Quantum entangled photon pair distributor, quantum entangled photon pair distributor device, and quantum entangled photon pair distributor system

Abstract

Obtain high-quality quantum entangled photon pairs. [Solution] In the photon pair distribution system 1000, the quantum entangled photon pair distributor 100 includes an optical path section 20 that receives and propagates a plurality of quantum entangled photon pairs, including a pulsed first quantum entangled photon pair E1, and has an optical path that separates and outputs the paired photons in each of the plurality of quantum entangled photon pairs, and an optical multiplexer group 30 including a first optical multiplexer 31 and a second optical multiplexer 32 that combine and output the plurality of photons output from the optical path section, and the optical path section The optical path length is configured such that the first difference, which is the difference between the output time of one photon separated from the first entangled photon pair and output from the first optical multiplexer and the output time of the other photon output from the second optical multiplexer, is different from the second difference, which is the difference between the output time of one of any two photon pairs separated from multiple entangled photon pairs and the output time of the other photon output from the second optical multiplexer.

Description

[Technical Field]

[0001] This invention relates to a quantum entangled photon pair distributor, a quantum entangled photon pair distributor, and a quantum entangled photon pair distributor system. [Background technology]

[0002] As a technique for distributing pulsed light in quantum communication, techniques disclosed in, for example, Patent Documents 1 to 4 are known. Patent Documents 1 and 2 describe a configuration in which the polarization states of odd-numbered pulses and even-numbered pulses are orthogonal, and pulse trains with an average of less than 1 photon per pulse are output alternately at equal intervals. Patent Document 3 describes a configuration in which pulses with an average number of photons per pulse of less than 1 and with different wavelengths are input to a multiplexer at different timings. Patent Document 3 also describes a configuration in which each pulse is input to the multiplexer with an equal delay. Furthermore, Patent Document 4 describes a configuration in which pulses with phases of 0 and π / 2 are output alternately. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 4591972 [Patent Document 2] Japanese Patent Publication No. 2022-169070 [Patent Document 3] Japanese Patent Publication No. 2020-31319 [Patent Document 4] Chinese Patent No. 110851111 Specification [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In information communication, one photon and the other photon of a quantum-entangled photon pair must be received simultaneously by two different receivers that share the quantum-entangled photon pair. However, if we consider the phenomenon of simultaneous reception to correspond to the phenomenon of zero time difference in reception times, then in known techniques, there may be a pair of photons that are not the target of reception (a pair of photons that are not quantum-entangled) among the photon pairs that are received simultaneously. In this case, the pair of photons that are not the target of reception can be considered accidental light with respect to the target photon pair, and thus act as noise, which may degrade the quality of the quantum-entangled photons that are being received. When such a degradation in quality occurs, for example, the CAR (Coincidences-to-Accidentals Ratio) decreases.

[0005] The present invention has been made in view of the above, and aims to provide a quantum entangled photon pair distributor, a quantum entangled photon pair distributor, and a quantum entangled photon pair distributor system that can obtain higher quality quantum entangled photon pairs. [Means for solving the problem]

[0006] To solve the above-mentioned problems and achieve the objective, one aspect of the present invention includes an optical path section having an optical path that receives and propagates a plurality of entangled photon pairs, including a pulsed first entangled photon pair, and separates and outputs the paired photons from each of the plurality of entangled photon pairs; and a plurality of optical multiplexers, including a first optical multiplexer and a second optical multiplexer, that combine and output the photons separated from the plurality of entangled photon pairs output from the optical path section, wherein the optical path section includes at least the first quantum This quantum entangled photon pair distributor has an optical path length configured such that the first difference, which is the difference between the output time of one photon separated from an entangled photon pair and output from the first optical multiplexer and the output time of the other photon output from the second optical multiplexer, is different from the second difference, which is the difference between the output time of one of any two photon pairs separated from the plurality of quantum entangled photon pairs and output from the first optical multiplexer and the output time of the other photon output from the second optical multiplexer.

[0007] Let T be the temporal period of the pulse in the plurality of entangled photon pairs, let N be an integer of 2 or more that is the number of shared entangled photon pairs among the plurality of entangled photon pairs, where one photon is output from the first optical multiplexer and the other photon is output from the second optical multiplexer, let n1 be an integer of 0 or more that is the number of photons other than the photons of the shared entangled photon pairs output from the first optical multiplexer, and let n1 be an integer of 0 or more that is the number of photons other than the photons of the shared entangled photon pairs output from the second optical multiplexer, then the optical path section sets the timing of the photon output in the first optical multiplexer and the second optical multiplexer to T = (N 2 The optical path length of the optical path may be configured such that one or fewer photons are placed in each time slot, which is a time interval obtained by dividing by an integer between -N+1+n1 and N(N+n1).

[0008] Let T be the temporal period of the pulse in the plurality of entangled photon pairs, let N be an integer of 1 or more that the number of shared entangled photon pairs among the plurality of entangled photon pairs, in which one photon is output from the first optical multiplexer and the other photon is output from the second optical multiplexer, let n1 be an integer of 1 or more that the number of photons other than the photons of the shared entangled photon pairs output from the first optical multiplexer, and let n2 be an integer of 1 or more that the number of photons other than the photons of the shared entangled photon pairs output from the second optical multiplexer, then the optical path section sets the timing of the photon output in the first optical multiplexer and the second optical multiplexer to T = (N 2 The optical path length of the optical path may be configured such that one or fewer photons are placed in each time slot, which is a time interval obtained by dividing by an integer between (N+n1)(N+n2) and (N+n1)(N+n2).

[0009] Let T be the temporal period of the pulse in the plurality of entangled photon pairs, let r be an integer of 3 or more, and let the number of the plurality of entangled photon pairs be rWhen C2 is used, the optical path length of the optical path section may be configured such that for each of the plurality of optical multiplexers, the timing of photon output is such that there is at most one photon placed in each time slot of a time interval obtained by dividing T by an integer that is at least r(r - 1) / 2 and at most ((r - 1)×(r - 2)+1)×(r - 1).

[0010] Let the temporal period of the pulses in the plurality of entangled photon pairs be T, the number of the plurality of optical multiplexers be r which is an integer of 2 or more, i be an integer from 1 to r - 1, j be an integer from i + 1 to r, x be an integer from 1 to r, and for the plurality of entangled photon pairs, let the number of the entangled photon pairs in which one photon is output from the i-th optical multiplexer and the other photon is output from the j-th optical multiplexer among the optical multiplexers be N which is an integer of 1 or more, and let the number of photons other than the photons of the entangled photon pairs output from the x-th optical multiplexer among the optical multiplexers be n which is an integer of 1 or more x Then, the optical path section may be configured such that the timing of photon output in the i-th optical multiplexer and the j-th optical multiplexer is such that there is at most one photon placed in each time slot of a time interval obtained by dividing T by an integer that is at least (N 2 / 2×r 2 -(N 2 +2N - 2) / 2×r+2(N - 1)+Σ x=1 r (n x ) and at most an integer obtained by dividing T by an integer that is at least (N

[0011] Let the temporal period of the pulses in the plurality of entangled photon pairs be T, the number of the plurality of optical multiplexers be r which is an integer of 2 or more, i be an integer from 1 to r - 1, j be an integer from i + 1 to r, x be an integer from 1 to r, and for the plurality of entangled photon pairs, let the number of the entangled photon pairs in which one photon is output from the i-th optical multiplexer and the other photon is output from the j-th optical multiplexer among the optical multiplexers be N which is an integer of 1 or more, and let the number of photons other than the photons of the entangled photon pairs output from the x-th optical multiplexer among the r optical multiplexers, when arranged in descending order, be n' which is an integer of 1 or more xLet S be the set S = {(x-1)((r-1)N+n' x )|x is an integer between 1 and r}, and if x is m, then the optical path section takes its maximum value for the i optical multiplexer and the j optical multiplexer, and the timing of the photon output is such that T is {(r-1)N+n'1}[(m-1){(r-1)N+n' m The optical path length of the optical path may be configured such that one or fewer photons are placed in each time slot, which is a time interval obtained by dividing by an integer less than or equal to [-1] + 1].

[0012] Let T be the temporal period of the pulse in the plurality of entangled photon pairs, let r be an integer of 2 or more, let i be an integer between 1 and r-1, let j be an integer between i+1 and r, and let x be an integer between 1 and r. Let N be an integer of 1 or more, the number of shared entangled photon pairs among the plurality of entangled photon pairs, where one photon is output from the i-th photon multiplexer and the other photon is output from the j-th photon multiplexer. Let n be an integer of 0 or more, the number of photons other than those in the shared entangled photon pairs, output from the x-th photon multiplexer. x Assuming that the number of photons other than the shared quantum entangled photon pair output from one or more of the optical multiplexers is zero, the optical path section determines that the timing of the photon output in the i-th and j-th optical multiplexers is such that T is ((N 2 / 2×r 2 -(N 2 (+2N-2) / 2×r+(N-1)+Σ x=1 r (n x The optical path length of the optical path may be configured such that one or fewer photons are placed in each time slot of a time interval obtained by dividing by an integer greater than or equal to 1. However, this excludes the case where N=1, r=2, and at least one of n1 and n2 is zero.

[0013] Let T be the temporal period of the pulse in the plurality of entangled photon pairs, let r be an integer of 2 or more, let i be an integer from 1 to r-1, let j be an integer from i+1 to r, and let x be an integer from 1 to r. Let N be an integer of 1 or more, the number of shared entangled photon pairs among the plurality of entangled photon pairs in which one photon is output from the i-th photon multiplexer and the other photon is output from the j-th photon multiplexer. Let n' be an integer of 0 or more, the number of the x-th photon other than the photon of the shared entangled photon pair, when the number of photons other than the photons of the shared entangled photon pair output from each of the r photon multiplexers is arranged in descending order. x Assume that the number of photons other than the shared entangled photon pair output from one or more of the optical multiplexers is zero, and set S = {(x-1)((r-1)N+n' x )|x is an integer between 1 and r}, and if x is m, then the optical path section takes its maximum value for the i optical multiplexer and the j optical multiplexer, and the timing of the photon output is such that T is {(r-1)N+n'1}[(m-1){(r-1)N+n' m The optical path length of the optical path may be configured such that one or fewer photons are placed in each time slot of a time interval obtained by dividing by an integer less than or equal to [-1] + 1], except when N=1, r=2, and at least one of n'1 and n'2 is zero.

[0014] One aspect of the present invention is a quantum entangled photon pair distribution device comprising the quantum entangled photon pair distributor and a quantum entangled photon pair generator that generates the plurality of quantum entangled photon pairs.

[0015] One aspect of the present invention is a quantum entangled photon pair distribution system comprising: a photon pair distribution device; a plurality of receivers that receive the combined photons output from each of the plurality of optical multiplexers; and a plurality of optical transmission paths connecting each of the plurality of optical multiplexers to each of the plurality of receivers.

[0016] The aforementioned multiple optical transmission paths may have the same optical path length. [Effects of the Invention]

[0017] According to the present invention, higher quality entangled photon pairs can be obtained. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 is a schematic diagram of a quantum entangled photon pair distribution system equipped with a quantum entangled photon pair distributor according to Embodiment 1. [Figure 2] Figure 2 is a schematic diagram of an example of a quantum entanglement photon pair generator shown in Figure 1. [Figure 3] Figure 3 is a schematic diagram of a quantum entangled photon pair distribution system equipped with a quantum entangled photon pair distributor according to Embodiment 2. [Figure 4] Figure 4 shows an example of the reception conditions for entangled photon pairs using known techniques. [Figure 5] Figure 5 shows an example of the reception status of entangled photon pairs in Embodiment 2. [Figure 6] Figure 6 shows an example of the reception status of entangled photon pairs in a modified example of Embodiment 2. [Figure 7] Figure 7 is a schematic diagram of the quantum entangled photon pair distribution system according to Embodiment 3. [Figure 8] Figure 8 shows an example of the reception conditions for entangled photon pairs using known techniques. [Figure 9] Figure 9 shows an example of the reception status of entangled photon pairs in Embodiment 3. [Figure 10] Figure 10 shows an example of the reception status of entangled photon pairs in a modified example of Embodiment 3. [Figure 11] Figure 11 shows an example of the reception conditions for entangled photon pairs using known techniques. [Figure 12] Figure 12 shows an example of the reception status of entangled photon pairs in Embodiment 1 when M=3 and r=3. [Figure 13]Figure 13 shows an example of the reception status of entangled photon pairs in a modified example of Embodiment 1 where M=3 and r=3. [Figure 14] Figure 14 shows the case where time slots are set by dividing T by (N2 - N+1 + n1). [Figure 15] Figure 15 shows the case where time slots are set by dividing T by N(N+n1). [Figure 16] Figure 16 shows the case where time slots are set by dividing T by (1+n1+n2) with N=1 in (N2-N+1+n1). [Figure 17] Figure 17 shows the case where time slots are set by dividing T by (N2 + n1 + n2) (where N ≥ 2). [Figure 18] Figure 18 shows the case where time slots are set by dividing T by (N+n1)(N+n2). [Figure 19] Figure 19 shows the case where time slots are set by dividing T by r(r-1) / 2. [Figure 20] Figure 20 shows the case where time slots are set by dividing T by ((r-1)×(r-2)+1)×(r-1). [Figure 21] Figure 21 shows an example of the reception status of entangled photon pairs when the optical path length of the optical transmission line is different in Embodiment 2 shown in Figure 5. [Figure 22] Figure 22 shows an example of the reception status of entangled photon pairs when the optical path length of the optical transmission line is different in a modified example of Embodiment 1 shown in Figure 13, where M=3 and r=3. [Figure 23] Figure 23 shows the case in Example 4-1 where N≧2, and the time slot is set by dividing T by (N² / 2×r²-(N²+2N-2) / 2×r+2(N-1)+Σr x=1(nx). [Figure 24] Figure 24 shows the case in Example 4-2 where N≧2, and the time slot is set by dividing T by {(r-1)N+n'1}[(m-1){(r-1)N+n'm-1}+1]. [Figure 25] Figure 25 shows a specific example of Example 4-1 where N=2, r=2, and n1=n2=1. [Figure 26] Figure 26 shows a specific example of Example 4-2 where N=2, r=2, n'1=n'2=1, and m=2. [Figure 27] Figure 27 shows the case in Example 4-1 where N=1, and the time slot is set by dividing T by (N² / 2 × r² - (N² + 2N - 2) / 2 × r + 2(N - 1) + Σr x = 1(nx). [Figure 28] Figure 28 shows a specific example of Example 4-1 where N=1, r=2, and n1=n2=1. [Figure 29] Figure 29 shows a specific example of Example 4-2 where N=1, r=2, n'1=n'2=1, and m=2. [Figure 30] Figure 30 shows the case in Example 5-1 where N≧2, and the time slot is set by dividing T by N² / 2×r²-(N²+2N-2) / 2×r+(N-1)+Σr x=1(nx). [Figure 31] Figure 31 shows a specific example of Example 5-1 where N=2, r=2, and n1=n2=0. [Figure 32] Figure 32 shows a specific example of Example 5-2 where N=2, r=2, n'1=n'2=0, and m=2. [Figure 33] Figure 33 shows a specific example of Example 5-1 where N=1, r=3, and n1=n2=n3=1. [Figure 34] Figure 34 shows a specific example of Example 5-1 where N=1, r=3, and n1=n2=n3=1. [Figure 35] Figure 35 shows a specific example of Example 5-2 where N=1, r=3, n'1=n'2=n'3=0, and m=2. [Figure 36] Figure 36 shows a specific example of Example 5-2 where N=1, r=3, n'1=n'2=n'3=0, and m=3. [Modes for carrying out the invention]

[0019] Embodiments will be described below with reference to the drawings. However, this embodiment does not limit the present invention. Furthermore, in the drawings, the same or corresponding elements are denoted by the same reference numerals as appropriate, and redundant explanations are omitted as appropriate. It should also be noted that the drawings are schematic, and the dimensional relationships and ratios of each element may differ from reality. Even between drawings, there may be parts where the dimensional relationships and ratios differ.

[0020] (Embodiment 1) <Configuration of a quantum entangled photon pair distribution system> Figure 1 is a schematic diagram of a quantum entangled photon pair distribution system equipped with a quantum entangled photon pair distributor according to Embodiment 1. The quantum entangled photon pair distribution system 1000 comprises a quantum entangled photon pair generator 10, an optical path unit 20, an optical multiplexer group 30 which is a plurality of optical multiplexers, an optical transmission path group 40 which is a plurality of optical transmission paths, a receiver group 50 which is a plurality of receivers, and a processing unit 60. The optical path unit 20 and the optical multiplexer group 30 constitute the quantum entangled photon pair distributor 100. The quantum entangled photon pair distributor 100 and the quantum entangled photon pair generator 10 constitute the quantum entangled photon pair distribution device 200.

[0021] The quantum entanglement photon pair generator 10 generates and outputs multiple quantum entanglement photon pairs E1 to EM. Here, M is an integer greater than or equal to 2. The quantum entanglement photon pair E1 included in the multiple quantum entanglement photon pairs E1 to EM is an example of the first quantum entanglement photon pair.

[0022] Figure 2 is a schematic diagram of an example of a quantum entangled photon pair generator 10. The quantum entangled photon pair generator 10 comprises an excitation light generator 11 and a nonlinear optical unit 12. The excitation light generator 11 generates and outputs pulsed excitation light with a period T. The excitation light generator 11 is equipped with, for example, a fiber laser or a semiconductor laser as a light source, but is not particularly limited. Furthermore, the method of generating pulsed light in the excitation light generator 11 is not particularly limited, and for example, a mode-locked method, a method of directly modulating a CW (Continuous Wave) laser with a pulsed drive current, or a method of inputting CW laser light into a modulator and extracting it with a predetermined duty cycle can be used.

[0023] The nonlinear optics unit 12 receives an input of excitation light and generates signal photons and idler photons by degenerate four-wave mixing. Degenerate four-wave mixing utilizes a type of third-order nonlinear optical effect. Here, the signal photons and idler photons, which are frequency-symmetric with respect to the excitation light, have a strong correlation and form entangled photon pairs. Note that the method for generating signal photons and idler photons that are frequency-symmetric with respect to the excitation light is not limited to this; SPDC (Spontaneous Parametric Down Conversion), which utilizes a second-order nonlinear optical effect, may also be used.

[0024] The configuration of the nonlinear optical unit 12 is not particularly limited, but for example, when generating polarization-entangled photon pairs, a configuration can be adopted in which an optical fiber loop is formed using an optical fiber such as a dispersion-shifted optical fiber (DSF) with relatively high optical nonlinearity. In this case, it is preferable that the zero-dispersion wavelength of the DSF is the same as or near the wavelength corresponding to the peak frequency of the excitation light. Also, for example, when generating quantum-entangled photon pairs with respect to the number of photons, the configuration of the nonlinear optical unit 12 can be such that a DSF is used, and when excitation is input from one end of the DSF, a signal photon and an idler photon are output from the other end.

[0025] Returning to Figure 1, the optical path unit 20 has an optical path that receives and propagates entangled photon pairs E1~EM, and separates and outputs the photons that are part of each pair in multiple entangled photon pairs. For example, as shown in Figure 1, the optical path unit 20 propagates the input entangled photon pair E1 and separates and outputs the pulsed photons (triangles in the figure) that are part of the pair in the entangled photon pair E1. Such an optical path unit 20 can be configured to include, for example, optical fibers for optical communication, optical couplers, or spatial optical transmission lines.

[0026] The optical multiplexer group 30 includes a first optical multiplexer 31, a second optical multiplexer 32, ..., and an r-th optical multiplexer 3r, where r is an integer greater than or equal to 3. The optical multiplexer group 30 combines and outputs photons separated from multiple entangled photon pairs. For example, the first optical multiplexer 31 combines and outputs photons separated from at least the entangled photon pairs E1, E2, and E3. The second optical multiplexer 32 combines and outputs photons separated from at least the entangled photon pairs E1 and EM. The r-th optical multiplexer 3r combines and outputs photons separated from at least the entangled photon pairs E2, E3, and EM. Such an optical multiplexer group 30 can be configured to include, for example, optical fiber couplers or AWGs (Arrayed Waveguide Gratings) for optical communication.

[0027] The optical transmission path group 40 includes optical transmission paths 41 to 4r having the same optical path length. Each of the optical transmission paths 41 to 4r transmits photons output from the optical multiplexer group 30. Such an optical transmission path group 40 can be configured to include, for example, optical fibers for optical communication or spatial optical transmission paths.

[0028] The receiver group 50 includes a first receiver 51, a second receiver 52, ..., and an r-th receiver 5r. Optical transmission lines 41-4r connect each of the first optical multiplexer 31, the second optical multiplexer 32, ..., and the r-th optical multiplexer 3r to each of the first receiver 51, the second receiver 52, ..., and the r-th receiver 5r. The first receiver 51, the second receiver 52, ..., and the r-th receiver 5r each receive the combined photons output from each of the first optical multiplexer 31, the second optical multiplexer 32, ..., and the r-th optical multiplexer 3r, and output an electrical signal corresponding to the received photons. Such a receiver group 50 can be configured to include, for example, a photomultiplier tube or a photodiode.

[0029] The processing unit 60 receives electrical signals output from the receiver group 50, converts them into digital signals, counts the number of photons received by each of the first receiver 51, second receiver 52, ..., and the rth receiver 5r based on the digital signals, and analyzes the difference in the reception times of the photons. The processing unit 60 can also output the number of photons detected at a certain reception time difference as a histogram with the horizontal axis representing the difference in reception times. Such a processing unit 60 can be configured, for example, by including a computer and its peripheral devices.

[0030] <Example of operation of a quantum entangled photon pair distribution system> In the quantum entangled photon pair distribution system 1000 configured as described above, one photon of a quantum entangled photon pair is distributed to one of two receivers that wish to share the pair, and the other photon is distributed to the other receiver. In the quantum entangled photon pair distribution system 1000, the optical paths of one photon and the other photon pair are adjusted so that one photon and the other photon pair are received simultaneously at their respective receivers. In addition, in the quantum entangled photon pair distribution system 1000, the optical paths in the quantum entangled photon pair distributor 100 are adjusted so that one photon and the other photon are output simultaneously from the optical multiplexers corresponding to their respective receivers, since the optical transmission paths 41 to 4r have the same optical path length.

[0031] Here, in the entangled photon pair distributor 100, the optical path length of the optical path section 20 is configured such that the first difference, which is the time difference between the output time of one photon separated from the first entangled photon pair E1 and output from the first optical multiplexer 31 and the output time of the other photon output from the second optical multiplexer 32, is different from the second difference, which is the time difference between the output time of one of any two photon pairs separated from the entangled photon pair E1~EM that is output from the first optical multiplexer 31 and the output time of the other photon that is output from the second optical multiplexer 32.

[0032] As a result, when considering the difference in photon reception times at the receiver, the time difference between the reception of one photon separated from the first entangled photon pair E1 and the other photon is such that any other arbitrary photon pair separated from the entangled photon pair E1~EM is not received, thus enabling the acquisition of higher quality entangled photon pairs.

[0033] To simplify the explanation, the present invention will be described below using a more basic configuration.

[0034] (Embodiment 2) Figure 3 is a schematic diagram of a quantum entangled photon pair distribution system equipped with a quantum entangled photon pair distributor according to Embodiment 2. The quantum entangled photon pair distribution system 1000A comprises a quantum entangled photon pair generator 10A, an optical path section 20A, an optical multiplexer group 30A, an optical transmission path group 40A, a receiver group 50A, and a processing unit 60A. The optical path section 20A and the optical multiplexer group 30A constitute the quantum entangled photon pair distributor 100A. The quantum entangled photon pair distributor 100A and the quantum entangled photon pair generator 10A constitute the quantum entangled photon pair distribution system 200A.

[0035] The quantum entanglement photon pair generator 10A generates and outputs multiple quantum entanglement photon pairs E1 and E2. Quantum entanglement photon pairs E1 and E2 are examples of first quantum entanglement photon pairs.

[0036] The optical path section 20A has an optical path that receives and propagates entangled photon pairs E1 and E2, and separates and outputs the paired photons in each. Specifically, the optical path section 20A propagates the input entangled photon pairs E1 and E2, and separates and outputs the pulsed photons (triangles in the figure) that are paired in each of the entangled photon pairs E1 and E2.

[0037] The optical multiplexer group 30A includes a first optical multiplexer 31 and a second optical multiplexer 32. The first optical multiplexer 31 combines and outputs photons separated from the entangled photon pair E1 and E2. The second optical multiplexer 32 also combines and outputs photons separated from the entangled photon pair E1 and E2.

[0038] The optical transmission path group 40A includes optical transmission paths 41 and 42 having the same optical path length. Optical transmission paths 41 and 42 each transmit photons output from the optical multiplexer group 30A.

[0039] The receiver group 50A includes a first receiver 51 and a second receiver 52. Optical transmission lines 41 and 42 connect the first optical multiplexer 31 and the second optical multiplexer 32, respectively, to the first receiver 51 and the second receiver 52, respectively. The first receiver 51 and the second receiver 52 each receive the combined photons output from the first optical multiplexer 31 and the second optical multiplexer 32, respectively, and output an electrical signal corresponding to the received photons.

[0040] The processing unit 60A receives the electrical signals output from the receiver group 50A, processes them in analog / digital format, counts the number of photons received by the first receiver 51 and the second receiver 52, and analyzes the difference in the photon reception times.

[0041] In this embodiment, for the first receiver 51 and the second receiver 52, both entangled photon pairs E1 and E2 are the entangled photon pairs to be received, but for one entangled photon pair, the other entangled photon pair is noise.

[0042] Figure 4 shows an example of the reception of entangled photon pairs using known techniques. Figure 4(a) shows the detection time (reception time) of the photons in the first and second receivers. Here, T is the period of the pulses of the entangled photon pairs E1 and E2. Pulse E_1 is the pulse of one photon in entangled photon pair E1, and pulse E_-1 is the pulse of the other photon in entangled photon pair E1. Similarly, pulse E_2 is the pulse of one photon in entangled photon pair E2, and pulse E_-2 is the pulse of the other photon in entangled photon pair E2. Figure 4(b) shows the difference in detection time between the two receivers.

[0043] It should be noted that since optical transmission paths 41 and 42 have the same optical path length, the detection time in Figure 4 is equal to the output time from the optical multiplexer plus the propagation time through optical transmission paths 41 and 42, and the difference in detection time is equal to the difference in output time.

[0044] In known techniques, when receiving two different entangled photon pairs, time slots (shown as dashed lines in the figure) were set with a time interval of T / 2 (period T divided by 2), and one photon pulse was placed in each of these time slots (Figure 4(a)). The dashed lines in the figure indicate the positions of the time slots. This ensures that pulses from one photon and the other photon of the same entangled photon pair are received simultaneously.

[0045] However, in this case, as shown in Figure 4(b), when viewed in terms of the difference in detection time between the two receivers, the pair of pulses E_1 and E_-1 (i.e., entangled photon pair E1) and the pair of pulses E_2 and E_-2 (i.e., entangled photon pair E2) are received simultaneously. In this case, entangled photon pair E2 acts as noise to entangled photon pair E1, degrading the quality of the entangled photon pair E1 being received. Also, entangled photon pair E1 acts as noise to entangled photon pair E2, degrading the quality of the entangled photon pair E2 being received.

[0046] In contrast, Figure 5 shows an example of the reception status of entangled photon pairs in Embodiment 2. Figure 5(a) shows the photon detection time (reception time) in the first receiver and the second receiver. Figure 5(b) shows the difference in detection time between the two receivers.

[0047] In Embodiment 2, the optical path section 20A is configured such that the timing of the photon outputs in the first optical multiplexer 31 and the second optical multiplexer 32 is such that one or fewer photons are placed in each time slot of a time interval obtained by dividing T by 3 (i.e., T / 3). Specifically, the optical path length is adjusted so that the first receiver 51 receives pulse E_1 at time 0 and pulse E_2 at time T / 3, and the second receiver 52 receives pulse E_-1 at time 0 and pulse E_-2 at time 2T / 3. As a result, the pair of pulses E_1 and E_-1 (i.e., the entangled photon pair E1) is received simultaneously with a difference of zero, the photon pair of pulses E_2 and E_-2 is received simultaneously with a difference of T / 3, and the photon pairs of pulses E_1 and E_-2, and pulses E_-1 and E_2 are received simultaneously with a difference of 2T / 3. This realizes a state in which the optical path length is configured such that the first difference (=0), which is the time difference between the output time of pulse E_1 of one photon separated from the entangled photon pair E1 and output from the first optical multiplexer 31 and the output time of pulse E_-1 of the other photon output from the second optical multiplexer 32, is different from the second difference, which is the time difference between the output time of any two photon pairs separated from the entangled photon pairs E1 and E2 that are output from the first optical multiplexer 31 and the output time of the other photon that are output from the second optical multiplexer 32. Furthermore, a state is realized in which the optical path length is configured such that the first difference (=T / 3), which is the time difference between the output time of pulse E_2 of one photon separated from quantum entangled photon pair E2 and output from the first optical multiplexer 31 and the output time of pulse E_-2 of the other photon separated from the second optical multiplexer 32, is different from the second difference, which is the time difference between the output time of one of any two photon pairs separated from quantum entangled photon pairs E1 and E2 being output from the first optical multiplexer 31 and the output time of the other photon being output from the second optical multiplexer 32.

[0048] As a result, during the time difference (=0) between the reception of one photon separated from the first entangled photon pair E1 and the other photon, any other arbitrary photon pair separated from the entangled photon pairs E1 and E2 can be prevented from being received. Similarly, during the time difference (=T / 3) between the reception of one photon separated from the second entangled photon pair E2 and the other photon, any other arbitrary photon pair separated from the entangled photon pairs E1 and E2 can be prevented from being received. Therefore, higher quality entangled photon pairs can be obtained.

[0049] In this embodiment, time slots are set with time intervals obtained by dividing T by 3. According to the inventor's considerations, the value "3" is set as follows.

[0050] First, let N be an integer greater than or equal to 2, the number of shared entangled photon pairs, where one photon is output from the first optical multiplexer 31 and the other photon is output from the second optical multiplexer 32. Let n1 be an integer greater than or equal to 1, the number of photons other than those in a shared entangled photon pair output from the first optical multiplexer 31. Let zero be the number of photons other than those in a shared entangled photon pair output from the second optical multiplexer. Then, the optical path unit 20A sets the timing of photon output in the first optical multiplexer 31 and the second optical multiplexer to T = (N 2 If the optical path length is configured such that one or fewer photons are placed in each time slot obtained by dividing T by an integer greater than or equal to (N+1+n1), then the time difference between the reception of one photon and the other photon separated from a shared quantum entangled photon pair will prevent the other photon pair from being received. One example of the upper limit of the integer to which T is divided is N(N+n1), which will be explained later.

[0051] In Embodiment 2, the shared entangled photon pair is the entangled photon pair E1 and E2, so N=2. Also, the number of photons other than those in the shared entangled photon pair output from the first optical multiplexer 31 is zero, so n1=0. Therefore, (N 2 Since (-N+1+n1)=3, we arrive at the setting of a time slot where T is divided by 3.

[0052] (Modified version of Embodiment 2) Figure 6 shows an example of the reception status of entangled photon pairs in a modified example of Embodiment 2. Figure 6(a) shows the photon detection time (reception time) in the first receiver and the second receiver. Figure 6(b) shows the difference in detection time between the two receivers.

[0053] In a modified embodiment of the second, the optical path section 20A is configured such that the timing of the photon output in the first optical multiplexer 31 and the second optical multiplexer 32 is such that one or fewer photons are placed in each time slot of a time interval obtained by dividing T by 4 (i.e., T / 4). Specifically, the optical path length is adjusted so that the first receiver 51 receives pulse E_1 at time 0 and pulse E_2 at time 2T / 4, and the second receiver 52 receives pulse E_-1 at time 0 and pulse E_-2 at time 3T / 4. As a result, the pair of pulses E_1 and E_-1 (i.e., the quantum entangled photon pair E1) is received simultaneously with a difference of zero, the photon pair of pulses E_2 and E_-2 is received simultaneously with a difference of T / 4, the photon pair of pulses E_-1 and E_2 is received simultaneously with a difference of 2T / 4, and the photon pair of pulses E_1 and E_-2 is received simultaneously with a difference of 3T / 4. This realizes a state in which the optical path length is configured such that the first difference (=0), which is the time difference between the output time of pulse E_1 of one photon separated from quantum entangled photon pair E1 and output from the first optical multiplexer 31 and the output time of pulse E_-1 of the other photon output from the second optical multiplexer 32, is different from the second difference (i.e., T / 4, 2T / 4, or 3T / 4), which is the time difference between the output time of one of any two photon pairs separated from quantum entangled photon pairs E1 and E2 being output from the first optical multiplexer 31 and the output time of the other photon being output from the second optical multiplexer 32. Furthermore, a state is realized in which the optical path length is configured such that the first difference (=T / 4), which is the time difference between the output time of pulse E_2 of one photon separated from quantum entangled photon pair E2 and output from the first optical multiplexer 31 and the output time of pulse E_-2 of the other photon output from the second optical multiplexer 32, is different from the second difference, which is the time difference between the output time of one of any two photon pairs separated from quantum entangled photon pairs E1 and E2 being output from the first optical multiplexer 31 and the output time of the other photon being output from the second optical multiplexer 32.

[0054] As a result, during the time difference (=0) between the reception of one photon separated from the first entangled photon pair E1 and the other photon, any other arbitrary photon pair separated from the entangled photon pairs E1 and E2 can be prevented from being received. Similarly, during the time difference (=T / 4) between the reception of one photon separated from the second entangled photon pair E2 and the other photon, any other arbitrary photon pair separated from the entangled photon pairs E1 and E2 can be prevented from being received. Therefore, higher quality entangled photon pairs can be obtained.

[0055] Furthermore, as shown in Figure 6, in a modified version of Embodiment 2, the time difference in the reception of all photon pairs can be made different.

[0056] In this modified example, time slots are set with time intervals obtained by dividing T by 4, which is derived from setting time slots with time intervals obtained by dividing T by N(N+n1), as described above. In this modified example, N=2 and n1=0, so N(N+n1)=4 is derived. N(N+1) is one example of the upper limit of the integer used to divide T.

[0057] (Embodiment 3) Figure 7 is a schematic diagram of a quantum entangled photon pair distribution system equipped with a quantum entangled photon pair distributor according to Embodiment 3. The quantum entangled photon pair distribution system 1000B comprises a quantum entangled photon pair generator 10B, an optical path unit 20B, an optical multiplexer group 30B, an optical transmission path group 40B, a receiver group 50B, and a processing unit 60B. The optical path unit 20B and the optical multiplexer group 30B constitute the quantum entangled photon pair distributor 100B. The quantum entangled photon pair distributor 100B and the quantum entangled photon pair generator 10B constitute the quantum entangled photon pair distribution system 200B.

[0058] The quantum entanglement photon pair generator 10B generates and outputs multiple quantum entanglement photon pairs E1, E2, and E3. Quantum entanglement photon pair E1 is an example of the first quantum entanglement photon pair.

[0059] The optical path section 20B has an optical path that receives and propagates entangled photon pairs E1 to E3, and separates and outputs the corresponding paired photons in each of these pairs. Specifically, the optical path section 20B propagates the input entangled photon pairs E1 to E3 and separates and outputs the corresponding pulsed photons (triangles in the figure) in each of the entangled photon pairs E1 to E3.

[0060] The optical multiplexer group 30B includes a first optical multiplexer 31 and a second optical multiplexer 32. The first optical multiplexer 31 combines and outputs photons separated from entangled photon pairs E1, E2, and E3. The second optical multiplexer 32 also combines and outputs photons separated from entangled photon pair E1.

[0061] The optical transmission path group 40B includes optical transmission paths 41 and 42 having the same optical path length. Optical transmission paths 41 and 42 each transmit photons output from the optical multiplexer group 30B.

[0062] The receiver group 50B includes a first receiver 51 and a second receiver 52. Optical transmission lines 41 and 42 connect the first optical multiplexer 31 and the second optical multiplexer 32, respectively, to the first receiver 51 and the second receiver 52, respectively. The first receiver 51 and the second receiver 52 each receive combined photons output from the first optical multiplexer 31 and the second optical multiplexer 32, respectively, and output an electrical signal corresponding to the received photons.

[0063] The processing unit 60B receives the electrical signals output from the receiver group 50B, processes them in analog / digital format, counts the number of photons received by the first receiver 51 and the second receiver 52, and analyzes the difference in the photon reception times.

[0064] In this embodiment, for the first receiver 51 and the second receiver 52, the entangled photon pair E1 is the entangled photon pair to be received. The first receiver 51 also receives photons that are not the target of reception, which are separated from the entangled photon pairs E2 and E3.

[0065] Figure 8 shows an example of the reception of entangled photon pairs using known techniques. Figure 8(a) shows the detection time (reception time) of photons in the first and second receivers. Here, T is the period of the pulses of the entangled photon pairs E1 to E3. Pulse E_1 is the pulse of one photon from entangled photon pair E1, and pulse E_-1 is the pulse of the other photon from entangled photon pair E1. Pulse E_2 is the pulse of one photon from entangled photon pair E2. Pulse E_3 is the pulse of one photon from entangled photon pair E3. Figure 8(b) shows the difference in detection time between the two receivers.

[0066] In known techniques, time slots were set such that the time interval was T / 2 (period T divided by 2), and pulses of photons were placed in each of these time slots (Figure 8(a)). This ensures that pulses E_1 from one of the entangled photon pairs E1 and pulse E_-1 from the other photon are received simultaneously.

[0067] However, in this case, as shown in Figure 8(b), when viewed in terms of the difference in detection time between the two receivers, the pair of pulses E_1 and E_-1 (i.e., the entangled photon pair E1) and the pair of pulses E_2 and E_3 are received simultaneously. In this case, pulses E_2 and E_3 act as noise to the entangled photon pair E1, degrading the quality of the entangled photon pair E1 being received.

[0068] In contrast, Figure 9 shows an example of the reception status of entangled photon pairs in Embodiment 3. Figure 9(a) shows the photon detection time (reception time) in the first receiver and the second receiver. Figure 9(b) shows the difference in detection time between the two receivers.

[0069] In Embodiment 3, the optical path section 20B is configured such that the timing of the photon outputs in the first optical multiplexer 31 and the second optical multiplexer 32 is such that one or fewer photons are placed in each time slot of a time interval obtained by dividing T by 3 (i.e., T / 3). Specifically, the optical path length is adjusted so that the first receiver 51 receives pulse E_1 at time 0 and pulse E_2 at time T / 3, and the second receiver 52 receives pulse E_-1 at time 0 and pulse E_3 at time 2T / 3. As a result, the pair of pulses E_1 and E_-1 (i.e., the quantum entangled photon pair E1) is received simultaneously with a difference of zero, the photon pair of pulses E_2 and E_3 is received simultaneously with a difference of T / 3, and the photon pair of pulses E_-1 and E_2 and the photon pair of pulses E_1 and E_3 are received simultaneously with a difference of 2T / 3. This realizes a state in which the optical path length is configured such that the first difference (=0), which is the time difference between the output time of pulse E_1 of one photon separated from quantum entangled photon pair E1 and output from the first optical multiplexer 31 and the output time of pulse E_-1 of the other photon output from the second optical multiplexer 32, is different from the second difference (i.e., T / 3 or 2T / 3), which is the time difference between the output time of one of any two photon pairs (pulse E_2 and pulse E_3, pulse E_-1 and pulse E_2, and pulse E_1 and pulse E_3) separated from quantum entangled photon pairs E1~E3 that is output from the first optical multiplexer 31 and the output time of the other photon that is output from the second optical multiplexer 32.

[0070] As a result, during the time difference (=0) between the reception of one photon separated from quantum entangled photon pair E1 and the other photon, any other photon pair separated from quantum entangled photon pair E1~E3 can be prevented from being received, thus enabling the acquisition of higher quality quantum entangled photon pairs.

[0071] In this embodiment, time slots are set with time intervals obtained by dividing T by 3. According to the inventor's considerations, the value "3" is set as follows.

[0072] First, let N be an integer greater than or equal to 1, the number of shared entangled photon pairs, where one photon is output from the first optical multiplexer 31 and the other photon is output from the second optical multiplexer 32. Let n1 be an integer greater than or equal to 1, the number of photons other than those in a shared entangled photon pair output from the first optical multiplexer 31. Let n2 be an integer greater than or equal to 1, the number of photons other than those in a shared entangled photon pair output from the second optical multiplexer 32. Then, the optical path unit 20B sets the timing of photon output in the first optical multiplexer 31 and the second optical multiplexer 32 to T = (N 2 If the optical path length is configured such that one or fewer photons are placed in each time slot obtained by dividing T by an integer greater than or equal to (N+n1+n2), then the time difference between the reception of one photon and the other photon separated from a shared quantum entangled photon pair will prevent the other photon pair from being received. One example of the upper limit of the integer to which T is divided is (N+n1)(N+n2), which will be explained later.

[0073] In Embodiment 3, the shared entangled photon pair is the entangled photon pair E1, so N=1. Also, the number of photons other than those of the shared entangled photon pair output from the first optical multiplexer 31 is 1, so n1=1. Also, the number of photons other than those of the shared entangled photon pair output from the second optical multiplexer 32 is 1, so n2=1. Therefore, (N 2 Since (+n1+n2) = 3, we derive the setting of a time slot where T is divided by 3.

[0074] (Modified form of Embodiment 3) Figure 10 shows an example of the reception status of entangled photon pairs in a modified example of Embodiment 3. Figure 10(a) shows the photon detection time (reception time) in the first receiver and the second receiver. Figure 10(b) shows the difference in detection time between the two receivers.

[0075] In a modified embodiment of the third, the optical path section 20B is configured such that the timing of the photon output in the first optical multiplexer 31 and the second optical multiplexer 32 is such that one or fewer photons are placed in each time slot of a time interval obtained by dividing T by 4 (i.e., T / 4). Specifically, the optical path length is adjusted so that the first receiver 51 receives pulse E_1 at time 0 and pulse E_2 at time 2T / 4, and the second receiver 52 receives pulse E_-1 at time 0 and pulse E_-2 at time 3T / 4. As a result, the pair of pulses E_1 and E_-1 (i.e., the quantum entangled photon pair E1) is received simultaneously with a difference of zero, the photon pair of pulses E_2 and E_3 is received simultaneously with a difference of T / 4, the photon pair of pulses E_-1 and E_2 is received simultaneously with a difference of 2T / 4, and the photon pair of pulses E_1 and E_3 is received simultaneously with a difference of 3T / 4. This realizes a state in which the optical path length is configured such that the first difference (=0), which is the time difference between the output time of pulse E_1 of one photon separated from quantum entangled photon pair E1 and output from the first optical multiplexer 31 and the output time of pulse E_-1 of the other photon output from the second optical multiplexer 32, is different from the second difference (i.e., T / 4, 2T / 4, or 3T / 4), which is the time difference between the output time of one of any two photon pairs (pulse E_2 and pulse E_3, pulse E_-1 and pulse E_2, and pulse E_1 and pulse E_3) separated from quantum entangled photon pairs E1~E3 that is output from the first optical multiplexer 31 and the output time of the other photon that is output from the second optical multiplexer 32.

[0076] As a result, during the time difference (=0) between the reception of one photon separated from quantum entangled photon pair E1 and the other photon, any other arbitrary photon pair separated from quantum entangled photon pairs E1-3 can be prevented from being received, thus enabling the acquisition of higher quality quantum entangled photon pairs.

[0077] Furthermore, as shown in Figure 10, in a modified embodiment of Embodiment 3, the time difference in the reception of all photon pairs can be made different.

[0078] In this modified example, time slots are set for time intervals obtained by dividing T by 4. This is derived from setting time slots for time intervals obtained by dividing T by an integer of the form (N+n1)(N+n2), as described above. In this modified example, N=1, n1=1, and n2=1, so (N+n1)(N+n2)=4 is derived. (N+n1)(N+n2) is an example of an upper limit of the integer used to divide T.

[0079] (In Embodiment 1, when M=3 and r=3) Next, the case where M=3 and r=3 in Embodiment 1 will be described. In this case, in the quantum entangled photon pair distribution system 1000, the quantum entangled photon pair generator 10 generates and outputs quantum entangled photon pairs E1 to E3. The optical path unit 20 has an optical path that receives and propagates the quantum entangled photon pairs E1 to E3, and separates and outputs the photons that are part of each of the multiple quantum entangled photon pairs.

[0080] Furthermore, the optical multiplexer group 30 includes a first optical multiplexer 31, a second optical multiplexer 32, and a third optical multiplexer 33. The first optical multiplexer 31 combines and outputs photons separated from at least one entangled photon pair E1 and E2. The second optical multiplexer 32 combines and outputs photons separated from one entangled photon pair E1 and E3. The third optical multiplexer 33 combines and outputs photons separated from one entangled photon pair E2 and E3.

[0081] The optical transmission path group 40 includes optical transmission paths 41 to 43 having the same optical path length. The receiver group 50 includes a first receiver 51, a second receiver 52, and a third receiver 53. The optical transmission paths 41 to 43 connect the first optical multiplexer 31, the second optical multiplexer 32, and the third optical multiplexer 33, respectively, to the first receiver 51, the second receiver 52, and the third receiver 53, respectively. The first receiver 51, the second receiver 52, and the third receiver 53 each receive the combined photons output from the first optical multiplexer 31, the second optical multiplexer 32, and the third optical multiplexer 33, respectively, and output an electrical signal corresponding to the received photons.

[0082] In this embodiment, for the first receiver 51 and the second receiver 52, the entangled photon pair E1 is the entangled photon pair to be received (an example of the first entangled photon pair). For the first receiver 51 and the third receiver 53, the entangled photon pair E2 is the entangled photon pair to be received (an example of the first entangled photon pair). For the second receiver 52 and the third receiver 53, the entangled photon pair E3 is the entangled photon pair to be received (an example of the first entangled photon pair). In this case, the number of entangled photon pairs required for one photon of the entangled photon pair to be received by one of any two receivers and the other photon to be received by the other receiver is 3C2 = 3, which is equal to M.

[0083] Figure 11 shows an example of the reception of entangled photon pairs using known techniques. Figure 11(a) shows the detection time (reception time) of photons in the first, second, and third receivers. Here, T is the period of the pulses of the entangled photon pairs E1 to E3. Pulse E_1 is the pulse of one photon in entangled photon pair E1, and pulse E_-1 is the pulse of the other photon in entangled photon pair E1. Similarly, pulse E_2 is the pulse of one photon in entangled photon pair E2, and pulse E_-2 is the pulse of the other photon in entangled photon pair E2. Furthermore, pulse E_3 is the pulse of one photon in entangled photon pair E3, and pulse E_-3 is the pulse of the other photon in entangled photon pair E3. Figure 8(b) shows the difference in detection time between the two receivers. Specifically, t 2-1 This shows the difference in detection time between the first receiver and the second receiver. 3-2 This shows the difference in detection time between the second receiver and the third receiver. Specifically, t 1-3 This shows the difference in detection time between the third receiver and the first receiver.

[0084] In known techniques, time slots were set such that the time interval was T / 2 (period T divided by 2), and pulses of photons were placed in each of these time slots (Figure 11(a)). This ensured that pulses E_1 and E_-1 of one of the entangled photon pairs E1 were received simultaneously, pulses E_2 and E_-2 of one of the entangled photon pairs E2 were received simultaneously, and pulses E_3 and E_-3 of one of the entangled photon pairs E3 were received simultaneously.

[0085] However, in this case, as shown in Figure 11(b), when viewed in terms of the difference in detection time between the two receivers, in both cases, the entangled photon pair that is the target of reception is received simultaneously, along with the photon pair that is not the target of reception. In this case, the quality of the entangled photon pair that is the target of reception deteriorates.

[0086] In contrast, Figure 12 shows an example of the reception status of entangled photon pairs in Embodiment 1 when M=3 and r=3. Figure 12(a) shows the detection time (reception time) of photons in the first receiver, second receiver, and third receiver. Figure 12(b) shows the difference in detection time between the two receivers.

[0087] In Embodiment 1, when M=3 and r=3, the optical path length of the optical path section 20 is configured such that the timing of the photon output in the first optical multiplexer 31 and the second optical multiplexer 32 is such that one or fewer photons are placed in each time slot of a time interval obtained by dividing T by 3 (i.e., T / 3). Specifically, the optical path length is adjusted so that the first receiver 51 receives pulse E_1 at time 0 and pulse E_2 at time T / 3, the second receiver 52 receives pulse E_-1 at time 0 and pulse E_3 at time 2T / 3, and the third receiver 53 receives pulse E_-2 at time T / 3 and pulse E_-3 at time 2T / 3. As a result, the pair of pulses E_1 and E_-1 (i.e., quantum entangled photon pair E1) is received simultaneously with zero difference, the pair of pulses E_2 and E_-2 (i.e., quantum entangled photon pair E2) is received simultaneously with zero difference, and the pair of pulses E_3 and E_-3 (i.e., quantum entangled photon pair E3) is received simultaneously with zero difference. Meanwhile, the other pairs of photons are received simultaneously with a difference of T / 3 or 2T / 3. This realizes a state in which the optical path length is configured such that the first difference (=0), which is the time difference between the output time of pulse E_1 of one photon separated from quantum entangled photon pair E1 and output from the first optical multiplexer 31 and the output time of pulse E_-1 of the other photon separated from the second optical multiplexer 32, is different from the second difference (i.e., T / 3 or 2T / 3), which is the time difference between the output time of one of any two photon pairs separated from quantum entangled photon pair E1~E3 that is output from the first optical multiplexer 31 and the output time of the other photon that is output from the second optical multiplexer 32. Furthermore, a state is realized in which the optical path length is configured such that the first difference (=0), which is the time difference between the output time of pulse E_2 of one photon separated from quantum entangled photon pair E2 and output from the first optical multiplexer 31 and the output time of pulse E_-2 of the other photon separated from the third optical multiplexer 33, is different from the second difference (i.e., T / 3 or 2T / 3), which is the time difference between the output time of one of any two photon pairs separated from quantum entangled photon pairs E1~E3 that is output from the first optical multiplexer 31 and the output time of the other photon that is output from the third optical multiplexer 33.Furthermore, a state is realized in which the optical path length is configured such that the first difference (=0), which is the time difference between the output time of pulse E_3 of one photon separated from quantum entangled photon pair E3 and output from the second optical multiplexer 32 and the output time of pulse E_-3 of the other photon separated from the third optical multiplexer 33, is different from the second difference (i.e., T / 3 or 2T / 3), which is the time difference between the output time of one of any two photon pairs separated from quantum entangled photon pair E1~E3 that is output from the second optical multiplexer 32 and the output time of the other photon that is output from the third optical multiplexer 33.

[0088] As a result, the time difference between receiving one photon separated from entangled photon pair E1 and the other photon separated from entangled photon pair E2 and the other photon separated from entangled photon pair E3 can be controlled so that no other arbitrary photon pairs separated from entangled photon pairs E1 to E3 are received, thereby obtaining higher quality entangled photon pairs.

[0089] In this embodiment, time slots are set with time intervals obtained by dividing T by 3. According to the inventor's considerations, the value "3" is set as follows.

[0090] First, let r be an integer greater than or equal to 3 for the number of optical multiplexers, and let r-1 be the number of entangled photon pairs. Then, if the optical path length of the optical path section 20 is configured such that the timing of the photon output in each of the optical multiplexers is such that one or fewer photons are placed in each time slot, which is a time interval obtained by dividing T by an integer greater than or equal to r(r-1) / 2, then it is possible to ensure that the other photon pair is not received during the time difference between the reception of one photon and the other photon separated from a shared entangled photon pair. Note that one example of the upper limit of the integer used to divide T is ((r-1)×(r-2)+1)×(r-1), which will be explained later.

[0091] In Embodiment 3, since r=3, r(r-1) / 2=3, which leads to the setting of a time slot where T is divided by 3.

[0092] (Modified example in Embodiment 1 where M=3 and r=3) Figure 13 shows an example of the reception status of entangled photon pairs in a modified example of Embodiment 1 where M=3 and r=3. Figure 13(a) shows the detection time (reception time) of photons in the first receiver, second receiver, and third receiver. Figure 13(b) shows the difference in detection time between the two receivers.

[0093] In a modified embodiment of the third, the optical path section 20 is configured such that the timing of the photon outputs in the first optical multiplexer 31, the second optical multiplexer 32, and the third optical multiplexer 33 is such that one or fewer photons are placed in each time slot of time interval obtained by dividing T by 6 (i.e., T / 6). Specifically, the optical path length is adjusted so that the first receiver 51 receives pulse E_1 at time 0 and pulse E_2 at time 3T / 6, the second receiver 52 receives pulse E_-1 at time 0 and pulse E_-2 at time 4T / 6, and the third receiver 53 receives pulse E_-2 at time 0 and pulse E_-3 at time 5T / 6. As a result, the pair of pulses E_1 and E_-1 (i.e., quantum entangled photon pair E1) is received simultaneously with a difference of zero, the pair of pulses E_2 and E_-2 (i.e., quantum entangled photon pair E2) is received simultaneously with a difference of 3T / 6, and the pair of pulses E_3 and E_-3 (i.e., quantum entangled photon pair E3) is received simultaneously with a difference of T / 6. Meanwhile, the other pairs of photons are received simultaneously with different differences. This realizes a state in which the optical path length is configured such that the first difference (=0), which is the time difference between the output time of pulse E_1 of one photon separated from quantum entangled photon pair E1 and output from the first optical multiplexer 31 and the output time of pulse E_-1 of the other photon output from the second optical multiplexer 32, is different from the second difference, which is the time difference between the output time of one of any two photon pairs separated from quantum entangled photon pairs E1~E3 that is output from the first optical multiplexer 31 and the output time of the other photon that is output from the second optical multiplexer 32. Furthermore, a state is realized in which the optical path length is configured such that the first difference (=3T / 6), which is the time difference between the output time of pulse E_2 of one photon separated from quantum entangled photon pair E2 and output from the first optical multiplexer 31 and the output time of pulse E_-2 of the other photon separated from the third optical multiplexer 33, is different from the second difference, which is the time difference between the output time of one of any two photon pairs separated from quantum entangled photon pairs E1~E3 that is output from the first optical multiplexer 31 and the output time of the other photon that is output from the third optical multiplexer 33.Furthermore, a state is realized in which the optical path length is configured such that the first difference (=T / 6), which is the time difference between the output time of pulse E_3 of one photon separated from quantum entangled photon pair E3 and output from the second optical multiplexer 32 and the output time of pulse E_-3 of the other photon separated from the third optical multiplexer 33, is different from the second difference, which is the time difference between the output time of one of any two photon pairs separated from quantum entangled photon pair E1~E3 being output from the second optical multiplexer 32 and the output time of the other photon being output from the third optical multiplexer 33.

[0094] As a result, the time difference between receiving one photon separated from entangled photon pair E1 and the other photon separated from entangled photon pair E2 and the other photon separated from entangled photon pair E3 can be controlled so that no other arbitrary photon pairs separated from entangled photon pairs E1 to E3 are received, thereby obtaining higher quality entangled photon pairs.

[0095] Furthermore, as shown in Figure 13, in a modified example of Embodiment 1 where M=3 and r=3, the time difference in the reception of all photon pairs can be made different.

[0096] In this modified example, we set time slots with time intervals obtained by dividing T by 6. This is derived from setting time slots with time intervals obtained by dividing T by the integer ((r-1)×(r-2)+1)×(r-1), as described above. In this modified example, r=3, so we derive N((r-1)×(r-2)+1)×(r-1)=6. ((r-1)×(r-2)+1)×(r-1) is an example of the upper limit of the integer used to divide T.

[0097] (Example 1 of setting time slots and arranging photon pulses) The above embodiment 2 and its modified form are such that T is (N 2This method sets a time slot by dividing by an integer in the first range between -N+1+n1 and N(N+n1), where N=2 and n1=0, but N and n1 are not limited to these values.

[0098] Figure 14 shows that T is the lower limit of the first range (N 2 This diagram shows the case where time slots are set by dividing by (-N+1+n1). In this case, the time interval of the time slot is T / (N 2 The result is (-N+1+n1). Pulses E_1, E_2, E_3, ..., E_N are pulses of one photon from the N entangled photon pairs, output from the first photomultiplexer and received (detected) by the first receiver. Pulses E_-1, E_-2, E_-3, ..., E_-N are pulses of the other photon, output from the second photomultiplexer and received (detected) by the second receiver. E'_1, ..., E'_n1 are photons other than the photons in the entangled photon pairs, output from the first photomultiplexer and received (detected) by the first receiver.

[0099] In this case, regarding the detection time at the first receiver (corresponding to the output time of the first optical multiplexer), pulse E_k (where 1 ≤ k ≤ N) is placed in time slot No. (k-1)N+1, and E'_1, ..., E'_n1 are placed in slots No. (N-1)N+2 to N 2 The optical path length in the optical path section is adjusted so that pulses E_-k (where 1≦k≦N) are placed in time slots up to -N+1+n1 in no particular order. Furthermore, regarding the detection time at the second receiver (corresponding to the output time of the second optical multiplexer), the optical path length in the optical path section is adjusted so that pulse E_-k (where 1≦k≦N) is placed in time slot No. (k-1)N-k+2.

[0100] By dividing T by the lower limit of the first range described above to set the time slot, it is possible to ensure that the other photon pair is not received during the time difference between the reception of one photon and the other photon separated from a shared quantum entanglement photon pair.

[0101] Figure 15 shows the case where time slots are set by dividing T by N(N+n1), which is an example of the upper limit of the first range described above. In this case, the time interval of the time slot is T / (N(N+n1)). Pulses P1_1, P1_2, P1_3, P1_4, ..., P1_N+n1 are pulses of photons output from the first optical multiplexer and received (detected) by the first receiver, and include entangled photon pairs and other photons. Pulses P2_1, P2_2, P2_3, P2_N are pulses of photons output from the second optical multiplexer and received (detected) by the second receiver, and include entangled photon pairs and other photons.

[0102] In this case, with respect to the detection time at the first receiver (corresponding to the output time of the first optical multiplexer), the optical path length in the optical path section is adjusted so that pulse P1_k (where 1≦k≦N+n1) is placed in the time slot No. (k-1)N+1. Similarly, with respect to the detection time at the second receiver (corresponding to the output time of the second optical multiplexer), the optical path length in the optical path section is adjusted so that pulse P2_l (where 1≦l≦N) is placed in the time slot No. (l-1)N+l.

[0103] By dividing T by an example of the upper limit of the first range described above to set the time slot, it is possible to ensure that the other photon pair is not received during the time difference between the reception of one photon separated from a shared quantum entanglement photon pair and the other photon, and to adjust the optical path length without distinguishing between photons separated from a shared quantum entanglement photon pair and other photons.

[0104] (Example 2 of setting time slots and arranging photon pulses) The above embodiment 3 and its modified form are such that T is (N 2 This method sets the time slot by dividing by an integer in the second range between (N+n1)(N+n2) and (N+n1)(N+n2), where N=1, n1=1, and n2=1, but N and n1 are not limited to these values.

[0105] Figure 16 shows that T is the lower limit of the second range (N2 This diagram shows the case where time slots are set by dividing by (1+n1+n2) with N=1 in (+n1+n2). In this case, the time interval of the time slot is T / (1+n1+n2). Pulse E_1 is the pulse of one photon from a single entangled photon pair, output from the first photo multiplexer and received (detected) by the first receiver. Pulse E_-1 is the pulse of the other photon, output from the second photo multiplexer and received (detected) by the second receiver. E'_1, ..., E'_n1 are photons other than the photons of the entangled photon pair, output from the first photo multiplexer and received (detected) by the first receiver. E'´_1, ..., E'´_n2 are photons other than the photons of the entangled photon pair, output from the second photo multiplexer and received (detected) by the second receiver.

[0106] In this case, with respect to the detection time at the first receiver (corresponding to the output time of the first optical multiplexer), the optical path length in the optical path section is adjusted so that pulse E_1 is placed in the time slot of slot No. 1, and E'_1, ..., E'_n1 are placed in any order in the time slots from slot No. 2 to (n1+1). Similarly, with respect to the detection time at the second receiver (corresponding to the output time of the second optical multiplexer), the optical path length in the optical path section is adjusted so that pulse E_-1 is placed in the time slot of slot No. 1, and E''_1, ..., E''_n2 are placed in any order in the time slots from slot No. (n1+2) to (n1+n2+1).

[0107] By dividing T by the lower limit of the second range described above and setting the time slot in this way, it is possible to ensure that the other photon pair is not received during the time difference between the reception of one photon and the other photon separated from a shared quantum entangled photon pair.

[0108] Figure 17 shows that T is the lower limit of the second range (N 2 This diagram shows the case where time slots are set by dividing by (+n1+n2) (where N≧2). In this case, the time interval of the time slot is T / (N 2The result is (+n1+n2). Pulses E_1, E_2, E_3, ..., E_N are pulses of one photon from the N entangled photon pairs, output from the first photomultiplexer and received (detected) by the first receiver. Pulses E_-1, E_-2, E_-3, ..., E_-N are pulses of the other photon, output from the second photomultiplexer and received (detected) by the second receiver. E'_1, ..., E'_n1 are photons other than those from the entangled photon pairs, output from the first photomultiplexer and received (detected) by the first receiver. E''_1, ..., E''_n2 are photons other than those from the entangled photon pairs, output from the second photomultiplexer and received (detected) by the second receiver.

[0109] In this case, regarding the detection time at the first receiver (corresponding to the output time of the first optical multiplexer), pulse E_k (where 1 ≤ k ≤ N) is placed in time slot No. (k-1)N+1 - k+2, and E'_1, ..., E'_n1 is in slot No. N 2 -N+n²+2 to N 2 The optical path length in the optical path section is adjusted so that the pulses are placed in no particular order in the time slots up to -N+n1+n2+1. Furthermore, regarding the detection time at the second receiver (corresponding to the output time of the second optical multiplexer), pulse E_-k is placed in the time slot of slot No. (k-1)N+1, and E''_1, ..., E''_n2 are placed in slot No. N 2 -N+2 to N 2 The optical path length in the optical path section is adjusted so that the time slots up to -N+n2+1 are arranged in no particular order.

[0110] Thus, even when N≧2, by dividing T by the lower limit of the second range mentioned above to set the time slot, it is possible to ensure that the other photon pair is not received during the time difference between the reception of one photon and the other photon separated from a shared quantum entangled photon pair.

[0111] Figure 18 shows the case where time slots are set by dividing T by (N+n1)(N+n2), which is an example of the upper limit of the second range described above. In this case, the time interval of the time slot is T / ((N+n1)(N+n2)). Pulses P1_1, P1_2, P1_3, P1_4, ..., P1_N+n1 are pulses of photons output from the first optical multiplexer and received (detected) by the first receiver, and include entangled photon pairs and other photons. Pulses P2_1, P2_2, P2_3, ..., P2_N+n2 are pulses of photons output from the second optical multiplexer and received (detected) by the second receiver, and include entangled photon pairs and other photons.

[0112] In this case, with respect to the detection time at the first receiver (corresponding to the output time of the first optical multiplexer), the optical path length in the optical path section is adjusted so that pulse P1_k (where 1≦k≦N+n1) is placed in the time slot No. (k-1)(N+n2+1). Also, with respect to the detection time at the second receiver (corresponding to the output time of the second optical multiplexer), the optical path length in the optical path section is adjusted so that pulse P2_l (where 1≦l≦N+n2) is placed in the time slot No. (l-1)(N+n2)+l.

[0113] By dividing T by an example of the upper limit of the second range described above to set the time slot, it is possible to ensure that the other photon pair is not received during the time difference between the reception of one photon separated from a shared quantum entanglement photon pair and the other photon, and to adjust the optical path length without distinguishing between photons separated from a shared quantum entanglement photon pair and other photons.

[0114] (Example 3 of setting time slots and arranging photon pulses) In the above embodiment 1, the case where M=3 and r=3 and its variations are cases where the time slot is set by dividing T by an integer in a third range of r(r-1) / 2 or more and ((r-1)×(r-2)+1)×(r-1), where r=3 and M=3C2=3, but r is not limited to these.

[0115] Figure 19 shows the case where time slots are set by dividing T by r(r-1) / 2, which is the lower limit of the third range mentioned above. In this case, the time interval of the time slot is T / (r(r-1) / 2). Pulse E_k (1≦k≦r(r-1) / 2) is the pulse of one photon of the shared entangled photon pair, output from the xth photomultiplexer (1≦x≦r) and received (detected) by the xth receiver. Pulse E_-k is the pulse of the other photon of the shared entangled photon pair, output from the x' (1≦x'≦r, where x' is different from x) photomultiplexer and received (detected) by the x' receiver. Pulse E_l (1≦l≦r-1, where l is different from k) is the pulse of one photon of the shared entangled photon pair, output from the x'' photomultiplexer (1≦x''≦r, where x'' is different from x and x') and received (detected) by the x'' receiver. Pulse E_-l is the pulse of the other photon of the shared entangled photon pair, output from the xth photomultiplexer and received (detected) by the xth receiver.

[0116] In this case, with respect to the detection time at receiver x (corresponding to the output time of the x-th optical multiplexer), the optical path length in the optical path section is adjusted so that pulse E_k is placed in the time slot of slot No. k and pulse E_-l is placed in the time slot of slot No. l. Also, with respect to the detection time at receiver x' (corresponding to the output time of the x' optical multiplexer), the optical path length in the optical path section is adjusted so that pulse E_-k is placed in the time slot of slot No. k. With respect to the detection time at receiver x'' (corresponding to the output time of the x'' optical multiplexer), the optical path length in the optical path section is adjusted so that pulse E_l is placed in the time slot of slot No. l.

[0117] By dividing T by the lower limit of the third range described above to set the time slot, it is possible to ensure that the other photon pair is not received during the time difference between the reception of one photon and the other photon separated from a shared quantum entangled photon pair.

[0118] Figure 20 shows the case where T is divided by ((r-1)×(r-2)+1)×(r-1), which is an example of the upper limit of the third range described above, to set the time slot. In this case, the time interval of the time slot is T / ((r-1)×(r-2)+1)×(r-1). Pulses P1_1, P1_2, ..., P1_r-1 are pulses of photons output from the first optical multiplexer and received (detected) by the first receiver, and include entangled photon pairs and other photons. Pulses Px_1, Px_2, Px_3, ..., Px_r-1 are pulses of photons output from the xth optical multiplexer and received (detected) by the xth receiver, and include entangled photon pairs and other photons. Pulses Pr_1, Pr_2, Pr_3, ..., Pr_r-1 are pulses of photons output from the r-th photomultiplexer and received (detected) by the r-th receiver, and include shared quantum entanglement photon pairs and other photons.

[0119] In this case, with respect to the detection time at receiver x (corresponding to the output time of optical multiplexer x), the optical path length in the optical path section is adjusted so that pulse Px_k (where 1 ≤ k ≤ r(r-1) / 2) is placed in time slot No. (k-1)((r-1) × (r-2) + x) + 1.

[0120] By dividing T by an example of the upper limit of the third range described above to set the time slot, it is possible to ensure that the other photon pair is not received during the time difference between the reception of one photon separated from the shared quantum entanglement photon pair and the other photon, and to adjust the optical path length without distinguishing between the photons separated from the shared quantum entanglement photon pair and the other photons.

[0121] The above shows examples of upper and lower limits for the first, second, and third ranges. However, with any value within these ranges, it is possible to ensure that the other photon pair is not received during the time difference between the reception of one photon and the other photon separated from a shared quantum entanglement photon pair.

[0122] Furthermore, in the above embodiment, the optical transmission paths have the same optical path length, but the optical path differences may be different. For example, if L1 is the length of the optical transmission path through which one photon of the entangled photon pair is transmitted, and L2 is the length of the optical transmission path through which the other photon is transmitted, then the reception (detection) time of the photons will be shifted by (L2-L1) / (n×c). Here, n is the refractive index or effective refractive index of the optical transmission path, and c is the speed of light in a vacuum. In this case, for example, in Figure 4(b) and Figure 5(b), the reception time of the photons will be shifted by (L2-L1) / (n×c) overall. However, even in this case, the time difference between the reception of one photon separated from the first entangled photon and the other photon will be such that any other arbitrary photon pair separated from the other entangled photon pair will not be received.

[0123] For example, Figure 21 shows an example of the reception status of entangled photon pairs when the optical path lengths of the optical transmission lines are different in Embodiment 2 shown in Figure 5. If the length of optical transmission line 41 in Figure 3 is L1 and the length of optical transmission line 42 is L2, then as shown in Figure 21(a), the reception (detection) time at the second receiver 52 is shifted by (L2-L1) / (n×c) compared to the case in Figure 5(a). Here, n is the refractive index or effective refractive index of optical transmission lines 41 and 42. In this case as well, as shown in Figure 21(b), the time difference between the reception of one photon separated from the other entangled photon E1 and E2 is maintained such that no other arbitrary photon pair separated from another entangled photon pair is received.

[0124] Furthermore, for example, Figure 22 shows an example of the reception status of entangled photon pairs when the optical path lengths of the optical transmission lines are different in a modified example of Embodiment 1 shown in Figure 13, where M=3 and r=3. In Figure 1, the length of optical transmission line 41 is L1, the length of optical transmission line 42 is L2, and the length of optical transmission line 43 is L3. In this case, as shown in Figure 22(a), the reception (detection) time at the second receiver 52 is T compared to the case in Figure 13(a). 2-1 The shift is =(L2-L1) / (n×c). Also, the reception (detection) time at the third receiver 53 is T compared to the case in Figure 13(a). 3-1 =-T 1-3The shift is =(L3-L1) / (n×c). Here, n is the refractive index or effective refractive index of the optical transmission paths 41, 42, and 43. In this case as well, as shown in Figure 22(b), the time difference between the reception of one photon separated from the entangled photons E1, E2, and E3 and the other photon maintains the state in which no other arbitrary photon pair separated from the other entangled photon pair is received. Note that in Figure 22(b), T 3-2 = (L3 - L2) / (n × c).

[0125] (Example 4-1 of setting time slots and arranging photon pulses) In this invention, T is N 2 / 2×r 2 -(N 2 (+2N-2) / 2×r+2(N-1)+Σ x=1 r (n x The time slot may be set by dividing by an integer greater than or equal to 1. Here, let T be the temporal period of the pulse in multiple entangled photon pairs, let r be an integer greater than or equal to 2 for the number of multiple photomultiplexers, let i be an integer between 1 and r-1, let j be an integer between i+1 and r, and let x be an integer between 1 and r. Among the multiple entangled photon pairs, let N be an integer greater than or equal to 1 for the number of shared entangled photon pairs, where one photon is output from the i-th photomultiplexer and the other photon is output from the j-th photomultiplexer. The number of photons other than those in shared entangled photon pairs output from the x-th photomultiplexer is an integer greater than or equal to 1, n x This is the explanation. Photons other than those in a shared quantum entanglement pair are also called noise photons. They are originally one of the photons separated from the shared quantum entanglement pair, but the other photon is not received by the receiver.

[0126] Figure 23 shows that in Example 4-1, when N≧2, T is set to N 2 / 2×r 2 -(N 2 (+2N-2) / 2×r+2(N-1)+Σ r x=1 (n x This diagram shows the case where time slots are set by dividing by ).

[0127] The following describes the procedure for placing pulses in time slots. (Step 1) First, pulse E_R1R2_+1 is placed in slot No. 1 of the first receiver, and pulse E_R1R2_-1 is placed in slot No. 1 of the second receiver. Pulse E_R1R2_+1 is the pulse of one of the first entangled photon pairs received by the first receiver, and E_R1R2_-1 is the pulse of the other photon of the first entangled photon pair received by the second receiver.

[0128] (Step 2) For slots No. 2 and beyond, N-2 empty slots (shown as white triangles in the diagram) are placed in the first receiver, and pulse E_R1R2_+2 is placed in the next slot No. (N-1)+1. Meanwhile, N-1 empty slots are placed in the second receiver, and pulse E_R1R2_-2 is placed in the next slot No. (N-1)+2. This is repeated until pulse E_R1R2_+h (h=3, ...) and the following N-2 empty slots are placed in the first receiver until h becomes N, and finally one more empty slot is placed. For the second receiver, pulse E_R1R2_-h and the following N-1 empty slots are placed until h becomes N-1, and finally pulse E_R1R2_-N is placed.

[0129] Up to this point (i.e., up to slot No. N(N-1)+1), all other receivers will have empty slots. This explanation pertains to the region S1 enclosed by the solid line in the diagram.

[0130] (Step 3) Next, N-1 empty slots are placed for each receiver (region S2 enclosed by the dashed line in the figure).

[0131] (Step 4) Next, pulse E_R1R3_+1 is placed in slot No. {N(N-1)+1}×1+(N-1)×1+1 for the first receiver, and pulse E_R1R3_-1 is placed in slot No. {N(N-1)+1}×1+(N-1)×1+1 for the third receiver.

[0132] (Step 5) For the next slot and beyond, N-2 empty slots are placed for the first receiver, and pulse E_R1R3_+2 is placed in the next slot No.{N(N-1)+1}×1+{(N-1)+1}+(N-1)×1. Meanwhile, N-1 empty slots are placed for the third receiver, and pulse E_R1R3_-2 is placed in the next slot. This is repeated until pulse E_R1R3_+h (h=3, ...) and the following N-2 empty slots are placed for the first receiver until h becomes N, and finally one more empty slot is placed. Pulse E_R1R3_+h and the following N-1 empty slots are placed for the third receiver until h becomes N-1, and finally pulse E_R1R3_-N is placed (see region S3).

[0133] (Step 6) Next, N-1 empty slots are placed for each receiver (area S4 enclosed by the dashed line in the figure).

[0134] (Step 7) Repeat the above placement procedure (1) to (6) to place pulses and empty slots for the i-th receiver and the j-th receiver. Finally, place pulse E_R for the r-1 receiver. r-1 R r Arrange _+N and the following N-2 empty slots, and pulse E_R for the r-th receiver. r-1 R r Place _―N and the following N-1 empty slots (up to region S5). The slot number of the rightmost slot in region S5 is {N(N-1)+1}× r C2 + (N-1) × r-1 It is C2.

[0135] However, the procedure for all receivers to have N-1 empty slots is, pulse E_R i R r This procedure is not performed after the step of placing _+N (where i is an integer between 1 and r-1). For example, it should be noted that there are no regions with empty slots like region S4 to the right of region S5.

[0136] (Step 8) Following the arrangement up to region S5, for the r-th receiver, n corresponds to the photons other than the photons in the shared quantum entanglement photon pair. r Individual pulses P r _1~P r ibn r Arrange them in order. An empty slot will be placed to the right of these arrangements.

[0137] (Step 9) For receiver r-1, first n r n empty slots are placed. Then, n r-1 Individual pulses P r-1 _1~P r-1 ibn r-1 Arrange them in order. An empty slot will be placed to the right of these arrangements.

[0138] (Step 10) Similarly, for the third receiver, first Σ r i=4 (n i ) empty slots are placed. Next, n3 pulses P3_1 to P3_n3 are placed in order. Empty slots are placed to the right of these arrangements.

[0139] (Step 11) For the second receiver, first Σ r i=3 (n i ) empty slots are placed. Next, n2 pulses P2_1 to P2_n2 are placed in order. Empty slots are placed to the right of these arrangements.

[0140] (Step 12) For the first receiver, first Σr i=2 (n i ) empty slots are placed. Next, n1 pulses P1_1 to P1_n1 are placed in order. To the right of these arrangements, N-1 empty slots are placed.

[0141] By arranging them in this way, it is possible to prevent the other photon from being received during the time difference between the reception of one photon separated from the entangled photon pair, thereby obtaining higher quality entangled photon pairs.

[0142] (Example 4-2 of setting time slots and arranging photon pulses) Furthermore, in this invention, T is {(r-1)N+n'1}[(m-1){(r-1)N+n' m You may set time slots with time intervals obtained by dividing by an integer less than or equal to [-1] + 1]. Here, let T be the temporal period of the pulse in multiple entangled photon pairs, let r be an integer of 2 or more, let i be an integer between 1 and r-1, let j be an integer between i+1 and r, and let x be an integer between 1 and r. Let N be an integer of 1 or more, the number of shared entangled photon pairs among the multiple entangled photon pairs in which one photon is output from the i-th photon multiplexer and the other photon is output from the j-th photon multiplexer. When the number of photons other than those of a shared entangled photon pair output from each of the r photon multiplexers is arranged in descending order, the number of photons other than those of a shared entangled photon pair at the x-th shared entangled photon pair is an integer of 1 or more, n'. x Let S be the set S = {(x-1)((r-1)N+n' x )|x is an integer between 1 and r}, and m is the value of x that takes the maximum value for this integer.

[0143] Figure 24 shows that in Example 4-2, when N≧2, T is {(r-1)N+n'1}[(m-1){(r-1)N+n' m This diagram shows the case where the time slot is set by dividing by [-1] + [1].

[0144] When arranging time slots in this way, first, place pulse P1_1 in slot No. 1 for the first receiver. For the x-th (2 ≤ x ≤ r - 1) receiver, place pulse P x _1 in slot No. 1. For the r-th receiver, place pulse P r _1 in slot No. 1. Here, pulse P x _k is the pulse of the k-th photon received by the x-th receiver, and it is either a photon of the (r - 1)N entangled photon pairs shared by the x-th receiver or a photon other than the n´ x entangled photon pairs. That is, in this Example 4-2, photons of entangled photon pairs and photons other than those of entangled photon pairs are not distinguished. Note that k is an integer greater than or equal to 1 and less than or equal to (r - 1)N + n´ x below.

[0145] Next, (m - 1){(r - 1)N + n´ m - 1} empty slots are arranged for the first receiver after slot No. 2. Then, place pulse P1_2 in slot No. (m - 1){(r - 1)N + n´ m - 1}+1+1. For the first receiver, repeat such arrangements of empty slots and pulses. Finally, place pulse P1_(r - 1)N + n´1 in slot No. {(r - 1)N + n´1 - 1}(m - 1){(r - 1)N + n´ m - 1}+{(r - 1)N + n´1 - 1}×1+1, and then (m - 1){(r - 1)N + n´ m - 1} empty slots are arranged.

[0146] Similarly, (m - 1){(r - 1)N + n´ m - 1}+(x - 1) empty slots are arranged for the x-th receiver after slot No. 2. Then, place pulse P m - 2 in slot No. (m - 1){(r - 1)N + n´ x - 1}+x+1. For the x-th receiver, repeat such arrangements of empty slots and pulses. Finally, in slot No. {(r - 1)N + n´ x - 1}(m - 1){(r - 1)N + n´m -1}+{(r-1)N+n' x Pulse P x _(r-1)N+n´ x These are placed, and empty slots are placed to the right of these placements.

[0147] Similarly, for the r-th receiver in slot No. 2 and beyond, (m-1){(r-1)N+n´ m -1}+(r-1) empty slots are then placed. After that, slot No.(m-1){(r-1)N+n´ m At -1}+r+1, pulse P r Place _2. Repeat this empty slot placement and pulse placement for the r-th receiver, and finally slot No. {(r-1)N+n´ r -1}(m-1){(r-1)N+n´ m -1}+{(r-1)N+n' r -1} × r+1, pulse P1_(r-1)N+n' r These are placed, and empty slots are placed to the right of these placements.

[0148] By arranging them in this way, it is possible to prevent the other photon from being received during the time difference between the reception of one photon separated from the entangled photon pair, thereby obtaining higher quality entangled photon pairs.

[0149] (Examples 4-1 and 4-2 show specific cases where N≧2) Next, we will explain specific examples of N≧2 in Examples 4-1 and 4-2 above. First, Figure 25 shows a specific example of Example 4-1 where N=2, r=2, and n1=n2=1. In this case, the number of time slots is N 2 / 2×r 2 -(N 2The number of photons is 6 (+2N-2) / 2×r+2(N-1)+n1+n2. In this case, the reception status at the first and second receivers is shown as in Figure 25(a). The difference in detection time between the two receivers is shown as in Figure 25(b). As shown in Figure 25(b), no other photons are received at the time when pulses E_R1R2_+1 and E_R1R2_-1 are received. Also, no other photons are received at the time when pulses E_R1R2_+2 and E_R1R2_-2 are received.

[0150] Figure 26 shows a specific example of Example 4-2 where N=2, r=2, n'1=n'2=1, and m=2. The reason why m is 2 is that (x-1)((r-1)N+n' x This is because when x=1, it is 0, and when x=2, it is 3. In this case, the number of time slots is {(r-1)N+n'1}[(m-1){(r-1)N+n' m The number of photons is 9. In this case, the reception status in the first and second receivers is shown in Figure 26(a). The difference in detection time between the two receivers is shown in Figure 26(b). As shown in Figure 26(b), no other photons are received at the time when pulses E_R1R2_+1 and E_R1R2_-1 are received. Also, no other photons are received at the time when pulses E_R1R2_+2 and E_R1R2_-2 are received. Furthermore, only two photons are received in every time slot.

[0151] (In the case of N=1 in Example 4-1) Figure 27 shows the case where N=1 in Example 4-1, where T is set to N 2 / 2×r 2 -(N 2 (+2N-2) / 2×r+2(N-1)+Σ r x=1 (n x This diagram shows the case where the time slot is set by dividing by ). In this case, T is r(r-1) / 2+Σ r x=1 (n x The time slot will be set by dividing by ).

[0152] Figure 27 shows the x-th, x'-th, and x''-th receivers out of r receivers. Note that x, x'-th, and x''-th are distinct integers between 1 and r, inclusive.

[0153] First, assign integer numbers such as a, b, c, d, e, f, ... to the time slots as slot numbers. Note that a, b, c, d, e, f, ... are 1 or greater and are r(r-1) / 2+Σ r x=1 (n x They are all distinct integers less than or equal to ) . The following explanation assumes a=1, b=2, c=3, d=4, e=5, and f=6.

[0154] r(r-1)+Σ r x=1 (n x Of the photons in this case, the pulse of photons in a shared quantum entanglement pair contains pulse E +1 , E -1 ...and the noise photon pulses are named P2, P3, ...and so on. +1 , E -1 This is received by receiver x and receiver x', respectively. Also, E +4 , E -4 These are received by receiver x and receiver x'', respectively. In this way, pulses of photons in a shared quantum entanglement photon pair are assigned the same subscript with different signs (for example, +1 and -1). Furthermore, the subscripts of different quantum entanglement photon pairs and noise photons do not overlap (i.e., a≠b≠c≠···). Then, the pulses are placed in the slots with the same slot number as the pulse subscript.

[0155] By arranging them in this way, it is possible to prevent the other photon from being received during the time difference between the reception of one photon separated from the entangled photon pair, thereby obtaining higher quality entangled photon pairs.

[0156] (Examples 4-1 and 4-2 show specific cases where N=1) Next, we will explain specific examples of N=1 in Examples 4-1 and 4-2 above. First, Figure 28 shows a specific example of Example 4-1 where N=1, r=2, and n1=n2=1. In this case, the number of time slots is N 2 / 2×r 2 -(N 2 (+2N-2) / 2×r+2(N-1)+n1+n2=3. In this case, the reception status in the first receiver and the second receiver is shown as in Figure 28(a). The difference in detection time between the two receivers is shown as in Figure 28(b). As shown in Figure 28(b), pulse E +1 and E -1 At the time when this photon is received, no other photons are received.

[0157] Figure 29 shows a specific example of Example 4-2 where N=1, r=2, n'1=n'2=1, and m=2. In this case, the number of time slots is {(r-1)N+n'1}[(m-1){(r-1)N+n' m -1}+1]=4. In this case, the reception status in the first receiver and the second receiver is shown as in Figure 29(a). The difference in detection time between the two receivers is shown as in Figure 29(b). As shown in Figure 29(b), pulse E +1 and E -1 At the time when these two photons are received, no other photons are received. Furthermore, only two photons are received in any given time slot.

[0158] (Example 5-1 of setting time slots and arranging photon pulses) In this example 5-1, as in example 4-1, T is set to N 2 / 2×r 2 -(N 2 (+2N-2) / 2×r+(N-1)+Σ r x=1 (n x The time slot may also be set by dividing by an integer greater than or equal to n. However, in this example 5-1, the number of photons other than shared entangled photons output from the x-th optical multiplexer is an integer greater than or equal to n. x The only difference from Example 4-1 is that in this example, nx There are cases where this value becomes 0.

[0159] Figure 30 shows that in Example 5-1, when N≧2, T is set to N 2 / 2×r 2 -(N 2 (+2N-2) / 2×r+(N-1)+Σ r x=1 (n x This diagram shows the case where time slots are set by dividing by ).

[0160] The procedure for placing pulses in the time slots of the arrangement in Example 5-1 is the same as in steps 1 to 12 of Example 4-1. However, the number of noise photon pairs in the first receiver becomes zero, i.e., n x The only differences from Example 4-1 are that the receiver numbers are set so that =0, and that the placement of N-1 empty slots in step 12 is omitted.

[0161] By arranging them in this way, it is possible to prevent the other photon from being received during the time difference between the reception of one photon separated from the entangled photon pair, thereby obtaining higher quality entangled photon pairs.

[0162] (Example 5-2 of setting time slots and arranging photon pulses) In this example 5-2, similar to example 4-2, T is {(r-1)N+n'1}[(m-1){(r-1)N+n' m You may also set time slots with time intervals obtained by dividing by an integer less than or equal to [-1] + 1]. However, in this example 5-2, the number of photons other than shared entangled photon pairs output from the x-th optical multiplexer is a non-negative integer n. x This differs from Example 4-2 only in that respect. The procedure for placing pulses in the time slots of the arrangement in Example 5-2 is the same as the procedure in Example 4-2, so the explanation is omitted.

[0163] By arranging them in this way, it is possible to prevent the other photon from being received during the time difference between the reception of one photon separated from the entangled photon pair, thereby obtaining higher quality entangled photon pairs.

[0164] (Examples 5-1 and 5-2 show specific cases where N≧2) Next, we will explain specific examples of N≧2 in the above examples 5-1 and 5-2. First, Figure 31 is a diagram showing a specific example in Example 5-1 where N=2, r=2, and n1=n2=0. In this case, the number of time slots is N 2 / 2×r 2 -(N 2 The number of photons is 3 (+2N-2) / 2×r+(N-1)+n1+n2. In this case, the reception status at the first and second receivers is shown as in Figure 31(a). The difference in detection time between the two receivers is shown as in Figure 31(b). As shown in Figure 31(b), no other photons are received at the time when pulses E_R1R2_+1 and E_R1R2_-1 are received. Also, no other photons are received at the time when pulses E_R1R2_+2 and E_R1R2_-2 are received.

[0165] Figure 32 shows a specific example of Example 5-2 where N=2, r=2, n'1=n'2=0, and m=2. In this case, the number of time slots is {(r-1)N+n'1}[(m-1){(r-1)N+n' m The number of photons is 4. In this case, the reception status at the first and second receivers is shown in Figure 32(a). The difference in detection time between the two receivers is shown in Figure 32(b). As shown in Figure 32(b), no other photons are received at the time when pulses E_R1R2_+1 and E_R1R2_-1 are received. Also, no other photons are received at the time when pulses E_R1R2_+2 and E_R1R2_-2 are received. Furthermore, only two photons are received in each time slot.

[0166] (Examples 5-1 and 5-2, where N=1) In Example 5-1, if N=1, the time slot settings and pulse placement should be done in the same way as in Example 4-1 where N=1, so the explanation is omitted. Similarly, in Example 5-2, if N=1, the time slot settings and pulse placement should be done in the same way as in Example 4-2 where N=1, so the explanation is omitted.

[0167] (Examples 5-1 and 5-2 show specific cases where N=1) Next, we will explain specific examples of N=1 in the above examples 5-1 and 5-2. First, Figures 33 and 34 show specific examples of N=1, r=3, and n1=n2=n3=1 in example 5-1. In this case, the number of time slots is N 2 / 2×r 2 -(N 2 (+2N-2) / 2×r+(N-1)+n1+n2+n3=3. In this case, the reception status in the first receiver, second receiver, and third receiver is shown as in Figure 33. The difference in detection time between the two receivers is shown as in Figure 34. As shown in Figure 34, pulse E in the first receiver +1 And in the second receiver E -1 At the time when this is received, no other photons are received. Also, in the second receiver, pulse E +2 And in the third receiver E -2 At the time when this is received, no other photons are received. Also, in the second receiver, pulse E +3 And in the third receiver E -3 At the time when this photon is received, no other photons are received.

[0168] Figures 35 and 36 show a specific example of Example 5-2 where N=1, r=3, n'1=n'2=n'3=0, and m=3. In this case, the number of time slots is {(r-1)N+n'1}[(m-1){(r-1)N+n' m -1}+1] = 6. In this case, the reception status in the first receiver and the second receiver is shown as in Figure 35. The difference in detection time between the two receivers is shown as in Figure 36. As shown in Figure 36, pulse E in the first receiver +1 And in the second receiver E -1At the time when this is received, no other photons are received. Also, in the second receiver, pulse E +2 And in the third receiver E -2 At the time when and are received, no other photons are received. Also, in the first receiver, pulse E +3 And in the third receiver E -3 At the time when two photons are received, no other photons are received. Furthermore, in any given time slot, only two photons are received, or no photons are received at all.

[0169] Furthermore, in the above embodiment, the quantum entangled photon pair generator 10 inputs excitation light from one excitation light generator 11 to one nonlinear optical unit 12 and generates multiple quantum entangled photon pairs from the nonlinear optical unit 12, but the configuration of the quantum entangled photon pair generator is not limited to this. For example, the quantum entangled photon pair generator may be configured to input excitation light from one excitation light generator 11 to multiple nonlinear optical units and generate quantum entangled photon pairs from each of the multiple nonlinear optical units 12.

[0170] Furthermore, the present invention is not limited by the embodiments described above. Configurations that appropriately combine the above-described components are also included in the present invention. Moreover, further effects and modifications can be easily derived by those skilled in the art. Therefore, broader aspects of the present invention are not limited to the embodiments described above, and various modifications are possible. [Explanation of Symbols]

[0171] 10, 10A, 10B: Photon pair generator 11: Excitation light generator 12: Nonlinear Optics Section 20,20A,20B: Optical path section 30,30A,30B: Optical multiplexer group 31:First optical multiplexer 32:Second optical multiplexer 33: Third optical multiplexer 3r: rth optical multiplexer 40, 40A, 40B: Optical transmission path group 41, 42, 43, 4r: Optical transmission path 50, 50A, 50B: Receiver group 51: First receiver 52: Second receiver 53: Third receiver 5r: Receiver r 60, 60A, 60B: Processing equipment 100, 100A, 100B: Photon pair distributor 200, 200A, 200B: Photon pair distribution device 1000, 1000A, 1000B: Photon Pair Distribution System

Claims

1. An optical path section having an optical path that receives and propagates multiple entangled photon pairs, including a pulsed first entangled photon pair, and separates and outputs the paired photons in each of the multiple entangled photon pairs, Multiple optical multiplexers, including a first optical multiplexer and a second optical multiplexer, which combine and output photons separated from the plurality of entangled photon pairs output from the optical path section, Equipped with, The optical path portion comprises at least, The first difference, which is the difference between the output time of one photon separated from the first entangled photon pair and output from the first optical multiplexer and the output time of the other photon output from the second optical multiplexer, is different from the second difference, which is the difference between the output time of one of any two photon pairs separated from the plurality of entangled photon pairs and output from the first optical multiplexer and the output time of the other photon output from the second optical multiplexer. The optical path length of the optical path is configured Quantum entanglement photon pair distributor.

2. Let T be the temporal period of the pulse in the plurality of entangled photon pairs, let N be an integer of 2 or more that is the number of shared entangled photon pairs among the plurality of entangled photon pairs, where one photon is output from the first optical multiplexer and the other photon is output from the second optical multiplexer, let n1 be an integer of 0 or more that is the number of photons other than the photons of the shared entangled photon pairs output from the first optical multiplexer, and let n1 be an integer of 0 or more that is the number of photons other than the photons of the shared entangled photon pairs output from the second optical multiplexer be zero, The optical path section is The timing of the photon output in the first and second optical multiplexers is such that T is (N ２ So that one or fewer photons are placed in each time slot, which is a time interval obtained by dividing by an integer between -N+1+n1 and N(N+n1) and less than or equal to N(N+n1). The optical path length of the optical path is configured The quantum entangled photon pair distributor according to claim 1.

3. Let T be the temporal period of the pulse in the plurality of entangled photon pairs, and let N be an integer of 1 or more that the number of shared entangled photon pairs among the plurality of entangled photon pairs is such that one photon is output from the first optical multiplexer and the other photon is output from the second optical multiplexer, and let n1 be an integer of 1 or more that the number of photons other than the photons of the shared entangled photon pairs output from the first optical multiplexer be an integer of 1 or more, and let n2 be an integer of 1 or more that the number of photons other than the photons of the shared entangled photon pairs output from the second optical multiplexer, The optical path section is The timing of the photon output in the first and second optical multiplexers is such that T is (N ２ So that one or fewer photons are placed in each time slot of a time interval obtained by dividing by an integer between (N+n1)(N+n2) and (N+n1)(N+n2) inclusive. The optical path length of the optical path is configured The quantum entangled photon pair distributor according to claim 1.

4. Let T be the temporal period of the pulse in the plurality of entangled photon pairs, let r be an integer of 3 or more for the number of the plurality of optical multiplexers, and let (r-1) be the number of the plurality of entangled photon pairs. The optical path section is The timing of the photon output in each of the aforementioned multiple optical multiplexers is such that one or fewer photons are placed in each time slot of a time interval obtained by dividing T by an integer between r(r-1) / 2 and ((r-1) × (r-2) + 1) × (r-1). The optical path length of the optical path is configured The quantum entangled photon pair distributor according to claim 1.

5. Let T be the temporal period of the pulse in the plurality of entangled photon pairs, let r be an integer of 2 or more, let i be an integer from 1 to r-1, let j be an integer from i+1 to r, and let x be an integer from 1 to r. Let N be an integer of 1 or more, the number of shared entangled photon pairs among the plurality of entangled photon pairs, where one photon is output from the i-th photon multiplexer and the other photon is output from the j-th photon multiplexer. Let n be an integer of 1 or more, the number of photons other than those in the shared entangled photon pairs, output from the x-th photon multiplexer. ｘ So, The optical path unit is configured such that the timing of photon output from the i-th optical combiner and the j-th optical combiner is T divided by N ２ / 2×r ２ -(N ２ +2N - 2) / 2×r + 2(N - 1)+Σ ｒ ｘ＝１ (n ｘ ) or less photons are arranged in each time slot of the time interval obtained by dividing by an integer greater than or equal to 1 The optical path length of the optical path is configured The quantum entangled photon pair distributor according to claim 1.

6. Let T be the temporal period of the pulse in the plurality of entangled photon pairs, let r be an integer of 2 or more, let i be an integer from 1 to r-1, let j be an integer from i+1 to r, and let x be an integer from 1 to r. Let N be an integer of 1 or more, the number of shared entangled photon pairs among the plurality of entangled photon pairs in which one photon is output from the i-th photon multiplexer and the other photon is output from the j-th photon multiplexer. Let n' be an integer of 1 or more, the number of the x-th photon other than the photon of the shared entangled photon pair when the number of photons other than the photons of the shared entangled photon pair output from each of the r photon multiplexers is arranged in descending order. ｘ Let the set S = {(x-1)((r-1)N+n') ｘ ) | x is an integer between 1 and r} Let m be the value of x that takes the maximum value, The optical path section is configured such that the timing of the photon output in the i-optical multiplexer and the j-optical multiplexer is such that T is {(r-1)N+n' １ }[(m-1){(r-1)N+n' ｍ So that one or fewer photons are placed in each time slot of a time interval obtained by dividing by an integer less than or equal to [-1] + 1]. The optical path length of the optical path is configured The quantum entangled photon pair distributor according to claim 1.

7. Let T be the temporal period of the pulse in the plurality of entangled photon pairs, let r be an integer of 2 or more, let i be an integer from 1 to r-1, let j be an integer from i+1 to r, and let x be an integer from 1 to r. Let N be an integer of 1 or more, among the plurality of entangled photon pairs, the number of shared entangled photon pairs in which one photon is output from the i-th photon multiplexer and the other photon is output from the j-th photon multiplexer. Let n be an integer of 0 or more, the number of photons other than those in the shared entangled photon pairs that are output from the x-th photon multiplexer. ｘ Assuming that the number of photons other than the shared entangled photon pair output from one or more of the optical multiplexers is zero, The optical path section is configured such that the timing of the photon output in the i-optical multiplexer and the j-optical multiplexer is such that T is N ２ / 2 × r ２ - (N ２ +2N-2) / 2×r+(N-1)+Σ ｒ ｘ＝１ (n ｘ Each time slot obtained by dividing by an integer greater than or equal to ) contains one or fewer photons. The optical path length of the optical path is configured The quantum entangled photon pair distributor according to claim 1. However, N=1, r=2, and n １ to n ２ Except when at least one of them is zero.

8. Let T be the temporal period of the pulse in the plurality of entangled photon pairs, let r be an integer of 2 or more, let i be an integer from 1 to r-1, let j be an integer from i+1 to r, and let x be an integer from 1 to r. Let N be an integer of 1 or more, the number of shared entangled photon pairs among the plurality of entangled photon pairs in which one photon is output from the i-th photon multiplexer and the other photon is output from the j-th photon multiplexer. Let n' be an integer of 0 or more, the number of the x-th photon other than the photon of the shared entangled photon pair, when the number of photons other than the photons of the shared entangled photon pair output from each of the r photon multiplexers is arranged in descending order. ｘ Assume that the number of photons other than the shared quantum entanglement photon pair output from one or more of the optical multiplexers is zero, and set S = {(x-1)((r-1)N+n' ｘ ) | x is an integer between 1 and r} Let m be the value of x that takes the maximum value, The optical path section is configured such that the timing of the photon output in the i-optical multiplexer and the j-optical multiplexer is such that T is {(r-1)N+n' １ }[(m-1){(r-1)N+n' ｍ So that one or fewer photons are placed in each time slot of a time interval obtained by dividing by an integer less than or equal to [-1] + 1]. The optical path length of the optical path is configured The quantum entangled photon pair distributor according to claim 1. However, N=1, r=2, and n' １ to n' ２ Except when at least one of them is zero.

9. A quantum entangled photon pair distributor according to any one of claims 1 to 8, A quantum entangled photon pair generator that generates the aforementioned plurality of quantum entangled photon pairs, A quantum entangled photon pair distribution device equipped with [the following].

10. The quantum entangled photon pair distribution device according to claim 9, Multiple receivers that receive the combined photons output from each of the multiple optical multiplexers, Multiple optical transmission paths connecting each of the multiple optical multiplexers and each of the multiple receivers, A quantum entangled photon pair distribution system equipped with [the following features].

11. The plurality of optical transmission paths have the same optical path length. The quantum entangled photon pair distribution system according to claim 10.

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