JP2005286485A - Quantum encryption communication method and quantum encryption communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and method capable of accurately detecting a signal in quantum encryption communication. <P>SOLUTION: In communication processing on the basis of quantum encryption, a first communication terminal outputs a plurality of pulse lights transmitted with time differences on a communication path and a second communication terminal executes attenuation and modulation processing for only pulse lights selected from the received pulse lights and returns the attenuated pulse lights and the pulse lights not attenuated to the first communication terminal, the first communication terminal receives the attenuated pulse lights and the pulse lights not attenuated to execute analysis of communication information by means of interference measurement on the basis of the attenuated pulse lights and the pulse lights not attenuated. Moreover, since the apparatus is configured to execute the interference measurement on the basis of each pulse light by matching a forward path with a return path between the communication terminals for each pulse light, the apparatus can carry out accurate interference measurement and information detection. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a quantum cryptography communication method and a quantum cryptography communication device. More specifically, the present invention relates to a quantum cryptography communication method and a quantum cryptography communication apparatus that execute communication of secret information using quantum cryptography.

  In recent years, with the development of network communication and electronic commerce, ensuring security in communication has become an important issue. One method of ensuring security is encryption technology, and communication using various encryption methods is performed.

  Encryption methods are roughly classified into a common key method and a public key method. The common key method is also called a symmetric encryption method, and holds a secret key common to both the sender and the receiver. As a typical method of the common key method, there is DES (Data Encryption Standard). A feature of the DES algorithm is that encryption and decryption can be executed by almost the same algorithm.

  The public key system or the asymmetric encryption system is a configuration in which the sender and receiver have different keys for the common key encryption. Unlike the common key cryptosystem that uses a common secret key for encryption and decryption, the public key cryptosystem is advantageous in key management because the secret key that needs to be kept secret must be held by a specific person. is there. However, the public key cryptosystem has a slower data processing speed than the common key cryptosystem, and is generally used for a small amount of data such as secret key distribution and digital signature. A typical public key cryptosystem is RSA (Rivest-Shamir-Adleman) cryptography. This uses a product of two very large prime numbers (for example, 150 digits), and utilizes the difficulty of the process of factoring the product of two large prime numbers (for example, 150 digits).

  However, it has been proved that the difficulty of calculation can be eliminated by using a quantum computer that uses the principle of quantum mechanics, and there is no information-theoretic proof about the difficulty of calculation. There is a possibility that an efficient algorithm to be used will be discovered, and there is a question about the security of the public key cryptosystem.

  On the other hand, in the common key method for sharing the secret key, it is necessary to share the secret key so as not to be known to a third party. For example, when a secret key sharing process is performed via a network, it is necessary to take sufficient measures against eavesdropping on the network.

  By applying quantum cryptography, it becomes possible to share secret keys securely using physical laws. The communication of the secret information using the quantum cryptography is performed by transmitting weak signal light (average photon number is about 1) through an optical fiber, for example. Security in communication of secret information using quantum cryptography is based on the fact that the weak light state cannot be accurately determined by a single measurement in signal detection from a communication channel to which quantum cryptography is applied.

  An outline of secret information communication using quantum cryptography will be described. Secret data is shared on the basis that transmission is performed by applying polarization processing or phase modulation processing to light on the transmission side, and this is detected on the reception side.

  An example of a secret information communication process to which the phase modulation process is applied will be described with reference to the drawings. As shown in FIG. 1, an optical signal is transmitted from a sender (Alice) 10 to a receiver (Bob) 20 via a data communication path 30 such as an optical fiber.

  On the sender (Alice) 10 side, the modulator 11 is applied, and any one of {0, π / 2, π, 3π / 2} phase modulation is applied to the coherent light and output. For example, as shown in the figure, 0 or π / 2 phase modulated light is output for bit 0, and π or 3π / 2 phase modulated light is output for bit 1.

  For example, in the table shown in the lower part of FIG. 1, when the selected bit string is the bit sequence of (a), the phase-modulated light output from the modulator 11 is received by the receiver (Bob) as a phase modulation sequence signal as shown in (b). ) Sent to the 20 side. Here, a setting example in which the modulation process corresponding to the selected bit sequence is performed after the setting of the selected bit sequence in (a) will be described. However, a random setting can be made without setting the selected bit sequence in (a). You may modulate by a sequence. That is, the configuration in which the phase modulation shown in (b) is executed randomly without setting the selected bit sequence in (a) and then the bit sequence corresponding to the modulation sequence data, that is, the selected bit sequence in (a) is derived. Good.

Next, processing on the receiver (Bob) 20 side will be described with reference to FIG. On the receiver (Bob) 20 side, the observer 21 randomly selects any one of {0, π / 2}, performs phase modulation, and measures interference. Cases in which interference can be detected by interference measurement are the following two cases.
(1) When phase modulation of data transmission side = 0, π → 0 in the observer 21 (2) Phase modulation of data transmission side = π / 2, 3π / 2 → π / in the observer 21 This is the case where phase modulation of 2 is performed.

  In other combinations, bit detection based on interference is not possible. For example, in the observer 21 on the receiver (Bob) 20 side, when the phase modulation process (c) shown in the lower table of FIG. 2 is executed, the bit detection shown in (d) is possible. (D) In the data shown in the confirmation bit based on interference, [0] and [1] are combinations that satisfy the above condition (1) or (2), and the bit can be identified. X] is a combination that does not satisfy the above conditions (1) and (2), and is a portion where bit identification could not be performed.

  Next, as shown in FIG. 3, the receiver (Bob) 20 uses the modulation sequence information applied in the observer 21 on the receiver (Bob) 20 side, that is, the information sequence (c) in the lower table of the figure. Notify the sender (Alice) 10 side. It is {0, 0, π / 2, π / 2, 0.

  Based on the modulation sequence information received from the receiver (Bob) 20, the sender (Alice) 10 satisfies a portion where correct modulation suitable for bit detection has been performed, that is, the above condition (1) or (2). Information indicating a part that is a combination and a part that has been subjected to incorrect modulation, that is, a part that does not satisfy the conditions (1) and (2) is generated and transmitted to the receiver (Bob) 20. That is, the receiver (Bob) 20 side is notified of the information column (e) in the lower table of the figure. {◯, ×, ○, ×, ○, ○ ··} shown in the figure.

  Note that the modulation sequence information {0, 0, π / 2, π / 2, 0... From the receiver (Bob) 20 side shown in FIG. 3, the information {O, × from the sender (Alice) 10 side , ○, ×, ○, ○ ··} may apply public communication paths.

  Next, as shown in FIG. 4, the receiver (Bob) 20 notifies the sender (Alice) 10 side of the bit information sequence detected by the observer 21. {0, 0, 1, 0... On the other hand, the sender (Alice) 10 notifies the receiver (Bob) 20 of the constituent bit string information of only the part that is a combination satisfying the condition (1) or (2). {0, 0, 1, 0... This is a bit sequence in the table in the lower part of the figure selected from (a) transmission bits and (e) only those for which [O] is set for modulation on the transmission / reception side. These notification processes may also be executed via a public communication path.

  When the communication data is not wiretapped on the data communication path 30, all the confirmation bits match in the bit mutual notification process shown in FIG. However, when communication data is wiretapped on the data communication path 30, as shown in FIG. 5, the mutual notification bit shift occurs in the bit mutual notification processing. This is because the modulation state changes due to wiretapping of the data communication path 30. When there is no eavesdropping on the data communication path 30, there is no occurrence of misalignment between the notification bits.

  Such data communication makes it possible to share secret information such as a secret key in a common key cryptosystem. For example, when n bits of the secret key are shared, after confirming that the bits subjected to the mutual notification processing described with reference to FIG. 4 match each other, the common bit selection processing that has been notified to each other in advance is performed. Processing such as selecting n bits from m bits (m> n) that can be shared by the above processing is executed.

Note that in data communication to which the above-described quantum cryptography is applied, it is necessary for a legitimate receiver to detect weak pulse light transmitted from the transmitter. As a method for detecting weak pulse light, there are a single photon detection method and a homodyne detection method. In homodyne detection method how weak signal light (the average number of photons 1 or so) for measuring the state of the relatively strong strong LO light (typical mean photon number 10 about ⁶⁾ by superimposing the signal light is there.

  The advantage of the homodyne detection method is that it can operate at room temperature and can be measured close to the theoretical limit with current technology, and more detailed information about the measurement state such as the probability distribution function of quadrature amplitude Can be obtained.

  However, in the secret information communication device and method using the conventional quantum cryptography, accurate signal detection is difficult due to the disturbance of the polarization state of the optical fiber or the optical path length generated in the optical fiber or free space used as the communication path. The current situation is that it has become a hindrance to practical use.

  On the other hand, in the case of quantum cryptography using single photon detection, a method for automatically correcting these disturbances and deviations has already been reported. However, when single photon detection is used, there is a problem that there is no detection element with high detection efficiency. For example, when using an avalanche photodiode that can be applied to single photon detection, there are many practical problems such as the need to keep the element at a low temperature.

  Although there is an idea to apply the homodyne detection method to the method of automatically correcting signal disturbance and shift proposed in quantum cryptography using single photon detection, it has been proposed in quantum cryptography using single photon detection. In the method of automatically correcting the disturbance or deviation of the signal, when two pulse lights overlap and cause interference, the intensity of the two becomes equal, and in the case of homodyne detection where the intensity of the signal light and the LO light are different. There is a problem that it is difficult to apply as it is.

  As described above, in the secret information communication apparatus and method to which the quantum cryptography proposed so far is applied, it is possible to prevent disturbance of the polarization state of light and deviation of the optical path length in the optical fiber or free space used as the communication path. As a result, there has been a problem that accurate signal detection cannot be performed.

  The present invention has been made in view of the above-described problems, and eliminates the disturbance of the polarization state of light and the deviation of the optical path length that occur in the communication of secret information to which quantum cryptography is applied, and enables accurate signal detection. An object is to provide a quantum cryptography communication method and a quantum cryptography communication device.

The first aspect of the present invention is:
A quantum cryptography communication method for performing communication processing based on quantum cryptography,
A pulsed light output step for outputting a plurality of pulsed light having a time difference on the communication path from the first communication terminal;
In the second communication terminal, the plurality of pulse lights are received via the communication path, and attenuation and modulation processing of only the pulse light selected from the plurality of pulse lights is executed, and the attenuated pulse light and the non-attenuated pulse are executed. A pulsed light reply step of returning light to the first communication terminal;
Information for receiving, in the first communication terminal, attenuated pulsed light and non-attenuated pulsed light from the second communication terminal, and analyzing communication information by interference measurement based on the attenuated pulsed light and non-attenuated pulsed light An analysis step;
The quantum cryptography communication method is characterized by comprising:

  Furthermore, in an embodiment of the quantum cryptography communication method of the present invention, the first communication terminal transmits each of two pulse lights having a time difference to be output on a communication path in the pulse light output step. After passing through different paths in the terminal, output to the communication path, and in the information analysis step, attenuated pulse light and non-attenuated pulse light corresponding to the two pulse lights received from the second communication terminal, In the pulsed light output step, the paths through which each pulsed light has passed are interchanged, and the round trip paths between the communication terminals of each pulsed light are matched to perform interference measurement based on each pulsed light. Features.

  Furthermore, in an embodiment of the quantum cryptography communication method of the present invention, the pulse light return step in the second communication terminal is a step including a reflection process of pulse light by a Faraday mirror.

  Furthermore, in an embodiment of the quantum cryptography communication method of the present invention, the pulse light return step in the second communication terminal is an attenuation of only the pulse light selected from the plurality of pulse lights received from the first communication terminal. And performing modulation processing to generate signal light, and performing processing for returning the signal light and LO light as non-attenuated pulsed light to the first communication terminal.

  Furthermore, in one embodiment of the quantum cryptography communication method of the present invention, the information analysis step executed in the first communication terminal includes signal light that is attenuated pulse light from the second communication terminal and non-attenuated pulse light. This is a step of performing a homodyne detection process based on the LO light.

  Furthermore, in one embodiment of the quantum cryptography communication method of the present invention, the pulsed light return step executed in the second communication terminal includes a step of executing attenuation processing of the selected pulsed light to which the acoustooptic element is applied. Features.

Furthermore, in one embodiment of the quantum cryptography communication method of the present invention, the pulsed light return step executed in the second communication terminal includes a step of executing a phase modulation process of the selected pulsed light based on the LiNbO ₃ phase modulator. It is characterized by that.

  Furthermore, in an embodiment of the quantum cryptography communication method of the present invention, in the quantum cryptography communication method, the first communication terminal further includes a step of performing a phase modulation process of pulsed light.

Furthermore, in an embodiment of the quantum cryptography communication method of the present invention, the phase modulation processing of the pulsed light is a phase modulation processing of pulsed light based on a LiNbO ₃ phase modulator.

  Furthermore, in one embodiment of the quantum cryptography communication method of the present invention, the pulse light return step executed in the second communication terminal is performed by separating the pulse light received via the communication path by a beam splitter, and performing attenuation and modulation. The present invention includes a step of detecting arrival timing of a pulse for executing processing and executing attenuation and modulation processing of only the pulse light selected from the plurality of pulse lights by control based on the detection information.

  Furthermore, in one embodiment of the quantum cryptography communication method of the present invention, the quantum cryptography communication method further includes, in the first communication terminal, separating a plurality of pulse lights received via the communication path by a beam splitter. Detecting the arrival timing of the pulses for executing the modulation process and the homodyne detection process, and performing the modulation process of only the pulsed light selected from the plurality of pulsed light and the homodyne detection by the control based on the detection information It is characterized by including.

  Furthermore, in one embodiment of the quantum cryptography communication method of the present invention, at least one of the first communication terminal or the second communication terminal is configured by a plurality of terminals, and wavelength division is performed on the output pulse light for the communication path. Multiplexing processing is executed, and terminal-to-terminal communication is executed as a multiplexed optical signal.

Furthermore, the second aspect of the present invention provides
A quantum cryptography communication device that executes communication processing based on quantum cryptography,
A first communication terminal that outputs a plurality of pulse lights having a time difference on the communication path;
Receiving the plurality of pulse lights via the communication path, performing attenuation and modulation processing of only the pulse light selected from the plurality of pulse lights, and supplying attenuated pulse light and non-attenuated pulse light to the first A second communication terminal that replies to the communication terminal,
The first communication terminal receives attenuated pulsed light and non-attenuated pulsed light from the second communication terminal, and performs analysis of communication information by interference measurement based on the attenuated pulsed light and non-attenuated pulsed light In the quantum cryptography communication device,

  Furthermore, in an embodiment of the quantum cryptography communication device of the present invention, the first communication terminal receives each of the two pulse lights having a time difference to be output on a communication path in the pulse light output process. After passing through different paths in the communication terminal, the output to the communication path, attenuated pulsed light and non-attenuated pulsed light corresponding to the two pulsed light received from the second communication terminal, It is configured to perform interference measurement based on each pulsed light by passing the path through which each pulsed light passes at the time of output of the pulsed light, and matching the round-trip path between the communication terminals of each pulsed light. Features.

  Furthermore, in one embodiment of the quantum cryptography communication device of the present invention, the second communication terminal has a configuration for performing a pulsed light reflection process by a Faraday mirror.

  Furthermore, in an embodiment of the quantum cryptography communication device of the present invention, the second communication terminal executes attenuation and modulation processing only for pulsed light selected from a plurality of pulsed light received from the first communication terminal. Then, the signal light is generated, and the process of returning the signal light and the LO light as the non-attenuated pulse light to the first communication terminal is performed.

  Furthermore, in an embodiment of the quantum cryptography communication device of the present invention, the first communication terminal is based on signal light that is attenuated pulse light from the second communication terminal and LO light as non-attenuated pulse light. The homodyne detection process is performed.

  Furthermore, in one embodiment of the quantum cryptography communication device of the present invention, the second communication terminal has a configuration for executing attenuation processing of selective pulse light to which an acoustooptic element is applied.

Furthermore, in one embodiment of the quantum cryptography communication device of the present invention, the second communication terminal has a configuration for executing phase modulation processing of selected pulsed light based on a LiNbO ₃ phase modulator.

  Furthermore, in an embodiment of the quantum cryptography communication device of the present invention, the quantum cryptography communication device further has a configuration in which the first communication terminal executes a phase modulation process of pulsed light.

Furthermore, in one embodiment of the quantum cryptography communication device of the present invention, the pulse light phase modulation processing is executed as pulse light phase modulation processing based on a LiNbO ₃ phase modulator.

  Furthermore, in an embodiment of the quantum cryptography communication device of the present invention, the second communication terminal separates the pulsed light received via the communication path by a beam splitter, and performs arrival of a pulse for performing attenuation and modulation processing. The present invention is characterized in that a timing is detected, and attenuation and modulation processing of only the pulse light selected from the plurality of pulse lights is executed by control based on the detection information.

  Furthermore, in one embodiment of the quantum cryptography communication device of the present invention, the first communication terminal separates a plurality of pulse lights received via the communication path by a beam splitter, and executes modulation processing and homodyne detection processing. It is characterized by detecting the arrival timing of a pulse to be detected, and performing modulation processing of only the pulsed light selected from the plurality of pulsed light and homodyne detection by control based on the detection information.

  Furthermore, in one embodiment of the quantum cryptography communication device of the present invention, at least one of the first communication terminal or the second communication terminal is configured by a plurality of terminals, and wavelength division for output pulse light with respect to the communication path It is characterized in that it has a configuration for executing multiprocessing and performing inter-terminal communication as a multiplexed optical signal.

  Furthermore, in an embodiment of the quantum cryptography communication device of the present invention, at least one of the first communication terminal and the second communication terminal is a beam including a polarization beam splitter and a half-wave plate as components. It has a splitter.

  Furthermore, in one embodiment of the quantum cryptography communication device of the present invention, the first communication terminal includes a circulator having a polarizer, a half-wave plate, a polarization beam splitter, and a Faraday rotator as constituent elements. To do.

  According to the configuration of the present invention, in communication processing based on quantum cryptography, the first communication terminal outputs a plurality of pulse lights having a time difference on the communication path, and the second communication terminal is selected from the received pulse lights. Attenuation and modulation processing of only the pulsed light is executed, the attenuated pulsed light and the non-attenuated pulsed light are returned to the first communication terminal, and the attenuated pulsed light and the non-attenuated pulsed light are received at the first communication terminal. Since the communication information is analyzed by interference measurement based on the attenuated pulsed light and the non-attenuated pulsed light, the signal light applicable in homodyne detection by selective attenuation processing of the pulsed light in the second communication terminal. And LO light are generated, and information communication by interference detection based on these signal light and LO light becomes possible.

  Further, according to the present invention, in the pulse light output process, the first communication terminal passes each of two pulse lights having a time difference output on the communication path through different paths in the first communication terminal. After that, the path through which each pulsed light passes when the pulsed light is output is replaced with the attenuated pulsed light and the non-attenuated pulsed light that are output to the communication path and received from the second communication terminal. And the interference measurement based on each pulsed light is performed by matching the round-trip path between the communication terminals of each pulsed light, so that the polarization state of the light in the optical fiber or free space constituting the communication path is disturbed And the deviation of the optical path length is eliminated, and accurate signal detection becomes possible.

  Details of the quantum cryptography communication method and quantum cryptography communication device of the present invention will be described below.

  FIG. 6 is a diagram illustrating a configuration of a quantum cryptography communication device that performs communication of secret information to which quantum cryptography processing is applied according to an embodiment of the present invention. Secret information is transmitted between the communication terminal 100 and the communication terminal 200 via the communication path 300 made of an optical fiber. The transmission secret information is secret information such as a shared secret key applied in the common key cryptosystem, for example.

  The communication terminal 100 includes a light source 104, a circulator 105, a beam splitter 106 having a branching ratio of 1: 1, a phase modulator 107, a delay unit 108, a beam splitter 109, a detector 110, a polarization beam splitter 111, a homodyne detector 112, and a controller. 119.

  On the other hand, the communication terminal 200 includes a beam splitter 213, a delay unit 214, a phase modulator 215, a variable attenuator 216, a Faraday mirror 217, a detector 218, and a controller 220.

  An optical fiber or a free space can be used for the communication path 300. When using free space as a communication path, the influence of light diffraction can be reduced by using a telescope to increase the diameter of the light beam in the communication path.

  A semiconductor laser can be used as the light source 104 of the communication terminal 100. When a long-distance optical fiber is used for the communication path 300, the influence of optical loss can be reduced by using a semiconductor laser having a wavelength of 1.55 μm. The light source modulates the injection current into the semiconductor laser in a pulsed manner so as to generate pulsed light, or uses an absorption light modulator (EAM). As the semiconductor laser, a Fabry-Perot type can be used, but when a DFB laser is used, the spectrum width of the light source can be narrowed.

  Hereinafter, details of processing in each component will be described in accordance with an operation sequence of communication processing to which quantum cryptography is applied.

  The pulsed light generated by the light source 104 of the communication terminal 100 is transmitted to the communication terminal 200 via the communication path 300, and the transmission data is returned to the communication terminal 100 via the communication path 300 again. Therefore, it demonstrates according to the order.

  The circulator 105 of the communication terminal 100 performs optical path control so that the light from the light source 104 is output to the beam splitter 106 and the light returned from the beam splitter 106 is output to the homodyne detector 112.

  When the pulsed light generated from the light source 104 of the communication terminal 100 is input to the beam splitter 106 via the circulator 105, the beam splitter 106 separates the pulsed light into two pulsed lights P1 and P2.

  The pulsed light traveling through the phase modulator 107, the delay unit 108, and the beam splitter 109 to the polarization beam splitter 111 is denoted by P1. Further, the pulsed light directly output from the beam splitter 106 to the polarization beam splitter 111 is P2. In the figure, pulsed light P1 and P2 heading from the communication terminal 100 to the communication terminal 200 are indicated by solid arrows, and pulsed light P1 and P2 returning from the communication terminal 200 to the communication terminal 100 are indicated by dotted arrows.

  The two paths from the beam splitter 106 to the polarizing beam splitter 111 are connected between the components by a polarization-maintaining fiber. When the pulse lights P1 and P2 merge at the polarization beam splitter 111 and enter the communication path 300, the pulse light P1 And P2 are linearly polarized light orthogonal to each other.

  However, the delay device 108 inputs the pulsed light P1 to the communication path 300 later than the pulsed light P2. The time difference between the pulsed light P1 and the pulsed light P2 must be sufficiently longer than the coherence time of the pulsed light from the light source 104, and the phase modulator 107 on the communication terminal 100 side and the phase modulator on the communication terminal 200 side The response time of 215 and variable attenuator 216 is selected to be longer.

  The communication terminal 200 receives the pulsed lights P1 and P2 from the communication terminal 100 via the communication path 300. In the communication terminal 200, input pulse light (pulse light P 1, P 2) from the communication path 300 is input to the beam splitter 213. The beam splitter 213 outputs most of the light to the delay device 214 side. The input light is split so that only a part of the light is output to the detector 218.

  The branching ratio of the beam splitter 213 is set so that as much light as possible travels to the delayer 214 side within a range where the detector 218 can monitor the arrival of the pulsed light P2. For example, the branching ratio is set to 9: 1.

  The detector 218 is used for monitoring the arrival of the pulsed light P2. As the detector 218, for example, a configuration in which a photodiode or an avalanche photodiode and an amplifier are combined with this can be applied. For the photodiode and the avalanche photodiode, Si can be used when the wavelength of the pulsed light is in the visible range or near infrared, and Ge or InGaAs can be used when the wavelength is 1.3 μm to 1.6 μm.

  The output of the detector 218 is input to the controller 220. Controller 220 controls phase modulator 215 and variable attenuator 216. 6 shows an example in which the phase modulator 215 is installed on the communication path 300 side from the variable attenuator 216. However, the variable attenuator 216 is installed on the communication path 300 side from the phase modulator 215. The setting order of the phase modulator 215 and the variable attenuator 216 may be any.

  The controller 220 controls the phase modulator 215 and the variable attenuator 216 so that the transmittance of the variable attenuator 216 increases with respect to the pulsed light P2, and the phase modulator 215 does not act. On the other hand, for the pulsed light P1, the attenuation of the variable attenuator 216 is increased to reduce the transmittance, and the phase modulator 216 executes appropriate phase modulation processing.

For example, when performing quantum cryptography using four quantum states, phase modulation of 0 degrees, 90 degrees, 180 degrees, and 270 degrees is randomly added for each pulse. As the variable attenuator 216, an acousto-optic element or a LiNbO ₃ intensity modulator can be used. As the phase modulator 215, a LiNbO ₃ phase modulator can be used.

  The pulsed light P1 and the pulsed light P2 input from the communication terminal 100 to the communication terminal 200 via the communication path 300 are reflected by the Faraday mirror 217 of the communication terminal 200 and returned to the communication terminal 100. Accordingly, the pulsed light P1 and the pulsed light P2 pass through the variable attenuator 216 and the phase modulator 215 of the communication terminal 200 twice, in both directions.

  The attenuation amount of the variable attenuator 216 is set so that the average number of photons per pulse of the pulsed light P1 returning from the communication terminal 200 to the communication terminal 100 is about one.

  The pulse light of the pulsed light P1 is weakened in this way in order to ensure communication safety as the quantum cryptography communication device. First, as described with reference to FIGS. 1 to 5, whether or not wiretapping has occurred in the communication path is determined by collation processing (see FIGS. 4 and 5) between the communication terminal 100 and the communication terminal 200. It becomes possible.

On the other hand, the average number of photons per pulse of the pulsed light P2 returning from the communication terminal 200 to the communication terminal 100 is selected so that the signal-to-noise ratio of the homodyne detector 112 on the communication terminal 100 side is optimized. The typical intensity of the pulsed light P2 is about 10 ⁶ average photons per pulse. At this time, a typical ratio of the relative transmittance of the variable attenuator 216 on the communication terminal 200 side with respect to the pulsed light P1 and the pulsed light P2 is about 10 ⁻⁶ : 1.

As described above, homodyne detection method weak signal light (the average number of photons 1 or so) with relatively strong strong LO light (typical mean photon number 10 about ⁶⁾ by superimposing the signal light state The pulsed light P1 returning from the communication terminal 200 to the communication terminal 100 corresponds to the signal light having an average photon number of about 1, and the pulsed light returning from the communication terminal 200 to the communication terminal 100. P2 corresponds to LO light having an average number of photons of about 10 ⁶ .

Both the phase modulator 215 and the variable attenuator 216 on the communication terminal 200 side need to provide phase modulation and attenuation independent of the polarization state of the pulsed light entering the communication terminal 200 from the communication path 300. By using the Faraday mirror 217 for reflection of the light P2, this condition can be automatically satisfied. When an acousto-optic element is used for the variable attenuator 216, the transmittance is almost independent of the polarization state of the light. In this case, the transmittance of the variable attenuator 216 for the pulsed light P1 is 10 ^−3. Set to degree.

  The attenuated pulsed light and the non-attenuated pulsed light, that is, the pulsed light P1 that is the attenuated pulsed light and the pulsed light P2 that is the non-attenuated pulsed light that have been subjected to the above-described processing in the communication terminal 200 are transmitted via the communication path 300 to the communication terminal 100. Is input. The pulsed light P1 that is attenuated pulsed light corresponds to signal light, and the pulsed light P2 that is non-attenuated pulsed light becomes an optical signal corresponding to LO light.

  The pulsed light P1 (signal light) and the pulsed light P2 (LO light) input from the communication terminal 200 to the communication terminal 100 via the communication path 300 are directly beamed by the polarization beam splitter 111. It is output to a short path that is input to the splitter 106, and the pulsed light P2 (LO light) is branched to a long path that passes through the beam splitter 109, the delay device 108, and the like. In the figure, pulsed light P1 (signal light) and pulsed light P2 (LO light) are indicated by dotted arrows.

  Since the pulsed light P1 (signal light) and the pulsed light P2 (LO light) are light reflected by the Faraday mirror 217 installed in the communication terminal 200, the pulsed light returned to the polarization beam splitter 111 of the communication terminal 100. P1 (signal light) and pulsed light P2 (LO light) are linearly polarized light whose planes of polarization are rotated by 90 degrees with respect to pulsed light P1 and pulsed light P2 output from the communication terminal 100, respectively.

  Due to this polarization, the pulsed light P1 (signal light) input to the communication terminal 100 is output to the short path directly input to the beam splitter 106 by the polarization beam splitter 111, and the pulsed light P2 (LO light). Is branched to a long path through the beam splitter 109, the delay device 108, and the like.

  That is, the paths between the polarization beam splitter 111 and the beam splitter 106 of the communication terminal 100 are pulsed light P1 and P2 when traveling from the communication terminal 100 to the communication terminal 200, and pulsed light P1 returned from the communication terminal 200 to the communication terminal 100. (Signal light) and P2 (LO light) are switched.

  In this configuration, the weak pulse light P1 (signal light) attenuated by the attenuation process in the communication terminal 200 returns to the communication terminal 100 because the communication terminal 100 side passes through a short path without extra optical components. The optical loss of the pulsed light P1 (signal light) can be reduced.

On the other hand, typical number of photons per pulse is the pulse light is 10 ⁶ or so P2 (LO light), by the beam splitter 109, divided into pulse proceeds to the pulse detector 110 which proceeds to the delay 108. A typical branching ratio of the beam splitter 109 is 9 to 1, and is set so that most of the pulses travel to the delay unit 108 side.

  The configuration of the detector 110 of the communication terminal 100 is the same as that of the detector 218 of the communication terminal 200, and the beam splitter 109 also has as much light as possible within the range where the arrival of the pulsed light P2 (LO light) can be detected. The output is set to the delay unit 108 side.

  The output of the detector 110 is input to the controller 119. In addition to controlling the phase modulator 107, the controller 119 has a function of controlling the timing for reading the output of the homodyne detector 112.

  The phase modulator 107 applies appropriate phase modulation to the pulsed light P2 (LO light) that has passed through the delay unit. In the case of quantum cryptography using four quantum states, phase modulation of 0 degree or 90 degrees is given randomly.

  When going from the communication terminal 100 to the communication terminal 200, the pulsed light P1 that has passed through a long path (phase modulator 107, delay unit 108, beam splitter 109 side) is a short path (polarization beam splitter 111) in the return path. → Arrive at the beam splitter 106 via the beam splitter 106).

  On the other hand, when going from the communication terminal 100 to the communication terminal 200, the pulsed light P2 that has passed through a short path (polarization beam splitter 111 → beam splitter 106) is a long path (phase modulator 107, delay device) on the return path. 108, the beam splitter 109 side) and arrive at the beam splitter 106.

  In this way, the pulsed lights P1 and P2 pass through a completely equidistant path in the round trip between the communication terminal 100 and the communication terminal 200, and the pulsed light P1 (signal light) and the pulsed light P2 (LO light) are At the same time, it arrives at the beam splitter 106.

  The pulsed light P1 is signal light in which quantum mechanical properties appear, and the homodyne detection of the pulsed light P1 is performed by using the pulsed light P2 having a stronger intensity as local oscillation light (LO light). The two outputs of the beam splitter 106 are input to the homodyne detector 112, one directly through the circulator 105 and the other.

  Photodiodes are installed at the two input parts of the homodyne detector 112, respectively. For the photodiode, Si can be used when the wavelength of the pulsed light is in the visible range or near infrared, and Ge or InGaAs can be used when the wavelength is 1.3 μm to 1.6 μm. The outputs of the two photodiodes are input to an amplifier with low noise and high gain. Further, when the output of this amplifier is normalized using the intensity of the local oscillation light (pulse light P2), the gain of the amplifier, etc., signal light The quadrature amplitude of (pulse light P1) is obtained. Communication secret information such as a secret key can be obtained from the detection information of the homodyne detector 112.

  An outline of a secret information sharing sequence through communication between the communication terminal 100 and the communication terminal 200 shown in FIG. 6 will be described with reference to FIGS.

  7 corresponds to the one-way communication type quantum cryptography communication processing described above with reference to FIGS. 1 to 5 with respect to the secret information sharing processing by the round-trip communication between the communication terminal 100 and the communication terminal 200 described above. FIG.

  In FIG. 7, the communication terminal 200 shown on the left side and the communication terminal 100 shown on the right side correspond to the communication terminal 200 and the communication terminal 100 of FIG. First, the forward pulse lights P 1 and P 2 are output from the communication terminal 100 to the communication terminal 200, and the backward pulse lights P 1 and P 2 are returned from the communication terminal 200 to the communication terminal 100.

  Here, the communication terminal 200 applies the phase modulator 215 to the received pulsed light P1 among the received pulsed lights P1 and P2 from the communication terminal 100, and any one of {0, π / 2, π, 3π / 2}. Apply phase modulation. This phase modulation sequence corresponds to the data transmission side phase modulation sequence in (b) of the table at the bottom of FIG.

  The phase modulation sequence (table (b) in FIG. 7) executed by the communication terminal 200 on the received pulsed light P1 may be a sequence selected at random. Alternatively, (a) a selection bit in the lower table of FIG. 7 may be set in advance, and then modulation corresponding to the selection bit may be performed.

  For example, it is assumed that phase modulation light of 0 or π / 2 is associated with bit 0, and phase modulation of π or 3π / 2 is associated with bit 1.

  The pulse light P1 subjected to such phase modulation is returned to the communication terminal 100 as signal light attenuated by the variable attenuator 216 (see FIG. 6). The pulsed light P2 is returned to the communication terminal 100 without being attenuated.

The pulsed light P1 returned from the communication terminal 200 to the communication terminal 100 is weak signal light (the average number of photons is about 1), and the pulsed light P2 returned from the communication terminal 200 to the communication terminal 100 is relatively strong. LO light (typical mean photon number 10 about ^6).

  The communication terminal 100 that has received the return pulse light P1 (signal light) and the pulse light P2 (LO light) selects, for example, one of {0, π / 2} at random in the phase modulator 107, Phase modulation is performed on the pulsed light P2 (LO light), and the homodyne detector 112 measures interference.

  For example, when (c) phase modulation processing shown in the lower table of FIG. 7 is executed in the phase modulator 107 of the communication terminal 100, the homodyne detector 112 can perform bit detection shown in (d). . (D) In the data shown in the confirmation bit based on interference, [0] and [1] are portions where bit identification due to interference can be performed, and [×] is a portion where bit identification cannot be performed. Whether or not bit identification is possible is determined by a combination of phase modulation processing executed in the communication terminal 200 and the communication terminal 100 as described above.

  For example, the homodyne detector 112 of the communication terminal 100 is used only when the combination of phase modulation processing satisfies a predetermined condition as shown in the data shown in the confirmation bit based on (d) interference in the lower table of FIG. Bit [0] or [1] will be detected. [×] is a portion where bit identification could not be executed.

  Thereafter, as shown in FIG. 8, communication terminal 100 notifies communication terminal 200 of the modulation sequence information applied in communication terminal 100, that is, the information sequence (c) in the lower table of the figure. It is {0, 0, π / 2, π / 2, 0.

  Based on the modulation sequence information received from communication terminal 100, communication terminal 200 generates information indicating a part where correct modulation adapted to bit detection is performed and a part where incorrect modulation is performed, and thereby communication terminal 100 Send to. That is, the information sequence (e) in the lower table of the figure is notified to the receiver communication terminal 100 side. {◯, ×, ○, ×, ○, ○ ··} shown in the figure.

  Note that the modulation sequence information {0, 0, π / 2, π / 2, 0...} From the communication terminal 100 shown in FIG. 8 and information {◯, ×, ○, ×, ○, from the communication terminal 200 side are shown. ○ ··} may apply a public communication path.

  Next, as illustrated in FIG. 9, the communication terminal 100 notifies the communication terminal 200 of the detected bit information sequence. {0, 0, 1, 0... On the other hand, the communication terminal 200 notifies the communication terminal 100 of bit string information of only a portion subjected to phase modulation that can be detected on the communication terminal 100 side. {0, 0, 1, 0... This is a bit sequence in the table in the lower part of the figure selected from (a) transmission bits and (e) only those for which [O] is set for modulation on the transmission / reception side. These notification processes may also be executed via a public communication path.

  When the communication data is not wiretapped on the data communication path 300, all the confirmation bits match in the bit mutual notification process shown in FIG. However, when communication data is wiretapped in the data communication path 300, a mutual notification bit shift occurs in the bit mutual notification processing. This is because the modulation state changes due to wiretapping of the data communication path 300. When there is no eavesdropping on the data communication path 300, there is no occurrence of misalignment between the notification bits.

  Such data communication makes it possible to share secret information such as a secret key in a common key cryptosystem. For example, when n bits of the secret key are shared, after confirming that the bits subjected to the mutual notification processing described with reference to FIG. 9 match each other, the common bit selection processing in which mutual notification is performed in advance is performed. Processing such as selecting n bits from m bits (m> n) that can be shared by the above processing is executed.

  According to the configuration of FIG. 6, a round-trip communication path is formed between communication terminals, and the round-trip path distance between the pulsed light P1 used as signal light and the pulsed light P2 used as LO light is the same, and the communication terminal The pulse light P1 used as signal light and the pulse light P2 used as LO light have exactly the same timing when arriving at the 100 beam splitter 106, and the interference measurement in the homodyne detector 112 is accurately executed. Is possible.

  Specifically, the path between the beam splitter 106 and the deflection beam splitter 111 of the communication terminal 100 in FIG. 6 is configured to be switched between the forward path and the return path, and the pulsed light P1 and P2 are switched, thereby communicating with the communication terminal 100. The two-way path distances of the two pulsed lights P1 and P2 that reciprocate between the terminals 200 are set to be equal, and as a result, the interference measurement in the homodyne detector 112 can be performed accurately.

  FIG. 10 is a diagram illustrating an example in which the circulator 105 and the beam splitter 106 configured in the communication terminal 100 of FIG. 6 are configured by individual optical components.

  As the circulator 105, it is simplest to use a commercially available optical circulator. However, there are cases in which the use of fiber optical components is not compact and the mounting surface becomes compact. In such a case, the circulator constituting apparatus shown in FIG. 410 may be applied.

  The circulator constituting device 410 includes a polarizer 411, a half-wave plate 412, a polarizing beam splitter 413, and a Faraday rotator 414. The polarizer 411 is used to improve the extinction ratio when the extinction ratio of the light source 104 of the communication terminal 100 shown in FIG. 6 is poor.

  The half-wave plate 412 is used to rotate the polarization plane of light so that the light from the light source 104 is transmitted through the polarization beam splitter. The Faraday rotator 414 rotates the plane of polarization by 45 degrees so that when the light exiting the circulator component 410 is reflected back, it is reflected by the polarization beam splitter 413.

  It is simplest to use a commercially available 50%: 50% beam splitter as the beam splitter 106 of the communication terminal 100 shown in FIG. 6, but a beam splitter constituting apparatus 420 as shown in FIG. 10 may be applied. The beam splitter constituting apparatus 420 shown in FIG. 10 has a feature that the branching ratio can be adjusted.

  The beam splitter constituting apparatus 420 includes a polarizing beam splitter 421, a half-wave plate 422, and a polarizing beam splitter 423. The polarization plane of the light entering the beam splitter constituting apparatus 420 is transmitted through the polarizing beam splitter 421 by adjusting the half-wave plate 431.

  Next, by changing the rotation angle of the polarization plane by the half-wave plate 422, the ratio between the light transmitted through the polarization beam splitter 423 and the light reflected can be controlled. The branching ratio when the light returned to the beam splitter constituting apparatus 420 is divided into transmitted light and reflected light by the polarization beam splitter 421 is also determined by the rotation angle of the polarization plane by the half-wave plate 422.

  FIG. 11 is a diagram illustrating a configuration example in which wavelengths of light sources are multiplexed and transmitted / received between communication terminals. The communication path 551 is composed of an optical fiber, and a first wavelength division multiplexing processing apparatus 531 and a second wavelength division multiplexing processing apparatus 532 are set at both ends of the communication path 551.

  The first wavelength division multiplex processing apparatus 531 includes a plurality of communication terminals corresponding to the communication terminal 100 described with reference to FIG. 6, that is, communication terminals a1 and 511 including the first light source, and a second light source. The communication terminals a2 and 512 including the communication terminal an and 51n including the nth (n is an integer) light source are connected.

  On the other hand, the second wavelength division multiplexing processing apparatus 541 includes a plurality of communication terminals corresponding to the communication terminal 200 described with reference to FIG. 6, that is, communication terminals b1, 521 including the first Faraday mirror, Communication terminals b2 and 522 including the Faraday mirror and communication terminals bn and 52n including the nth Faraday mirror are connected.

  Communication terminals a1 to an and 511 to 51n including the first to nth light sources have the same configuration as the communication terminal 100 described with reference to FIG. However, it is assumed that the light sources included in each generate light pulses having slightly different wavelengths.

  The communication terminals b1 to bn and 521 to 52n including the first to nth Faraday mirrors have the same configuration as that of the communication terminal 200 described with reference to FIG.

  By using the first wavelength division multiplexing processing device 531 and the second wavelength division multiplexing processing device 541 to multiplex the wavelengths of light traveling through the communication path 551, the amount of information that can be transmitted using one communication path is reduced. Can be increased. As a result, the generation rate of transfer information such as a secret key can be improved.

  The first wavelength division multiplex processing device 531 and the second wavelength division multiplex processing device 541 execute processing for outputting the light that has entered from the communication path 551 to different ports for each wavelength. The separation process is not perfect, and a plurality of wavelengths are output to one port. However, since homodyne detection has a feature of selectively detecting signal light having the same wavelength as LO light, even if the separation processing by wavelength division multiplexing processing is incomplete, each communication terminal a1 to an, 511 to In the homodyne detection process at 51n, selective detection of signal light having the same wavelength as the LO light is performed, and detection does not become impossible even if signals of other wavelengths exist. Therefore, a plurality of communication terminals can share a transmission line such as one optical fiber by applying different optical pulses of different wavelengths and performing wavelength division multiplexing processing.

  Note that in a quantum cryptography communication device of a type that performs single photon detection, the photodetector is easily affected by light of other wavelengths, and particularly in the case of plug & play where intense pulsed light flows through the communication path, It is difficult to perform wavelength multiplexing.

  Since the present invention is configured to perform homodyne detection processing, as described above, selective detection of signal light having the same wavelength as LO light is performed, and detection is performed even if signals of other wavelengths exist. Will not be disabled. Therefore, a plurality of communication terminals can share a transmission line such as one optical fiber by applying different optical pulses of different wavelengths and performing wavelength division multiplexing processing. For example, a configuration in which a communication path is a ring shape and a plurality of transmitting and receiving terminals share the same ring-shaped communication path is possible, and a large number of communication terminals can share a single communication path.

  The present invention has been described in detail above with reference to specific embodiments. However, it is obvious that those skilled in the art can make modifications and substitutions of the embodiments without departing from the gist of the present invention. In other words, the present invention has been disclosed in the form of exemplification, and should not be interpreted in a limited manner. In order to determine the gist of the present invention, the claims section described at the beginning should be considered.

  According to the configuration of the present invention, in communication processing based on quantum cryptography, the first communication terminal outputs a plurality of pulse lights having a time difference on the communication path, and the second communication terminal is selected from the received pulse lights. Attenuation and modulation processing of only the pulsed light is executed, the attenuated pulsed light and the non-attenuated pulsed light are returned to the first communication terminal, and the attenuated pulsed light and the non-attenuated pulsed light are received at the first communication terminal. Since the communication information is analyzed by interference measurement based on the attenuated pulsed light and the non-attenuated pulsed light, the signal light applicable in homodyne detection by selective attenuation processing of the pulsed light in the second communication terminal. And LO light are generated, and information communication by interference detection based on these signal light and LO light becomes possible.

  Further, according to the present invention, in the pulse light output process, the first communication terminal passes each of two pulse lights having a time difference output on the communication path through different paths in the first communication terminal. After that, the path through which each pulsed light passes when the pulsed light is output is replaced with the attenuated pulsed light and the non-attenuated pulsed light that are output to the communication path and received from the second communication terminal. And the interference measurement based on each pulsed light is performed by matching the round-trip path between the communication terminals of each pulsed light, so that the polarization state of the light in the optical fiber or free space constituting the communication path is disturbed And the deviation of the optical path length is eliminated, and accurate signal detection becomes possible.

It is FIG. (1) explaining the information communication process to which the quantum cryptography process is applied. It is FIG. (2) explaining the information communication process to which a quantum cryptography process is applied. It is FIG. (3) explaining the information communication process to which the quantum cryptography process is applied. It is FIG. (4) explaining the information communication process to which a quantum cryptography process is applied. It is FIG. (5) explaining the information communication process to which the quantum cryptography process is applied. It is a figure which shows the structure of the quantum cryptography communication apparatus concerning this invention. It is FIG. (1) explaining the information communication process to which the quantum cryptography communication apparatus which concerns on this invention is applied. It is FIG. (2) explaining the information communication process to which the quantum cryptography communication apparatus which concerns on this invention is applied. It is FIG. (3) explaining the information communication process to which the quantum cryptography communication apparatus concerning this invention is applied. It is a figure which shows the alternative structure of the circulator and beam splitter in the quantum cryptography communication apparatus which concerns on this invention. It is a figure explaining the wavelength division multiplexing communication processing structure to which the quantum cryptography communication apparatus concerning this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Transmitter 11 Modulator 20 Receiver 21 Observer 30 Communication path 100 Communication terminal 104 Light source 105 Circulator 106 Beam splitter 107 Phase modulator 108 Delay device 109 Beam splitter 110 Detector 111 Polarizing beam splitter 112 Homodyne detector 119 Controller 200 Communication Terminal 213 Beam splitter 214 Delay device 215 Phase modulator 216 Variable attenuator 217 Faraday mirror 218 Detector 220 Controller 300 Communication path 410 Circulator configuration device 411 Polarizer 412 1/2 wavelength plate 413 Polarization beam splitter 414 Faraday rotator 420 Beam splitter configuration Device 421 Polarizing beam splitter 422 1/2 wavelength plate 423 Polarizing beam splitter 431 1/2 wavelength plate 51 1 to 51n communication terminal 521 to 52n communication terminal 531 and 541 wavelength division multiplexing processing device 551 communication path

Claims (26)

A quantum cryptography communication method for performing communication processing based on quantum cryptography,
A pulsed light output step for outputting a plurality of pulsed light having a time difference on the communication path from the first communication terminal;
In the second communication terminal, the plurality of pulse lights are received via the communication path, and attenuation and modulation processing of only the pulse light selected from the plurality of pulse lights is executed, and the attenuated pulse light and the non-attenuated pulse are executed. A pulsed light reply step of returning light to the first communication terminal;
Information for receiving, in the first communication terminal, attenuated pulsed light and non-attenuated pulsed light from the second communication terminal, and analyzing communication information by interference measurement based on the attenuated pulsed light and non-attenuated pulsed light An analysis step;
A quantum cryptography communication method comprising: In the pulse light output step, the first communication terminal passes each of two pulse lights having a time difference to be output on the communication path through different paths in the first communication terminal, and then outputs them to the communication path. And
In the information analysis step, the attenuated pulsed light and the non-attenuated pulsed light corresponding to the two pulsed lights received from the second communication terminal are mutually connected through the path through which each pulsed light has passed in the pulsed light output step. The quantum cryptography communication method according to claim 1, wherein interference measurement based on each pulsed light is performed by making the two-way path between the communication terminals of each pulsed light coincide with each other and performing the interference measurement based on each pulsed light. The pulsed light reply step in the second communication terminal includes
The quantum cryptography communication method according to claim 1, wherein the quantum cryptography communication method is a step including reflection processing of pulsed light by a Faraday mirror. The pulsed light reply step in the second communication terminal includes
Attenuating and modulating only the pulsed light selected from the plurality of pulsed lights received from the first communication terminal to generate signal light, and the signal light and the LO light as non-attenuated pulsed light The quantum cryptography communication method according to claim 1, wherein a process of returning to the first communication terminal is executed. The information analysis step executed in the first communication terminal includes:
2. The quantum cryptography communication according to claim 1, wherein the homodyne detection process is performed based on signal light that is attenuated pulsed light from the second communication terminal and LO light that is non-attenuated pulsed light. Method. The pulsed light reply step executed in the second communication terminal is:
The quantum cryptography communication method according to claim 1, further comprising a step of executing attenuation processing of the selected pulse light to which the acoustooptic device is applied. The pulsed light reply step executed in the second communication terminal is:
2. The quantum cryptography communication method according to claim 1, comprising a step of performing phase modulation processing of selective pulse light based on a LiNbO ₃ phase modulator. In the quantum cryptography communication method,
The quantum cryptography communication method according to claim 1, wherein the first communication terminal includes a step of performing phase modulation processing of pulsed light. 9. The quantum cryptography communication method according to claim 8, wherein the phase modulation process of the pulsed light is a phase modulation process of the pulsed light based on a LiNbO ₃ phase modulator. The pulsed light reply step executed in the second communication terminal is:
The pulse light received via the communication path is separated by a beam splitter, the arrival timing of a pulse for executing attenuation and modulation processing is detected, and a pulse selected from the plurality of pulse lights by control based on the detection information The quantum cryptography communication method according to claim 1, further comprising a step of performing attenuation and modulation processing of only light. The quantum cryptography communication method further includes:
In the first communication terminal, a plurality of pulse lights received via the communication path are separated by a beam splitter, a pulse arrival timing for executing modulation processing and homodyne detection processing is detected, and control based on the detection information 2. The quantum cryptography communication method according to claim 1, further comprising: performing modulation processing of only the pulsed light selected from the plurality of pulsed light and homodyne detection.   At least one of the first communication terminal or the second communication terminal is configured by a plurality of terminals, performs wavelength division multiplexing on the output pulse light for the communication path, and performs inter-terminal communication as a multiplexed optical signal. The quantum cryptography communication method according to claim 1, wherein the quantum cryptography communication method is executed. A quantum cryptography communication device that executes communication processing based on quantum cryptography,
A first communication terminal that outputs a plurality of pulse lights having a time difference on the communication path;
Receiving the plurality of pulse lights via the communication path, performing attenuation and modulation processing of only the pulse light selected from the plurality of pulse lights, and supplying attenuated pulse light and non-attenuated pulse light to the first A second communication terminal that replies to the communication terminal,
The first communication terminal receives attenuated pulsed light and non-attenuated pulsed light from the second communication terminal, and performs analysis of communication information by interference measurement based on the attenuated pulsed light and non-attenuated pulsed light A quantum cryptography communication device comprising: In the output processing of the pulse light, the first communication terminal passes each of two pulse lights having a time difference to be output on the communication path through different paths in the first communication terminal, and then enters the communication path. Output configuration,
The attenuated pulsed light and the non-attenuated pulsed light corresponding to the two pulsed lights received from the second communication terminal are allowed to pass through each other by passing through the paths through which each pulsed light passes at the time of output of the pulsed light, The quantum cryptography communication device according to claim 13, wherein interference measurement based on each pulse light is performed by matching a round-trip path between communication terminals of each pulse light. The second communication terminal is
The quantum cryptography communication device according to claim 13, wherein the quantum cryptography communication device has a configuration for performing reflection processing of pulsed light by a Faraday mirror. The second communication terminal is
Attenuating and modulating only the pulsed light selected from the plurality of pulsed lights received from the first communication terminal to generate signal light, and the signal light and the LO light as non-attenuated pulsed light The quantum cryptography communication device according to claim 13, wherein the quantum cryptography communication device is configured to execute a process of returning to the first communication terminal. The first communication terminal is
14. The quantum cryptography communication according to claim 13, wherein homodyne detection processing is performed based on signal light that is attenuated pulsed light from the second communication terminal and LO light that is non-attenuated pulsed light. apparatus. The second communication terminal is
The quantum cryptography communication device according to claim 13, wherein the quantum cryptography communication device has a configuration for executing attenuation processing of selective pulse light to which an acoustooptic device is applied. The second communication terminal is
The quantum cryptography communication device according to claim 13, wherein the quantum cryptography communication device has a configuration for executing phase modulation processing of selective pulse light based on a LiNbO ₃ phase modulator. In the quantum cryptography communication device,
The quantum cryptography communication device according to claim 13, wherein the first communication terminal has a configuration for performing a phase modulation process of pulsed light. 21. The quantum cryptography communication device according to claim 20, wherein the pulse light phase modulation processing is executed as pulse light phase modulation processing based on a LiNbO ₃ phase modulator. The second communication terminal is
The pulse light received via the communication path is separated by a beam splitter, the arrival timing of a pulse for executing attenuation and modulation processing is detected, and a pulse selected from the plurality of pulse lights by control based on the detection information The quantum cryptography communication device according to claim 13, wherein the quantum cryptography communication device has a configuration for executing attenuation and modulation processing of only light. The first communication terminal is
A plurality of pulse lights received via the communication path are separated by a beam splitter, a pulse arrival timing for executing a modulation process and a homodyne detection process is detected, and control based on the detection information is performed to control the plurality of pulse lights. The quantum cryptography communication device according to claim 13, wherein the quantum cryptography communication device has a configuration for performing modulation processing of only selected pulsed light and homodyne detection.   At least one of the first communication terminal or the second communication terminal is configured by a plurality of terminals, performs wavelength division multiplexing on the output pulse light for the communication path, and performs inter-terminal communication as a multiplexed optical signal. The quantum cryptography communication device according to claim 13, wherein the quantum cryptography communication device has a configuration to execute.   The quantum according to claim 13, wherein at least one of the first communication terminal or the second communication terminal includes a polarization beam splitter and a beam splitter including a half-wave plate as a component. Cryptographic communication device. The first communication terminal is
The quantum cryptography communication device according to claim 13, further comprising a circulator including a polarizer, a half-wave plate, a polarization beam splitter, and a Faraday rotator.

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