System for sharing quantum entanglement

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 a system for sharing quantum entanglement. [Background technology]

[0002] A quantum communication system that transmits and receives signals using quantum is known. Patent Document 1 discloses a multiplexed quantum communication system that transmits and receives photons by optical wavelength multiplexing (paragraph

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

[0003] [Patent Document 1] Japanese Patent Application 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 the communication efficiency is necessarily good.

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

[0006] In order to solve the above problems, a system according to one aspect of the present invention is a system for sharing quantum entanglement, comprising: a first device; a plurality of second devices; a classical communication path connecting the first device and each of the plurality of second devices; and a multiplexing device connected to the second device. separation device, the first device, and the multiple separation a quantum communication channel connecting the first device and a second device, the first device outputs photons multiplexed by a combination of the degrees of freedom of time, frequency, and space to the quantum communication channel, and the multiplexing separationThe device performs demultiplexing by combining the time, frequency and spatial degrees of freedom. Effect 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 description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram illustrating a multiple quantum communication system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram illustrating a more specific example of a multiple quantum communication system according to an embodiment of the present invention. [Diagram 3] FIG. 13 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. [Diagram 5] FIG. 2 is a schematic diagram showing a time-multiplexed state. [Figure 6] FIG. 2 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. 1 is a flow diagram showing a procedure for generating an encryption key. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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) and 2(2), a transmitting device 10, receiving devices 20(1) and 20(2), and a multiple separation The present invention includes a device 30, and quantum entanglement is shared between a transmitting device 10 and receiving devices 20(1) and 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 is multiplexed with a transmitting device 10 (first device). separation The multiple quantum communication channels 1 are connected to the device 30. Note that multiple quantum communication channels 1 may be arranged in parallel. As described later, spatial multiplexing using multiple quantum communication channels 1 is 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 the multiplexed photons via the quantum communication channel 1. separation device 30 and, ultimately, to 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 transmitting device 10 transmits one of the pair of photons and holds the other photon.

[0015] The transmitting device 10 transmits a photon (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 (in effect, multiple photons) is multiplexed by a combination of the degrees of freedom of time, frequency, and space.

[0016] Figures 4 to 6 1A and 1B are schematic diagrams showing frequency multiplexing, time multiplexing, and space multiplexing of photons, respectively.

[0017] In frequency multiplexing, one of a plurality of pairs of photons (hereinafter referred to as "multiple photons") is multiplexed and transmitted so that the photons have different frequencies (wavelengths). The range of the multiplexed frequencies may be a wide band, 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] Figure 6 In the figure, 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 is possible. Here, the phases of all the multiplexed photons are equal (for example, e 0 = 1). In this case, the multiplicity (number of modes) is Figure 7 It is expressed as the number of lattices inside a rectangular parallelepiped of the frequency, time, and space multiplexing. If phase multiplexing is performed in addition to frequency 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] Moreover, 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 on the right side of formula (4). Note that multiplexing does not have to be performed in all of time, frequency, and space. Any of time, frequency, and space may not be used for multiplexing.

[0024] Multiple separation Device 30 receives the multiplexed photons from transmitting device 10, performs a demultiplexing process by combining the time, frequency, and space degrees of freedom, and sends the demultiplexed photons to receiving devices 20(1), 20(2).

[0025] Receiving devices 20(1), 20(2) (multiple second devices) receive the demultiplexed photons and recover the information transmitted from transmitting device .

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

[0027] The classical communication channels 2(1), 2(2) transmit and receive control information for generating an encryption key. 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.

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

[0029] [Example of functional configuration] Figure 2 FIG. 1 is a diagram showing an example of a 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 generating unit 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 a plurality of wavelength modes (photons in a wavelength multiplexed state) can be generated.

[0031] The optical crystal has a high nonlinear optical constant (or a high effective nonlinear optical constant) and forms photons. Here, the optical crystal can generate quantum entangled photon pairs over a broader wavelength band than the wavelength used for communication by forward-propagating spontaneous parametric down-conversion. The resonator restricts (subdivides) this broad wavelength band into multiple wavelength modes (repeated structures) by making light go back and forth (resonating) inside the resonator. As a result, by combining the optical crystal with the resonator, photons having multiple wavelength modes (wavelength multiplexed state) can be generated. Note that the photons do not need to go back and forth (circulate) within the resonator a predetermined number of times.

[0032] Here, the optical crystal may include a dispersion compensation crystal or a birefringence phase compensation crystal. By using a dispersion compensation crystal, it is possible to broaden the wavelength band in which each wavelength mode peak exists and to increase the fidelity of the quantum state to the Bell state. By increasing the fidelity of the quantum state, it is possible to reduce the number of entanglement purifications and improve the communication rate.

[0033] The generating unit 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, for example, time multiplexing utilizing pulse train generation by mode synchronization of a resonator constituting the generating unit 11 can be used in combination. 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. Furthermore, the control unit 12 executes a process for generating an encryption key.

[0035] The detection unit 21 is a multiple separation The photons output from device 30 are detected and the received bits are decoded 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 the 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 operation by supplying a square wave or sine wave voltage consisting of a voltage exceeding the breakdown voltage and a voltage less than 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] Figure 31 is a diagram showing another example of the functional configuration of a transmitting device 10 and a receiving device 20 according to an embodiment. The transmitting device 10 includes generating units 11(1), 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 a plurality of quantum light sources arranged in space. 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 multiplexing quanta (photons). In other words, if there is variation in the phase of the quanta to be multiplexed, this variation becomes noise and impedes demultiplexing. By using a quantum light source with a pulsed correlation function, it is possible to align the phase relationship at the location 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 executes 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 space multiplexing. By adding a multiplexing unit 13, the degree of multiplexing can be increased. In this case, a single generating unit 11 does not have the multiplicity, and the multiplicity 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 related to the photons from the generation units 11(1) and 11(2) are different from each other. Examples of frequency shifters include an acousto-optic modulator and an electro-optic modulator. The frequency of light can be multiplexed by applying a modulation frequency to the acousto-optic modulator. In addition, 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, the light is diffracted in a manner that depends on the modulation frequency (generation of a diffraction angle), but the effect of diffraction can be reduced by making the light go back and forth within the acousto-optic modulator.

[0046] The delayer 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 are different. The delayer may be configured by combining a beam splitter with multiple optical fibers of different lengths. For example, the delayer can be configured from a beam splitter that splits light into two lights with 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 as a part of a Mach-Zehnder interferometer or a Michelson interferometer in the multiplexing unit 13. In this case, the Mach-Zehnder interferometer may be a multi-arm Mach-Zehnder interferometer using a plurality of optical fibers having 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 the distributor 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 a lens that is slightly rotated to change the direction of light. 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] It should be noted that a distributor (for example, an optical switch) may be synchronized in time with the pulses of pump light from the generating unit 11 (quantum light source). The pulses can be distributed by feedforward control.

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

[0051] The multiplexing unit 13 may have a plurality of components selected from a frequency shifter, a delay unit, and a distributor, or may have all of a frequency shifter, a delay unit, and a distributor. For example, the multiplexing unit 13 can be configured by combining the following (1) frequency shifter, (2) delay unit, and (3) distributor.

[0052] (1) Using multiple electro-optical modulators as a frequency shifter, multiple frequency modes are generated and frequency multiplexed. In other words, multiple frequency modes are generated by applying sine waves with different frequencies and a voltage larger than a 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 to perform time multiplexing. In this way, a time mode can be equally assigned to each frequency-multiplexed frequency mode without being affected by the frequency. In other words, it is possible to prevent decoherence caused by interference between frequency multiplexing and time multiplexing.

[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 equally assigned a spatial mode without being affected by frequency and time.

[0055] As described above, by combining (1) to (3), it is possible to configure multiplexing unit 13 that performs frequency, time, and space multiplexing, prevents interference between frequency multiplexing, time multiplexing, and space multiplexing, and is optical fiber-based and easy to assemble. Note that any two of (1) to (3) may be appropriately combined, or 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. Hereinafter, the private key generation process will be described with reference to Fig. 8 and Fig. 1.

[0058] (1) Quantum communication (steps S1a and S1b) The transmitting device 10 includes a quantum communication channel 1 and a multiplexing separation One of the photon pairs in the quantum entangled state is transmitted to the receiver 20 via the device 30. N(1+2ζ) photons are multiplexed and transmitted. separationThe multiplexing is eliminated by device 30 and the photon pairs are received by receiving device 20. As a result, receiving device 20 holds one of the N(1+2ζ) photon pairs (N(1+2ζ) photons), and 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 communication channel 2. Here, it is assumed that the transmitting device 10 measures them in the HV basis.

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

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

[0062] (4) Quantum selection and measurement (Step S3a) The transmitter 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 receiver 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 unmeasured photons.

[0065] (5) Quantum conversion (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. On the other hand, the receiver 20 applies a unitary transformation Ub(C1) to the N photons on the receiver 20 side.

[0066] (6) Measuring the quantum (Step S5a) The transmitter 10 measures Kz photons from the (N-Kz+1)th to the Nth photons in the HV basis and outputs the resulting Kz-bit sequence z A is transmitted to the receiving device 20 via the classical 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 outputs the resulting Kz-bit sequence z B and the result z of the transmitting device 10 A So, s1=z B -z A The receiving device 20 performs HV inversion on the (N-Kz) photons from the 1st to the (N-Kz)th photons using s1.

[0068] (8) Quantum conversion (steps S6a and S6b) The transmitting device 10 selects a (N-Kz)×(N-Kz) regular binary matrix C2 and a mapping h2, and transmits them to the receiving device 20 via a classical channel 2. The transmitting device 10 applies a unitary transformation UA(C2) to the (N-Kz) photons. Meanwhile, the receiving device 20 applies a unitary transformation UB(C2) to the (N-Kz) photons from the 1st to the (N-Kz)th photons.

[0069] (9) Measuring the quantum (Step S7a) The transmitter 10 transmits Kx photons from the (N-Kz-Kx+1)th to the (N-Kz)th photons as a digital analog signal. base Measure the resulting Kx-bit sequence x A is transmitted to the receiving device 20 via the classical 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 converts the obtained Kx-bit sequence x B and the result x of the transmitting device 10 A So, 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. That is, the transmitting device 10 generates a plurality of photon pairs in a quantum entangled state and multiplexes them. separationOne of the photon pairs is transmitted to the receiving device 20 via the 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 correspond, a cryptographic key sequence is generated based on the photons for which the measurement results have not been transmitted.

[0073] Although an example using the polarization basis has been described above, a time bin basis may be used instead of the polarization basis. In this case, the time bin basis 1-0, 1-1, 2-0, and 2-1 are randomly selected and used for measurement. When the values ​​on the left side match between the transmitting device 10 and the receiving device 20, the value on the right side is used as the sequence for the key.

[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, and a multiplexing channel (MC) connected to the second devices. separation A device (30), the first device, and the multiplexing device. separationand a quantum communication channel (1) connecting the first device to a second device, the first device outputs photons multiplexed by a combination of the degrees of freedom of time, frequency, and space to the quantum communication channel, and the multiplexed separation The device performs the demultiplexing process by combining the time, frequency and spatial degrees of freedom.

[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 relates to 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 based on the first or second aspect, in which 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 multiple-wavelength state.

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

[0083] In embodiment 4 of the present invention, photons from multiple spatially arranged quantum light sources can be multiplexed.

[0084] (5) A fifth aspect of the present invention relates to a system according to the fourth aspect, wherein the first device receives light from the plurality of quantum light sources. photon The multiplexing unit (13) executes multiplexing processing by combining 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 section.

[0086] (6) A sixth aspect of the present invention relates to a system in accordance with the fifth aspect, wherein the multiplexing section has a frequency shifter that makes the frequencies of photons from the multiple quantum light sources different from each other.

[0087] In a sixth aspect of the present invention, a frequency shifter allows frequency multiplexing of photons from multiple quantum light sources.

[0088] (7) A seventh aspect of the present invention relates to a system in accordance with any one of the fifth and sixth aspects, wherein the multiplexing unit has a delay device that causes the times at which photons from the multiple quantum light sources pass through the quantum communication channel to differ from one another.

[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 an eighth aspect of the present invention is any one of the fifth to seventh aspects, further comprising: separation The multiplexing unit has a distributor that distributes photons from the multiple 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 by multiple quantum communication paths (eg, multiple optical fibers) and a distributor. [Explanation of symbols]

[0092] 1 Quantum communication channel 2 Classical Channels 10 Transmitting device 11 Generation part 12, 22 Control section 13 Multiplexer 20 Receiving device 21 Detection unit 30 Multiple separation Device 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 path 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 comprises: 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 the quantum communication paths connecting the first device and the multiplexing / demultiplexing device; 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 paths.

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