values of prior photon measurements.
A single photon is operated upon by a Hadamard transform, with the effect of Hadamard transforms on multiple photons representing an entire wave function is represented by the combined Hadamard transform.
Wave Function Transform
The total wave function made of arbitrary superposed states is operated on by the combined Hadamard transform
ψ′
where
Ĥ _{gate} =H I . . . I. (20)
Here the direct product of the identities is repeated until all of the qubits are taken into account.
With reference now to
P=ψψ* (21)
(where ψ represents the wave function and ψ* is the complex conjugate of the wavefunction) and sets the number of times on the average that a photon lands in an index space interval. For n qubits there are 2^{n }index space intervals (
A determination as to the polarization of each photon is provided by signal measurement at one of the single photon counting modules 84 and 86. The polarization of each photon is measured by the counting modules 84, 86 which represent the end of the photon path through the Hadamard gate and electrooptics. If horizontal (0) is measured, for example by single photon counting module 86, then no phase operations are applied to the remaining qubits. Otherwise, a controlled phase operation R_{m }is applied to remaining operations. Note that the phase polarization 44 and phase modulator 46 are controlled by the computer or processor 207 which is connected to the coincident circuitry 42, which is in turn receives the outputs of the detectors 84, 86. The R_{m }set is defined as
The term Δn represents the distance between the n_{k }indices of the binary tree levels under consideration,
Δn=n _{k} −n _{k′} (23)
Where n_{k }represents the maximum number of levels on the binary tree and n_{k′} represents the level of the binary tree currently being operated on. The output of an inventive system is provided to a buffer store. From the buffer store it may be provided to an output device on either a realtime or delayed basis as still images, video images, movies, audio sound representations, and the like.
Quantum Teleportation of Information
Turning to another facet of the preferred embodiments depicted in
The matrices are called unitary because they do not change the length, √{square root over (a^{2}+b^{2})}, of the vector that the matrix multiplies. After this operation, the receiver will possess the quantum information of the qubit that the sender transmitted. The unitary transformation operation (performed by element 260) may be performed by an element comprising, for example, a half wave plate and a quarter wave plate. For example, if the identity matrix is to be applied, nothing is done with the remaining portion of the initially shared entangled state. If the two bits (from the detectors 252, 253) indicate that the matrix T2 is to be applied then a half wave plate will perform a ninety degree rotation. If T1 is to be applied, then two suitable quarter wave plate operations will be performed. If T3 is to be applied, then two suitable quarter wave plate operations followed by a suitable half wave plate operation will be performed. Upon completion of this unitary transformation operation (260 in
With reference now to
Note that while the entanglement of two photons is shown in
It is noted that with respect to the Bell state measurement, for entanglement using a single qubit variable, difficulties are presented when only three distinct classes out of four Bell states are generally distinguishable. By using multiple qubit variables, for example, polarization, orbital angular momentum, or energy states, tracing or redundancy of variables can be used to in effect achieve complete Bell state measurements.
Referring now to
In contrast to system 10 depicted in
The controlled phase shift transformed entangled photon wavefunction components representing a recombined phase state in path 74 (of the qubit Q1) then interacts with a half wave plate oriented at 22.5 degrees 78 in order to implement a quantum Hadamard gate transformation therein and thus complete a quantum Fourier transform.
Continuing to the left side of
In the general context of the entangled photons P1 and P2 being separated with photon P1 being at the receiving side and the photon P2 being at the sender, information contained in the qubit Q1 may be transmitted from the sender to the receiver with only the twobit measurement (recorded by detectors 252, 253) being physically transmitted. That is, the information contained in the qubit Q1, as shown in
As explained in the foregoing (regarding the unitary transformation operation) when the sender wishes to send a qubit (quantum teleportation) the sender will perform a Bell measurement with sender's half of the shared entangled quantum system and the qubit to be transferred to the receiver (at elements 251, 252, 253). The outcome of the Bell measurement will be sent to the receiver over classical channels and consists of two bits. When the receiver gets the two bits (transferred via computer 211 to the unitary transformation element 260) the receiver applies to their remaining portion of the initially shared entangled state one of four unitary operations depending upon what the two bits indicate. Typically these operations can be represented by a matrix and correspond to the Identity matrix and three other matrices. For example,
The matrices are called unitary because they do not change the length, √{square root over (a^{2}+b^{2})}, of the vector that the matrix multiplies. After this operation, the receiver will possess the quantum information of the qubit that the sender transmitted. The unitary operation may (260) be performed by an element comprising, for example, a half wave plate and a quarter wave plate. For example, if the identity matrix is to be applied, nothing is done with the remaining portion of the initially shared entangled state. If the two bits indicate that the matrix T2 is to be applied the half wave plate will perform a ninety degree rotation. If T1 is to be applied, then two suitable quarter wave plate operations will be performed. If T3 is to be applied, then two suitable quarter wave plate operations followed by a suitable half wave plate operation will be performed. The outcome of the unitary transformation operation is detected by detectors 84, 86 via beamsplitter 82.
Thus, the information contained in qubit Q1 is passed from the sender to the receiver with only the physical transfer of the twobit measurement via “classical channels.” Thus, data relating to how to perform the Bell state measurement is transferred while the properties of entanglement between photons P1 and P2 result in the transference of information by teleportation of information; i.e., when the photon P2 “encounters” the qubit Q1 in the Bell state measurement element 251, the other photon P1 is effected by the “encounter” so as to in effect impart information from qubit Q1 to the entangled photons P1 and P2 simultaneously. Photons P1 and P2 may be significant distances from each other and still achieve the effects of entanglement, i.e., P1 is impacted by the conditions affecting P2.
The half wave plate 78 provides a qubit prioritized input 80 to a polarization beam splitter 82. Note that the half wave plate 78 may optionally be positioned following the Unitary Transformation circuitry 260 (as shown by dotted lines).
Referring now to
Specifically, as shown in
The light source 14 may be a laser, such as Nd:YAG, ion lasers, diode lasers, excimer lasers, dye lasers, and frequency modified lasers. Photons in path 16 emitted from the light source 14 are optionally passed through a spatial filter 18. Filter 18 converts the photons in path 16 in an image space domain to a spatial frequency domain and serves the purpose of removing, for example, stripe noise of low frequency and/or high frequency noise as described above in connection with
Unlike the system 10 depicted in
Continuing to the left side of
It is noted again that in the general context of the entangled photons P1 and P2 being separated with photon P1 being at the receiving side and the photon P2 being at the sender, information contained in the qubit Q1 may be transmitted from the sender to the receiver with only the twobit measurement (recorded by detectors 252, 253) being physically transmitted. The half wave plate 78 provides a qubit prioritized input 80 to a polarization beam splitter 82. Note that the half wave plate 78 may optionally be positioned following the Unitary Transformation circuitry 260 (as shown by dotted lines).
As explained in the foregoing (regarding the unitary transformation operation) when the sender wishes to send a qubit (quantum teleportation) the sender will perform a Bell measurement with sender's half of the shared entangled quantum system and the qubit to be transferred to the receiver (at elements 251, 252, 253). The outcome of the Bell measurement will be sent to the receiver over classical channels and consists of two bits. When the receiver gets the two bits (transferred via computer 211 to the unitary transformation element 260) the receiver applies to their remaining portion of the initially shared entangled state one of four unitary operations depending upon what the two bits indicate. Typically these operations can be represented by a matrix and correspond to the Identity matrix and three other matrices. For example,
The matrices are called unitary because they do not change the length, √{square root over (a^{2}+b^{2})}, of the vector that the matrix multiplies. After this operation, the receiver will possess the quantum information of the qubit that the sender transmitted. The unitary operation may (260) be performed by an element comprising, for example, a half wave plate and a quarter wave plate. For example, if the identity matrix is to be applied, nothing is down with the remaining portion of the initially shared entangled state. If the two bits indicate that the matrix T2 is to be applied the half wave plate will perform a ninety degree rotation. If T1 is to be applied, then two suitable quarter wave plate operations will be performed. If T3 is to be applied, then two suitable quarter wave plate operations followed by a suitable half wave plate operation will be performed. The outcome of the unitary transformation operation is detected by detectors 84, 86 via beamsplitter 82.
Continuing, in the left side of
Referring now to
Continuing to the left side of
It is noted again that in the general context of the entangled photons P1 and P2 being separated with photon P1 being at the receiving side and the photon P2 being at the sender, information contained in the qubit Q1 may be transmitted from the sender to the receiver with only the twobit measurement (recorded by detectors 252, 253) being physically transmitted. The half wave plate 78 provides a qubit prioritized input 80 to a polarization beam splitter 82. Note that the half wave plate 78 may optionally be positioned following the Unitary Transformation circuitry 260 (as shown by dotted lines).
As explained in the foregoing (regarding the unitary transformation operation) when the sender wishes to send a qubit (quantum teleportation) the sender will perform a Bell measurement with sender's half of the shared entangled quantum system and the qubit to be transferred to the receiver (at elements 251, 252, 253). The outcome of the Bell measurement will be sent to the receiver over classical channels and consists of two bits. When the receiver gets the two bits (transferred via computer 211 to the unitary transformation element 260) the receiver applies to their remaining portion of the initially shared entangled state one of four unitary operations depending upon what the two bits indicate. Typically these operations can be represented by a matrix and correspond to the Identity matrix and three other matrices. For example,
The matrices are called unitary because they do not change the length, √{square root over (a^{2}+b^{2})}, of the vector that the matrix multiplies. After this operation, the receiver will possess the quantum information of the qubit that the sender transmitted. The unitary operation may (260) be performed by an element comprising, for example, a half wave plate and a quarter wave plate. For example, if the identity matrix is to be applied, nothing is down with the remaining portion of the initially shared entangled state. If the two bits indicate that the matrix T2 is to be applied the half wave plate will perform a ninety degree rotation. If T1 is to be applied, then two suitable quarter wave plate operations will be performed. If T3 is to be applied, then two suitable quarter wave plate operations followed by a suitable half wave plate operation will be performed. The outcome of the unitary transformation operation is detected by detectors 84, 86 via beamsplitter 82.
Continuing, in the left side of
Referring now to
It is noted again that in the general context of the entangled photons P1 and P2 being separated with photon P1 being at the receiving side and the photon P2 being at the sender, information contained in the qubit Q1 may be transmitted from the sender to the receiver with only the twobit measurement (recorded by detectors 252, 253) being physically transmitted.
As explained in the foregoing (regarding the unitary transformation operation), when the sender wishes to send a qubit (quantum teleportation) the sender will perform a Bell measurement with sender's half of the shared entangled quantum system and the qubit to be transferred to the receiver (at elements 251, 252, 253). The outcome of the Bell measurement will be sent to the receiver over classical channels and consists of two bits. When the receiver gets the two bits (transferred via computer 211 to the unitary transformation element 260) the receiver applies to their remaining portion of the initially shared entangled state one of four unitary operations depending upon what the two bits indicate. Typically these operations can be represented by a matrix and correspond to the Identity matrix and three other matrices. For example,
The matrices are called unitary because they do not change the length, √{square root over (a^{2}+b^{2})}, of the vector that the matrix multiplies. After this operation, the receiver will possess the quantum information of the qubit that the sender transmitted. The unitary operation may (260) be performed by an element comprising, for example, a half wave plate and a quarter wave plate. For example, if the identity matrix is to be applied, nothing is done with the remaining portion of the initially shared entangled state. If the two bits indicate that the matrix T2 is to be applied the half wave plate will perform a ninety degree rotation. If T1 is to be applied, then two suitable quarter wave plate operations will be performed. If T3 is to be applied, then two suitable quarter wave plate operations followed by a suitable half wave plate operation will be performed. The outcome of the unitary transformation operation is detected by detectors 84, 86 via beamsplitter 82. Note that in all embodiments of
Continuing, in the left side of
Referring now to
In connection with the embodiments depicted in
Continuing to the left side of
It is noted again that in the general context of the entangled photons P1 and P2 being separated with photon P1 being at the receiving side and the photon P2 being at the sender, information contained in the qubit Q1 may be transmitted from the sender to the receiver with only the twobit measurement (recorded by detectors 252, 253) being physically transmitted. The half wave plate 78 provides a qubit prioritized input 80 to a polarization beam splitter 82 and yields a single photon registered on one of the single photon counting modules 84 or 86. Note that the half wave plate 78 may optionally be positioned following the Unitary Transformation circuitry 260 (as shown by dotted lines).
As explained in the foregoing (regarding the unitary transformation operation) when the sender wishes to send a qubit (quantum teleportation) the sender will perform a Bell measurement with sender's half of the shared entangled quantum system and the qubit to be transferred to the receiver (at elements 251, 252, 253). The outcome of the Bell measurement will be sent to the receiver over classical channels and consists of two bits. When the receiver gets the two bits (transferred via computer 211 to the unitary transformation element 260) the receiver applies to their remaining portion of the initially shared entangled state one of four unitary operations depending upon what the two bits indicate. Typically these operations can be represented by a matrix and correspond to the Identity matrix and three other matrices. For example,
The matrices are called unitary because they do not change the length, √{square root over (a^{2}+b^{2})}, of the vector that the matrix multiplies. After this operation, the receiver will possess the quantum information of the qubit that the sender transmitted. The unitary operation may (260) be performed by an element comprising, for example, a half wave plate and a quarter wave plate. For example, if the identity matrix is to be applied, nothing is done with the remaining portion of the initially shared entangled state. If the two bits indicate that the matrix T2 is to be applied the half wave plate will perform a ninety degree rotation. If T1 is to be applied, then two suitable quarter wave plate operations will be performed. If T3 is to be applied, then two suitable quarter wave plate operations followed by a suitable half wave plate operation will be performed. The outcome of the unitary transformation operation is detected by detectors 84, 86 via beamsplitter 82. Note that in all embodiments of
Continuing, in the left side of
The coincidence electronics 42 feed the result back to the computer 207 via lines 209 and 210 so that the computer 207 determines which portion of the data to process next and how to prepare the data bases on the last measurement detected by the coincident electronics. The feature is depicted in
It is noted the foregoing depicts the functions of respective elements that are controlled or implemented by a computer. Such operations may be performed, for example by or in conjunction with the computer labeled as Computer 207 in
In order to evaluate the ability of the inventive quantum algorithm to compress and transmit a signal representative of the data set with a comparatively small number of photons, 32 sound samples defining a normalized arbitrary spectrum are provided in the top left panel of
An example of a Bell state measurement device is shown to the right in
Referring again to
As is the case of
Referring now to
The unitary transfer element 260 in
Referring now to
The modulated entangled photon pair P3P4 is then transmitted to the receiver for measurement on a second Bell state measurement element 255. Detectors 256 and 257 record the Bell state measurement. The measurement from the second Bell state measurement is transferred to computer 211 along path 258. Computer 211 then specifies the setting of unitary transformation element 260 in accordance with the value of the second Bell state measurement. Unitary transformation element 260 in
The arrowed double lines indicate the travel paths for the combined pump photons and qubit photons. Polarizing beam splitter 305 transmits and reflects the orthogonal polarization components of the wavefunction of the qubit photon and pump photons. Polarizing Beamsplitter (PBS) 305 and 309 always transmit one of the orthogonal components and reflects the other. Polarization controller 306 operates to rotate pump polarization and single photon wavefunction polarization by 90 degrees. The nonlinear media boxes 307 and 310 are the locations where the quantum frequency conversion takes place employing either sumfrequencygeneration or differencefrequencygeneration. An optical delay line 311 operates to ensure wavefunction overlap at the polarizing beamsplitter 309 (PBS 2). The Box 313 labeled beamstop is a device to capture excess pump photons and noise photons produced in the SFG or DFG device. The arrowed dashed line indicates the travel path of the frequency/wavelength converted qubit. This converted qubit Q1 may then be coupled into transmission optics or into optical devices for manipulation or detection. The net result of the system 300 operation is to in essence create a “quantum information waveguide” for the single photon produced at generator 304, the orthogonal components of which are split by beam splitter 305, frequency “converted” by nonlinear media 307, 310, recombined at beamsplitter 309, and filtered at elements 312, 313.
Referring to the details of
The arrowed double lines indicate the travel paths for the combined pump photons and qubit photons. Next, polarizing beam splitter 305 transmits and reflects the orthogonal polarization components of the wavefunction of the qubit photon and pump photons. Polarizing Beamsplitter (PBS) 305 and 309 always transmit one of the orthogonal components and reflects the other. Polarization controller 306 operates to rotate pump polarization and single photon wavefunction polarization by 90 degrees. The nonlinear media boxes 307NL and 310NC are the locations where the quantum frequency conversion takes place employing either sumfrequencygeneration or differencefrequencygeneration. Specifically, at 307 NL, the nonlinear media is oriented 90 degrees from nonlinear nonlinear media 310NC. An optical delay line 311 operates to ensure wavefunction overlap at the polarizing beamsplitter 309 (PBS 2). The beam stop 313 is a device to capture excess pump photons and noise photons produced in the SFG or DFG device. Wave division multiplexer or dichroic mirror 312 transmits λ_{0 }and reflects all other λ. The arrowed dashed line indicates the travel path of the frequency/wavelength converted qubit Q1. This converted qubit Q1 may then be coupled into transmission optics or into optical devices for manipulation or detection. The net result of the system 300A operation is to in essence create a “quantum information waveguide” for the single photon produced at 304, the orthogonal components of which are split by beam splitter 305, frequency “converted” by nonlinear media 307NL, 310NC, recombined at beamsplitter 309, and filtered at elements 312, 313.
Referring to the details of
The arrowed double lines indicate the travel paths for the combined pump photons and qubit photons. Next, polarizing beam splitter 305 transmits and reflects the orthogonal polarization components of the wavefunction of the qubit photon and pump photons. Polarizing Beamsplitter (PBS) 305 always transmits one of the orthogonal components and reflects the other. The nonlinear media boxes 307NL and 310NC are the locations where the quantum frequency conversion takes place employing either sumfrequencygeneration or differencefrequencygeneration. Specifically, at 307 NL, the nonlinear media is oriented parallel to the nonlinear media 310 NC. An optical delay line 311 operates to ensure recombining wavefunction overlap at the polarizing beamsplitter 305. Halfwave plates (HWP) 320A and 320B operate to rotate polarization by pump polarization and single photon wavefunction polarization by 90 degrees to ensure proper phase matching for interaction and noninteraction with the nonlinear media 307NL and 310NC for both clock wise and counter clock wise propagating photons. The beam stop 313 is a device to capture excess pump photons and noise photons produced in the SFG or DFG device. Wave division multiplexer or dichroic mirror 312 transmits λ_{0 }and reflects all other λ. The arrowed dashed line indicates the travel path of the frequency/wavelength converted qubit Q1. This converted qubit Q1 may then be coupled into transmission optics or into optical devices for manipulation or detection. The net result of the system 300B operation is to in essence create a “quantum information waveguide” for the single photon produced at 304, the orthogonal components of which are split by beam splitter 305, frequency “converted” by nonlinear media 307NL, 310NC, recombined at beamsplitter 305, and filtered at elements 312, 313.
The system 400 of
The qubit Q1 travels along path 80 to Quantum Frequency Converter A (see 300, 300A, 300B of
Following the frequency conversions of elements 401 and 402, returning now to
The outcomes of the successive steps sum to the values 0 through 4^{n}−1, where n is the number of Bell state qubits. The means of obtaining the 0, 1, 2, or 3 depends on the specific experimental and corresponding simulation implementation. There are several conventional rules that are possible for determining the 0, 1, 2 or 3 value. For example, a 0 state may correspond to a Bell state measurement of Ψ^{+}, the 1 may correspond to a measurement of Ψ^{−}, the 2 to a measurement of Ψ^{+}, and the 3 to a measurement of Ψ^{−}, or other alternative assignments may be true. In general, the series of Bell state measurements are prepared such that each value of the state preparation is conditioned to determine the 0, 1, 2, or 3 at each branch.
In the simulation depicted in
Photons P1 pass through paths 34 and 48 to beam splitter 251. Photons P3 enter beam splitter 251 as shown in
Delay element 520 operates to ensure coincidence in the interaction on beam splitter 251 between photons P1 and P3 and delay element 521 operates to ensure coinciding interaction on beam splitter 81 between photons P2 and P4. The delay element is controlled by computer 207 through line 49 The receiver performs a Bell state measurement at 82 and the results of that measurement are recorded by processor/computer 211. Computer 211 may have a coincidence detector 42 associated therewith. Optionally, a communications channel may interconnect computers 207 and 211 as represented by the parallel dashed lines.
Optionally, computer/processor 207 controls an optional shutter device 525 that is operational to prevent photons P1 from interacting with element 251 and prevent a swap of entanglement from photons P1P3 to photons P2P4. Alternatively device 525 may be controlled by an operator to prevent photons P1 from interacting with element 251 and prevent a swap of entanglement from photons P1P3 to photons P2P4. In a second alternative computer/processor 207 may control entangled photon source 511 or 511A to emit or not emit entangled photon pairs to enable or disable swapping of entanglement from photons P1P3 to photons P2P4. The sender operates to perform a Bell measurement between photons P1 and P3 or to block photon P 1. When a Bell measurement is performed with photons P2 and P4 their quantum states will either possess a nonzero valued correlation or a zero valued correlation. A zero correlation value may be referred to as uncorrelated. The transfer of information may utilize encoding methods such as Morse code or ASCII. When the shutter 525 is “open,” P2 and P4 will strike Bell measurement device (polarization beam splitter) 82 and a correlated measurement will be recorded. From the aspect of detectors 84 and 86 when the photons P2 and P4 are correlated, both photons will be detected by either of detectors 84 or 86. If the shutter 525 is “closed” so as to block P1, then P2 will still enter Bell state measurement element 82 but no correlation will occur; i.e., the photons P2 and P4 will not have a preponderance of measurements in which the one of the detectors 84 or 86 measures both photons P2 and P4. The transfer of information for preferred embodiment 501 may include encodings such as Morse code or ASCII. The information being transferred may be, for example, binary representations of Bell state measurements, images, sound, or other types of quantum, digital and/or analog data to be communicated.
An example of a Bell state measurement device or element is shown to the right in
The embodiment shown in
In the embodiment of
As an example, consider a case where three entangled photon sources are located at the sender. The sender is going to teleport a sequence of information photons (qubits) to the receiver using only quantum information channels and Bell state encoding for the two bit information transfer to the receiver. The sender will prepare the information photon Q1 in the desired state and interact that photon with an entangled photon P5 from entangled photon source 511C on beam splitter 251A, the remaining photon P6 from that entangled pair is directed towards the receiver and element 260. A Bell state measurement will be performed between photons P5 and Q1 and the results of that measurement directed to encoder 12. Specifically, Photons P1 pass through paths 34 and 48 to beam splitter 251. Photons P3 enter beam splitter 251 as shown in
The results of the measurement of P2P4 by the receiver on beam splitter 82 and detectors 84, 86 will be recorded by computer 211 and used to set the unitary transformation circuitry 260 to the unitary transformation prescribed by the encoded Bell state. Photon P6 then passes through element 260 with the prescribed unitary transformation to recover the information contained in photon Q1. The values of that information photon, Q1′, are measured on detectors 84A and 86A after passing through polarizing beam splitter 82A. The results of the measurements from 84A and 86A are recorded by computer 211. The sender may then repeat the steps until a sequence of encoded data has been teleported to the receiver using only quantum channels for increased stealth and security.
The entanglement sources may be colocated with either the sender or receiver or may be distant from both. Each entangled photon source provides an entangled photon pair. Entangled photon pairs from each entangled photon source must be synchronized or time stamped to ensure interactions between photons from entangled pairs generated by the different entangled sources.
Further as to the optional shutter device 525, computer/processor 207 controls an shutter device 525 that prevents photons P1 from interacting with element 251 and prevent a swap of entanglement from photons P1P3 to photons P2P4. Alternatively device 525 may be controlled by an operator to prevent photons P1 from interacting with element 251 and prevent a swap of entanglement from photons P1P3 to photons P2P4. In a second alternative computer/processor 207 may control entangled photon source 511 or 511A to emit or not emit entangled photon pairs to enable or disable swapping of entanglement from photons P1P3 to photons P2P4. The sender operates to perform a Bell measurement between photons P1 and P3 or to block photon P1. When a Bell measurement is performed with photons P2 and P4 they will either be correlated or uncorrelated, depending on the position of shutter 525. When a Bell measurement is performed with photons P2 and P4 their quantum states will either possess a nonzero valued correlation or a zero valued correlation. A zero correlation value may be referred to as uncorrelated. When the shutter 525 is “open,” P2 and P4 will interact with Bell measurement device 82 and a correlated measurement will be recorded. From the aspect of detectors 84 and 86 when the photons P2 and P4 are correlated, both photons will be detected by either of detectors 84 or 86. If the shutter 525 is “closed” so as to block P1, then P3 will still enter Bell state measurement device or element 82 but no correlation will occur, i.e., the photons P2 and P4 will not have a preponderance of measurements in which the one of the detectors 84 or 86 measures both photons P2 and P4. The transfer of information for preferred embodiment 501 may include encodings such as Morse code or ASCII.
(2) P5 and Q1 are reflected. Q1 travels to through Port B to photonic element 251, which may be a beam splitter. P5 travels to 251B. When P1 and Q1 interact, P2 becomes an inverse transformation of Q1. When P5 interacts with P3, entanglement is swapped to P4.
(3) P5 interacts with Q1 at Beam splitter 351. Q1 and P5 exit ports A and B respectively. Photon Q1 travels to Bell state measurement device or element 251B without P5. Photon P5 travels to Bell state measurement device or element 251B. Photon P5 entanglement is swapped (via P3) to P4. Photon Q1 travels to Bell state measurement device or element 251 and information from Photon Q is imparted to Photon P2 via entanglement of Photons P1 & P2.
(4) Photon P5 is transmitted and Q1 is reflected. Photons P1, P5 and Q1 all interact on Bell state measurement device or element 251. No outcome is determinable.
Until the photons are measured each of these outcomes are equally likely. With respect to single photon interaction a 50/50 beam splitter has the property that it is equally likely for the single photon to be measured at either output port of the beam splitter 351. The interfered Q1P5 photon states, e.g. polarization, are directed towards Bell state measurement device or elements 251 and 251B respectively. There are two ways to generate valid Bell state measurements at both Bell state measurement device or elements 251 and 251B. These are the cases where both the information photon Q and photon P5 are transmitted through beam splitter 351 (outcome 2) or where both photons Q1 and P5 are reflected on interacting with beam splitter 351 (outcome 3). In the case where the information photon is reflected though beam splitter 351 a Bell state measurement between the information photon Q1 and entangled photon P1 will take place at components Bell state measurement device or element 251, and absorbers or detectors 252, and 253. This effectively teleports the information photon onto photon P2.
Specifically, Photons P1 pass through delay 520 to beam splitter 251. Photons P3 enter beam splitter 251 as shown in
Photon P5 for this instance will interact with photon P3 on beam splitter 251B. Specifically, Photons P3 pass through element 522 to the beam splitter 251B. Photons P3 enter beam splitter 251 as shown in
This Bell state measurement will perform and entanglement swap and entangle photons P4 and P6. When a Bell measurement is performed between photons P2 and P4 the outcome of that measurement applied through the unitary operation on photon P6 will recover the state of the information photon Q1 as Q1′. In the case where the information photon Q1 is transmitted through beam splitter 351 (outcome 3) a Bell state measurement between Q1 and entangled photon P3 will take place at Bell state measurement device or photonic element 251B (including elements 252B and 253B) effectively teleporting the state of Q1 onto entangled photon P4. Photon P5 will interact with photon P1 on Bell state measurement device or element 251, (including detectors 252, and 253) generating a Bell measurement and performing an entanglement swap to entangle photons P2 and P6. When a Bell measurement is performed between photons P2 and P4 the outcome of that measurement applied through the unitary operation on photon P6 will recover the state of the information photon Q1 as Q1′.
It must also be noted that interaction on a beam splitter between two photons does not necessarily entangle photons. In the case of entanglement swapping each photon interacting on a beamsplitter and measured and/or absorbed is generated as one photon of an entangled pair of photons. Similarly, the interaction of information photon Q1 with, for example, entangled photon P5 on beam splitter 351 does not entangle the photon Q1 with photon P6.
As in the embodiment illustrated in
The entangled photon sources 511A, 511B, and 511C may be colocated with either the sender or receiver or may be distant from both. Each entangled photon source provides an entangled photon pair. Entangled photon pairs from each entangled photon source must be synchronized or time stamped to ensure interactions between photons from entangled pairs generated by the different entangled sources. Delay elements 520 and 521 are components that operate to ensure photon interaction on Bell state measurement devices or elements 251 and 81 respectively. Delay element 520 is controlled by computer 207, as computer 207 is used to track delay. The information detected by detectors 252 and 253 is processed by computer 207.
Polarization analyzers 531A and 531B may be comprised of polarizers, half wave plates, and quarter wave plates that are operative to set photons P3 and P4 to specified polarizations for measurement by detectors 84 and 86 for quantum state tomography. Quantum state tomography provides an assessment of the multiple states of each photon (such horizontal or vertical polarization, and/or circular polarizations). Delay line element 521 operates to insure coincident photon measurements on detectors 84 and 86. Computer 211 computes a quantum state tomography that will be representative of the polarization value specified by polarizer 530.
The receiver performs a Bell state measurement at Bell state measurement device or element 82 and the results of that measurement are recorded by processor/computer 211 and the results of measurement are provided to processor 207 to prepare the next branch of the quantum quadtree for information transfer. Computers and processors 211 and 207 operate to control sending, receiving, recording and display of the information and 207 operates to control sending and receiving of the information.
As an option, computer/processor 207 controls an optional shutter 525 that is operational to prevent photons P1 from interacting with Bell state measurement device or element 251 and prevent a swap of entanglement from photons P1P3 to photons P2P4. The sender operates to perform a Bell measurement between photons P1 and P3 or to block photon P 1. When a Bell measurement is performed with photons P2 and P4 their quantum states will either possess a nonzero valued correlation or a zero valued correlation, depending upon whether the shutter 525 is in an open, for a nonzero correlation, or closed position for a zero correlation. A zero correlation value may be referred to as uncorrelated. Using the variable pulsing like effect of shutter 525, the transfer of information may include encodings such as Morse code or ASCII.
As a further option for the embodiment of
At the receiver (or second) subassembly, photon P2_{T1 }is the photon P2 entering the sender subassembly at time T_{1 }and photon P2_{T2 }is the photon P1 entering the sender subassembly at time T_{2}. Independent photons P2_{TN }enter the beam splitter 543 at times T_{1}, T_{2}, T_{3 }. . . T_{N }(separated by a ΔT).
There is an equal probability that the photons will enter the short or long paths as shown in
Optionally, shutters 525 may be included as shown in the sender side of
Beamsplitters 542 and 543 operate to direct photon components of photons P1 (P1_{T1}, P1_{T2}, P1_{T3 }. . . P1_{TN}) and P2 ((P2_{T1}, P2_{T2}, P2_{T3 }. . . . P2_{TN}) along their respective paths as shown in
Optionally, computer/processor 207 controls at least one optional shutter 525, that operates to prevent the photons P1 on the long, short, or both paths from interacting with element 251 and prevent a swap of entanglement from photons P1_{TN }and P1_{TN+1 }to P2_{TN }and P2_{TN+1}, The sender operates to perform a joint measurement between photons P1_{TN }and P1_{TN+1 }or to block photon P1 paths. When a joint measurement is performed with photons P2_{TN }and P2_{TN+1}, they will either be correlated or uncorrelated. The transfer of information may include encodings such as Morse code or ASCII. The type of information that may be transferred also includes the outcomes of a Bell state measurement between one photon of an entangled photon pair and an information photon (qubit) as would be used for quantum teleportation. Thus this embodiment can be used to transfer the outcome of a Bell state measurement by a quantum channel. It is to be appreciated that the speed of information transfer from the sender subsystem to the receiver subsystem is limited by the speed of quantum information.
During the fourth step, the sender processor directs controller 526A to direct a pulse sequence on memory QM3 or QM4 to perform a read operation on one or both memories in accordance with the encoding prescribed by encoder 12. The photons from memories QM3 and QM4 are directed towards Bell state measurement device or element 251. Specifically, Photons P1 pass through shutter 525 to beam splitter 251. Photons P3 enter beam splitter 251 as shown in
During the interaction with absorbers or detectors 252 and 253 one or both photons from memories QM3 and QM4 are measured and or absorbed on detectors 252 and 253. The absorption or measurement entangling quantum memories QM1 and QM2 in the case where a photon was emitted by memories QM3 and QM4 or not entangling quantum memories QM 1 and QM2 if the photon emission was suppressed.
During the fifth step, the receiver computer 211 directs controller 526B to direct a pulse sequence on quantum memories to perform a read operation on quantum memories QM1 and QM2. Photons from the read operations being directed towards detectors 84 and 86 through optionally present Bell state measurement device or element 82.
During the sixth step, the measurements of detectors 84 and 86 (considered to be part of the Bell state measurement device or element) are recorded by computer 211. In the instance where the entanglement was swapped between QM3 and QM4 the recorded measurements will be correlated, in the instance where the entanglement swapping was suppressed the recorded measurements will be uncorrelated. Steps 1 to 6 are repeated until the sequence of encoded data has been transmitted.
Preferred embodiment 506 may utilize either a common entangled photon source 511 or, in the alternative, two entangled photon sources 511A and 511B. As a further option for preferred embodiment 506, data transfer may be accomplished via quantum quadtree decomposition of a message or signal using computer 211 to reconstruct a data set, such as determining the next branch of a quantum tree, as explained in the foregoing (see
Alternate preferred embodiment 506 (
Either the optional common entangled photon source 511 or the entangled photon source 511A will emit an entangled photon P2 towards Bell state measurement device or element 544B where entangled photon P2 will interfere with a photon from quantum memory QM2. Quantum memory QM2 is controlled by controller 526B to emit a photon when directed by computer/processor 211. The photon from quantum memory QM2 may be directed through optional delay element 547 to Bell state measurement device or element 544B to interact with entangled photon P2. After interaction on Bell state measurement device or element 544B the entangled photon P2 and the photon from quantum memory QM2 are measured by photon detectors/measurement devices 545 (considered to be part of the Bell state measurement device or element). Subsequent to the measurements of the entangled photon P1 with the photon from QM4 and entangled photon P2 with the photon from QM2 the entanglement of P1P2 will be transferred to quantum memories QM2 and QM4 due to the properties of entanglement.
Either the optional common entangled photon source 511 or the entangled photon source 511B will emit an entangled photon P3 towards a Bell state measurement device or element 544D where P3 will interact with a photon from quantum memory QM3 (after passage through an optional delay element 547). Quantum memory QM3 being directed by controller 526A to emit a photon when instructed by processor 207. After interaction between the photon P3 and the photon from quantum memory QM3 on Bell state measurement device or element 544D the entangled photon P3 and the photon from QM3 are measured by measurement devices/photon detectors 545 (considered to be part of the Bell state measurement device or element).
Referring again to
Subsequent to the interaction of the entangled photon P3 with the photon from QM3 and entangled photon P4 with the photon from QM1 the entanglement of P3P4 will be transferred to quantum memories QM1 and QM3 due to the properties of quantum entanglement.
Quantum memory element 546A provides photons from quantum memory QM3 and quantum memory QM4. Positioned between the sender processor 207 and the quantum memory element 546B is a controller 526A that controls the outputting of photons from the quantum memory element 546A in a similar manner to the shutter 525 that optionally accompanies preferred embodiment 503; i.e., controller 526A operates to prevent the passage of photons from quantum memory element 546A at predetermined times as controlled by processor 207. A photon from quantum memory QM3 passes through delay element 520 towards beam splitter 251. Delay elements 520 and 521 (which may be for example optical delay lines, quantum memories, slow light medium, etc.) are components that operate to ensure timely photon interaction on beam splitters 251 and 81 respectively. A joint measurement at beam splitter 251 is performed with a photon from quantum memory QM4. When the photons from QM3 and QM4 are measured or absorbed by detectors 252,253 the quantum state is transferred to the quantum memories QM1, QM2 and entangling them by the process of entanglement swapping. The receiver may perform a measurement at Bell state measurement device or element 82 and the results of that measurement are recorded by processor/computer 211. The sender may then repeat the steps until a sequence of encoded data has been transmitted.
Controller 526A also regulates the passage of photon from QM3 and/or QM4 which prevents interaction with element 251 and prevents a swap of entanglement from quantum memories QM3QM4 to quantum memories QM1QM2. Through the operation of controller 526A, the sender operates to perform a joint measurement between photons from QM3 and QM4 or to block photon interaction on 251. When a measurement is performed with quantum memories QM1 and QM2 they will either be correlated or uncorrelated, depending upon whether the shutter 525 or 526A is in an open or closed position. Using the variable pulsing like effect of controller 526A, the transfer of information may include encodings such as Morse code or ASCII.
Cloud Computing
An alternate embodiment comprises a system for quantum cloud computing in support of tactical intelligence operations and other operations. Utilizing more than one computer processor and computing resources to solve a problem nearly simultaneously is referred to as parallel processing. Even though the processors are relatively far apart, they can be connected by communications systems, networks and links to enable problem solving; also know as distributed computing. The collection of the distributed computing resources is often called “cloud computing.” Resources may include, but are not limited to quantum and classical computer nodes, quantum and classical memory, quantum and classical computer codes, quantum and classical storage, quantum and classical communications, and the like.
DWave and PiCloud have announced a joint venture to develop cloud computing software for remote access to one or more DWave quantum computers at a center or centers. The DWave/PiCloud quantum computing cloud is for a central computing resource available remotely. The communications between the quantum computers and the remote devices in this instance are classical.
One problem is that it is not designed or built to be used in support of tactical operations, intelligence or otherwise. Tactical communications resources are different from commercial enterprises which depend heavily on stationary infrastructure support. A tactical environment has a connectivity which needs to be adhoc and continually changing to account for mobility. Bandwidth is often restricted because of the smaller throughput of fielded system vs. commercial infrastructure supported systems.
A new method for quantum cloud computing improves security and compression between the nodes by applying the methods and techniques of quantum security and compression of data in transmission described in U.S. patent application Ser. No. 12/705,566 entitled “Quantum Based Information Transmission System and Method,” filed Feb. 12, 2010, by Ronald E. Meyers and Keith S. Deacon (and issued Aug. 6, 2013 as U.S. Pat. No. 8,503,885 ('885 patent) (ARL0462CIP1) (herein incorporated by reference) to provide the communications links between quantum computing or classical computing nodes operating in a tactical environment. As described in the '885 patent, the information sent to each location at each step in the process depends of the information previously measured by one or more receivers in the preceding step or steps.
Entanglement Swapping
As described herein, entanglement swapping may be applied to information transfer, sharing, or communication without the need for a classical communications channel. Optionally, this can be accomplished without the sender or receiver having access to information or resources held by the other.
Entanglement swapping is a quantum process by which particles that are not entangled become entangled with each other. For example, consider that particles 1 (P1) and 2 (P2) are entangled with each other and that particles 3 (P3) and 4 (P4) are entangled with each other. To entangle P1 and P4, particles P2 and P3 are interfered on a beam splitter and then are measured. The interference and measurement swaps the entanglements P1P2 and P3P4 to P1P4. Particles P2 and P3 are also affected by the measurement device and may be absorbed. The process of entanglement swapping has previously been verified. See, e.g., J.W. Pan, D. Bouwmeester, H. Weinfurter, and A. Zeilinger, “Experimental Entanglement Swapping: Entangling Photons That Never Interacted,” Physical Review Letters 80, 38913894 May (1998), which described a process of entanglement swapping with experimental verification using entangled photons. Swapping may be considered as the teleportation of an unknown photon/particle state onto another photon/particle.
Thus far, relatively few applications have found uses for entanglement swapping. Potential applications for entanglement swapping in quantum technology include quantum computing, quantum communications and quantum imaging. There are potentially many benefits to using entanglement swapping for quantum imaging that have not yet been described or exploited. The reason for this is that entanglement swapping has required high precision in its implementation and great expense for equipment that achieves the high precision. The lack of robust applications for entanglement swapping has been another drawback to its implementation in technology. This technology is being miniaturized in solid state devices and some components are being tested on chips. These quantum chips, can generated entangled particles and perform interference operations and measurements of quantum states.
It would be beneficial to have an entanglement swapping application that is robust and can be implemented with both available and evolving technologies. One way to make entanglement swapping useful would be to apply it information transfer, sharing, or communication without the need for a classical communications channel. For example, the current Internet, radio, and telephone are generally considered to be a classical communications channels. Another way to make entanglement swapping useful would be to be able to transfer, share or communicate by quantum means without the sender or receiver needing access to information or resources held by the other. For example, the sender having access to photons P2, P3 and the receiver having access to photons P1, P4 is sufficient to transfer information from sender to receiver. Repetition of this process allows the transfer of images without sending classical information and by only sharing entanglement. This type of communication of information, such as data and/or images, would be difficult to detect by an external observer since there would be no particle or radiation going between the sender and the receiver that which an observer would be able to sense and follow. Military and domestic applications requiring stealth and/or security would benefit from this capability.
Benefits of entanglement swapping for quantum imaging may include performing an entanglement swap to optimize photon detection efficiency while simultaneously optimizing transmission properties from an illumination source to a target. Another benefit is that an entanglement swap may be used to measure absorption maps of a target without the need to measure reflected photons. Furthermore, entanglement swapping may be used to help compute the product of the absorption values at two locations on a target. Using the environment to enable entanglement swapping would provide a direct and remote measurement on the environment. For example, absorption of photons by a remote target can be sensed by the enabling of quantum swapping of entangled particles which can be measured remotely without need for the return of photons from the target. It should be noted that besides images of absorption fields of targets any property can be imaged by enabling quantum swapping when the quantum particle is sensitive to the effects of object. Furthermore, with time sequencing this provides range information from, for example, the source of entangled quantum particles to target features. It should be further realized that the source or sources of the entangled quantum particles need not be located with the equipment used to direct particles towards a target (sender) or located with the equipment that measured those entangled particles that never directly interacted with the target (receiver). For example, the source or sources of the entangled particles may be on a satellite that would send the entangled particle pairs to the “sender” equipment and “receiver” equipment. Alternately, both the sender and receiver may have a single entangled quantum particle source and each shares one particle of their entangled particle pairs with the other. The identification of which particles are entangled with each other relative to initial entangled pair creation times may be achieved using an auxiliary time stamp, e.g. a laser pulse encoded with time information for each entangled photon pair created, that propagates with each particle of each entangled particle pair. Although not obvious, we consider it possible to use thermal light photon number fluctuations and their correlations and quantum illumination for variations of teleportation and swapping in our current inventions with swapping. Further benefits of entanglement swapping applied to quantum imaging using measurements of reflected photons may include application to quantum imaging of remote targets and microscopy with the images being generated for the user at a distant location with entangled photons that did not interact directly with the target. The reflected photons may be further used to compute the product of reflectance or the product of reflected intensities of at least two locations on the target. Current imaging systems such as cameras are dependent on producing imaging using photons that have directly interacted with the target. The sharing of images taken by a camera normally requires communication by electromagnetic radiation that takes specific paths to communicate a facsimile of the image between sender and receiver. Even quantum teleportation may require a classical communication channel using electromagnetic radiation that takes specific paths to communicate. Entanglement swapping could be applied to quantum teleportation to replace the classical channel. The two bit Bell state measurement between the information quantum state (qubit) and one particle of the entangled particle pair could be transmitted to the receiver by manipulation of the Bell state of the entangled particles undergoing the quantum swapping to be the same Bell state that was measured for the teleportation. The receiver would then be able to measure the swapped Bell state and have the two bits to modulate the particle with the teleported information to recover the information qubit to complete the teleportation process. Alternatively, a sequence of onoff swapping representing the two bits could be used to transfer the information to the receiver to use to recover the teleported information qubit.
Representation of the onoff swapping may be accomplished by choosing to swap quantum entanglement with particles possessing a second quantum property. For photons this second quantum property may be, for example, wavelength where the first quantum property conveying the information may be, for example, polarization. Choosing to entanglement swap between two sets of entangled particles with distinct second quantum properties allows for a positive valued discrimination of not only those cases where swapping is enabled by a shutter being open (“on”) but a positive valued discrimination where swapping is in the “off” state. This would improve the transfer of information where there may be a high loss of entangled particles between the entanglement sources and the receiver. In that case 0 or off settings may be over reported due to that loss whereas when two properties are being used, one to represent the “on” or open case and the other quantum property representing the “off” or closed case loss of quantum particles from the entanglement source to the receiver would typically be the same for both quantum properties and potential over representation of the “off” case reduced. An alternate method to realize the transfer of information by quantum means from a sender to a receiver would be to send the values of 1 or 0 (zero) in a sequence that would correspond to a predetermined code. The individual values of 1 or 0 would be accomplished by a combination of “on” and “off” operations assigned to represent 1 and a separate combination of “on” and “off” operations assigned to represent 0. A particularly robust implementation of this alternate method was experimentally verified by the inventors and goes as follows. To turn “on”, for example, (a) the sender would operate on their portions of a sequence of entangled quantum particles with the shutter or other device operating to enable swapping of entanglement between the sender's quantum particles and the receiver's quantum particles, i.e. an “on” state, from time T1 to time T2. This would be followed by (b) operations on their portions of a sequence of entangled particles with the shutter or other device operating to disable swapping of entanglement between the sender's quantum particles and the receiver's quantum particles, i.e. an “off” state, from time T2 to time T3. Finally, (c) the sender would repeat the operations of step (a) from time T3 to time T4. The receiver would then make three sets of coincident measurements from time T1 to time T2, time T2 to time T3, and time T3 to time T4. Then the number of coincidences measured during T1 to T2 would be added to the number of coincidences measured to the number of coincidences measurements made during T3 to T4 and then subtract twice the number of coincidence measurements made during T2 to T3. This value would then be divided by its absolute value. The receiver computed value of 1 would indicate that the sender has transferred to the receiver a “1” value. To transfer a 0 value the sender would (d) operate on their portions of a sequence of entangled particles with the shutter or other device operating to disable swapping of entanglement between the senders particles and the receivers particles, i.e. an “off” state, from time T5 to T6 followed by (e) operations on their portions of a sequence of entangled particles with the shutter or other devices operating to enable swapping of entanglement between the senders particles and the receivers particles, i.e. an “on” state, from time T6 to T7. Finally, (f) the sender would repeat operations on their portions of a sequence of entangled particles with the shutter or other device operating to disable swapping of entanglement between the sender's particles and the receiver's particles from time T7 to time T8. The receiver would then make three sets of coincident measurements from time T5 to time T6, time T6 to time T7, and time T7 to time T8. Then the number of coincidences measured during T5 to T6 would be added to the number of coincidences measured during T7 to T8 and then twice the number of coincidence measurements made during T6 to T7 would be subtracted. This value would then be divided by its absolute value. The value computed would be −1. When the value is −1, then the number 1 is added to give the value 0. Thus sequences of values of 1 and 0 can be sent between sender and receiver. This method is robust in practice since it can work even when there is experimental noise or drift in coincidence counts. As observed our experiments, the on operations tend to give higher coincidence counts than nearby in time off operations. Analogously, off operations tend to give less coincidence counts than nearby in time on operations. This result is sufficient to verify the nonlocal quantum transfer of information between sender and receiver by embodiments of our inventions. It would be beneficial to use entanglement swapping to communicate images or quantum images that does not require a classical communications channel to complete the transfer of images between a sender and a distant user at the receiver in order to avoid having the classical communications channel blocked which would also block image communication. This means to transmit the two bit measurement is stealthier and faster and does not require the transmission of energy or particles between the sender and receiver that would ordinarily carry that information. Communication information transfer using entanglement swapping would be an entirely quantum process. Another embodiment would employ enabling, partially enabling, or disabling the swapping of entanglement to transfer from a sender to a receiver an “analog” type signal. The enabling, partially enabling, or disabling of an entanglement swap may be accomplished through the use of delay lines or similar components. A delay line is typically used to ensure entangled particle overlap on a beam splitter or other device to maximize the probability to achieve a swap of entanglement. For example, an optical delay line is a device that precisely controls the distances that a photon travels through the device. By varying the distance the photon travels one controls the delay time through the device. Delay lines may also be used instead to minimize quantum particle overlap on the beam splitter to disable the entanglement swap. The overlap of the entangled particles can be controlled and/or modulated from fully overlapped to nonoverlapped which allows for analog type signals to be transmitted. In the case of constructive interference the coincidence rate measured by the receiver will be enhanced when there is a high degree of overlap and the coincidence rate measured by the receiver will be decreased when there is a small degree of overlap. In the case of destructive interference, the measured coincidence rate by the receiver is decreased when there is a high degree of overlap and increased when the degree of overlap decreases. The constructive or destructive interference is related to the Bell state of the entangled particles interacting on a beam splitter. This effect is similar to HongOuMandel interference [Hong, C. K.; Ou, Z. Y. & Mandel, L. (1987), “Measurement of subpicosecond time intervals between two photons by interference”. Phys. Rev. Lett. 59 (18): 20442046]. In the limit of fully overlapped entangled particles this could be considered a binary “on” and when completely nonoverlapped as a binary “off”. Control of entanglement to transfer information from a sender to a receiver may be accomplished in a variety of ways. The process of control of the entanglement that enables the transfer the properties of entanglement from one pair of entangled photons to a second pair of entangled photons is often called entanglement swapping. In the case of using entangled photons for entanglement swapping, one way would be for the sender to control the reception of one or more of the entangled photons. This type control may be accomplished through the use of “interrupt” type components such as shutters or switches to fully block or unblock the reception of those photons. It is also appreciated that controlling the probability of an entanglement swap to transfer “analog” type information from a sender to a receiver may be accomplished through the use of components such as delay lines. In this case, the delay line is controlled to vary the degree of entangled photon overlap and interference on a beam splitter type device. A delay line is typically used to ensure entangled particle overlap on a beam splitter or other device to maximize the probability to achieve a swap of entanglement. For example, an optical delay line is a device that precisely controls the distance and therefore the time of travel through the device. That is, the device can be used to delay the time of arrival of a photon to the output port of the device. By varying the distance the photon travels one controls the time of travel through the device. Delay lines may also be used instead to minimize quantum particle overlap on the beam splitter to disable the entanglement swap. Other types of devices such as variable attenuators may also be used to control in a continuous manner the probability of an entanglement swap. The speed of quantum information has been recently been reported as being greater than or equal to 1.37*10^{4 }times the speed of light. See, J. Yin et al., “Lower Bound on the Speed of Nonlocal Correlations without Locality and Measurement Choice Loopholes,” Physical Review Letters 110, 260407 (2013). The benefits of utilizing swapping in the process of quantum communications is that communications would be at the speed of the quantum information even if it is faster than the speed of light which can be beneficial for many applications. Computers and processor are used to control sending and receiving of the information using entanglement swapping.
Frequency Conversion
Over short transmission distances photons of different frequencies may propagate satisfactorily for quantum communications between the sender and the receiver. However, over longer distances photons at some frequencies may be susceptible to appreciable absorption by the transmission media such as optical fiber, the atmosphere, or water. If the photon is absorbed then the quantum information associated with that photon would be lost. One way to extend the distance over which quantum information may be transmitted through a media is to convert the frequency of the photon carrying the quantum information to a frequency which is less readily absorbed. See Shahriar, et al, “Connecting processingcapable quantum memories over telecommunication links via quantum frequency conversion,” J. Phys. B: At. Mol. Opt. Phys. 45 (2012) 124018. A difficulty in doing this is that conventional frequency conversion methods tend to destroy the quantum information. In the following an invention is described to convert photon frequency while preserving the quantum information associated with that photon. A preferred embodiment is directed to mitigation of transmission loss; specifically towards mitigating the transmission loss of photon based qubits when propagating through absorbing and transmitting media and improving the efficiency for the detection of a photon based qubit. As an example, for a photon based qubit propagating through a typical optical fiber there are minima of attenuation for frequencies corresponding to 1310 nm and 1550 nm wavelengths. Other media such as the atmosphere or underwater would have different transmission properties that make it advisable to convert the frequency of the photon based qubit to minimize absorption and scattering losses along the path from the sender to the receiver.
A further advantage to be attained with frequency conversion is for detection efficiency. Many silicon based photon detectors have peak detection efficiencies at frequencies corresponding to approximately 780 nm wavelengths. However, for example cold atom ensembles or ion quantum systems, have peak emissions at frequencies corresponding to wavelengths for instance at 240 nm for one type of quantum system to 1400 nm for another type of quantum system.
In practice, one means by which frequency conversion of a photon based qubit would be to 1) convert the frequency of the photon based qubit to a frequency optimized for transmission through the media between the sender and the receiver; 2) the receiver would then convert the frequency of the transmitted qubit to a frequency optimized for their detection system.
Generally speaking, transmission of quantum information, or qubits, over long distances or in challenging environments is problematic. To mitigate absorption or scattering losses inherent in long distance transmission of quantum information the choice of an appropriate photon frequency or wavelength for transmission is desirable. Typically frequency/wavelength conversion for lasers is accomplished using the nonlinear processes of Sum Frequency Generation (SFG) or Difference Frequency Generation (DFG). To bridge the difference in wavelength between photons suited for fiberbased communication and the photons emitted and absorbed by the atomic memories, two strategies have been demonstrated. One strategy is sumfrequency generation (SFG) and differencefrequency generation (DFG) which are secondorder nonlinear processes that must satisfy energy conservation and phase matching conditions. For sumfrequency generation (SFG) the processes involves three frequencies interacting in a nonlinear crystal subject to the condition ν_{1}+ν_{2}=ν_{3 }where ν_{1 }is the frequency of the photon that one wants to change to a more desirable frequency (ν_{3}) and a pump source at frequency ν_{2}. Similarly in differencefrequency generation the conservation condition is ν_{1}−ν_{2}=ν_{3}. The nonlinear crystals used typically have phase matching conditions where the momentum and polarization of the light interacting with the crystal must be considered. Typically, in order to preserve quantum state information, which is often encoded in the polarization of a single photon, the wavefunction of that single photon needs to be split into orthogonal polarization components and each component would then be frequency individually before the wavefunctions are recombined for transmission or interaction with some device.
Differencefrequency generation and Sum Frequency Generation typically occur in materials with large χ^{2 }such as periodicallypoled lithium niobate (PPLN) and conversion efficiencies can approach 100%. Another proven method to bridge the wavelength gap is the thirdorder nonlinear process of fourwave mixing (FWM). Under the correct conditions a nearIR photon can be converted to a telecom wavelength photon via fourwave mixing using two pump lasers and an atomic ensemble. Cold Rb atoms in a magnetooptical trap (MOT) combined with the correct pump lasers can achieve high efficiency fourwave mixing with very little noise added to the signal. See in this regard, A Quantum Network with Atoms and Photons (QNETAP), by Ronald E. Meyers, et al., US Army Research Laboratory, Adelphi, Md. 20783, Proc. SPIE 8518, Quantum Communications and Quantum Imaging X, 85180G (Oct. 17, 2012); doi:10.1117/12.97414, herein incorporated by reference.
It is to be appreciated that frequency conversion may also be done to transform the frequency of light from some quantum system that may be difficult to manipulate or detect into another frequency where those operations, such as photon detection are more efficiently accomplished {see L. Ma, et al., “Single photon frequency upconversion and its applications,” Proc. SPIE 8163 81630N (2011)}. The nonlinear media used may be bulk crystals such as BBO or LBO, newer periodically poled media such as periodically poled lithium niobate (PPLN), or even nonlinear interactions in doped optical fibers. Each type of nonlinear media must be engineered to meet the requirements of the particular application, i.e. what frequencies to be converted between, what polarizations and what momentum are to be phase matched. A further concern with many nonlinear crystals is their inherent property of birefringence. This birefringence property leads to a delay in the time it takes one polarization to travel across these crystals relative to a different polarization. With respect to quantum frequency conversion, any such delay must be accounted for and corrected or quantum information would be lost in the frequency conversion process. A further motivation to perform quantum frequency conversion would be to mitigate temporal dispersion effects which would typically lead to timing and synchronization problems between a sender and a receiver.
Quantum Channel
A quantum communications channel, or quantum channel, is a communications channel that can preserve quantum information such as a) the horizontal and vertical amplitudes of a photon polarization based qubit or b) the entanglement between two qubits of quantum information. Examples of quantum channels may include fiber optics for single/entangled photon propagation, and freespace propagation for single/entangled photons. Another distinction between a quantum channel and a classical channel is that information sent via a quantum channel need not travel along a well defined path from the sender to a receiver by some underlying physical carrier particle, e.g., electrons or photons. Quantum teleportation is one example of a quantum channel where the state of an information qubit is transferred directly to the receiver and where the reliever needs two bits of information transferred along a classical channel that contain instructions for the receiver to use on measuring the teleported information qubit that recovers the state of the initial information qubit.
Quantum Memory/Quantum Repeater
As used herein, a quantum repeater is a quantum memory coupled to at least one other quantum memory. The quantum memories may be composed of atoms, ions, nitrogenvacancy (NV) diamonds, quantum dots, superconducting quantum interference devices (SQUIDs), or other systems capable of representing and storing quantum states. Quantum memories can be entangled with each other and transfer of information from one such quantum memory node to another quantum memory node is accomplished with Bell measurements and transmission of two bits over classical, i.e. fiber optic, electronic, wireless radio, freespace optical, or quantum communications channels representing the result of the Bell measurement. Quantum memories, as used herein, are typically manipulated using a series of pulses that adjust a particular quantum state within the material that constitutes the quantum memory. See for example Sangouard, et al., “Quantum repeaters based on atomic ensembles and linear optics,” Review of Modern Physics, 83, 1, pp 3380 (2011). These pulses may include laser, radio frequency, microwave, voltage, current, etc. pulse sequences on the material that makes up the quantum memory to perform reset, “write”, and “read” operations. A reset or initialization operation involves a sequence of pulses that would establish a specified superposition of the quantum state or qubit of the quantum memory. The write operation would consist of a sequence of pulses that allows the quantum memory state to be accessed for an external qubit value to be stored in the quantum memory. Similarly, the read operation is a sequence of pulses that causes the state of the quantum memory to be removed from the quantum memory as a photon or some other quantum particle to be measured. The quantum memories may be composed of atoms, ions, nitrogenvacancy (NV) diamonds, quantum dots, superconducting quantum interference devices (SQUIDs), or other systems capable of representing and storing quantum states. Quantum memories may be used for applications such as quantum information processing where multiple operations for a quantum algorithm maybe performed on the stored quantum state, entanglement swapping, and storage of entangled photon pairs while maintaining their entanglement. It is to be further noted that quantum memories may store entangled photon pairs and preserve the entanglement of those photon pair. Challenges are presented in the transmission and exfiltration of quantum information, or qubits, over long distances or in challenging environments. To overcome the absorption or scattering losses inherent in long distance transmission of quantum information networks of quantum repeaters have been proposed to entangle remote quantum memories because Quantum information is typically fragile and not readily amplified. Entanglement is established between distant locations though a chain of entanglement swapping processes between nearby entanglement resources that ultimately leave the quantum particles at the ends of the chain entangled with each other even when the probability to directly entangle the two quantum particles is vanishingly small due to cumulative absorption and scattering losses between them. By swapping entanglement between nearby nodes losses due to absorption and scattering are greatly reduced.
Quantum Teleportation
Quantum teleportation, as used herein, refers to the transfer of quantum information (a qubit) from one location to another without that qubit being transmitted directly through the space between the sender and the receiver. As an example, this can be accomplished by the sender and the receiver each possessing one photon of an entangled photon pair. In other words, they are often said to be sharing the entangled photon pair quantum state. When the sender wishes to send a qubit by quantum teleportation the sender performs a Bell measurement with sender's photon of the shared entangled photon pair and the qubit to be transferred to the receiver. A Bell state measurement with photons may use a beam splitter to interfere the photons and their wavefunctions prior to being measured with photon detectors. The outcome of the Bell measurement will be sent to the receiver over classical channels and consists of two bits. Embodiments of our invention replace the classical channel with quantum channels. When the receiver gets the two bits the receiver then applies to their photon of the of the initially shared entangled photon one of four unitary operations depending upon what the two bits indicate. The sender and receiver each may be said to operate on one half of an entangled photon pair system or in other words half of an entangled quantum system or entangled system. Typically these operations can be represented by a matrix and correspond to the Identity matrix and three other matrices. For example,
The matrices are called unitary because they do not change the length, √{square root over (a^{2}+b^{2})}, of the vector that the matrix multiplies. After this operation, the receiver will possess the quantum information of the qubit that the sender transmitted. The unitary operation may be performed by an element comprising, for example, a half wave plate and a quarter wave plate. For example, if the identity matrix is to be applied, nothing is done with the remaining portion of the initially shared entangled state. If the two bits indicate that the matrix T2 is to be applied the half wave plate will perform a ninety degree rotation. If T1 is to be applied, then two suitable quarter waveplate operations will be performed. If T3 is to be applied, then two suitable quarter wave plate operations followed by a suitable half wave plate operation will be performed.
Quantum teleportation may operate in nonlineofsight (NLOS) configurations where one or both of the entanglement resources are distributed to senders and receivers where there is no direct path from the entangled resource source. In the case of entangled photon transmission in the atmosphere this feature may be enabled for example by using scattering and photons with a wavelength in the ultraviolet wavelength bands. After the distribution of the entanglement resources the teleportation process would proceed as described above. In the current invention the outcome of the Bell measurement (a first measured Bell state) between the information qubit and one photon of an entangled pair of photons can be transferred to the receiver in the following ways (a) the classical channel as described above, (b) generation of a Bell state using a second entangled particle source and appropriate modulators such as electrooptics for photons that is the same as the measured Bell state and transferring this new entangled photon pair to the receiver for measurement to recreate the information qubit, (c) utilizing an entanglement swapping process to transfer the first measured Bell state to the receiver wherein the first measured Bell state is generated using appropriate modulators, (d) utilization of an onoff entanglement swapping information encoding, (e) if an upconversion Bell state measurement process for photon based teleportation is used then the unconverted photon may be transferred to the receiver on a path that is specific to the measured value; this path could then be interfered with the remaining photon of the first entangled pair on, for instance a hologram where the specific measurement outcome paths are directed towards the hologram and interact with the remaining entangled photon, the interaction then directing the remaining entangled photon towards appropriate waveguides and/or polarization and phase modulators to recreate the information qubit, and other means apparent to those skilled in the art.
As used herein the terminology “Bell measurement” or Bell State measurement” is a joint quantummechanical measurement of two qubits or photons that determines the Bell state (one of four possible states) of the two qubits or photons.
As used herein, the terminology Bell state measurement device or element comprises, for example, a beam splitter and at least two detectors.
As used herein, the terminology Bell state “two bit measurement” refers to the two bits of data associated with representing a Bell state measurement outcome.
As used herein, the term “quantum state tomography” refers to a method of verifying a quantum state. Quantum tomography or quantum state tomography refers to the process of reconstructing the quantum state (density matrix) by measurements. Measurements that are tomographically complete; i.e., provide all the information about the state, are sometimes called a quorum.
A photonic element is needed to receive quantum particles and enable interference between the received quantum particles. For example, a photonic element may have two inputs and two outputs. Quantum particles entering such a photonicelement will a) a quantum particle enters at input 1 and a quantum particle enters at input 2 and both particles then exit from output 1, b) a quantum particle enters at input 1 and a quantum particle enters at input 2 and both particles then exit from output 2, c) a quantum particle entering at input 1 will exit output 1 and a quantum particle entering input 2 will exit output 2, or d) a quantum particle entering input 1 will exit output 2 and a quantum particles entering input 2 will exit output 1. This allows for two alternative but indistinguishable ways to measure a joint detection of two input quantum particles. An optical 50/50 beam splitter is an example of a component that may be used as a photonic element for entangled and nonentangled photons. The beam splitter is a traditional element to enable interference between two quantum particle probability amplitudes. However, there are many other photonic elements used individually or in combination that are not traditionally described as beam splitters but can enable interference. These include but are not limited to, optical elements for photons such as halfsilvered mirrors, pellicle beam splitters, 2×2 fiber couplers, N×M fiber couplers, etched photonic chips, waveguides, polarizing beam splitters, Wollaston prisms, GlanThomson prisms, holograms, photonic crystals, a thin film coating of silver on glass, and the like. It must be noted that when only a single input, i.e. a quantum particle entering at input 1 or input 2, is provided to an interference element the interference or photonic element then acts as a beam splitter where the quantum particle probability amplitude is directed into two or more output paths, e.g. output 1 or output 2. It is to be further appreciated that charged or neutral quantum particles such as neutral atoms, ions, electrons, neutrons, may require other interference or photonic elements that are appropriate for those types of quantum particles.
With respect to the terminology “entanglement swapping,” a simplified example is if a first particle or photon is entangled with a second particle and the second particle is teleported to a third particle (or photon), afterwards, the first particle (or photon) is entangled with the third particle (or photon).
The terminology “computer” as used herein means processor, microprocessor, CPU, multiprocessor, personal computer, quantum computer, or any device which has the capability of performing the functions of a computer. The terminology “processor” as used herein means as used herein means computer, microprocessor, CPU, multiprocessor, personal computer or any device which has the capability of performing the functions of a computer.
As used herein the terminology “unitary transformation device” relates to a device that performs a unitary transformation operation on the entangled state. As an example, the identity function is trivially a unitary operator and rotations in R2 are a nontrivial example of unitary operators. Rotations do not change the length of a vector or the angle between 2 vectors.
The terminology “interrupt” as used herein relates to a switch, shutter, electronic, optical, or other delay, or any device which has the capability to start or stop a signal.
As used herein the terminology “sender” relates to a “transmitter” or “broadcaster” of information.
Measurement of a photon by a detector typically entails the absorption of the photon by a photosensitive material. The photosensitive material would then typically produce an excess charge or change in current that would be recorded as a detection of a photon. As such, some embodiments of the current invention illustrated in
As used herein the terminology correlated means that the correlation value is nonzero, i.e. positive or negative, and uncorrelated means that the correlation value is zero.
The foregoing description is illustrative of particular embodiments of the invention, but is not meant to be a limitation upon the practice thereof. The following claims, including all equivalents thereof, are intended to define the scope of the invention.
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