Quantum entanglement sharing system

Abstract

To provide a system that efficiently shares quantum entanglement.SOLUTION: A system (100) for sharing quantum entanglement includes a first device (10), a plurality of second devices (20), and a multiplexing device. The first device outputs photons multiplexed by a combination of degrees of freedom in time, frequency, and space to a quantum communication channel. The multiplexing device performs a demultiplexing process by combining the degrees of freedom in time, frequency, and space.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to systems that share quantum entanglement. [Background technology]

[0002] Quantum communication systems that use quantum to transmit and receive signals are known. Patent Document 1 discloses a multiplexed quantum communication system that transmits and receives photons by optical wavelength multiplexing (paragraph

[0018] , Figure 1, claim 9). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2018-157405 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned multiplexed quantum communication system, multiplexing is limited to multiplexing at optical wavelengths, and it is difficult to say that communication efficiency is necessarily good.

[0005] One aspect of the present invention aims to realize a system that efficiently shares quantum entanglement. [Means for solving the problem]

[0006] In order to solve the above problem, a system according to one embodiment of the present invention is a system for sharing quantum entanglement, comprising a first device, a plurality of second devices, a classical communication channel connecting the first device and each of the plurality of second devices, a demultiplexing device connected to the second device, and a quantum communication channel connecting the first device and the demultiplexing device, wherein the first device outputs photons multiplexed by combining the degrees of freedom of time, frequency, and space to the quantum communication channel, and the demultiplexing device performs demultiplexing by combining the degrees of freedom of time, frequency, and space. [Effects of the Invention]

[0007] According to one aspect of the present invention, efficient sharing of quantum entanglement can be achieved in a system that shares quantum entanglement. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating a multiple quantum communication system according to an embodiment of the present invention. [Figure 2] FIG. 1 is a schematic diagram illustrating a more specific example of a multiple quantum communication system according to an embodiment of the present invention. [Figure 3] FIG. 10 is a schematic diagram illustrating another more specific example of a multiple quantum communication system according to an embodiment of the present invention. [Figure 4] FIG. 2 is a schematic diagram showing a frequency multiplexing state. [Figure 5] FIG. 10 is a schematic diagram showing a time-multiplexed state. [Figure 6] FIG. 1 is a schematic diagram showing a state of spatial multiplexing. [Figure 7] FIG. 1 is a schematic diagram showing a state in which frequency multiplexing, time multiplexing, and space multiplexing are combined. [Figure 8] FIG. 10 is a flow diagram showing a procedure for generating an encryption key. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described in detail. Fig. 1 is a diagram showing the device configuration of a multiple quantum communication system 100 according to an embodiment.

[0010] The multiple quantum communication system 100 includes a quantum communication channel 1, classical communication channels 2(1), 2(2), a transmitting device 10, receiving devices 20(1), 20(2), and a demultiplexing device 30, and quantum entanglement is shared between the transmitting device 10 and the receiving devices 20(1), 20(2).

[0011] In the following, when the classical communication channels 2(1) and 2(2) are collectively described, they are referred to as the classical communication channel 2, and when the receiving devices 20(1) and 20(2) are collectively described, they are referred to as the receiving device 20.

[0012] The quantum communication channel 1 is an optical fiber that transmits and receives a single photon, and connects a transmitting device 10 (first device) and a demultiplexing device 30. Note that multiple quantum communication channels 1 may be arranged in parallel. As will be described later, spatial multiplexing using multiple quantum communication channels 1 becomes possible. Here, the multiple quantum communication channels 1 may be configured not only by multiple optical fibers, but also by a single optical fiber. If a single optical fiber has multiple propagation modes, it can function as multiple quantum communication channels 1.

[0013] The transmitting device 10 (first device) sequentially generates pairs of photons corresponding to information, multiplexes one of the pair of photons, and transmits it via the quantum communication channel 1 to the demultiplexing device 30 and ultimately to the receiving device 20.

[0014] The pair of photons are in a quantum entangled state, and when the state of one photon is determined, the state of the other photon is correspondingly determined. The transmitter 10 transmits one of the pair of photons and retains the other photon.

[0015] The transmitting device 10 transmits photons (one of a pair of photons) multiplexed by a combination of the degrees of freedom of time, frequency, and space. That is, one of multiple pairs of photons (ultimately, multiple photons) is multiplexed by a combination of the degrees of freedom of time, frequency, and space.

[0016] 4 to 6 are schematic diagrams showing frequency multiplexing, time multiplexing, and space multiplexing of photons, respectively.

[0017] In frequency multiplexing, one of multiple pairs of photons (hereinafter referred to as "multiple photons") is multiplexed and transmitted so that each photon has a different frequency (wavelength). The range of multiplexed frequencies may be broadband, for example, greater than 100 GHz.

[0018] In time multiplexing, multiple photons are spaced at narrow time intervals. For example, photons may be spaced at time intervals of less than 10 ns to form a time-multiplexed band with a bandwidth greater than 100 ns.

[0019] 6, spatial multiplexing is represented as a state in which signals are stored in different locations such as quantum memories. When performing communication using spatial multiplexing, it is possible to use multiple quantum communication channels 1 (for example, multiple optical fibers arranged in parallel).

[0020] Figure 7 is a schematic diagram showing a combination of frequency multiplexing, time multiplexing, and space multiplexing. By combining the degrees of freedom of time, frequency, and space, more efficient information transmission and reception becomes possible. Here, all the multiplexed photons are in phase (for example, e 0 = 1). The degree of multiplexing (number of modes) in this case is expressed as the number of lattices inside the rectangular parallelepiped in Figure 7. Note that if phase multiplexing is performed in addition to frequency multiplexing, time multiplexing, and space multiplexing, the number of modes increases dramatically.

[0021] Here, frequency multiplexing, time multiplexing, and space multiplexing can be expressed by the following equations (1), (2), and (3), respectively.

number

number

number

[0022] Furthermore, a combination of frequency multiplexing, time multiplexing, and space multiplexing can be expressed by the following equation (4).

number

[0023] That is, in the embodiment, the multiplexed quantum state obtained by combining the degrees of freedom of time, frequency, and space is |φ> expressed by the multiplication of the right side of equation (4). Note that multiplexing does not necessarily have to be performed in all of time, frequency, and space. Any of time, frequency, and space may not be used for multiplexing.

[0024] The demultiplexer 30 receives the multiplexed photons from the transmitter 10, performs a demultiplexing process by combining the degrees of freedom of time, frequency, and space, and sends the demultiplexed photons to the receivers 20(1) and 20(2).

[0025] The receiving devices 20(1), 20(2) (plurality of second devices) receive the demultiplexed photons and recover the information transmitted from the transmitting device 10.

[0026] Here, the transmitting device 10 encrypts information using an encryption key (common key) and transmits it as encrypted information, and the receiving devices 20(1) and (2) decrypt the received encrypted information using the encryption key (common key). For this reason, a process for generating an encryption key is carried out between the transmitting device 10 and the receiving devices 20(1) and (2).

[0027] The classical communication channels 2(1) and 2(2) transmit and receive control information for generating encryption keys. The control information is, for example, a synchronization signal for synchronizing between the transmitting device 10 and the receiving device 20. The classical communication channel 2 may be wired, such as optical fiber, or wireless, or may be realized by combining wired and wireless communication.

[0028] In the embodiment, for convenience of explanation, the device that transmits photons is called the transmitting device 10, but the transmitting device 10 may also have a function of receiving photons. Similarly, the receiving device 20 may also have a function of transmitting photons.

[0029] [Example of functional configuration] 2 is a diagram illustrating an example of the functional configuration of a transmitting device 10 and a receiving device 20 according to an embodiment. The transmitting device 10 includes a generating unit 11 and a control unit 12. The receiving device 20(1) includes a detecting unit 21(1) and a control unit 22(1). The receiving device 20(2) includes a detecting unit 21(2) and a control unit 22(2).

[0030] The generator 11 is a quantum light source that generates photons (photon pairs) in a wavelength-multiplexed state. The quantum light source includes, for example, an optical crystal and a resonator. As shown below, by combining an optical crystal and a resonator, photons in multiple wavelength modes (photons in a wavelength-multiplexed state) can be generated.

[0031] Optical crystals have a high nonlinear optical constant (or a high effective nonlinear optical constant) and form photons. Here, optical crystals can generate quantum entangled photon pairs over a wavelength band wider than the wavelengths used for communication through forward-propagating spontaneous parametric down-conversion. A resonator limits (subdivides) this wide wavelength band into multiple wavelength modes (repeated structures) by causing light to travel back and forth (resonate) within it. As a result, by combining an optical crystal and a resonator, photons with multiple wavelength modes (wavelength multiplexed state) can be generated. Note that photons do not need to travel back and forth (circulate) within the resonator a predetermined number of times. In order to increase the fidelity of the quantum state to the Bell state, the optical crystal may include not only a crystal that induces spontaneous parametric down-conversion but also a birefringent phase compensation crystal.

[0032] Here, the optical crystal may include a dispersion compensation crystal or a birefringence phase compensation crystal. When a dispersion compensation crystal is used, Presence (of a peak) Widening the wavelength band Can do. The use of birefringent phase compensation crystals makes it possible to increase the fidelity of the generated state to the ideal quantum entanglement state. This makes it possible to reduce the number of entanglement purifications and improve the communication rate.

[0033] The generator 11 is capable of combining not only wavelength multiplexing (i.e., frequency multiplexing) but also time multiplexing and spatial multiplexing. In addition to frequency multiplexing, it is also possible to use time multiplexing, which utilizes pulse train generation by mode locking of the resonator that constitutes the generator 11. In addition to wavelength multiplexing, spatial multiplexing is also possible by forming a higher-order Hermite or Laguerre Gaussian spatial mode using the transverse mode of the resonator.

[0034] The control unit 12 controls the operation of the generation unit 11. The control unit 12 also executes a process for generating an encryption key.

[0035] The detector 21 detects the photons output from the demultiplexer 30 and decodes the received bits from the single photons, for example, based on polarization, to recover the encrypted information.

[0036] Photons may be received (detected) using a photon detection element such as an avalanche photodiode (APD) in the detection unit 21. The APD is a photodetection element made of, for example, indium gallium arsenide, silicon, germanium, or gallium nitride.

[0037] The APD is driven in an operation mode called Geiger mode. In Geiger mode, the reverse voltage of the APD is set to a breakdown voltage or higher, and a large pulse is generated in response to the incidence of a received photon due to the avalanche effect. As a result, single photon detection becomes possible. The detection unit 21 continuously performs single photon detection operations by supplying a square wave or sinusoidal voltage consisting of a voltage above the breakdown voltage and a voltage below the breakdown voltage.

[0038] The control unit 22 controls the operation of the detection unit 21 to output the encrypted information and reproduces the information before encryption using the encryption key. The control unit 22 also executes a process for generating an encryption key.

[0039] 3 is a diagram showing another example of the functional configuration of the transmitting device 10 and the receiving device 20 according to the embodiment. The transmitting device 10 includes generating units 11(1) and 11(2), a control unit 12, and a multiplexing unit 13. The receiving device 20(1) includes a detecting unit 21(1) and a control unit 22(1). The receiving device 20(2) includes a detecting unit 21(2) and a control unit 22(2).

[0040] The generators 11(1) and 11(2) are multiple quantum light sources spatially arranged. As described above, the quantum light source may be configured to include, for example, an optical crystal and a resonator. Here, for ease of understanding, two generators 11 are shown, but three or more generators 11 may be used. Also, although the number of generators 11 and receivers 20 is the same, the numbers may be different.

[0041] Here, the phase relationship is important for quantum (photon) multiplexing. In other words, if there is variation in the phase of the quanta being multiplexed, this variation will become noise and hinder demultiplexing. By using a quantum light source with a pulsed correlation function, it is possible to align the phase relationship at a point where the probability of existence of photons is non-zero. Similarly, there is a Fourier transform relationship in which pulsation occurs at the timing when the phases of the frequencies are aligned, and this can be achieved by including a resonator in the quantum light source.

[0042] Regarding spatial modes, it is possible to align the phase by obtaining interference using a separate laser.

[0043] The multiplexing unit 13 performs multiplexing processing by combining the degrees of freedom of time, frequency, and space of the light from the generating units 11(1) and 11(2) (multiple quantum light sources). As described above, the generating unit 11 is capable of combining not only wavelength multiplexing (i.e., frequency multiplexing) but also time multiplexing and spatial multiplexing. The degree of multiplexing can be increased by adding a multiplexing unit 13. In this case, a single generating unit 11 may not have multiplexing, and multiplexing may be ensured only by the multiplexing unit 13.

[0044] The multiplexing unit 13 can be configured by combining a frequency shifter, a delay unit, and a distributor.

[0045] The frequency shifter shifts the frequency so that the frequencies associated with the photons from the generation units 11(1) and 11(2) differ from each other. Examples of frequency shifters include an acousto-optic modulator and an electro-optic modulator. Frequency multiplexing of light can be achieved by applying a modulation frequency to the acousto-optic modulator. Furthermore, the frequency (wavelength) of light can be shifted at high speed by applying a sawtooth wave to the electro-optic modulator. When light passes through the acousto-optic modulator, it is diffracted in a manner that depends on the modulation frequency (generation of a diffraction angle), but the effects of diffraction can be reduced by making the light go back and forth within the acousto-optic modulator.

[0046] The delay device delays the photons from the generation units 11(1) and 11(2) so that the times at which they pass through the quantum communication channel 1 differ from each other. The delay device may be configured by combining a beam splitter with multiple optical fibers of different lengths. For example, the delay device can be configured from a beam splitter that splits light into two lights at a 50:50 ratio and two optical fibers of different lengths. Here, a polarizing beam splitter may be used as the beam splitter to split the light into two polarized lights.

[0047] The delay device may be included in the multiplexing unit 13 as part of a Mach-Zehnder interferometer or a Michelson interferometer. In this case, the Mach-Zehnder interferometer may be a multi-arm Mach-Zehnder interferometer using a plurality of optical fibers of different lengths.

[0048] The distributor distributes photons from the generators 11(1) and 11(2) to different quantum communication channels 1. The distributor is, for example, a switching mechanism that switches the quantum communication channel 1 to which the generators 11(1) and 11(2) are connected. Examples of distributors include an optical switch and an acousto-optic modulator. The optical switch enables high-speed switching of the quantum communication channel 1. The acousto-optic modulator can switch the quantum communication channel 1 by changing the diffraction angle of light depending on the modulation frequency. Note that the optical switch may be configured to change the direction of light by slightly rotating a lens. The distributor may also be configured by combining a frequency shifter (for example, an acousto-optic modulator and an electro-optic modulator) with a spectrometer (for example, a diffraction grating).

[0049] The distributor (for example, an optical switch) may be synchronized in time with the pulses of pump light from the generator 11 (quantum light source). The pulses can be distributed by feedforward control.

[0050] Here, by connecting the generation unit 11(1) to the quantum communication channel 1(1) and the generation unit 11(2) to the quantum communication channel 1(2), it is possible to configure a distributor (a fixed connection that does not switch the connection destination).

[0051] The multiplexing unit 13 may have a plurality of frequency shifters, delayers, and dividers, or may have all of the frequency shifters, delayers, and dividers. For example, the multiplexing unit 13 can be configured by combining the following (1) frequency shifter, (2) delayer, and (3) divider.

[0052] (1) Multiple electro-optical modulators are used as frequency shifters to generate and frequency multiplex multiple frequency modes. That is, multiple frequency modes are generated by applying sinusoidal waves with different frequencies and voltages greater than half-wave voltage to each of the multiple electro-optical modulators.

[0053] (2) A multi-arm Mach-Zehnder interferometer is used as a delay device for time multiplexing. This allows each frequency-multiplexed frequency mode to be given an equivalent time mode without being affected by the frequency. In other words, interference between frequency multiplexing and time multiplexing, which causes decoherence, can be prevented.

[0054] (3) A star coupler or tree coupler is used as a distributor for spatial multiplexing, which allows each frequency and time multiplexed frequency mode and each time mode to be given an equivalent spatial mode without being affected by frequency or time.

[0055] As described above, by combining (1) to (3), it is possible to perform multiplexing in frequency, time, and space, prevent interference between frequency multiplexing, time multiplexing, and space multiplexing, and configure an optical fiber-based, easily assembled multiplexing unit 13. Note that any two of (1) to (3) may be appropriately combined, or the multiplexing unit 13 may be configured with only one of (1) to (3).

[0056] The multiplexing unit 13 may have a diffraction grating or a fiber Bragg grating, and may be capable of wavelength resolution or projection onto a time axis.

[0057] [Quantum key generation process] An example of the private key generation process according to the embodiment will be described. Fig. 8 is a diagram showing an example of the private key generation process according to the embodiment. The private key generation process will be described below with reference to Fig. 8 and Fig. 1.

[0058] (1) Quantum communication (steps S1a and S1b) The transmitting device 10 transmits one of the quantum entangled photon pairs to the receiving device 20 via the quantum communication channel 1 and the demultiplexing device 30. N(1+2ζ) photons are multiplexed and transmitted, demultiplexed by the demultiplexing device 30, and received by the receiving device 20. As a result, the receiving device 20 holds one of the N(1+2ζ) photon pairs (N(1+2ζ) photons), and the transmitting device 10 holds the other of the N(1+2ζ) photon pairs (N(1+2ζ) photons).

[0059] (2) Quantum selection and measurement (Step S2a) The transmitting device 10 randomly selects Nζ photons from the N(1+2ζ) photons, measures them in the HV basis or the DA basis, and transmits the results to the receiving device 20 via the classical channel 2. Here, it is assumed that the transmitting device 10 measures them in the HV basis.

[0060] Here, the HV basis and DA basis correspond to the polarization states of photons. The H (Horizontal) state, V (Vertical) state, D (Diagonal) state, and A (Anti-diagonal) state refer to linear polarization states in the horizontal direction, vertical direction, diagonal +45°, and diagonal -45°, respectively. The H state and V state are orthogonal to each other, and the D state and A state are orthogonal to each other.

[0061] (3) Quantum selection and measurement (Step S2b) The receiving device 20 selects Nζ photons from the received N(1+2ζ) photons that correspond to the photons measured by the transmitting device 10 and measures them in the HV basis. The receiving device 20 calculates the error rate by comparing the measurement result with the measurement result of the transmitting device 10. If the error rate exceeds a predetermined value, the generation of the encryption key is stopped.

[0062] (4) Quantum selection and measurement (Step S3a) The transmitting device 10 randomly selects Nζ photons from the remaining N(1+ζ) photons, measures them in the DA basis, and transmits the measurement results to the receiving device 20 via the classical channel 2.

[0063] (5) Quantum selection and measurement (step S3b) The receiver 20 measures the Nζ corresponding photons in the DA basis. The receiver 20 calculates the error rate by comparing the measurement result with the measurement result of the transmitter 10. If the error rate exceeds a predetermined value, the generation of the encryption key is stopped.

[0064] As a result of the above, the transmitting device 10 and the receiving device 20 each hold N photons that have not yet been measured.

[0065] (5) Quantum transformation (steps S4a and S4b) The transmitter 10 determines an N×N regular binary matrix C1 and a mapping h1, and transmits them to the receiver 20 via a classical channel 2. The transmitter 10 applies a unitary transformation Ua(C1) to the N photons on the transmitter 10 side. Meanwhile, the receiver 20 applies a unitary transformation Ub(C1) to the N photons on the receiver 20 side.

[0066] (6) Quantum measurement (step S5a) The transmitter 10 measures Kz photons from the (N-Kz+1)th to the Nth photons in the HV basis and generates the resulting Kz-bit sequence z A is transmitted to the receiving device 20 via the classical communication channel 2.

[0067] (7) Quantum measurement, s1 calculation, and inversion (step S5b) The receiver 20 measures Kz photons from the (N-Kz+1)th to the Nth photons in the HV basis and generates the resulting Kz-bit sequence z B and the result z of the transmitting device 10 A Therefore, s1=z B -z A The receiving device 20 performs HV inversion on the (N-Kz) photons from the first to the (N-Kz)th photons using s1.

[0068] (8) Quantum transformation (steps S6a and S6b) The transmitter 10 selects a (N-Kz) × (N-Kz) regular binary matrix C2 and a mapping h2, and transmits them to the receiver 20 via a classical channel 2. The transmitter 10 applies a unitary transformation UA(C2) to the (N-Kz) photons. Meanwhile, the receiver 20 applies a unitary transformation UB(C2) to the (N-Kz) photons from the first to the (N-Kz)th.

[0069] (9) Quantum measurement (step S7a) The transmitter 10 measures Kx photons from the (N-Kz-Kx+1)th to the (N-Kz)th photons in the DA basis, and generates the resulting Kx-bit sequence x A is transmitted to the receiving device 20 via the classical communication channel 2.

[0070] (10) Quantum measurement, s2 calculation, and inversion (step S7b) The receiver 20 measures Kx photons from the (N-Kz-Kx+1)th to the (N-Kz)th photons in accordance with the DA rule, and generates the obtained Kx-bit sequence x B and the result x of the transmitting device 10 A Therefore, s2=x B -x A The receiving device 20 performs DA inversion on the (N-Kz-Kx) photons from the first to the (N-Kz-Kx)th photons using s2.

[0071] (11) Quantum measurement (steps S8a and S8b) The transmitting device 10 measures the remaining photons in the HV basis and uses the obtained bit string as the encryption key. The receiving device 20 measures the remaining photons in the HV basis and uses the obtained bit string as the encryption key.

[0072] The above can be summarized as follows: The transmitting device 10 generates multiple photon pairs in a quantum entangled state and transmits one of the photon pairs to the receiving device 20 via the demultiplexing device 30. The receiving device 20 measures some of the received photons, and the transmitting device 10 measures some of the photons and transmits the measurement results. If the measurement results match, an encryption key sequence is generated based on the multiple photons for which measurement results have not been transmitted.

[0073] Although the above examples show the use of polarization bases, time bin bases may be used instead of polarization bases. In this case, the time bin bases 1-0, 1-1, 2-0, and 2-1 are randomly selected and used for measurement. If the values ​​on the left side match between the sending device 10 and the receiving device 20, the value on the right side is used as the key sequence.

[0074] where the time bin basis 1-0 etc. represents: Time bin basis 1-0: Selection of early from two bases {early, late} Time bin basis 1-1: Selection of late from two bases {early, late} Time bin basis 2-0: Selection of early+late from two bases {early+late, early-late} Time bin basis 2-1: Selection of early-late from two bases {early+late, early-late}

[0075] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0076] (summary) (1) A system according to a first aspect of the present invention is a system for sharing quantum entanglement, comprising a first device (transmitting device 10), a plurality of second devices (receiving devices 20(1), 20(2)), classical communication channels (2(1), 2(2)) connecting the first device and each of the plurality of second devices, a demultiplexing device (30) connected to the second devices, and a quantum communication channel (1) connecting the first device and the demultiplexing device, wherein the first device outputs photons multiplexed by combining the degrees of freedom of time, frequency, and space to the quantum communication channel, and the demultiplexing device performs demultiplexing processing by combining the degrees of freedom of time, frequency, and space.

[0077] In the first aspect of the present invention, quantum entanglement can be efficiently shared by multiplexing through a combination of the degrees of freedom of time, frequency, and space.

[0078] (2) A second aspect of the present invention provides a system according to the first aspect, wherein the first device is a transmitting device and the second device is a receiving device.

[0079] In the second aspect of the present invention, efficient communication using quantum entanglement is made possible by multiplexing by combining the degrees of freedom of time, frequency, and space.

[0080] (3) A system according to a third aspect of the present invention is the system of the first or second aspect, wherein the first device includes a quantum light source (generation unit 11) that generates photons in a wavelength-multiplexed state.

[0081] In the third aspect of the present invention, multiplexing is possible using a quantum light source that generates photons in a wavelength-multiplexed state.

[0082] (4) A system according to aspect 4 of the present invention is the system of aspect 1 or 2, wherein the first device has a plurality of spatially arranged quantum light sources (generation units 11(1), 11(2)).

[0083] In the fourth aspect of the present invention, photons from a plurality of spatially arranged quantum light sources can be multiplexed.

[0084] (5) A system according to aspect 5 of the present invention is the system according to aspect 4, wherein the first device has a multiplexing unit (13) that performs multiplexing processing by combining photons from the multiple quantum light sources in terms of the degrees of freedom of time, frequency, and space.

[0085] In the fifth aspect of the present invention, photons from a plurality of quantum light sources can be multiplexed by the multiplexing unit.

[0086] (6) A sixth aspect of the present invention provides a system according to the fifth aspect, wherein the multiplexing unit includes a frequency shifter that makes the frequencies of photons from the plurality of quantum light sources different from each other.

[0087] In a sixth aspect of the present invention, photons from multiple quantum light sources can be frequency multiplexed by a frequency shifter.

[0088] (7) A seventh aspect of the present invention relates to a system in the fifth or sixth aspect, wherein the multiplexing unit includes a delay device that causes the photons from the plurality of quantum light sources to pass through the quantum communication channel at different times.

[0089] In embodiment 7 of the present invention, photons from multiple quantum light sources can be time-multiplexed by a delay device.

[0090] (8) A system according to aspect 8 of the present invention is any of aspects 5 to 6, and includes a plurality of quantum communication paths connecting the first device and the demultiplexing device, and the multiplexing unit has a distributor that distributes photons from the plurality of quantum light sources to different quantum communication paths.

[0091] In embodiment 8 of the present invention, photons from multiple quantum light sources can be spatially multiplexed using multiple quantum communication paths (eg, multiple optical fibers) and a splitter. [Explanation of symbols]

[0092] 1 Quantum communication channel 2 Classical communication channels 10 Transmitting device 11 Generation part 12, 22 Control section 13 Multiplexer 20 Receiving device 21 Detection unit 30 Demultiplexer 100 Multiple quantum communication system

Claims

1. In a system that shares quantum entanglement, a first device; a plurality of second devices; a classical communication path connecting the first device and each of the plurality of second devices; a demultiplexer connected to the second device; a quantum communication channel connecting the first device and the demultiplexing device; Equipped with the first device outputs photons multiplexed by a combination of the degrees of freedom of time, frequency, and space to the quantum communication channel; the demultiplexer performs a demultiplexing process by combining the degrees of freedom of time, frequency, and space; The first device is a plurality of spatially arranged quantum light sources; a multiplexing unit that performs multiplexing processing by combining the photons from the plurality of quantum light sources with each degree of freedom of time, frequency, and space, The multiplexing unit A system comprising at least one of a frequency shifter that causes the frequencies of photons from the plurality of quantum light sources to differ from one another, and a delay device that causes the times at which photons from the plurality of quantum light sources pass through the quantum communication path to differ from one another.

2. the first device is a transmitting device; The system of claim 1 , wherein the second device is a receiving device.

3. a plurality of quantum communication paths connecting the first device and the demultiplexing device; 3. The system according to claim 1, wherein the multiplexing unit includes a distributor that distributes photons from the plurality of quantum light sources to different quantum communication channels.

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