Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
  • H04B10/70—Photonic quantum communication
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B13/00—Optical objectives specially designed for the purposes specified below
  • G02B13/0095—Relay lenses or rod lenses
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06N—COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
  • G06N10/00—Quantum computing, i.e. information processing based on quantum-mechanical phenomena
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06N—COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
  • G06N10/00—Quantum computing, i.e. information processing based on quantum-mechanical phenomena
  • G06N10/40—Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06N—COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
  • G06N10/00—Quantum computing, i.e. information processing based on quantum-mechanical phenomena
  • G06N10/20—Models of quantum computing, e.g. quantum circuits or universal quantum computers

Definitions

• quantum repeaters using a backbone of quantum nodes to store intermediate quantum entangled states or perform active quantum error detection and correction to suppress loss and operation errors
• satellite- based quantum communication taking advantage of outer space that are essentially vacuum.
• Quantum repeaters are still under active investigation they require long-lived quantum memory or active quantum error correction; so far there is no scalable demonstration of quantum repeaters.
• the quantum satellite was launched in 2016, but it is very expensive, with limited bandwidth and weather dependent.
• the present invention is a quantum network, comprising: at least a first node comprising a first quantum system, and a second node comprising a second quantum system; and an optical guide in optical communication with the at least the first and the second nodes, wherein the optical guide comprises: a reduced pressure enclosure; and a lens cascade disposed in the reduced pressure enclosure.
• the present invention is a method of transmitting a quantum state between nodes of a quantum network.
• the method comprises: providing a first node comprising a first quantum system, and a second node, comprising a second quantum system; causing the first quantum system to generate at least one electromagnetic (EM) optical mode, the first quantum system being in a quantum state, the optical mode encoding a quantum state; directing the optical mode into an optical guide, the optical guide being in optical communication with the second node, wherein the optical guide comprises: a reduced pressure enclosure; and a lens cascade disposed in the reduced pressure enclosure, and causing the optical mode to interact with the second quantum system, thereby imparting the quantum state onto the second quantum system.
• EM electromagnetic
• Fig.1A is an example map of a series of VBG backbone networks over long distances, according to embodiments of the present disclosure.
• Fig.1B is an example map of a regional network of fiber or free-space quantum channels, according to embodiments of the present disclosure.
• Fig.1C is an exemplary design of a VBG, according to embodiments of the present disclosure.
• Figs.2A-D each is a graph of an effective rate as a function of wavelength under various conditions, according to embodiments of the present disclosure.
• FH11893796.1 UCT-00625 [0011]
• Figs.3A-B each is a plot of an effective rate of a quantum channel as a function of transmission distance, according to embodiments of the present disclosure.
• Fig.4 is a schematic diagram of an optical guide that can be used by the devices and methods disclosed herein.
• Fig.5 is a bar plot showing the power distribution among the modes after the last iteration.
• Fig.6 is a conversion tree.
• Fig.7 is a bar plot showing the loss rate at the last iteration.
• Fig.9A and Fig.9B are the plots showing that the distance travelled by an optical mode improves with the focal length of the lenses (A) and with the lens radius (B).
• Fig.10 is a table listing the adjustable parameters.
• Fig.11A is a plot showing the dependency of the distance travelled by an optical mode as a function of its center wavelength.
• Fig.11B is a plot showing the wavelength-dependent loss rate (in units of dB/km) as a function of wavelength and pressure.
• Fig.11C is a plot showing the dependency of the loss rate on the wavelength is shown for the misalignment conditions described in the text, assuming the air pressure is assumed to be 10 ⁇ ⁇ ⁇ .
• Fig.11D is a plot showing quantum channel capacity at particular wavelength.
• Fig.12 is a schematic diagram of an example embodiment of a vacuum enclosure.
• Fig.13A is a plot illustrating the reflective loss of a two-layer ARC on silica substrate.
• Fig.13B is a plot illustrating Q vs distance under losses.
• Fig.14 is a plot illustrating a characteristic length under various configurations.
• Fig.15 is a schematic diagram of an example of a computing node.
• the vacuum beam guide presents a completely different solution for quantum channels to overcome the limitations of existing fiber and satellite technologies for long-distance quantum communication. With an array of aligned lenses spaced kilometers apart, the VBG offers ultra-high transparency over a wide range of optical wavelengths. With FH11893796.1 UCT-00625 realistic parameters, the VBG can outperform the best fiber by three orders of magnitude in terms of attenuation rate.
• the VBG can enable long-range quantum communication over thousands of kilometers with quantum channel capacity beyond 10 13 qubit/sec, orders of magnitude higher than the state-of-the-art quantum satellite communication rate.
• the VBG can provide a ground-based, low-loss, high-bandwidth quantum channel that enables novel distributed quantum information applications for computing, communication, and sensing.
• Significant progress has been made in extending the communication distances for quantum networks, including satellite-based quantum entanglement distribution over 1200 km and memory-enhanced quantum communication beyond the repeater-less bounds.
• satellite-based quantum channels are fragile, expensive, and restricted by local weather conditions.
• the VBG channel is set up within a vacuum chamber tube, which eliminates air absorption and effectively isolates the channel from the outer environment, ensuring robustness against environmental perturbations.
• beam waveguides have been proposed for classical optical communication, communications were previously taken over by low-cost optical fiber sufficient for classical communication, despite its intrinsic loss.
• the design of the vacuum beam guide has the potential to achieve ultra-low-loss long-distance communication.
• the VBG is deployed as the back-bone quantum channel that can be a part of a global quantum network with a hierarchy structure as shown in Fig.1A-B.
• the system can be built by estimating the upper bound of the attenuation dominated by residue air absorption, optical losses introduced by lenses, and misalignment of the beam guide.
• the estimation demonstrates the VBG as state-of-the-art FH11893796.1 UCT-00625 under a practical and exemplifying con-figuration, establishing it as one of the most practical and potentially useful quantum communication techniques at a global scale.
• VBGs vacuum beam guides
• Figs.1A-C A hierarchical structure of large-scale quantum networks connected by vacuum beam guides (VBGs) is shown in Figs.1A-C.
• the VBG backbone network shon on map 100 can transfer quantum information with high capacity (with TeraQubits/sec) over long distances, connecting regional quantum networks shown in Fig.1B.
• Fig.1B depicts an example regional network 102 that comprises fiber or free-space quantum channels designed to distribute quantum information to branch nodes and quantum terminals (with GigaQubits/sec) across urban scales.
• VBG Ultra-High Transmission of VBG.
• the vacuum 112 has a typical pressure below ⁇ 1 Pascal, which ensures low absorption from the remaining gas at room temperature.
• the lenses 108 are shielded from seismic vibrations and are optically aligned with adaptive feedback.
• Fig.1C illustrates the design of the VBG 106, placing lenses 108 with identical focus length f and radius R at regular intervals within a vacuum chamber tube 112, constructing a VBG with ⁇ ⁇ sections. The positions of the lenses 108 are stabilized by an advanced alignment system.
• the fundamental Gaussian mode with waist ⁇ ⁇ can travel at an extremely low loss over a distance of ⁇ ⁇ .
• Quantum states can be transferred from quantum node A 110 at one end of the VBG to quantum node B 110 at the other end of the VBG.
• Optical signals encoding quantum information can transmit through the VBG with little loss, even after passing through an array of aligned lenses over thousands of kilometers.
• the total loss per lens can be reduced to less than 10 ⁇ 4 , resulting in an effective loss rate of ⁇ ⁇ ⁇ 10 ⁇ 4 dB/km at the wave-lengths ⁇ ⁇ 1550 nm, which can match the telecom band.
• Gas loss in the VBG is primarily due to the absorption from residual air in the vacuum chamber tube.
• the attenuation rate ⁇ ⁇ is computed at various levels of gas pressure with the components of air based on the HITRAN database.
• the attenuation rate is ⁇ ⁇ ⁇ 10 ⁇ 4 dB/km for optical wavelengths within the selected telecom bands. Further reducing the air pressure below 10 ⁇ 2 Pascal is sufficient to achieve negligible air absorption by reducing attenuation rate below 10 ⁇ 4 dB/km almost over the entire spectrum.
• An upper bound can be derived for the effective attenuation rate induced by imperfect in the confocal ⁇ ⁇ ⁇ ⁇ where ⁇ ⁇ and ⁇ ⁇ are the magnitudes of the fluctuations of transverse and longitudinal displacements for each lens, and ⁇ ⁇ is the deviation of the focal length.
• ⁇ ⁇ 0.6 mm
• ⁇ ⁇ ⁇ 10 ⁇ 2 dB/km can still be achieved, which is much better than the attenuation rate of fiber by at least an order of magnitude.
• each lens will be actively positioned using slow actuators, based on standard alignment sensing systems, bringing the residual miscentering to ⁇ 0.1 mm.
• the VBG can achieve an attenuation level as low as 3 ⁇ 10 ⁇ 5 dB/km for an optimized choice of wavelength within the atmospheric window, which corresponds to an effective attenuation length of 80,000 km, more than three orders of magnitude better than state-of-the-art fiber technology.
• Quantum Channel Capacities of VBG The VBG can be used as a highly transparent bosonic quantum channel to transmit quantum information over long distances.
• the one-way pure-loss capacity for a single wave packet at a ⁇ is ⁇ which vanishes for ⁇ [ ⁇ ] ⁇ 1/2.
• the pure-loss VBG chan-nel is further assisted by two- way classical communication (between Alice and Bob), the corresponding two-way pure-loss capacity at a ⁇ is: which is finite for all ⁇ [ ⁇ ] > 0. [0043]
• the VBG can have a broad band with a large one-way or two-way channel capacity over long distances.
• the frequency-integrated channel capacity can be calculated, which provides the maximum transmission rate of information, over the ⁇ ⁇ for one-way and two-way quantum communication protocols, respectively.
• the VBG has a significant advantage over other techniques, particularly due to its ultra-low attenuation rate over a wide range of wavelengths, leading to an extremely large quantum capacity exceeding 10 13 qubits/second over a distance of 10 4 km under one-way quantum communication FH11893796.1 UCT-00625 protocol as shown in Fig.3A.
• Fig.3A illustrates a one-way frequency-integrated quantum capacity with perfect couplings.
• Fig.3B illustrates a two-way frequency-integrated quantum capacity assuming 50% coupling efficiency.
• the inset of 10000 km in Fig.3B is in log scale to show finite two-way quantum capacity over a wide range of parameters.
• the ground-based VBG offers high reliability as it is operational at all times, and provides an extremely high throughput, at least eight orders of magnitude higher in terms of achievable quantum communication rate.
• the concept of a beam guide was investigated to address diffraction loss in satellite-relayed quantum communication.
• the VBG unlike quantum repeaters, the VBG only requires passive optical lenses to focus the optical beams and does not need any quantum memory or active quantum devices to perform quantum error detection or correction. Therefore, the VBG is feasible to implement with current technology. [0047]
• the VBG can be designed to operate with visible light, which would benefit from a larger air transmission window and low-loss lens materials if sufficiently small lens roughness is achievable, while better transversal alignment is required to match the reduced ⁇ beam waist ⁇ ⁇ ⁇ ⁇ ⁇ with shorter wavelengths.
• the present disclosure relates to the use of an optical guide implemented as a vacuum lens guide (VLG) in quantum communications.
• VLG vacuum lens guide
• An example embodiment 400 of a suitable VLG is shown in Fig.4.
• the VLG shown in Fig.4 comprises a vacuum enclosure FH11893796.1 UCT-00625 402 and a plurality of lenses 404a, 404b, 404c, etc.
• the VLG shown in Fig.4 can be used for ultra-low loss optical channel to achieve attenuation length beyond 10 3 km (or even 10 4 km), which will enable achieving continental (or global) scale ground-based ultra-low-loss quantum communication channel.
• the VLG such as the one shown in Fig.4 has the following merits: [0051] It can be employed in a ground-based long-range quantum channel, which is strongly preferred because of the low cost and high reliability. [0052]
• An ultra-low loss it can achieve effective attenuation length of above 10 3 kilometers, orders of magnitude larger than the attenuation length of air or state-of-the-art fiber.
• a high bandwidth it can have much higher bandwidth than the optical fiber because optical signals are propagating mostly in vacuum with little absorption.
• the dispersion in optical lens can be compensated using low-dispersion material or compensating elements.
• Weather resistance unlike satellite mediated optical channel, VLG can operate in all weather conditions.
• the proposed VLG is compatible with existing quantum technology of quantum cryptography (QKD), entanglement generation, quantum routers, as well as various classical communication protocols.
• QKD quantum cryptography
• entanglement generation quantum routers, as well as various classical communication protocols.
• network node or “node” refers to a redistribution point or a communication endpoint within a network, whether that network is classical or quantum.
• a physical network node may either be data communication equipment (DCE) such as a modem, hub, bridge or switch; or data terminal equipment (DTE) such as a digital telephone handset, a printer or a host computer.
• DCE data communication equipment
• DTE data terminal equipment
• the network in question is a local area network (LAN) or wide area network (WAN)
• every LAN or WAN node that participates on the data link layer must have a network address, typically one for each network interface controller it possesses. Examples are computers, a DSL modem with Ethernet interface and wireless access point.
• the network in question is the Internet or an intranet, many physical network nodes are host computers, also known as Internet nodes, identified by an IP address, and all hosts are physical network nodes.
• Quantum networks facilitate the transmission of information in the form of qubits between physically separated quantum processors.
• the basic structure of a quantum network is analogous to a classical network.
• a quantum network may include one or more end nodes, FH11893796.1 UCT-00625 which may include one or more quantum processors.
• a quantum network also includes one or more communication lines, for example utilizing optical guides such as telecom fibers or free space transmission.
• Some quantum networks further include optical switches capable of delivering qubits to an intended endpoint. Both switches and communication lines must preserve quantum coherence in order to be suitable for use in a quantum network. In particular, since qubits cannot be copied, classical signal amplification is not possible.
• ⁇ is the radius of the lenses, ⁇ is the distance between the lenses and ⁇ is the wavelength of the light.
• the VLG described herein can support a wide linewidth of wavelength, increasing wavelength gives rise to even larger attenuation length envelop. This is illustrated in Fig.11A(peaks are due to residue gas absorption).
• the vacuum beam guide (the VLG) can reduce the loss rate by four orders of magnitude ( ⁇ 10 4 ) compared to that of an optical fiber. This permits achieving global scale direct quantum networks. This is illustrated in Fig.11B which shows the wavelength-dependent loss rate (in units of dB/km) for different wavelength under various pressure for an exemplary beam guide described herein having the parameters listed below:.
• ⁇ 2 [ ⁇ ] ⁇ log 2 ⁇ ⁇ ( ⁇ ) ⁇ , where ⁇ ( ⁇ ) is the loss rate.
• ⁇ ( ⁇ ) is the loss rate.
• the materials of the vacuum enclosure can be selected from a wide variety of materials, for example, from a stainless steel, carbon steel, aluminum, or titanium.
• the lenses employed by the VLG described herein can be obtained from a commercial provider, for example from Laboratoire des Materiaux Avances (LMA).
• LMA Laboratoire des Materiaux Avances
• the lenses can be made of ultrapure fused silica (such as Suprasil 3002 available from Heraeus Quartz Glass), and optionally include a coating, such as Ti-Ta2O5 ⁇ SiO2 IBS multilayer.
• a coating such as Ti-Ta2O5 ⁇ SiO2 IBS multilayer.
• Fig.12 An example design of the vacuum enclosure and the means for obtaining the vacuum are illustrated in Fig.12.
• the vacuum enclosure 1200 includes an outer envelope 1202 that can be made of a mild steel, and an inner envelope 1204, made out of a low-outgassing material.
• the vacuum enclosure 1200 further includes vacuum pumps 1206 (only one pump is labelled).
• V. Optical Losses Due to the Lens Array [00100]
• a quantum network is paired with a classical network, which may include one or more classical computing nodes. The major sources of optical loss (and thereby decoherence) in the VBG are due to the lens array.
• the major losses are ⁇ ⁇ , the absorption loss in the lens substrate as well as ARC coating, ⁇ ⁇ , the scattering loss from the lens surface (this includes scattering into low order Laguerre-Gauss modes that scatter back into the mean beam), and ⁇ ⁇ , the reflection loss due to the non-zero reflectivity of practical anti-reflection coat-ings (it is assumed here that reflected light has a random phase and does not interfere with the signal beam).
• R ⁇ 10 cm For a large enough radius (R ⁇ 10 cm), lens loss is limited by residual ARC reflection and absorption. Commercially available telecom band ARC can achieve loss at the 100 ppm level, which can be further improved.
• Fig.13A illustrates the reflective loss of two-layer MgF2/ZrO2 ARC on silica substrate optimized around 1300nm and 1550nm compared with a commercially available telecom band ARC.
• the thickness of layers for 1300nm and 1550nm designs are 169/270nm and 371/45nm respectively.
• the refractive indexes used in the simulation are obtained from the empirical formula known in the art.
• the red curve shows that even with a commercial-level ARC loss, it is still possible to achieve significant low loss up to 10 4 km.
• Fig.13B shows the one-way quantum capacity Q1 under different levels of lens loss. Even with a 100-ppm level lens loss (red curve), it is still possible to achieve a non-zero communication rate over 10 thousand kilometers. Additionally, the maximum distance saturates when the lens loss reaches 1 ppm, with the performance mainly limited by misalignment.
• the loss in power ratio per section caused by misalignment can be written as a sum as follows when each term is small enough, FH11893796.1 UCT-00625 where ⁇ ⁇ , ⁇ ⁇ , and ⁇ ⁇ denote the losses caused by transversal displacement, parallel displacement and the fluctuation of the focal length of the lenses, and only depend on the misalignment parameter ⁇ ⁇ , ⁇ ⁇ and ⁇ ⁇ respectively.
• the loss may not necessarily be a constant for each section due to the power conversion back from higher order mode. However, neglecting such contributions will always give an upper bound of the loss.
• A. Loss Caused by Parallel Displacement [00109] If the field is in perfect fundamental mode while the next lens is shifted for a distance of ⁇ ⁇ , then the field of the fundamental mode right before the next lens can be simply written as ⁇ ⁇ ′ ⁇ ⁇ ⁇ ⁇ ( ⁇ , ⁇ , ⁇ ⁇ /2 + .
• the perturbation method can be adapted here for a more convenient derivation.
• the focal length deviation gives rise to an additional phase factor as: which slightly converts the fundamental mode into the first-order mode: FH11893796.1 UCT-00625 while the conversion to other modes is higher order in ⁇ f /f. Therefore, the fraction of excitation loss from the fundamental mode to the first order mode (1, 0) is: C. Loss Caused by Transversal Displacement [00111]
• a naive error model is that assuming there is a “correct” position for each lens determined by geodesic connecting two end-point of VBG, along which each lens’s transversal displacement is fluctuating with variance ⁇ ⁇ .
• the transverse displacement is the dominant contribution to the alignment loss, since the achievable longitudinal displacement and focal-length deviations can be sufficiently small ( ⁇ ⁇ , ⁇ ⁇ ⁇ 10 ⁇ 3).
• a 2-D contour plot is constructed of characteristic length ⁇ ⁇ with respect to the lens loss ⁇ ⁇ (or ⁇ ⁇ defined in Eq. (2)) and transversal displacement ⁇ ⁇ .
• Eq. (1) and Eq. (2) one can approximate the characteristic length as: FH11893796.1 UCT-00625 where ⁇ ⁇ includes all sources of lens-related loss as listed in Table 1 and ⁇ ⁇ ⁇ 2 ppm denotes some other losses including parallel perturbation and residue gas absorp-tion.
• the characteristic length of VBG is plotted under various lens and misalignment configurations in Fig.14.
• a quantum network is paired with a classical network, which may include one or more classical computing nodes.
• a classical network which may include one or more classical computing nodes.
• FIG.15 a schematic of an example of a computing node is shown.
• Computing node 10 is only one example of a suitable computing node and is not intended to suggest any limitation as to the scope of use or functionality of embodiments described herein. Regardless, computing node 10 is capable of being implemented and/or performing any of the functionality set forth hereinabove.
• computing node 10 there is a computer system/server 12, which is operational with numerous other general purpose or special purpose computing system environments or configurations.
• Computer system/server 12 Examples of well-known computing systems, environments, and/or configurations that may be suitable for use with computer system/server 12 include, but are not limited to, personal computer systems, server computer systems, thin clients, thick clients, handheld or laptop devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputer systems, mainframe computer systems, and distributed cloud computing environments that include any of the above systems or devices, and the like.
• Computer system/server 12 may be described in the general context of computer system-executable instructions, such as program modules, being executed by a computer system.
• program modules may include routines, programs, objects, components, FH11893796.1 UCT-00625 logic, data structures, and so on that perform particular tasks or implement particular abstract data types.
• Computer system/server 12 may be practiced in distributed cloud computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed cloud computing environment, program modules may be located in both local and remote computer system storage media including memory storage devices.
• computer system/server 12 in computing node 10 is shown in the form of a general-purpose computing device.
• the components of computer system/server 12 may include, but are not limited to, one or more processors or processing units 16, a system memory 28, and a bus 18 that couples various system components including system memory 28 to processor 16.
• Bus 18 represents one or more of any of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, and a processor or local bus using any of a variety of bus architectures.
• bus architectures include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, Peripheral Component Interconnect (PCI) bus, Peripheral Component Interconnect Express (PCIe), and Advanced Microcontroller Bus Architecture (AMBA).
• ISA Industry Standard Architecture
• MCA Micro Channel Architecture
• EISA Enhanced ISA
• VESA Video Electronics Standards Association
• PCI Peripheral Component Interconnect
• PCIe Peripheral Component Interconnect Express
• AMBA Advanced Microcontroller Bus Architecture
• System memory 28 can include computer system readable media in the form of volatile memory, such as random access memory (RAM) 30 and/or cache memory 32.
• Computer system/server 12 may further include other removable/non-removable, volatile/non-volatile computer system storage media.
• storage system 34 can be provided for reading from and writing to a non-removable, non-volatile magnetic media (not shown and typically called a "hard drive").
• a magnetic disk drive for reading from and writing to a removable, non-volatile magnetic disk (e.g., a "floppy disk")
• an optical disk drive for reading from or writing to a removable, non-volatile optical disk such as a CD-ROM, DVD-ROM or other optical media
• each can be connected to bus 18 by one or more data media interfaces.
• memory 28 may include at least FH11893796.1 UCT-00625 one program product having a set (e.g., at least one) of program modules that are configured to carry out the functions of embodiments of the disclosure.
• Program/utility 40 having a set (at least one) of program modules 42, may be stored in memory 28 by way of example, and not limitation, as well as an operating system, one or more application programs, other program modules, and program data. Each of the operating system, one or more application programs, other program modules, and program data or some combination thereof, may include an implementation of a networking environment.
• Program modules 42 generally carry out the functions and/or methodologies of embodiments as described herein.
• Computer system/server 12 may also communicate with one or more external devices 14 such as a keyboard, a pointing device, a display 24, etc.; one or more devices that enable a user to interact with computer system/server 12; and/or any devices (e.g., network card, modem, etc.) that enable computer system/server 12 to communicate with one or more other computing devices. Such communication can occur via Input/Output (I/O) interfaces 22. Still yet, computer system/server 12 can communicate with one or more networks such as a local area network (LAN), a general wide area network (WAN), and/or a public network (e.g., the Internet) via network adapter 20. As depicted, network adapter 20 communicates with the other components of computer system/server 12 via bus 18.
• LAN local area network
• WAN wide area network
• public network e.g., the Internet
• a “quantum system” refers to an information device that exploits quantum mechanical phenomena to enhance the computational power, communication security, sensor sensitivity, etc.
• a “lens cascade” refers to an optical train comprising at least two lenses sharing a common optical axis and disposed along the common optical axis at the distance approximately equal to the sum of the focal lengths of the two adjacent lenses.
• a lens cascade comprises lenses having the same focal lengths, where any two adjacent lenses are disposed at a distance approximately equal to twice the focal length.
• FH11893796.1 UCT-00625 [00132] It will be appreciated that lenses will have dispersion in general and thus the focal length for light of different wavelength may vary. Thus, multiple wavelength systems may be confocal for a certain wavelength, but non-confocal for other wavelengths of the system. Accommodating configurations that are not precisely confocal thus allows more flexibility. The below examples describe the performance of configurations that are not precisely confocal. In particular, this is shown in the misalignment loss formula provided above.
• a “qubit” refers to a unit of quantum information, analogous to a bit in classical computing.
• a qubit can exist in a superposition of two states, usually referred to as 0 and 1, and can be manipulated using quantum algorithms. For example, a single optical mode can be in a superposition of
• the present invention is a quantum network.
• the quantum network comprises at least a first node comprising a first quantum system, and a second node comprising a second quantum system; and an optical guide in optical communication with the at least the first and the second nodes, wherein the optical guide comprises: a reduced pressure enclosure; and a lens cascade disposed in the reduced pressure enclosure.
• the first quantum system is in a quantum state and is configured to generate at least one electromagnetic (EM) optical mode encoding the quantum state; the first node is configured to direct the optical mode into the optical guide; and the second node is configured to cause an interaction of the optical mode with the second quantum system, thereby imparting the quantum state onto the second quantum system.
• EM electromagnetic
• the remainder of the features and example features of the 2 nd aspect are as described above with respect to the 1 st aspect of the 1 st embodiment.
• the first quantum system and the second quantum system each comprises a qubit.
• the first and the second quantum systems each independently comprises a quantum processor, a quantum memory, a quantum sensor, or a quantum simulator.
• the remainder of the features and example features of the 4 th aspect are as described above with respect to the 1 st through 3 rd aspects of the 1 st embodiment.
• the first and the second quantum systems each independently comprises a neutral atom array, a trapped ion array, or a solid state emitter.
• the remainder of the features and example features of the 5 th aspect are as described above with respect to the 1 st through 4 th aspects of the 1 st embodiment.
• the first and the second nodes each independently comprises an optical mode quantum emitter.
• the quantum emitter can emit quantum states (e.g., single photons or entangled photons).
• the optical mode quantum emitter comprises one or more of a single photon source, a squeezed photon source, or a spin-photon entangled source.
• the remainder of the features and example features of the 7 th aspect are as described above with respect to the 1 st through 6 th aspects of the 1 st embodiment.
• the first and the second nodes each independently comprises an optical mode quantum detector.
• a quantum detector can projectively measure in photon number basis.
• the optical mode quantum detector is a single photon detector, a number resolving photon detector, a homodyne photon detector, or a heterodyne photon detector.
• the remainder of the features and example features of the 9 th aspect are as described above with respect to the 1 st through 7 th aspects of the 1 st embodiment.
• the first and the second nodes are interconnected by a classical network.
• the classical network is an optical signal or a radio frequency (RF) signal network.
• the remainder of the features and example features of the 11 th aspect are as described above with respect to the 1 st through 10 th aspects of the 1 st embodiment.
• FH11893796.1 UCT-00625 It is contemplated that the optical guide (the lens cascade and/or the reduced pressure enclosure) can be aligned and stabilized. For example, the optical guide can be divided into segments, and the segments can be individually aligned.
• a 10 4 km optical guide can be divided into 100 segments, each having 25 lenses separated by 4 km.
• the time of travel of an optical signal across such a segment is estimated to be 0.3 ms, so that the noise can suppressed within each segment with bandwidth up to a few kHz.
• the misalignments between sequential segments can then be performed using, for example, active optical elements disposed between neighboring segments.
• a suitable example of the alignment using the global positioning system (GPS) is described, for example, in Althouse et al. Review of scientific instruments 72, 3086-3094 (2001).
• GPS global positioning system
• a high-precision dual-frequency differential GPS can achieve millimeter level position precision (e.g., less than 5 mm deviation over 4 km. The relevant teachings of this publication is incorporated herein by reference.
• lens stabilization protocols can be employed to locally adjust misaligned elements.
• the relative alignment between neighboring lenses can be measured, and the lens positions adjusted.
• lens stabilization is lens self-alignment.
• a suitable example of self-aligning lens cascade is provided in R. Christian et al., “Self-Aligning Optical Beam Waveguides” IEEE J. of Quantum Electronics, vol. QE-3, No. 11, November 1967. The relevant teachings of this publication are incorporated herein by reference. Briefly, a plurality of lenses is mechanically adjustable under the control of a sending device. The sensing device indicates the displacement of the beam from the lens center.
• the lens cascade comprises a plurality of lenses, and wherein at least two lenses are stabilized. The remainder of the features and example features of the 12 th aspect are as described above with respect to the 1 st through 11 th aspects of the 1 st embodiment. [00150] In a 13 th aspect of the 1 st embodiment, at least two lenses are self-aligned.
• the lens cascade comprises at least one lens having a focal length of greater than 1 km.
• the remainder of the features and example FH11893796.1 UCT-00625 features of the 14 th aspect are as described above with respect to the 1 st through 13 th aspects of the 1 st embodiment.
• the lens cascade comprises a plurality of lenses, each lens having the same focal distance.
• the lens cascade comprises a plurality of lenses, each lens of the lens cascade having a focal length tolerance of about 2 m or less; lenses of the lens cascade being spaced apart at an interval, the interval having a tolerance of about 4 m or less; any two adjacent lenses of the lens cascade having a transversal offset of about 0.1 mm or less; each lens of the lens cascade having a radius of about 15 cm or more; and each lens of the lens cascade having a lens loss of about 210 ppm or less.
• the lens cascade is configured to operate at a temperature of about 300 K and wherein the reduced pressure enclosure is configured to operate at a pressure of about 10 Pa or less.
• the remainder of the features and example features of the 17 th aspect are as described above with respect to the 1 st through 16 th aspects of the 1 st embodiment.
• the present invention is a method of transmitting a quantum state between nodes of a quantum network.
• the method comprises: providing a first node comprising a first quantum system, and a second node, comprising a second quantum system; causing the first quantum system to generate at least one electromagnetic (EM) optical mode, the first quantum system being in a quantum state, the optical mode encoding a quantum state; directing the optical mode into an optical guide, the optical guide being in optical communication with the second node, and causing the optical mode to interact with the second quantum system, thereby imparting the quantum state onto the second quantum system.
• the optical guide comprises: a reduced pressure enclosure; and a lens cascade disposed in the reduced pressure enclosure.
• the first quantum system and the second quantum system each comprises a qubit.
• the remainder of the features and example features of the 2 nd aspect are as described above with respect to the 1 st aspect of the 2 nd embodiment.
• FH11893796.1 UCT-00625 [00160]
• the first and the second quantum systems each independently comprises a quantum processor, a quantum memory, a quantum sensor, or a quantum simulator.
• the remainder of the features and example features of the 3 rd aspect are as described above with respect to the 1 st and the 2 nd aspects of the 2 nd embodiment.
• the first and the second quantum systems each independently comprises a neutral atom array, a trapped ion array, or a solid state emitter. The remainder of the features and example features of the 4 th aspect are as described above with respect to the 1 st through the 3 rd aspects of the 2 nd embodiment.
• the first and the second nodes each independently comprises an optical mode quantum emitter. The remainder of the features and example features of the 5 th aspect are as described above with respect to the 1 st through the 4 th aspects of the 2 nd embodiment.
• the optical mode quantum emitter comprises one or more of a single photon source, a squeezed photon source, or a spin-photon entangled source. The remainder of the features and example features of the 6 th aspect are as described above with respect to the 1 st through the 5 th aspects of the 2 nd embodiment.
• the first and the second nodes each independently comprises an optical mode quantum detector. The remainder of the features and example features of the 7 th aspect are as described above with respect to the 1 st through the 6 th aspects of the 2 nd embodiment.
• the optical mode quantum detector is a single photon detector, a number resolving photon detector, a homodyne photon detector, or a heterodyne photon detector.
• the remainder of the features and example features of the 8 th aspect are as described above with respect to the 1 st through the 7 th aspects of the 2 nd embodiment.
• the method further comprises transmitting a classical signal from the first node to the second node. The remainder of the features and example features of the 9 th aspect are as described above with respect to the 1 st through the 8 th aspects of the 2 nd embodiment.
• the classical signal is an optical signal or an radio frequency (RF) signal.
• RF radio frequency

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