CN116382012A - System and method for generating superposition state of random time-bin quanta - Google Patents

System and method for generating superposition state of random time-bin quanta Download PDF

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CN116382012A
CN116382012A CN202310658600.6A CN202310658600A CN116382012A CN 116382012 A CN116382012 A CN 116382012A CN 202310658600 A CN202310658600 A CN 202310658600A CN 116382012 A CN116382012 A CN 116382012A
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beam splitter
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lower port
port
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CN116382012B (en
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丁禹阳
李泽忠
刘午
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Hefei Si Zhen Chip Technology Co ltd
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/3515—All-optical modulation, gating, switching, e.g. control of a light beam by another light beam
    • G02F1/3517—All-optical modulation, gating, switching, e.g. control of a light beam by another light beam using an interferometer
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference
    • G02F1/212—Mach-Zehnder type

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Abstract

The utility model discloses a random time-bin quantum superposition state generation system and method, the generation system includes the host computer, single photon source, equal arm MZ interferometer, crooked waveguide and controller, equal arm MZ interferometer comprises two beam splitters and the phase modulator who sets up between two beam splitters, the host computer calculates the photon from the input lower port of first beam splitter to the output lower port of second beam splitter of single photon source output and the photon from the input upper port of first beam splitter to the output lower port of second beam splitter of each circulation rate, the controller is based on each pass rate that obtains respectively corresponding adjustment each transmission in-process phase modulator, make the photon in each circulation input to the output lower port of second beam splitter from the input upper port of first beam splitter with corresponding probability respectively, after the preset circulation number of times in a period is accomplished, obtain the quantum superposition state.

Description

System and method for generating superposition state of random time-bin quanta
Technical Field
The application belongs to the technical field of quantum information, and particularly relates to a system and a method for generating any time-bin quantum superposition state.
Background
Superposition is one of the basic properties of quantum information, and preparation of quantum superposition states is a key step in most quantum information applications including quantum communication and quantum computing. The time bin (time-bin) superposition is a common superposition state preparation form, and the time-bin coding quantum bit can effectively resist the loss in a transmission channel, is suitable for long-distance transmission relative to quantum bit coding in other modes (polarization coding, phase coding and the like), and is widely applied to a quantum key distribution system, a quantum walking system and an optical quantum computing system.
At present, the generation mode of the multi-dimensional time-bin superposition state mainly adopts N unequal arm interferometers to be connected in series, different delay times are achieved by adjusting modulators on the unequal arm interferometers, and the N-dimensional time-bin superposition state is formed, specifically, as shown in fig. 1 and 2, the relative delay time of each unequal arm interferometer in fig. 1 is equal, and the relative delay time of each unequal arm interferometer in fig. 2 is linearly and equivalently increased. Therefore, N unequal arm interferometers are needed for realizing N-dimensional time-bin coding, the device requirement and occupied space are large, the resource consumption is high, the cost is high, and the dimension is fixed along with the design number of the unequal arm interferometers and cannot be adjusted adaptively.
Disclosure of Invention
In order to solve the problems, the application provides a system and a method for generating any time-bin quantum superposition state, which adopt an equal-arm MZ interferometer and a curved waveguide, and obtain the time-bin quantum superposition state with any dimension by electrically modulating phase modulators in different cycles, thereby saving resources and space and being independent of the number of the MZ interferometers. The specific scheme is as follows:
in a first aspect, the application discloses an arbitrary time-bin quantum superposition state generation system, which comprises an upper computer, a single photon source, an equal-arm MZ interferometer, a curved waveguide and a controller;
the single photon source is used for outputting photons;
the equal-arm MZ interferometer consists of a first beam splitter, an interference upper arm, an interference lower arm, a phase modulator and a second beam splitter, wherein two ends of the interference upper arm are respectively connected with an output upper port of the first beam splitter and the second beam splitterAn input upper port of the beam splitter, two ends of the interference lower arm are respectively connected with an output lower port of the first beam splitter and an input lower port of the second beam splitter, and the phase modulator is arranged on the interference upper arm and is used for adjusting the passing rate T of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter based on the control of the controller 0 And adjusting the pass rate of photons in each cycle from the input upper port of the first beam splitter to the output lower port of the second beam splitter, corresponding to T respectively 1 、T 2 …T N The input lower port of the first beam splitter is used for receiving photons output by the single photon source; the output lower port of the second beam splitter is used for outputting the generated time-bin quantum superposition state:
|φ>=a 0 |0>+a 1 |1>+…+a N |N>
wherein |phi>Representing the output quantum superposition state; i0>Representing the time component of the process of photons output by a single photon source from the input lower port of a first beam splitter to the output lower port of a second beam splitter, |1>、|2>…|N>Time components of the nth cycle process of the first cycle and the second cycle … … respectively; a, a 0 A probability amplitude of the process time component corresponding to photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter, a 1 、a 2 …a N Probability magnitudes corresponding to the nth cycle time components of the first cycle, the second cycle … …, respectively; n is the set cycle number; each circulating path is composed of two parts of transmission paths, namely a transmission path on a curved waveguide and a transmission path in the equal-arm MZ interferometer;
the two ends of the curved waveguide are respectively connected with the input upper port of the first beam splitter and the output upper port of the second beam splitter, and are used for transmitting photons output from the output upper port of the second beam splitter to the input upper port of the first beam splitter;
The upper computer is used for inputting parameters for generating superposition state and calculating single photon based on the prestored relation and the input parametersThe rate of passage T of photons from the input port of the first beam splitter to the output port of the second beam splitter 0 And the pass rate of photons in each cycle from the input upper port of the first beam splitter to the output lower port of the second beam splitter, respectively corresponding to T 1 、T 2 …T N ；
The controller is respectively connected with the phase modulator and the upper computer and is used for receiving the passing rate T output by the upper computer 0 、T 1 、T 2 …T N And based on T 0 、T 1 、T 2 …T N The phase modulators are adjusted correspondingly, respectively.
Further, the pre-stored relation satisfies:
a 0 2 =T 0 b 1 ；
a 1 2 =(1-T 0 )b 1 T 1 (b 2 b 1 )；
a 2 2 =(1-T 0 )(1-T 1 )b 1 T 2 (b 2 b 1 ) 2 ；
…
a N 2 =(1-T 0 )(1-T 1 )…(1-T N-1 )b 1 T N (b 2 b 1 ) N ；
and a 0 2 +a 1 2 +…+a N 2 =1；
Wherein b 1 Transmission transmittance, b, for an equal arm MZ interferometer 2 T is the transmission transmittance of the curved waveguide 0 The pass rate of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter, T 1 、T 2 …T N The pass rates of photons in the nth cycles of the first and second cycles … … from the input upper port of the first beam splitter to the output lower port of the second beam splitter respectively correspond.
Further, the parameters include: transmission transmittance b of equal arm MZ interferometer 1 Bending and bendingTransmission transmittance b of curved waveguide 2 The preset cycle number N, the probability amplitude a of the process time component of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter 0 And the probability amplitude a of each cyclic time component 1 、a 2 …a N 。
Further, the upper computer comprises a parameter setting module, a data processing module and a data transmission module which are sequentially connected; the parameter setting module is used for inputting parameters for generating superposition states; the data processing module calculates the passing rate T of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter based on a prestored relational expression and parameters input by the parameter setting module 0 And a rate of passage T of photons in each cycle from an input upper port of the first beam splitter to an output lower port of the second beam splitter 1 、T 2 …T N The method comprises the steps of carrying out a first treatment on the surface of the The data transmission module is used for transmitting T 0 、T 1 、T 2 …T N To the controller.
Further, the generating system further comprises an optical switch connected with the controller, wherein the optical switch is arranged on a transmission path of the single photon source and the input lower port of the first beam splitter and is used for controlling the on-off of the transmission light path of the single photon source and the input lower port of the first beam splitter.
Further, the generating system further comprises an on-chip tunable optical delay structure connected with the controller, the on-chip tunable optical delay structure is arranged on the curved waveguide and is used for adjusting the delay time of photons in each cycle from the output upper port of the second beam splitter to the input upper port of the first beam splitter, and the delay time of each cycle process is kept the same.
In a second aspect, the present application further discloses a method for generating an arbitrary time-bin quantum superposition state, where the method is applied to the foregoing arbitrary time-bin quantum superposition state generating system, and the method includes:
input on upper computer to generate stackThe method comprises the steps that the upper computer calculates the passing rate T of photons output by a single photon source from an input lower port of a first beam splitter to an output lower port of a second beam splitter based on the input parameters and a prestored relational expression by adding the parameters 0 And the rate of passage T of photons in each cycle from the input upper port of the first beam splitter to the output lower port of the second beam splitter 1 、T 2 …T N ；
The single photon source inputs photons to the input lower port of the first beam splitter, and the controller inputs photons according to T 0 Adjusting the phase modulator to make the photons output by the single photon source in T 0 From the input lower port of the first beam splitter to the output lower port of the second beam splitter, to (1-T) 0 ) The pass rate of the first beam splitter enters the first cycle from the output upper port of the second beam splitter, and is input to the input upper port of the first beam splitter through the bent waveguide;
the controller is according to T 1 Adjusting the phase modulator to T photons transmitted to the input port of the first beam splitter in the first cycle 1 Is input from the input lower port of the first beam splitter to the output lower port of the second beam splitter to (1-T) 1 ) The pass rate of the first beam splitter enters the second cycle from the output upper port of the second beam splitter, and is input to the input upper port of the first beam splitter through the bent waveguide;
the controller is according to T 2 Adjusting the phase modulator to T photons transmitted to the input port of the first beam splitter in the second cycle 2 The pass rate is input from the input lower port of the first beam splitter to the output lower port of the second beam splitter to (1-T) 2 ) The pass rate of the first beam splitter enters a third cycle from an output upper port of the second beam splitter, and is input to an input upper port of the first beam splitter through a bent waveguide; in this way circulate … …
The controller is according to T N-1 Adjusting the phase modulator to T photons transmitted to the input port of the first beam splitter in the N-1 th cycle N-1 Is input from the input lower port of the first beam splitter to the output lower port of the second beam splitter to (1-T) N-1 ) Through the curved waveguide from the output upper port of the second beam splitter into the nth cycleAn input upper port to the first beam splitter;
the controller is according to T N Adjusting the phase modulator to T photons transmitted to the input port of the first beam splitter in the Nth cycle N The probability of (1) is input from the input lower port of the first beam splitter to the output lower port of the second beam splitter, and the corresponding modulation of the phase modulator in one superposition state generation period is completed, so that the time-bin quantum superposition state output from the output lower port of the second beam splitter is as follows:
|φ>=a 0 |0>+a 1 |1>+…+a N |N>
wherein |phi>Representing the output quantum superposition state; i0>Representing the time component of the process of photons output by a single photon source from the input lower port of a first beam splitter to the output lower port of a second beam splitter, |1>、|2>……|N>Time components of the nth cycle process of the first cycle and the second cycle … … respectively; a, a 0 A probability amplitude of the process time component corresponding to photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter, a 1 、a 2 ……a N Probability magnitudes corresponding to the nth cycle time components of the first cycle, the second cycle … …, respectively; n is the set number of cycles.
Further, when the system includes an optical switch coupled to the controller, the method further includes:
The controller controls the optical switch to be turned on, a single photon source inputs photons to the input lower port of the first beam splitter, the optical switch is turned off after the photons are input, and time coding in the current superposition state generation period is carried out; after the modulation of the phase modulator in the current superposition state generation period is completed, the controller controls the optical switch to be turned on again, the single photon source inputs photons to the input lower port of the first beam splitter again, the optical switch is turned off after the photons are input, and the time coding of the next superposition state generation period is started.
Further, when the system includes an on-chip dimmable delay structure connected to the controller, the method further comprises:
the controller controls the delay time of photons in each cycle from the output upper port of the second beam splitter to the input lower port of the first beam splitter within one superposition state generation period, and keeps the photon delay time in each cycle the same.
Further, the pre-stored relation satisfies:
a 0 2 =T 0 b 1 ；
a 1 2 =(1-T 0 )b 1 T 1 (b 2 b 1 )；
a 2 2 =(1-T 0 )(1-T 1 )b 1 T 2 (b 2 b 1 ) 2 ；
…
a N 2 =(1-T 0 )(1-T 1 )…(1-T N-1 )b 1 T N (b 2 b 1 ) N ；
and a 0 2 +a 1 2 +…+a N 2 =1；
Wherein b 1 Transmission transmittance, b, for an equal arm MZ interferometer 2 T is the transmission transmittance of the curved waveguide 0 The pass rate of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter, T 1 、T 2 …T N The pass rates of photons in the nth cycles of the first and second cycles … … from the input upper port of the first beam splitter to the output lower port of the second beam splitter respectively correspond.
In general, compared with the prior art, the above technical solutions conceived by the present application can achieve the following beneficial effects:
the utility model provides a random time-bin quantum superposition state generation system and method, the generation system comprises an upper computer, a single photon source, an equal-arm MZ interferometer, a curved waveguide and a controller, wherein the equal-arm MZ interferometer consists of two beam splitters and a phase modulator arranged between the two beam splitters, and the upper computer calculates photons output by the single photon source from an input lower port of a first beam splitter to an output lower port of a second beam splitter based on input parameters and a prestored relational expressionRate of passage T of ports 0 And the rate of passage T of photons in each cycle from the input upper port of the first beam splitter to the output lower port of the second beam splitter 1 、T 2 …T N The controller correspondingly adjusts the phase modulator in each transmission process based on the acquired passing rate in each process, so that photons in each cycle are input from an input upper port of the first beam splitter to an output lower port of the second beam splitter with corresponding probability, and after the preset cycle times in one cycle are completed, a time-bin quantum superposition state is obtained. According to the method and the device, the time-bin quantum superposition state of the corresponding dimension can be obtained according to the preset cycle times and the preset time components corresponding to each process, and the method and the device have the advantage of adaptability adjustment. According to the scheme, the equal-arm MZ interferometer and the curved waveguide are adopted, and the phase modulators in different cycles are modulated to obtain the time-bin quantum superposition state with any dimension, so that resources and space are saved, and the number of the equal-arm MZ interferometers is not dependent.
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In order to more clearly illustrate the present embodiments or the technical solutions in the prior art, the drawings that are required for the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic view of a prior art structure of the present application;
FIG. 2 is another schematic view of the prior art of the present application;
FIG. 3 is a schematic structural diagram of an arbitrary time-bin quantum superposition state generating system according to an embodiment of the present application;
FIG. 4 is a schematic structural diagram of an upper computer in the present application;
FIG. 5 is a schematic structural diagram of an arbitrary time-bin quantum superposition state generating system according to another embodiment of the present application;
FIG. 6 is a schematic structural diagram of an arbitrary time-bin quantum superposition state generating system according to another embodiment of the present application;
fig. 7 is a schematic structural diagram of an arbitrary time-bin quantum superposition state generation system provided in the present application based on fig. 5 and 6.
Detailed Description
In order to make the above objects, features and advantages of the present application more comprehensible, embodiments accompanied with figures and detailed description are described in further detail below. It will be apparent that the described embodiments are only some, but not all, of the embodiments of the present application. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application, but the present application may be practiced in other ways other than those described herein, and persons skilled in the art will readily appreciate that the present application is not limited to the specific embodiments disclosed below.
In order to facilitate understanding and explanation of the technical solutions provided by the embodiments of the present application, the background art of the present application will be described first.
At present, the generation mode of the multi-dimensional time-bin superposition state mainly adopts N unequal arm interferometers to be connected in series, different delay times are achieved by adjusting modulators on the unequal arm interferometers, and the N-dimensional time-bin superposition state is formed, specifically, as shown in fig. 1 and 2, the relative delay time of each unequal arm interferometer in fig. 1 is equal, and the relative delay time of each unequal arm interferometer in fig. 2 is linearly and equivalently increased. Therefore, N unequal arm interferometers are needed for realizing N-dimensional time-bin coding, the device requirement and occupied space are large, the resource consumption is high, the cost is high, and the dimension is fixed along with the design number of the unequal arm interferometers and cannot be adjusted adaptively.
Based on the above, the application provides an arbitrary time-bin quantum superposition state generation system, which comprises a host computer, a single photon source, an equal-arm MZ interferometer, a curved waveguide and a controller as shown in fig. 3.
Specifically, the single photon source is used for outputting photons and transmitting the photons to the equal-arm MZ interferometer, and the single photon source can only emit one photon in unit time, and the unit time is the period of the output photons of the single photon source, and the period of the output photons can be modulated according to the specific implementation process.
The equal-arm MZ interferometer consists of a first beam splitter, an interference upper arm, an interference lower arm, a phase modulator and a second beam splitter, wherein two ends of the interference upper arm are respectively connected with an output upper port of the first beam splitter and an input upper port of the second beam splitter, two ends of the interference lower arm are respectively connected with an output lower port of the first beam splitter and an input lower port of the second beam splitter, and the phase modulator is arranged on the interference upper arm. The two ends of the curved waveguide are respectively connected with the input upper port of the first beam splitter and the output upper port of the second beam splitter, and are used for transmitting photons output from the output upper port of the second beam splitter to the input upper port of the first beam splitter.
The upper computer is used for inputting parameters for generating superposition states and calculating the passing rate T of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter based on the prestored relation and the input parameters 0 And the pass rate of photons in each cycle from the input upper port of the first beam splitter to the output lower port of the second beam splitter, the pass rate of photons in each cycle from the input upper port of the first beam splitter to the output lower port of the second beam splitter corresponding to T respectively 1 、T 2 …T N 。
The phase modulator adjusts the passing rate T of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter based on the control of the controller 0 And adjusting the pass rate (T 1 、T 2 …T N ). The input port of the first beam splitter is used for receiving photons output by the single photon source. The output lower port of the second beam splitter is used for outputting the generated time-bin quantum superposition state:
|φ>=a 0 |0>+a 1 |1>+…+a N |N>
wherein |phi>Representing the output quantum superposition state; i0>Representing the time component of the process of photons output by a single photon source from the input lower port of a first beam splitter to the output lower port of a second beam splitter, |1>、|2>…|N>Time components of the nth cycle process of the first cycle and the second cycle … … respectively; a, a 0 A probability amplitude of the process time component corresponding to photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter, a 1 、a 2 …a N Probability magnitudes corresponding to the nth cycle time components of the first cycle, the second cycle … …, respectively; n is the set cycle number; the path of each cyclic process consists of two part transmission paths, a transmission path on a curved waveguide and a transmission path in an equal arm MZ interferometer, respectively.
The controller is respectively connected with the phase modulator and the upper computer and is used for receiving the passing rate T output by the upper computer 0 、T 1 、T 2 …T N And based on T 0 、T 1 、T 2 …T N The phase modulators are respectively adjusted correspondingly.
Each pass rate T based on upper computer feedback by controller 0 、T 1 、T 2 …T N The phase modulation of the phase modulator is completed one by one. Specifically, the controller passes through each pass rate T 0 、T 1 、T 2 …T N And calculating and acquiring the modulation voltage or current of the phase modulator corresponding to each subsequent cycle process from the input lower port of the first beam splitter to the output lower port of the second beam splitter, wherein the controller sequentially completes the initial process and the phase modulation of each cycle process according to a preset phase modulation period (the retention time of each modulation voltage or current).
The specific process is as follows: photons output by the single photon source are input from the input lower port of the first beam splitter, and the controller adjusts the driving voltage or current of the phase modulator to enable the photons output by the single photon source to be in a T shape 0 The pass rate is input to the output lower port of the second beam splitter (corresponding to the initial procedure), thenCorrespondingly in (1-T) 0 ) The pass rate input to the output upper port of the second beam splitter enters the first cycle. The transmission path of the first cycle comprises a transmission path of photons on a curved waveguide and a transmission path on an equal-arm MZ interferometer, that is, photons output from the output upper port of the second beam splitter are transmitted through the curved waveguide to the input upper port of the first beam splitter and then enter the equal-arm MZ interferometer for transmission, and in the first cycle, the controller adjusts the driving voltage or current of the phase modulator to make photons entering the first cycle take the form of T 1 The pass rate is input to the output lower port of the second beam splitter, then the pass rate is correspondingly input in (1-T 1 ) And the pass rate is input to an output upper port of the second beam splitter to enter a second cycle, and the like until the phase modulation of the preset cycle process is completed.
In the present application, the relational expression stored in advance in the host computer satisfies:
a 0 2 =T 0 b 1 ；
a 1 2 =(1-T 0 )b 1 T 1 (b 2 b 1 )；
a 2 2 =(1-T 0 )(1-T 1 )b 1 T 2 (b 2 b 1 ) 2 ；
…
a N 2 =(1-T 0 )(1-T 1 )…(1-T N-1 )b 1 T N (b 2 b 1 ) N ；
and a 0 2 +a 1 2 +…+a N 2 =1；
Wherein b 1 Transmission transmittance, b, for an equal arm MZ interferometer 2 T is the transmission transmittance of the curved waveguide 0 The pass rate of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter, T 1 、T 2 …T N The pass rates of photons in the nth cycles of the first and second cycles … … from the input upper port of the first beam splitter to the output lower port of the second beam splitter respectively correspond.
The photons have light intensity loss in the structure transmission, the light intensity loss of the photons is caused by the transmission loss of the equal-arm MZ interferometer and the bending waveguide in the application, and the transmission passing rate of the equal-arm MZ interferometer is set as b 1 The transmission transmittance of the curved waveguide is b 2 The transmission transmittance is here the output light intensity/input light intensity, which is known and fixed for the equal arm MZ interferometer and curved waveguide in the present application.
The upper computer generates parameters of superposition state and pre-stored relation calculation T based on input 0 、T 1 、T 2 …T N . Specifically, the input parameters that produce the superposition state include the transmission transmittance b of the equal-arm MZ interferometer 1 Transmission transmittance b of curved waveguide 2 The preset cycle number N, the probability amplitude a of the process time component of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter 0 And the probability amplitude a of each cyclic time component 1 、a 2 …a N 。
Assuming that the 6-dimensional time-bin quantum superposition state is pre-generated, corresponding to six time components, and five times of circulation process, the six time components are respectively |0 >、|1>、|2>…|5>，|0>Representing the time component of the process of photons output by a single photon source from the input lower port of a first beam splitter to the output lower port of a second beam splitter, |1>、|2>…|N>The time components of the fifth cycle process of the first cycle and the second cycle … … respectively need to be set with 6 probability amplitude values a 0 、a 1 、a 2 …a 5 ，a 0 A probability amplitude of the process time component corresponding to photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter, a 1 、a 2 …a 5 The probability magnitudes for the fifth cycle time component of the first cycle, the second cycle … …, respectively. The parameters entered on the upper computer include: cycle number 5 and b 1 、b 2 、a 0 、a 1 、a 2 、a 3 、a 4 And a 5 Corresponding toIs calculated based on the inputted values to obtain T 0 、T 1 、T 2 、T 3 、T 4 And T 5 . Specifically T 0 The pass rate of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter, T 1 、T 2 …T 5 The pass rates of photons in the fifth cycle of the first cycle and the second cycle … … respectively from the input upper port of the first beam splitter to the output lower port of the second beam splitter.
In this application, the upper computer includes a parameter setting module, a data processing module, and a data transmission module, which are sequentially connected, as shown in fig. 4. The parameter setting module is used for inputting parameters for generating superposition state. The data processing module calculates the passing rate T of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter based on a prestored relational expression and parameters input by the parameter setting module 0 And a rate of passage T of photons in each cycle from an input upper port of the first beam splitter to an output lower port of the second beam splitter 1 、T 2 …T N . The data transmission module is used for transmitting T 0 、T 1 、T 2 …T N And transmitted to the controller.
In another embodiment of the present application, the arbitrary time-bin quantum superposition state generating system further includes an optical switch connected to the controller, as shown in fig. 5, where the optical switch is disposed on a transmission path between the single photon source and the input lower port of the first beam splitter, and is configured to control on-off of the transmission path between the single photon source and the input lower port of the first beam splitter, so as to ensure that only one photon is input to the input lower port of the first beam splitter in one superposition state generating period.
When the unit time of the photon output by the single photon source (the period of the photon output by the single photon source) is more than or equal to the superposition state generation period, only one photon can be ensured to be input to the input lower port of the first beam splitter in one superposition state generation period. However, when the unit time of the output photons of the single photon source is smaller than the superposition state generation period, the optical switch needs to be set to ensure that only one photon is input to the input lower port of the first beam splitter in one superposition state generation period. Specifically, the optical switch is connected with the controller, when the controller completes the phase modulation of the phase modulator one by one in the superposition state generation period, the optical switch is controlled to be turned on, the single photon source inputs photons to the input lower port of the first beam splitter again to start the quantum superposition state generation process of the next period, namely the time coding of the next period, the optical switch is turned off after the photons are input to the input lower port of the first beam splitter, and the time interval between the turning-off of the optical switch and the turning-on of the optical switch is controlled to be smaller than the period of the single photon source to output photons, so that the time coding of the next period is ensured when only one photon is input to the input lower port of the first beam splitter.
In this application, the optical switch may be a mechanical optical switch or an MZI-type optical switch. The mechanical optical switch is a 1X 1 optical switch, so that the on-off of a single photon source and a transmission light path of an input lower port of the first beam splitter can be realized. When the MZI type optical switch is adopted, the path selection of photons is realized by precisely adjusting the phase difference on the interference arm. Specifically, when it is required to input a photon to the input lower port of the first beam splitter, the phase difference on the interference arm is adjusted to enable the photon to be input from one output port of the beam combiner to the input lower port of the first beam splitter in the equal-arm MZ interferometer, and when it is required to block the photon from being input to the equal-arm MZ interferometer, the phase difference on the interference arm is adjusted to enable the photon to be output from the other output port of the beam combiner and consumed in free space.
In addition, the application further provides another embodiment, the arbitrary time-bin quantum superposition state generating system further comprises an on-chip tunable optical delay structure connected with the controller, as shown in fig. 6, the on-chip tunable optical delay structure is arranged on the curved waveguide, and is used for adjusting the delay time of photons in each cycle from the output upper port of the second beam splitter to the input upper port of the first beam splitter, and keeping the delay time of each cycle process the same.
Specifically, the on-chip dimmable delay structure is a dimmable delay line or a dimmable delay chip in the present application. The on-chip adjustable light delay structure is controlled by the controller to adjust the delay time of each cycle process in one superposition state generation period, and the delay time of each cycle process in one superposition state generation period is kept the same.
The delay time of the adjustable light delay structure can be input on the upper computer, the upper computer feeds the input delay time back to the controller, and the controller adjusts the delay time of each cycle process in one superposition state generation period based on the feedback delay time, namely, adjusts the time interval between time components in each period and keeps the time interval in one period equal.
Based on fig. 5 and fig. 6, the embodiment of the application further provides an arbitrary time-bin quantum superposition state generating system, as shown in fig. 7, where the time-bin quantum superposition state generating system includes an optical switch and an on-chip tunable optical delay structure, and the optical switch and the on-chip tunable optical delay structure are both connected with a controller.
According to the scheme, the time-bin quantum superposition state with corresponding dimension can be obtained according to the preset circulation times and the preset time component corresponding to each process, and the method has the advantage of adaptability adjustment. The equal-arm MZ interferometer and the curved waveguide are adopted, the phase modulators in different cycles are modulated to obtain the time-bin quantum superposition state with any dimension, and resources and space are saved and the number of the equal-arm MZ interferometers is not depended on.
Based on the arbitrary time-bin quantum superposition state generation system provided in the embodiment of the application, the embodiment of the application correspondingly provides an arbitrary time-bin quantum superposition state generation method, which includes:
s11: inputting parameters for generating superposition state on the upper computer, and calculating the pass rate T of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter by the upper computer based on the input parameters and a prestored relational expression 0 And the rate of passage T of photons in each cycle from the input upper port of the first beam splitter to the output lower port of the second beam splitter 1 、T 2 …T N 。
In S11 the process proceeds to the step of,the input parameters include the transmission transmittance b of the equal arm MZ interferometer 1 Transmission transmittance b of curved waveguide 2 The preset cycle number N, the probability amplitude a of the process time component of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter 0 And the probability amplitude a of each cyclic time component 1 、a 2 …a N . The pre-stored relationship satisfies:
a 0 2 =T 0 b 1 ；
a 1 2 =(1-T 0 )b 1 T 1 (b 2 b 1 )；
a 2 2 =(1-T 0 )(1-T 1 )b 1 T 2 (b 2 b 1 ) 2 ；
…
a N 2 =(1-T 0 )(1-T 1 )…(1-T N-1 )b 1 T N (b 2 b 1 ) N ；
and a 0 2 +a 1 2 +…+a N 2 =1。
The upper computer inputs b 1 、b 2 、a 0 、a 1 、a 2 …a N The relation calculation is used for obtaining T 0 、T 1 、T 2 …T N Each pass rate T based on upper computer feedback by the controller 0 、T 1 、T 2 …T N The phase modulation of the phase modulator is completed one by one, and the specific steps are as follows:
S12: the single photon source inputs photons to the input lower port of the first beam splitter, and the controller inputs photons according to T 0 Adjusting the phase modulator to make the photons output by the single photon source in T 0 From the input lower port of the first beam splitter to the output lower port of the second beam splitter, to (1-T) 0 ) The pass rate of the first beam splitter enters the first cycle from the output upper port of the second beam splitter and is input to the input upper port of the first beam splitter through the curved waveguide.
From S11, it is known that, in the input parameters, the probability amplitude of the time component of the process of the photons output by the single photon source from the input port of the first beam splitter to the output port of the second beam splitter is a 0 Thus, the photons output by the single photon source are denoted as a 0 2 From the input lower port of the first beam splitter to the output lower port of the second beam splitter, to (1-a) 0 2 ) Into the first cycle from the output upper port of the second splitter, through the curved waveguide to the input upper port of the first splitter.
S13: the controller is according to T 1 Adjusting the phase modulator to T photons transmitted to the input port of the first beam splitter in the first cycle 1 Is input from the input lower port of the first beam splitter to the output lower port of the second beam splitter to (1-T) 1 ) The pass rate of the first beam splitter enters the second cycle from the output upper port of the second beam splitter and is input to the input upper port of the first beam splitter through the curved waveguide.
From the above, the probability amplitude of the first cyclic time component is a 1 In one period of superposition generation, photons transmitted to the input port of the first beam splitter in the first cycle are then transmitted to the input port of the first beam splitter in a 1 2 /（1-a 0 2 ) From the input lower port of the first beam splitter to the output lower port of the second beam splitter to (1-a) 0 2 -a 1 2 ）/（1-a 0 2 ) Into the second cycle from the output upper port of the second splitter, through the curved waveguide to the input upper port of the first splitter.
S14: the controller is according to T 2 Adjusting the phase modulator to T photons transmitted to the input port of the first beam splitter in the second cycle 2 The pass rate is input from the input lower port of the first beam splitter to the output lower port of the second beam splitter to (1-T) 2 ) The pass rate of the first beam splitter enters a third cycle from an output upper port of the second beam splitter, and is input to an input upper port of the first beam splitter through a bent waveguide; in this way circulate … …
From the above, the second cycle timeThe probability amplitude of the component is a 2 In one period of superposition generation, photons transmitted to the input port of the first beam splitter in the second cycle are then transmitted to the input port of the first beam splitter in a 2 2 /（1-a 0 2 -a 1 2 ) From the input lower port of the first beam splitter to the output lower port of the second beam splitter to (1-a) 0 2 -a 1 2 -a 2 2 ）/（1-a 0 2 -a 1 2 ) Into the third cycle from the output upper port of the second splitter, through the curved waveguide to the input upper port of the first splitter.
S15: the controller is according to T N-1 Adjusting the phase modulator to T photons transmitted to the input port of the first beam splitter in the N-1 th cycle N-1 Is input from the input lower port of the first beam splitter to the output lower port of the second beam splitter to (1-T) N-1 ) The pass rate of the first beam splitter enters the nth cycle from the output upper port of the second beam splitter and is input to the input upper port of the first beam splitter through the curved waveguide.
From the above, the probability amplitude of the N-1 th cycle time component is a N-1 In one superposition state generation period, photons transmitted to the input upper port of the first beam splitter in the N-1 th cycle are transmitted to the input upper port of the first beam splitter in order to form a N-1 2 /（1-a 0 2 -a 1 2 -…-a N-2 2 ) From the input lower port of the first beam splitter to the output lower port of the second beam splitter to (1-a) 0 2 -a 1 2 -…-a N-2 2 -a N-1 2 ）/（1-a 0 2 -a 1 2 -…-a N-2 2 ) Into the nth cycle from the output upper port of the second beam splitter, through the curved waveguide, and into the input upper port of the first beam splitter.
S16: the controller is according to T N Adjusting the phase modulator to T photons transmitted to the input port of the first beam splitter in the Nth cycle N Is input from the input lower port of the first beam splitter to the second beam splitterAnd the output lower port of the beam splitter completes the corresponding modulation of the phase modulator in a superposition state generation period, and the time-bin quantum superposition state output from the output lower port of the second beam splitter is as follows:
|φ>=a 0 |0>+a 1 |1>+…+a N |N>
wherein |phi>Representing the output quantum superposition state; i0>Representing the time component of the process of photons output by a single photon source from the input lower port of a first beam splitter to the output lower port of a second beam splitter, |1>、|2>……|N>Time components of the nth cycle process of the first cycle and the second cycle … … respectively; a, a 0 A probability amplitude of the process time component corresponding to photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter, a 1 、a 2 ……a N Probability magnitudes corresponding to the nth cycle time components of the first cycle, the second cycle … …, respectively; n is the set number of cycles.
From the above, the probability amplitude of the nth cycle time component is a N In one superposition state generation period, photons transmitted to the input upper port of the first beam splitter in the nth cycle are then transmitted to the input upper port of the first beam splitter in order to form a N 2 /（1-a 0 2 -a 1 2 -…-a N-1 2 ) From the input lower port of the first beam splitter to the output lower port of the second beam splitter, due to a) 0 2 +a 1 2 +…+a N 2 It is known that photons transmitted to the input port of the first beam splitter in the nth cycle are input from the input port of the first beam splitter to the output port of the second beam splitter with 100% probability, that is, photons must be input to the output port of the second beam splitter in the nth cycle, and all the cycle processes preset in one superposition state generation period are completed.
Based on the method for generating any time-bin quantum superposition state provided by the embodiment of the application, when the system includes an optical switch connected with the controller, the method further includes:
the controller controls the optical switch to be turned on, a single photon source inputs photons to the input lower port of the first beam splitter, the optical switch is turned off after the photons are input, and time coding in the current superposition state generation period is carried out; after the modulation of the phase modulator in the current superposition state generation period is completed, the controller controls the optical switch to be turned on again, the single photon source inputs photons to the input lower port of the first beam splitter again, the optical switch is turned off after the photons are input, and the time coding of the next superposition state generation period is started.
When the period time of the photon output by the single photon source is smaller than the superposition state generation period, an optical switch is required to be arranged to ensure that only one photon is input to the input lower port of the first beam splitter in one superposition state generation period.
The controller controls the optical switch to be turned on, the single photon source inputs photons to the input lower port of the first beam splitter and then turns off the optical switch, wherein the time interval between the turning-off of the optical switch and the turning-on of the optical switch is smaller than the period of the single photon source outputting photons, so that only one photon is input to the input lower port of the first beam splitter to perform time coding in the current superposition state generation period. In a period, the time interval between the disconnection of the optical switch and the connection of the optical switch is set according to the frequency of the photons output by the single photon source, the time interval between the disconnection of the optical switch and the connection of the optical switch is input into the upper computer, then the upper computer feeds the data back to the controller, and the controller controls the disconnection time of the switch according to the fed-back time interval. When the controller finishes the phase modulation of the phase modulator in the current superposition state generation period one by one, the controller controls the optical switch to be conducted again, the single photon source inputs photons to the input lower port of the first beam splitter again, the time of the controller controlling the optical switch to be conducted is based on the phase modulation signal of the last cycle process in the superposition state generation period, when the controller finishes the phase modulation of the phase modulator in the last cycle process in the current superposition state generation period, the controller controls the optical switch to be conducted again, and the single photon source inputs photons to the input lower port of the first beam splitter again to start the time coding of the next superposition state generation period.
Based on the method for generating any time-bin quantum superposition state provided by the embodiment of the application, when the system comprises an on-chip tunable optical delay structure connected with the controller, the method further comprises:
the controller controls the delay time of photons in each cycle from the output upper port of the second beam splitter to the input lower port of the first beam splitter within one superposition state generation period, and keeps the photon delay time in each cycle the same.
The delay time of the adjustable light delay structure can be input on the upper computer, the upper computer feeds the input delay time back to the controller, and the controller adjusts the delay time of each cycle process in one superposition state generation period based on the feedback delay time, namely, adjusts the time interval between time components in each period and keeps the time interval in one period equal.
In the present specification, each embodiment is described in a progressive manner, or a parallel manner, or a combination of progressive and parallel manners, and each embodiment is mainly described as a difference from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.
It is noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that an article or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such article or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in an article or apparatus that comprises such element.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. The random time-bin quantum superposition state generation system is characterized by comprising an upper computer, a single photon source, an equal-arm MZ interferometer, a curved waveguide and a controller;
the single photon source is used for outputting photons;
the equal-arm MZ interferometer consists of a first beam splitter, an interference upper arm, an interference lower arm, a phase modulator and a second beam splitter, wherein two ends of the interference upper arm are respectively connected with an output upper port of the first beam splitter and an input upper port of the second beam splitter, two ends of the interference lower arm are respectively connected with an output lower port of the first beam splitter and an input lower port of the second beam splitter, the phase modulator is arranged on the interference upper arm and is used for adjusting the passing rate T of photons output by a single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter based on the control of the controller 0 And adjusting the pass rate of photons in each cycle from the input upper port of the first beam splitter to the output lower port of the second beam splitter, corresponding to T respectively 1 、T 2 …T N The input lower port of the first beam splitter is used for receiving photons output by the single photon source; the output lower port of the second beam splitter is used for outputting the generated time-bin quantum superposition state:
|φ>=a 0 |0>+a 1 |1>+…+a N |N>
wherein |phi>Representing the output quantum superposition state; i0>Representing the time component of the process of photons output by a single photon source from the input lower port of a first beam splitter to the output lower port of a second beam splitter, |1>、|2>…|N>Time components of the nth cycle process of the first cycle and the second cycle … … respectively; a, a 0 A probability amplitude of the process time component corresponding to photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter, a 1 、a 2 …a N Probability magnitudes corresponding to the nth cycle time components of the first cycle, the second cycle … …, respectively; n is the set cycle number; each circulating path is composed of two parts of transmission paths, namely a transmission path on a curved waveguide and a transmission path in the equal-arm MZ interferometer;
the two ends of the curved waveguide are respectively connected with the input upper port of the first beam splitter and the output upper port of the second beam splitter, and are used for transmitting photons output from the output upper port of the second beam splitter to the input upper port of the first beam splitter;
The upper computer is used for inputting parameters for generating superposition states and calculating the passing rate T of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter based on a prestored relational expression and the input parameters 0 And the pass rate of photons in each cycle from the input upper port of the first beam splitter to the output lower port of the second beam splitter, respectively corresponding to T 1 、T 2 …T N ；
The controller is respectively connected with the phase modulator and the upper computer and is used for receiving the passing rate T output by the upper computer 0 、T 1 、T 2 …T N And based on T 0 、T 1 、T 2 …T N The phase modulators are adjusted correspondingly, respectively.
2. The arbitrary time-bin quantum superposition state generation system according to claim 1, wherein said pre-stored relationship satisfies:
a 0 2 =T 0 b 1 ；
a 1 2 =(1-T 0 )b 1 T 1 (b 2 b 1 )；
a 2 2 =(1-T 0 )(1-T 1 )b 1 T 2 (b 2 b 1 ) 2 ；
…
a N 2 =(1-T 0 )(1-T 1 )…(1-T N-1 )b 1 T N (b 2 b 1 ) N ；
and a 0 2 +a 1 2 +…+a N 2 =1；
Wherein b 1 Transmission transmittance, b, for an equal arm MZ interferometer 2 T is the transmission transmittance of the curved waveguide 0 The pass rate of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter, T 1 、T 2 …T N The pass rates of photons in the nth cycles of the first and second cycles … … from the input upper port of the first beam splitter to the output lower port of the second beam splitter respectively correspond.
3. The arbitrary time-bin quantum superposition state generation system according to claim 1, wherein said parameters comprise: transmission transmittance b of equal arm MZ interferometer 1 Transmission transmittance b of curved waveguide 2 The preset cycle number N, the probability amplitude a of the process time component of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter 0 And the probability amplitude a of each cyclic time component 1 、a 2 …a N 。
4. The system for generating random time-bin quantum superposition state according to claim 1, wherein said upper computer comprises a parameter setting module, a data processing module and a data transmission module which are connected in sequence; the parameter setting module is used for inputting parameters for generating superposition states; the data processing module calculates the flux of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter based on the prestored relational expression and the parameters input by the parameter setting moduleRate T of excess 0 And a rate of passage T of photons in each cycle from an input upper port of the first beam splitter to an output lower port of the second beam splitter 1 、T 2 …T N The method comprises the steps of carrying out a first treatment on the surface of the The data transmission module is used for transmitting T 0 、T 1 、T 2 …T N To the controller.
5. The system of any one of claims 1-4, further comprising an optical switch connected to the controller, wherein the optical switch is disposed on a transmission path between the single photon source and the input port of the first beam splitter, and is configured to control on/off of a transmission path between the single photon source and the input port of the first beam splitter.
6. The arbitrary time-bin quantum superposition state generation system according to any of claims 1-4, further comprising an on-chip tunable optical delay structure coupled to said controller, said on-chip tunable optical delay structure disposed on said curved waveguide for adjusting the delay time of photons in each cycle from the output upper port of said second beam splitter to the input upper port of said first beam splitter, and maintaining the same delay time for each cycle.
7. A method for generating any time-bin quantum superposition state, wherein the method is applied to any time-bin quantum superposition state generating system according to any one of claims 1 to 6, the system comprising: the optical fiber optical system comprises an upper computer, a single photon source, an equal-arm MZ interferometer, a curved waveguide and a controller, wherein the equal-arm MZ interferometer consists of a first beam splitter, an interference upper arm, an interference lower arm, a phase modulator and a second beam splitter, two ends of the interference upper arm are respectively connected with an output upper port of the first beam splitter and an input upper port of the second beam splitter, two ends of the interference lower arm are respectively connected with an output lower port of the first beam splitter and an input lower port of the second beam splitter, and the phase modulator is arranged on the interference upper arm;
The method comprises the following steps:
inputting parameters for generating superposition state on the upper computer, and calculating the pass rate T of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter by the upper computer based on the input parameters and a prestored relational expression 0 And the rate of passage T of photons in each cycle from the input upper port of the first beam splitter to the output lower port of the second beam splitter 1 、T 2 …T N ；
The single photon source inputs photons to the input lower port of the first beam splitter, and the controller inputs photons according to T 0 Adjusting the phase modulator to make the photons output by the single photon source in T 0 From the input lower port of the first beam splitter to the output lower port of the second beam splitter, to (1-T) 0 ) The pass rate of the first beam splitter enters the first cycle from the output upper port of the second beam splitter, and is input to the input upper port of the first beam splitter through the bent waveguide;
the controller is according to T 1 Adjusting the phase modulator to T photons transmitted to the input port of the first beam splitter in the first cycle 1 Is input from the input lower port of the first beam splitter to the output lower port of the second beam splitter to (1-T) 1 ) The pass rate of the first beam splitter enters the second cycle from the output upper port of the second beam splitter, and is input to the input upper port of the first beam splitter through the bent waveguide;
The controller is according to T 2 Adjusting the phase modulator to T photons transmitted to the input port of the first beam splitter in the second cycle 2 The pass rate is input from the input lower port of the first beam splitter to the output lower port of the second beam splitter to (1-T) 2 ) The pass rate of the first beam splitter enters a third cycle from an output upper port of the second beam splitter, and is input to an input upper port of the first beam splitter through a bent waveguide; in this way circulate … …
The controller is according to T N-1 Adjusting the phase modulator to T photons transmitted to the input port of the first beam splitter in the N-1 th cycle N-1 Is input from the input lower port of the first beam splitter to the output of the second beam splitterLower port, in (1-T) N-1 ) The pass rate of the first beam splitter enters the Nth cycle from the output upper port of the second beam splitter, and is input to the input upper port of the first beam splitter through a bent waveguide;
the controller is according to T N Adjusting the phase modulator to T photons transmitted to the input port of the first beam splitter in the Nth cycle N The probability of (1) is input from the input lower port of the first beam splitter to the output lower port of the second beam splitter, and the corresponding modulation of the phase modulator in one superposition state generation period is completed, so that the time-bin quantum superposition state output from the output lower port of the second beam splitter is as follows:
|φ>=a 0 |0>+a 1 |1>+…+a N |N>
Wherein |phi>Representing the output quantum superposition state; i0>Representing the time component of the process of photons output by a single photon source from the input lower port of a first beam splitter to the output lower port of a second beam splitter, |1>、|2>……|N>Time components of the nth cycle process of the first cycle and the second cycle … … respectively; a, a 0 A probability amplitude of the process time component corresponding to photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter, a 1 、a 2 ……a N Probability magnitudes corresponding to the nth cycle time components of the first cycle, the second cycle … …, respectively; n is the set number of cycles.
8. The method of any time-bin quantum superposition state generation according to claim 7, wherein when said system comprises an optical switch coupled to a controller, said method further comprises:
the controller controls the optical switch to be turned on, a single photon source inputs photons to the input lower port of the first beam splitter, the optical switch is turned off after the photons are input, and time coding in the current superposition state generation period is carried out; after the modulation of the phase modulator in the current superposition state generation period is completed, the controller controls the optical switch to be turned on again, the single photon source inputs photons to the input lower port of the first beam splitter again, the optical switch is turned off after the photons are input, and the time coding of the next superposition state generation period is started.
9. The method of any time-bin quantum superposition state generation according to claim 7, wherein when said system comprises an on-chip tunable optical delay structure coupled to a controller, said method further comprises:
the controller controls the delay time of photons in each cycle from the output upper port of the second beam splitter to the input lower port of the first beam splitter within one superposition state generation period, and keeps the photon delay time in each cycle the same.
10. The method for generating any time-bin quantum superposition state according to claim 7, wherein said pre-stored relation satisfies:
a 0 2 =T 0 b 1 ；
a 1 2 =(1-T 0 )b 1 T 1 (b 2 b 1 )；
a 2 2 =(1-T 0 )(1-T 1 )b 1 T 2 (b 2 b 1 ) 2 ；
…
a N 2 =(1-T 0 )(1-T 1 )…(1-T N-1 )b 1 T N (b 2 b 1 ) N ；
and a 0 2 +a 1 2 +…+a N 2 =1；
Wherein b 1 Transmission transmittance, b, for an equal arm MZ interferometer 2 T is the transmission transmittance of the curved waveguide 0 The pass rate of photons output by the single photon source from the input lower port of the first beam splitter to the output lower port of the second beam splitter, T 1 、T 2 …T N The pass rates of photons in the nth cycles of the first and second cycles … … from the input upper port of the first beam splitter to the output lower port of the second beam splitter respectively correspond.
CN202310658600.6A 2023-06-06 2023-06-06 System and method for generating superposition state of random time-bin quanta Active CN116382012B (en)

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