JP2016072666A - Multi-terminal quantum key delivery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-terminal quantum key delivery system for enabling quantum key delivery between arbitrary two terminals of a plurality of terminals and simultaneous quantum key delivery between terminals of a plurality of pairs.SOLUTION: A multi-terminal quantum key delivery system comprises a quantum entanglement light source 1, a serial quantum key delivery transmission system 20, and a control unit 4. The quantum entanglement light source generates a quantum entanglement photon pair. The serial quantum key delivery transmission system includes 2N transmission/reception terminals 20-1 to 20-2N and is formed by a first transmission/reception terminal 20-1 to 2N-th transmission/reception terminal 20-2N being connected in series by optical transmission channels in which quantum entanglement light propagates. Each transmission/reception terminal originates measurement base information for generating a quantum encryption key while performing photon detection, receives measurement base information from another quantum key receiver, and executes an error correction and secrecy amplification function. The control unit combines transmission/reception terminals sharing an encryption key and controls generation of a shifted key and an error correction process after the generation.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a quantum key distribution system using a pair of quantum entangled photons, which enables quantum key distribution between any two terminals among a plurality of terminals, and is also different at the same time between two terminals different from the above two terminals. The present invention relates to a multi-terminal quantum key distribution system that enables encryption key sharing.

  The quantum cryptography system can be expected to realize the ultimate secret communication, and is expected to be applied to future high-security information communication systems. In order to realize secure cryptographic communication without information leakage by the quantum cryptography system, the sender / receiver is made aware of the encryption key used for encryption / decryption of information without being known to a third party such as an eavesdropper. Quantum key distribution system that can be shared is essential.

  The quantum key distribution system is attracting attention as an encryption key distribution system that guarantees ultimate security in accordance with the laws of physics, and research and development aimed at application to future information communication systems has recently been activated (for example, patents) References 1-3). The quantum key distribution system is ideally realized by using a single photon source that generates one photon per pulse or a quantum entangled light source that generates one set of entangled photon pairs per pulse.

  When using a single photon source, the sender generates a single photon and the receiver receives it with a single photon detector. Alternatively, the receiver generates a single photon and the sender receives it with a single photon detector. Thereafter, the final encryption key is shared through the process of measurement base information exchange, error correction, and secret amplification. Secret amplification is a technique for generating a secret key that is secure in terms of information theory by appropriately discarding and shortening a bit string partially known to an eavesdropper.

  On the other hand, when using a entangled light source, the sender and receiver share the encryption key by receiving one of the photons that make up each entangled photon pair (each called signal light and idler light) with a single photon receiver. I do.

JP 2012-049890 A JP 2012-004955 A JP 2014-086802 A

  Here, assuming a case where there are a plurality of senders / receivers who want to share an encryption key, an encryption key sharing session for sharing the encryption key between these senders / receivers in an arbitrary combination and different sender / receiver simultaneously ( Consider a series of communication processes for sharing an encryption key.

  In a quantum key distribution system using a single photon generator, the above-described session can be executed. That is, a sender / receiver sharing an encryption key prepares a transmission / reception terminal including both a single photon source and a single photon detector. Then, the sender / receiver performs each session while playing a role of either single photon generation or reception for each encryption key sharing session. Since the transmitter / receiver plays a role of either a sender or a receiver for each encryption key sharing session, a transmitter / receiver terminal having both a single photon source and a single photon detector is required.

  However, in the above-described quantum cryptography system, each terminal needs to include both a single photon generator and a single photon detector, so that the system becomes expensive and its size is large.

  In order to realize a practical quantum cryptography system that meets economic rationality, it is required to enable quantum key distribution between arbitrary terminals of a plurality of terminals with a simple configuration, simple and low cost. It is done. Also, it is desired to realize a multi-terminal quantum key distribution system that enables quantum key distribution between a plurality of two terminals at the same time.

The inventor of this application has come to realize that a multi-terminal quantum key distribution system is configured by using 2N optical add / drop filters (N is an integer of 2 or more). Then, the dropped wavelength lambda ₁ of the 2N tunable optical add-drop filters in the encryption key sharing session, the wavelength lambda _s1 to [lambda] _sN of the signal light to be mutually paired as entangled light, the wavelength lambda _i1 to [lambda] _iN idler light We focused on the fact that encryption keys can be shared by quantum key distribution among N pairs of 2N users at the same time if it can be set to match any one of the above and there is no duplication. We were convinced that quantum key distribution was possible between multiple terminals simultaneously.

Also, if the drop wavelength of the add / drop filter can be arbitrarily matched to any one of λ _s1 to λ _sN and λ _i1 to λ _iN , it has been thought that encryption key sharing can be realized between arbitrary users. .

  Accordingly, an object of the present invention is to provide a multi-terminal quantum key distribution system capable of quantum key distribution between any two terminals of a plurality of terminals and capable of simultaneous quantum key distribution between the plurality of two terminals. There is.

  Therefore, according to the gist of the present invention, a multi-terminal quantum key distribution system having the following configuration is provided.

  A first multi-terminal quantum key distribution system of the present invention includes a quantum entangled light source, a serial quantum key distribution transmission system, and a control unit, and performs quantum key distribution between any two transmission / reception terminals of 2N transmission / reception terminals. It is a system that executes and simultaneously performs quantum key distribution between a plurality of two transmitting / receiving terminals.

  The entangled light source generates a entangled photon pair having an optical frequency region of 2 Nf Hz or higher. Here, N is an integer of 2 or more, and f bit / s is an assumed maximum key generation rate of the quantum encryption key.

  The serial quantum key distribution / transmission system includes 2N transmission / reception terminals having a drop wavelength different from each other and provided with a tunable optical add / drop filter and a quantum key reception device, and 2N transmission / reception terminals are arranged in series.

  Each transmitting / receiving terminal receives the output light from the drop port of the wavelength tunable optical add / drop filter, performs photon detection, transmits measurement base information for generating a quantum encryption key, and other quantum key receiving devices And a quantum key receiving device including a signal processing circuit for executing error correction and secret amplification functions.

  The control unit selects a drop wavelength for the tunable optical add / drop filter provided in each of the 2N transmission / reception terminals, and receives each measurement base information output from the 2N quantum key receivers. , Transfer to another corresponding quantum key receiving device, perform quantum key distribution between any two transmitting / receiving terminals of 2N transmitting / receiving terminals equipped with the quantum key receiving device, and simultaneously perform quantum Perform key distribution.

  A second multi-terminal quantum key distribution system according to the present invention includes a quantum entangled light source, a 1 × 2 optical coupler that receives an output of the quantum entangled light source and branches it in two, and 2N bidirectional transmission / reception terminals having different drop wavelengths Including a closed loop quantum key distribution and transmission system including a control unit, and performs quantum key distribution between any two bidirectional bidirectional transmission / reception terminals of 2N bidirectional transmission / reception terminals, and a plurality of two bidirectional types This system performs quantum key distribution between transmitting and receiving terminals simultaneously.

  The entangled light source generates a entangled photon pair having an optical frequency region of 2 Nf Hz or higher.

  Each of the 2N bidirectional transmission / reception terminals includes first and second optical circulators, a first tunable optical add / drop filter whose drop wavelength is changeable, and a first quantum key receiving device. And a second light receiving and transferring block including a second tunable optical add / drop filter whose drop wavelength can be changed and a second quantum key receiving device.

  The closed loop quantum key distribution transmission system is formed as a closed loop including a 1 × 2 optical coupler and 2N bidirectional transmission / reception terminals.

  The first and second quantum key receivers provided by 2N bidirectional bidirectional transmission / reception terminals receive photons from adjacent bidirectional transmission / reception terminals or 1 × 2 optical couplers and perform photon detection. Includes signal processing circuits for transmitting measurement base information for generating an encryption key, receiving measurement base information from other bidirectional transmission / reception terminals, and further executing error correction and secret amplification functions Yes.

  The control unit selects the drop wavelength of the first and second variable wavelength add / drop filters provided in each of the 2N bidirectional transmission / reception terminals and outputs measurement base information output from the 2N bidirectional transmission / reception terminals. Receive and transfer to another corresponding bidirectional transmission / reception terminal, perform quantum key distribution between any two bidirectional transmission / reception terminals of 2N bidirectional transmission / reception terminals, and multiple two-way transmission / reception Quantum key distribution is executed between terminals simultaneously.

  According to the first or second multi-terminal quantum key distribution system of the present invention, a entangled photon pair over an optical frequency region of 2 Nf Hz or more is provided by a quantum entangled light source. The first multi-terminal quantum key distribution system includes a serial quantum key distribution transmission system in which 2N transmission / reception terminals having different drop wavelengths are connected in series. The second multi-terminal quantum key distribution system includes a closed-loop quantum key distribution transmission system formed as a closed loop including 2N bidirectional transmission / reception terminals each having a different drop wavelength.

Since the drop wavelength of the tunable optical add / drop filter (the first and second tunable optical add / drop filters in the second multi-terminal quantum key distribution system) can be changed, the first or second In the multi-terminal quantum key distribution system, the drop wavelength λ ₁ of each of 2N terminals (transmission / reception terminals or bidirectional transmission / reception terminals) is changed to the signal light wavelengths λ _{s1 to} λ _sN and idler in the same encryption key sharing session. It can be set so as to coincide with any of the wavelengths λ _{i1 to} λ _iN of light and not overlap. Accordingly, encryption keys can be shared by quantum key distribution among any N sets of 2N users at the same time.

  That is, according to the first or second multi-terminal quantum key distribution system of the present invention, the entangled photon pairs output from the quantum entangled light source are 2N quantum key receivers (second multi-terminal quantum key distribution). In the system, a user having a transmission / reception terminal including a quantum key reception device that has been transmitted to a bidirectional quantum key reception device and received quantum entangled light is a transmitter / receiver that shares the quantum encryption key. The signal processing circuit included in the quantum key receiving device receives measurement base information sent from another quantum key receiving device, and sends the measurement base information to the other quantum key receiving device. Key that generates time-matched measurement information, sends it to other quantum key receivers, and generates a sifted key (Sifted key) leaving only the photon bits observed at the time when the measurement basis matches A distillation process is performed. The control unit controls the key distillation process in each of the quantum key receiving devices, thereby realizing simultaneous quantum key distribution.

  In the first multi-terminal quantum key distribution system of the present invention, a serial quantum key distribution transmission system in which 2N transmission / reception terminals are connected in series can be adopted. If the part is damaged or disconnected, the entangled light does not reach the subsequent transmitting and receiving terminals, and quantum key distribution cannot be performed. Thus, although the configuration of the second multi-terminal quantum key distribution system is complicated, a closed-loop quantum key distribution transmission system in which 2N transmission / reception terminals are connected in a closed loop is employed. As a result, counterclockwise quantum key distribution can be performed even when part of the optical transmission line connecting the transmitting and receiving terminals is damaged or disconnected and clockwise quantum key distribution cannot be performed. .

1 is a block configuration diagram schematically showing a basic configuration of a first multi-terminal quantum key distribution system according to the present invention. FIG. FIG. 6 is a diagram for explaining the operation of a wavelength tunable optical add / drop filter (first and second wavelength tunable optical add / drop filters in the second multi-terminal quantum key distribution system). It is a block block diagram which shows roughly the basic composition of the quantum entangled light source using natural parametric down conversion (SPDC). It is a schematic block diagram which shows the structural example of a wavelength variable optical add / drop filter (In the 2nd multi-terminal quantum key distribution system, the 1st and 2nd wavelength variable optical add / drop filter), (A) is an optical band. An example of configuration using a pass filter is shown, and (B) shows an example of configuration using an optical circulator and a Bragg reflector. FIG. 2 is a configuration diagram schematically showing a basic configuration of a quantum key receiving device (a bidirectional quantum key receiving device in the second multi-terminal quantum key distribution system). FIG. 5 is a block configuration diagram schematically showing a basic configuration of a second multi-terminal quantum key distribution system of the present invention. FIG. 6 is a configuration diagram schematically showing a basic configuration of a bidirectional transmission / reception terminal of a second multi-terminal quantum key distribution system according to the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. In the following description, specific elements and operating conditions may be taken up. However, these elements and operating conditions are only one of preferred examples, and thus are not limited to these.

<Basic configuration of the first multi-terminal quantum key distribution system>
The basic configuration of the first multi-terminal quantum key distribution system of the present invention will be described with reference to FIG. The first multi-terminal quantum key distribution system includes a quantum entangled light source 1, a serial quantum key distribution transmission system 20, and a control unit 4.

  The entangled light source 1 generates a entangled photon pair. The optical frequency band of this photon pair is 2Nf Hz or more, assuming that the assumed maximum key generation rate of the generated quantum encryption key is f bit / s and the number of terminals sharing the quantum encryption key is 2N. Here, there are a total of N sets of connections between two terminals formed by selecting 2 terminals from 2N terminals, which enables simultaneous communication by one-to-one communication. Can be executed.

  The assumed maximum key generation rate of the quantum encryption key is the repetition frequency of the excitation light pulse light source (not shown) used to generate the entangled photon pair and the single photon detector that receives the photons. Means the smaller value of the repetition frequency of the periodic gate according to the above. In other words, this corresponds to a value obtained by dividing the photon detection rate by the average number of photons per pulse when all the entangled light can be detected by the single photon detector without any loss.

Tandem quantum key distribution transmission system 20 includes 2N number of the transmitting and receiving terminals 20-1～20-2N, transmitting and receiving terminals 20-1 includes a wavelength tunable optical add-drop filters A ₁ and the quantum key receiving device B _1, the transmitting and receiving terminals 20-2 includes a tunable optical add / drop filter A ₂ and a quantum key receiving device B ₂ , and similarly, the transmitting / receiving terminal 20-2N includes a tunable optical add / drop filter A _2N and a quantum key receiving device B _2N . . The serial quantum key distribution transmission system 20 is connected to the through port of the wavelength tunable optical add / drop filter A ₁ of the _first transmission / reception terminal 20-1 by the optical transmission path (quantum channel 2) for propagating the entangled light. The input port of the tunable optical add / drop filter A ₂ of the second transmitting / receiving terminal 20-2 is connected, and the through port of the tunable optical add / drop filter A ₂ of the second transmitting / receiving terminal 20-2 and the third transmitting / receiving terminal 20 are connected. -3 wavelength tunable optical add / drop filter A ₃ input port, and sequentially through the optically (2N-1) th tunable optical add / drop filter A _2N-1 through port of the _2N-1 transceiver terminal 2N-1 Quantum entangled light propagates from the first transmitting / receiving terminal 20-1 to the 2Nth transmitting / receiving terminal 20-2N by connecting the input port of the tunable optical add / drop filter A _2N of the 2N transmitting / receiving terminal 20-2N Formed in series connected by optical transmission line The The entangled light output from the entangled light source 1 is input to the input port of the wavelength tunable optical add / drop filter A ₁ of the _first transmitting / receiving terminal 20-1.

  In each quantum key receiving device, the signal processing circuit included in each quantum key receiving device accepts the output light from the drop port of the wavelength tunable optical add / drop filter, performs photon detection, and generates a quantum encryption key. The measurement base information is transmitted and the measurement base information from another quantum key receiving apparatus is received, and the error correction and the secret amplification function are executed.

  The control unit 4 selects a drop wavelength for the tunable optical add / drop filter provided in each of the 2N transmission / reception terminals, and obtains each measurement base information output from the 2N quantum key receivers. Receive, transfer to another corresponding quantum key receiving device, perform quantum key distribution between any two transmitting / receiving terminals of 2N transmitting / receiving terminals equipped with the quantum key receiving device, and simultaneously between a plurality of two transmitting / receiving terminals Perform quantum key distribution.

  It is assumed that the entangled light output from the entangled light source 1 is generated by spontaneous parametric down conversion (hereinafter sometimes abbreviated as SPDC) in a second-order nonlinear optical device. The optical spectrum characteristic of the entangled light output from the entangled light source 1 is schematically shown as a curve 100 in FIG. 1 with the horizontal axis as the wavelength axis.

Now, if the wavelength of the pumping light in the SPDC process is λ _p , the optical spectrum of the entangled light is generated symmetrically with respect to the wavelength 2λ _p . An optical frequency component symmetric with respect to the optical frequency of the excitation light (c / λ _p , where c is the speed of light) is a correlated photon pair generated simultaneously by the SPDC process, and is an optical component that is the source of quantum entangled light. Here, for convenience, it is assumed that the idler light region wavelength region on the longer wavelength side than 2 [lambda] _p, a wavelength region of shorter wavelength side than 2 [lambda] _p is referred to as a signal light region.

Energy conservation when a wavelength component λ _sk in the signal light region and a wavelength component λ _ik in the idler light region (where k = 1, 2, 3,…, 2N) are photon pairs generated simultaneously by SPDC The following equation (1) is satisfied by the rule.
1 / λ _sk + 1 / λ _ik = 1 / λ _p (1)
If the expression (1) is expressed by the optical frequency, the following expression (2) is obtained.
f _sk + f _ik = f _p (2)
Then, as combinations of the wavelength of the signal light and the wavelength of the idler light (λ _sk , λ _ik ) satisfying the above formula (1), N combinations (λ _s1 , λ _i1 ) to (λ _sN , λ _iN ) can be provided by the entangled light source 1. Of these 2N wavelengths, when the wavelength on the shortest wavelength side is λ _min and the wavelength on the longest wavelength side is λ _max , the difference between the optical frequencies is 2Nf or less. That is, the following equation (3)
c / λ _min + c / λ _amx ≦ 2Nf (3)
Shall be satisfied.

Next, the operation of the wavelength tunable optical add / drop filters A _{1 to} A _2N with variable drop wavelengths will be described with reference to FIG. For example, as shown in FIG. 2, the tunable optical add / drop filter A ₁ outputs only the optical wavelength component in the vicinity of the drop wavelength component λ ₁ among the input light components to the drop port, and the other wavelength components pass through. Output to port. The frequency band of light output to the drop port shall be at least f Hz. In FIG. 2, the schematic shapes of the optical spectrum 100 of the input light component, the optical spectrum 200 of the drop light output from the drop port, and the optical spectrum 300 of the through light output from the through port are illustrated using an insertion drawing. Schematically, the horizontal axis indicates the wavelength.

The drop wavelength λ ₁ matches any one of the above-described signal light wavelengths λ _{s1 to} λ _sN and idler light wavelengths λ _{i1 to} λ _iN , and arbitrarily matches any one of them. Shall be able to. Also, it is assumed that the drop wavelengths of these 2N wavelength tunable optical add / drop filters have different values for each encryption key sharing session.

  These 2N wavelength tunable optical add / drop filters are optically connected to each input port and through port sequentially through free space, optical fiber, etc., so that quantum entangled light propagates in the quantum key distribution process. A quantum key distribution transmission system is formed through the quantum channel 2. That is, 2N transmission / reception terminals 20-1 to 20-2N are sequentially optically connected via an optical fiber or the like to form a serial quantum key distribution transmission system 20.

Outputs from the drop ports of the tunable optical add / drop filters A _{1 to} A _2N are coupled to quantum key receivers _{B 1 to} B _2N each including a corresponding single photon detector. The quantum key receiving devices B _{1 to} B _2N are coupled to the control unit 4 via the classical channel 3. The control unit 4 switches the drop wavelength of each of the wavelength tunable optical add / drop filters A _{1 to} A _2N , acquires and exchanges measurement base information in the quantum key receivers B _{1 to} B _2N , and then corrects errors. Execute processes and so on.

  Here, a quantum channel is a term for distinguishing transmission paths that transmit quantum states called quantum entanglement, whereas classical information transfer paths that are not intended for transmission of quantum states are called classical channels. is there. That is, the quantum channel means a transmission path that sends information to a distant place using the effect of quantum entanglement. Even if the information propagating through the classical channel is intercepted on the way, the information is not damaged and lost. On the other hand, when entangled light is observed (wiretapped) somewhere in the quantum channel, EPR (Einstein-Podolsky-Rosen) correlation between two photons (between signal photon and idler photon) in the entangled relationship disappears. However, the quantum state of quantum entanglement is damaged and information is lost.

<Operation principle of the first multi-terminal quantum key distribution system>
In general, the SPDC process is known to have a wide optical spectrum. As an example, it has become clear from the research of the inventors of the present invention that SPDC light of about 60 nm in the wavelength region in the 1550 nm band is generated from a 6 cm long periodically poled lithium niobate waveguide. (Non-Patent Document 1: S. Arahira, N. Namekata, T. Kishimoto, H. Yaegashi, and S. Inoue, “Generation of polarization entangled photon pairs at telecommunication wavelength using cascaded χ ⁽²⁾ processes in a periodically poled LiNbO ₃ ridge waveguide ”, Optics express vol. 19, No. 17, pp. 16032-16043, 2011).

Here, increments the optical spectrum of the output light output from the entangled light source 1 every 0.4 nm, corresponding to each wavelength a wavelength lambda _s1 to [lambda] _sN of the signal light, the wavelength lambda _i1 to [lambda] _iN idler light It is possible to store about N = 60 / 0.4 / 2 = 75 users using this light source. Here, the increment of 0.4 nm is a wavelength grid for general wavelength division multiplexing (WDM) optical communication.

  The quantum entangled light source 1 using the SPDC process can be formed as shown in FIG. 3, for example. The quantum entangled light source shown in FIG. 3 is a light source for generating a polarization entangled photon pair, and a second-order nonlinear optical medium 502 using a WDM filter 504, a polarization separation / combination circuit 501, and a periodically poled lithium niobate waveguide. , 90-degree polarization plane rotation and optical phase adjustment unit 503, and low-pass optical filter 505, polarization separation and synthesis circuit 501, second-order nonlinear optical medium 502, 90-degree polarization plane rotation and optical phase adjustment unit 503 from Sagnac type light It is formed by constructing an interferometer (Patent Document 1 and Non-Patent Document 2: HC Lim, A. Yoshizawa, H. Tsuchida, and K. Kikuchi, "Stable source of high quality telecom-band polarization-entangled photon -pairs based on a single, pulse-pumped, short PPLN waveguide, "Optics Express, vol. 16, No. 17, pp. 12460-12468, 2008).

The input pump light having the wavelength λ _p passes through the WDM filter 504, becomes 45-degree polarized light, and is input to the polarization beam splitting / combining circuit 501. In the polarization separation / combination circuit 501, the 45-degree polarized excitation light is branched into p-polarized light that rotates clockwise and s-polarized light that rotates counterclockwise through the Sagnac optical interferometer, and circulates around the Sagnac optical interferometer. The signal light and idler light generated by the second-order nonlinear optical medium 502 are reflected by the WDM filter 504, and the input excitation light having the wavelength λ _p is removed by the low-pass optical filter 505, so that the signal light and idler light are converted into quantum entangled light. Is output.

The entangled photon pairs from the entangled light source 1 are sequentially passed through wavelength tunable optical add / drop filters (A ₁ , A ₂ ,..., A _2N ). Here, it is assumed that the drop wavelength of the wavelength tunable optical add / drop filter A ₁ is set to λ _s1 . At this time, the single photon detector included in the quantum key receiving device B ₁ connected to the drop port receives only the component of the wavelength λ _{s1 in} the quantum entangled light.

On the other hand, the other wavelength components output from the through port of the wavelength tunable optical add / drop filter A ₁ are sequentially sent to the wavelength tunable optical add / drop filters (A ₂ , A ₃ ,... A _2N ). Then, the wavelength components that match the respective drop wavelengths are output to the drop port and received by the quantum key receivers connected thereto.

Since the 2N wavelength tunable optical add / drop filters have different drop wavelengths, the wavelength components of the signal light λ _{s1 to} λ _sN and the idler wavelengths λ _{i1 to} λ _iN are respectively the quantum key receiving device B ₁ , B ₂ ,..., B _2N are received by any one of the quantum key receiving apparatuses, and do not overlap.

Here, it is assumed that the drop wavelength of the wavelength tunable optical add / drop filter A ₄ is set to λ _i1 . At this time, the single photon detector included in the quantum key receiving device B ₄ connected to the drop port receives only the component of the wavelength λ _i1 .

At this time, the wavelength component received by the quantum key receiving device B ₁ and the wavelength component received by the quantum key receiving device B ₄ satisfy the relationship of Equation (1), that is, the photon pair in the quantum entangled state. Each one of them has been received. As a result, the user having the quantum key receiving device B ₁ and the user having the quantum key receiving device B ₄ execute measurement base information acquisition / exchange, a subsequent error correction process, and the like according to a known quantum key distribution protocol. This makes it possible to share encryption keys.

On the other hand, suppose that in the same encryption key sharing session, the drop wavelength of the tunable optical add / drop filter A ₂ is set to λ _i4 and the drop wavelength of the tunable optical add / drop filter A ₆ is set to λ _s4 . At this time, since the wavelength components of both satisfy the relationship of equation (1), both of them received one of the photon pairs in the quantum entangled state, and as a result, the user having the quantum key receiving device B ₂ And the user having the quantum key receiving device B ₆ can share the encryption key.

From the above consideration, the same encryption key sharing session, 2N number of the dropped wavelength lambda ₁ of the tunable optical add-drop filter, the wavelength lambda _s1 to [lambda] _sN of the signal light, the wavelength lambda _i1 to [lambda] _iN idler light If it can be set so as to match any one of the above and there is no duplication, it can be understood that encryption key sharing by quantum key distribution can be simultaneously performed among N sets of 2N users. And in the example mentioned above, for example, in the encryption key sharing session between the users having the quantum key receiving device B ₁ and the quantum key receiving device B ₆ , the wavelength of the received light does not satisfy the relationship of equation (1) In this case, one of the photon pairs in the quantum entangled state is not received, and encryption key sharing becomes impossible. That is, the N sets of users can simultaneously perform secure encryption key sharing without correlation.

If the drop wavelength of the wavelength tunable optical add / drop filter is variable and the drop wavelength can be arbitrarily matched to any of λ _s1 to λ _sN and λ _i1 to λ _iN , any combination of quantum key receiving devices, That is, the encryption key can be shared by any combination of users.

A configuration example of the above-described wavelength tunable optical add / drop filters A _{1 to} A _2N will be described with reference to FIG.

  The wavelength tunable optical add / drop filter shown in FIG. 4A has a configuration using an optical bandpass filter 5 formed of a dielectric multilayer filter. By outputting the transmitted light output of the dielectric multilayer filter as through light and outputting the reflected light output as drop light, the optical add / drop function desired in the present invention can be realized. For example, since the transmission wavelength can be changed by changing the transmission angle of the dielectric multilayer filter, the wavelength tunability desired in the present invention can be realized.

  The wavelength tunable optical add / drop filter shown in FIG. 4B has a configuration using an optical circulator 6 and a wavelength tunable Bragg reflector 7. The light input to the first port 6-1 of the optical circulator 6 is output from the second port 6-2, and the light input to the second port 6-2 is output from the third port 6-3. To do. A wavelength tunable Bragg reflector 7 is connected to the second port 6-2. Of the light output from the second port 6-2 of the optical circulator 6, the wavelength component that matches the Bragg wavelength of the wavelength tunable Bragg reflector 7 is Bragg-reflected and input to the second port 6-2 again. This wavelength component is output to the third port 6-3 of the optical circulator 6. On the other hand, components other than the Bragg wavelength are transmitted through the wavelength variable Bragg reflector 7 and output. Therefore, the third port 6-3 of the optical circulator 6 can be used as a drop port, and the output port of the transmitted light of the wavelength variable Bragg reflector 7 can be used as a through port.

  As such a tunable Bragg reflector 7, a fiber grating, a diffraction grating formed on a glass waveguide or a semiconductor waveguide, or the like can be used. For example, it is possible to change the Bragg wavelength by changing the refractive index by heating with a microheater or by a method of applying current / voltage (in the case of a semiconductor), thereby obtaining a wavelength variable characteristic.

The control unit 4 controls the drop wavelength of the wavelength tunable optical add / drop filter A _k (where k = 1, 2, 3,..., 2N) in order to determine the combination of users who share the encryption key. The control unit 4 is used to collect measurement basis information in the quantum key receivers (B ₁ , B ₂ ,..., B _2N ) through the classical channel 3 to generate a sieve key and a subsequent error correction process. Control.

Referring to FIG 5, it will be described a typical device structure of the quantum key receiving device B _k that receives a polarization entangled light. The quantum key receiving device B _k that receives polarization entangled light includes a half mirror 401, a half-wave plate 402, a first polarization separation circuit 403, a second polarization separation circuit 404, a first single photon detector 405, a first 2 single photon detector 406, third single photon detector 407, and fourth single photon detector 408.

  Arriving photons are probabilistically divided into two paths by the half mirror 401, photons passing through one path are guided to the first polarization separation circuit 403, and photons passing through the other path are half-wave plate 402 And is guided to the second polarization separation circuit 404.

  The first polarization separation circuit 403 separates the photons that have passed through one of the paths described above into polarization components that are probabilistically orthogonal to each other, and supplies the first single photon detector 405 and the second single photon detector 406, respectively. Let them enter. On the other hand, the second polarization separation circuit 404 also separates the photons that have been guided to the other path described above and passed through the half-wave plate 402 into polarization components that are probabilistically orthogonal to each other, and the third single-photon detector 407 , Input to the fourth single photon detector 408, respectively.

The quantum key receiving device B _k that receives the polarization entangled light has the above-described configuration, so that the measurement base is automatically selected by the half mirror 401 and the half-wave plate 402. That is, when the detector of the single photon detector 405 or 406 detects a photon, the measurement base is a longitudinal / horizontal polarization base, while the detector of the single photon detector 407 or 408 detects a photon. In this case, the measurement base is a 45-degree oblique polarization base.

A transmitter / receiver having a transmission / reception terminal including a quantum key receiving device B _k that receives polarization entangled light transmits measurement base information to the control unit 4 or the like via the signal processing circuit 409 and the classical channel 3. The control unit 4 discriminates the time information that the measurement basis of the sender / receiver matches and sends it to the sender / receiver. And when the measurement bases match (for example, longitudinal and horizontal polarization bases), the transmitter and receiver must always detect photons with the same single photon detector (405 or 406). A random bit string can be shared by setting bit “1” when the photon detector 405 detects, and setting bit “0” when the second single photon detector 406 detects. In this way, after the key distillation process such as error correction and confidential amplification by mutual communication and signal processing between the control unit 4 and the signal processing circuit 409 and the signal processing, the final quantum cryptographic key is shared. Can do. Of course, such a process can also be executed by the paired users directly communicating with each other without using the control unit 4. In this case, a part of the function of the control unit 4 such as exchange of measurement base information may be assigned to the signal processing circuit 409.

The quantum entangled light source 1 and the control unit 4 described above are arranged in a centralized node of a communication network in the form of a central control unit, thereby collectively managing the quantum key sharing process among multiple terminals. Can do. In this case, a sender / receiver (user) who performs cryptographic communication has only an optical add / drop filter (A ₁ , A ₂ ,..., A _2N ) and a quantum key receiver (B ₁ , B ₂ ,..., B _2N ). This makes it possible to provide a quantum key distribution system that is simpler and less expensive.

<Basic configuration of the second multi-terminal quantum key distribution system>
The basic configuration of the second multi-terminal quantum key distribution system of the present invention will be described with reference to FIG. However, the description of the same components as the basic configuration of the first multi-terminal quantum key distribution system described above is omitted.

  The second multi-terminal quantum key distribution system includes a entangled light source 1, a 1 × 2 optical coupler 8 that accepts the output of the entangled light source, and 2N bi-directional transceiver terminals 22- A closed loop quantum key distribution / transmission system 22 including 1 to 22-2N and a control unit 4 are provided, and 2N bidirectional transmission / reception terminals 22-1 to 22-2N between any two bidirectional transmission / reception terminals This is a multi-terminal quantum key distribution system that is capable of quantum key distribution at the same time and that can simultaneously distribute quantum keys with a plurality of two bidirectional transmission / reception terminals.

In FIG. 6, each of the bidirectional transmission / reception terminals 22-1 to 22-2N is shown so as to be easily associated with the transmission / reception terminals 20-1 to 20-2N of the first multi-terminal quantum key distribution system described above. FIG. 7 shows a simplified configuration of each of the bidirectional transmission / reception terminals 22-1 to 22-2N. That is, in FIG. 6, each of the bidirectional transmission / reception terminals shown in FIG. 7 is illustrated as comprising a bidirectional wavelength variable add / drop filter and a bidirectional quantum key receiving device. That is, in FIG. 6, the bidirectional transmission / reception terminal 22-1 includes the bidirectional variable wavelength add / drop filter C ₁ and the bidirectional quantum key reception device D _1. -2 to 22-2N are also shown to be configured similarly.

  The configuration of the bidirectional transmission / reception terminal will be described with reference to FIG. Each of the bidirectional transmission / reception terminals 22-1 to 22-2N includes a first optical circulator 9, a second optical circulator 10, a first light reception transfer block 31, and a second light reception transfer block 32. The first light receiving / transferring block 31 includes a first quantum key receiving device 31-D and a first wavelength variable optical add / drop filter 31-F, and the second light receiving / transferring block 32 includes a second quantum key receiving device 32- D and a second tunable optical add / drop filter 32-F.

  The first port 9-1 of the first optical circulator 9 is coupled to the through port of the first wavelength tunable optical add / drop filter 31-F, and the third port 9-3 is coupled to the second wavelength tunable optical add / drop filter 32- Coupled to F input port. The first port 10-1 of the second optical circulator 10 is coupled to the through port of the second wavelength variable optical add / drop filter 32-F, and the third port 10-3 is coupled to the first wavelength variable optical add / drop filter 31- Coupled to F input port. Further, the first quantum key receiving device 31-D is connected to the drop port of the first wavelength tunable optical add / drop filter 31-F, and the second quantum is connected to the drop port of the second wavelength tunable optical add / drop filter 32-F. A key receiving device 32-D is connected.

The first quantum key receiving device 31-D and the second quantum key receiving device 32-D are both quantum key receiving devices (B ₁ , B ₂ , ..., B _2N ). The first wavelength tunable optical add / drop filter 31-F and the second wavelength tunable optical add / drop filter 32-F are both wavelength tunable optical add / drop components that are components of the first multi-terminal quantum key distribution system described above. The configuration is the same as the filters (A ₁ , A ₂ ,..., A _2N ).

  Note that the bidirectional wavelength tunable optical add / drop filter and the bidirectional quantum key receiving device described below are configured to be able to perform the same function even if they are configured differently from FIG. Any configuration may be used.

As shown in FIG. 6, the closed-loop quantum key distribution transmission system 22 is connected to the first optical input / output terminal 8-1 of the 1 × 2 optical coupler 8 by an optical transmission path (quantum channel 2) for propagating quantum entangled light. Bidirectional tunable optical add / drop filter C ₁ input port C ₁ -1 is connected, bidirectional tunable optical add / drop filter C ₁ through port C ₁ -2 and bidirectional tunable optical add / drop filter connects the input port C ₂ -1 of C _2, connected in sequence to the interactive tunable optical add-drop filter C _2N, through port of the last interactive tunable optical add-drop filter C _2N C _2N -2 And the second optical input / output terminal 8-2 of the 1 × 2 optical coupler 8 is connected.

  When the configuration shown in FIG. 7 is adopted as the bidirectional transmission / reception terminals 22-1 to 22-2N, the closed-loop quantum key distribution transmission system 22 is a 1 × 2 optical coupler depending on the optical transmission path for propagating quantum entangled light. 8 first optical input / output terminal 8-1 and the second port 9-2 of the first optical circulator 9 of the first bidirectional transmission / reception terminal 22-1 are connected, and the first bidirectional transmission / reception terminal 22- 2nd port 10-2 of the 1st 2nd optical circulator 10 and 2nd port 9-2 of the 1st optical circulator 9 of the 2nd bidirectional type transmission / reception terminal 22-2, and (2N-1) sequentially The second port 10-2 of the second optical circulator 10 of the second bidirectional transmission / reception terminal 22- (2N-1) and the second port 9 of the first optical circulator 9 of the 2Nth bidirectional transmission / reception terminal 22-2N. -2 and the 2nd port 10-2 of the 2nd optical circulator 10 of the 2Nth bidirectional transmission / reception terminal 22-2N and the 2nd optical input / output terminal 8-2 of the 1 × 2 optical coupler 8 are connected. 1 × 2 optical coupler 8 and 2N bidirectional transmission / reception It formed as a closed loop including the end 22-2～22-2N.

  Here, the first and second optical circulators 9 and 10 provided in each of the bidirectional transmission / reception terminals 22-1 to 22-2N use the same specification in all the bidirectional transmission / reception terminals. The first optical circulator 9 and the second optical circulator 10 are displayed in common without distinguishing between the bidirectional transmission / reception terminals 22-1 to 22-2N, but the first light of the same specification is separately provided for each bidirectional transmission / reception terminal. It should be understood that the circulator 9 and the second optical circulator 10 are used.

The difference between the configuration of the second multi-terminal quantum key distribution system and the first multi-terminal quantum key distribution system is that a closed-loop quantum key distribution transmission system is adopted instead of the serial quantum key distribution transmission system. is there. Therefore, in the second multi-terminal quantum key distribution system, in order to provide an optical add / drop function and a quantum entangled light receiving function for any of the entangled light propagating in the closed loop type quantum key distribution transmission system around both the left and right sides of the loop In addition to the wavelength variable optical add / drop filters A _{1 to} A _{2N and the} quantum key receiving devices B _{1 to} B _2N that repeat input and output in only one direction used in the first multi-terminal quantum key distribution system, both Bidirectional tunable optical add / drop filters C _{1 to} C _2N and bidirectional quantum key receivers D _{1 to} D _2N that input and output in the direction are used.

The control unit 4 controls the drop wavelength of the bidirectional wavelength tunable optical add / drop filter C _k (where k = 1, 2, 3,..., 2N) to determine the combination of users sharing the quantum encryption key. . In addition, the control unit 4 is used to collect measurement base information in the bidirectional quantum key receivers D _{1 to} D _2N through the classical channel 3 to control generation of a sieve key, a subsequent error correction process, and the like.

<Operation principle of the second multi-terminal quantum key distribution system>
In the first multi-terminal quantum key distribution system, unidirectional wavelength tunable optical add / drop filters (A ₁ , A ₂ ,...) Are connected by quantum channels 2 that propagate quantum entangled light through 2N wavelength tunable optical add / drop filters. , A _2N ), by sequentially connecting each input port and through port optically. Therefore, the entangled light propagates in this quantum channel 2 only in one direction. Therefore, for example, in FIG. 1, when the optical path connecting the wavelength tunable optical add / drop filters A ₁ and A ₂ is broken or cut, the entangled light cannot reach the subsequent optical add / drop filters A _{2 to} A _2N. Quantum key distribution cannot be executed.

In order to solve this problem, in the second multi-terminal quantum key distribution system, each input of the bidirectional wavelength tunable optical add / drop filters (C ₁ , C ₂ ,..., C _2N ) is applied by the quantum channel 2. A closed loop quantum key distribution transmission system 22 formed by optically connecting ports and through ports in sequence is adopted, and it is possible to supply entangled light in both directions around the left and right sides. .

In this way, as shown in FIG. 6, even if the optical path connecting the bidirectional wavelength tunable optical add / drop filters C ₁ and C ₂ is broken or cut, the entangled light propagated counterclockwise in the loop. drop the bidirectional type tunable optical add-drop filters C _1, by dropping the entangled light propagated in the loop clockwise in interactive tunable optical add-drop filters C _2, it is possible to quantum key distribution .

For this purpose, the entangled light from the entangled light source 1 is branched into two by the 1 × 2 optical coupler 8 and is output both clockwise and counterclockwise in the loop. At this time, the entangled light reaching the bidirectional wavelength tunable optical add / drop filters C _{1 to} C _2N is a entangled light propagated counterclockwise through the loop of the closed loop quantum key distribution transmission system 22, and the loop May be entangled light propagating clockwise. Therefore, the optical add / drop filter used as the bi-directional tunable optical add / drop filter C _{1 to} C _2N needs to be bi-directional to perform an add / drop operation with respect to the entangled light propagating around both right and left. There is. Similarly, two-way quantum key receiving apparatuses D ₁ quantum key receiver is used as to D _2N, capable receiving and signal processing to entangled light propagates around the left and right, it requires a bi-directional There is.

  Such a bi-directional wavelength tunable optical add / drop filter and bi-directional quantum key receiving device can be realized by the configuration example shown in FIG. 7 as described above.

  Now, the entangled light propagated counterclockwise through the loop of the closed loop quantum key distribution transmission system 22 is input to the second port 9-2 of the first optical circulator 9 and output to the third port 9-3. This output light is input to the second variable wavelength optical add / drop filter 32-F, and the output light from this drop port is received by the second quantum key receiving device 32-D. On the other hand, the output light from the through port of the second tunable optical add / drop filter 32-F is input to the first port 10-1 of the second optical circulator 10 and output to the second port 10-2, and the closed loop quantum key. After propagating counterclockwise again in the loop formed by the delivery transmission system 22, it is transmitted to the next bidirectional transmission / reception terminal (that is, another user).

  On the other hand, the entangled light propagating in the clockwise direction through the loop of the closed loop quantum key distribution transmission system 22 is input to the second port 10-2 of the second optical circulator 10 and output to the third port 10-3. The output light is input to the first wavelength variable optical add / drop filter 31-F, and the output light from the drop port is received by the first quantum key receiving device 31-D. On the other hand, the output light from the through port of the first tunable optical add / drop filter 31-F is input to the first port 9-1 of the first optical circulator 9 and output to the second port 9-2, and the closed-loop quantum key After propagating clockwise again in the loop formed by the delivery transmission system 22, it is transmitted to the next bidirectional transmission / reception terminal (that is, another user).

  Therefore, the second multi-terminal quantum key distribution system adopts the closed loop quantum key distribution system 22 so that the drop light can be applied to any of the entangled light propagated around the left and right sides of the loop. Can be received by the quantum key receiving device (first quantum key receiving device 31-D or second quantum key receiving device 32-D), and through light is transmitted to the next bidirectional transmission / reception terminal via quantum channel 2 It becomes possible.

For example, even if the optical path connecting the bidirectional wavelength tunable optical add / drop filters C ₁ and C ₂ shown in FIG. 6 is broken or disconnected, it propagates counterclockwise in the loop formed by the closed loop quantum key distribution transmission system 22 by dropping the entangled light interactive tunable optical add-drop filters C _1, to drop the entangled light propagated in the loop clockwise in interactive tunable optical add-drop filters C _2, bidirectional wavelength Quantum key distribution between a user having the variable optical add / drop filter C ₁ and a user having the bidirectional wavelength variable optical add / drop filter C ₂ becomes possible. Further, by selecting an optical path that bypasses the above-mentioned damaged portion in the same manner, a user having the bidirectional wavelength tunable optical add / drop filter C ₁ and a user having the bidirectional wavelength tunable optical add / drop filter C _2N Quantum key distribution in any combination such as Such a detour route selection can be easily realized by adding to the control unit 4 a network monitor function for monitoring the communication network for breakage or disconnection.

Also, according to the second multi-terminal quantum key distribution system, it is possible to configure a quantum key distribution system that is resistant to eavesdropping. For example, the eavesdropping by eavesdropper in the light path connecting the interactive tunable optical add-drop filters C ₁ and bidirectional tunable optical add-drop filter C ₂ is performed. At this time, for the entangled light loops to form a closed loop quantum key distribution transmission system 22 has propagated counterclockwise, the reception result the effect of eavesdroppers bidirectional quantum key receiving device D ₂ to D _2N (Errors occur). On the other hand, for the entangled light propagating clockwise in the loop, the reception results of the bidirectional quantum key receiving devices D _{2 to} D _2N are not affected by the eavesdropper. Therefore, each user having the _two- way quantum key receivers D _{2 to} D _2N creates a cryptographic key from the reception result for the entangled light propagating clockwise in the loop, thereby enabling secure cryptographic key sharing. Can be executed. Whether the first quantum key receiver 31-D or the second quantum key receiver 32-D has received the entangled light propagating in the direction of the loop formed by the closed-loop quantum key distribution transmission system 22 It can be easily determined by seeing whether the light is received. Further, by observing the correlation between the loop propagation direction and the error rate of the sieve key, it is possible to estimate where the wiretapping has been performed.

<Modifications of the first and second multi-terminal quantum key distribution systems>
In the above description, SPDC is assumed as a process of generating entangled light used in the first and second multi-terminal quantum key distribution systems, but other nonlinear optical processes are used as a process of generating entangled light. It is also possible. For example, a so-called cascade nonlinear effect that causes the second-order nonlinear optical effect described twice in the same nonlinear optical device described in Non-Patent Document 1 may be used.

  Alternatively, natural four-wave mixing, which is a third-order nonlinear optical effect in an optical fiber or the like, may be used. In both cases, there is a strong excitation light component in the center of the SPDC spectrum, so the wavelength component near the wavelength of the excitation light cannot be used for quantum key generation, but this only reduces the number of users that can be stored. Quantum key distribution is possible between any two terminals of a plurality of terminals, and there is no difference in obtaining a basic effect that quantum key distribution can be simultaneously performed between a plurality of two terminals.

  Also, the device structure of the quantum entangled light source illustrated in FIG. 3 and the structure of the quantum key receiver illustrated in FIG. 5 are only suitable examples in the case of a system configuration using polarization quantum entangled photon pairs. The effects of the present invention can also be obtained with a configuration example. The multi-terminal quantum key distribution system according to the present invention can also be realized by using a so-called time-position quantum entangled photon pair, in which case the device structure of the quantum entangled light source and the quantum key receiving device shown in FIG. 5 are used. Similar effects can be obtained by following the form.

1: entangled light source
2: Quantum channel
3: Classical channel
4: Control unit
5: Optical bandpass filter
6: Optical circulator
7: Tunable Bragg reflector
8: 1 × 2 optical coupler
9: 1st optical circulator
10: Second optical circulator
A _{1 to} A _2N : Tunable optical add / drop filter
B ₁ ~B _2N: quantum key receiving device
C _{1 to} C _2N : Bidirectional tunable optical add / drop filter
D _{1 to} D _2N : Bidirectional quantum key receiver
20: Serial quantum key distribution transmission system
20-1 to 20-2N: Transmission / reception terminals
22: Closed loop quantum key distribution transmission system
22-1 to 22-2N: Two-way transmission / reception terminal
31: First light receiving transfer block
31-D: 1st quantum key receiver
31-F: 1st tunable optical add / drop filter
32: Second light receiving transfer block
32-D: Second quantum key receiver
32-F: Second tunable optical add / drop filter
401: Half mirror
402: 1/2 wave plate
403: First polarization separation circuit
404: Second polarization separation circuit
405: First single photon detector
406: Second single photon detector
407: Third single photon detector
408: Fourth single photon detector
409: Signal processing circuit
501: Polarization separation / synthesis circuit
502: Second-order nonlinear optical medium
503: 90 degree polarization plane rotation and optical phase adjustment unit
504: WDM filter
505: Low-pass optical filter

Claims (11)

N is an integer of 2 or more, and f bit / s is the assumed maximum key generation rate of the quantum encryption key.
A entangled light source that generates a entangled photon pair having an optical frequency region of 2 Nf Hz or more, a serial quantum key distribution transmission system, and a control unit,
The serial quantum key distribution / transmission system includes 2N transmission / reception terminals having different drop wavelengths, each having a tunable optical add / drop filter and a quantum key reception device, and the 2N transmission / reception terminals are arranged in series. ,
Each transmitting / receiving terminal receives the output light from the drop port of the wavelength tunable optical add / drop filter, performs photon detection, transmits measurement base information for generating a quantum encryption key, and receives other quantum keys Comprising a quantum key receiving device for receiving measurement base information from the device, and further including a signal processing circuit for executing an error correction and secret amplification function;
The control unit selects a drop wavelength for a tunable optical add / drop filter provided in each of the 2N transmission / reception terminals and outputs each measurement base output from the 2N quantum key reception devices. Receive information, transfer it to another corresponding quantum key receiver,
The quantum key distribution is performed between any two transmission / reception terminals of the 2N transmission / reception terminals including the quantum key reception apparatus, and the quantum key distribution is simultaneously performed between a plurality of two transmission / reception terminals. Terminal quantum key distribution system. The serial quantum key distribution transmission system is:
By connecting the through port of the tunable optical add / drop filter of the first transmitter / receiver terminal and the input port of the tunable optical add / drop filter of the second transmitter / receiver terminal by the optical transmission path that propagates the entangled light, the second transmitter / receiver Connect the thru port of the wavelength tunable optical add / drop filter of the terminal and the input port of the wavelength tunable optical add / drop filter of the third transmitting / receiving terminal, and sequentially optically add the wavelength tunable optical add of the (2N-1) th transmitting / receiving terminal. An optical transmission path through which quantum entangled light propagates from the first transmitting / receiving terminal to the 2Nth transmitting / receiving terminal by connecting the through port of the drop filter and the input port of the tunable optical add / drop filter of the 2Nth transmitting / receiving terminal The multi-terminal quantum key distribution system according to claim 1, wherein the multi-terminal quantum key distribution system is connected in series with each other. The wavelength tunable optical add / drop filter is:
The multi-terminal quantum according to claim 1, further comprising a dielectric multilayer filter, wherein the transmitted light output of the dielectric multilayer filter is output as through light, and the reflected light output is output as drop light. Key distribution system. The wavelength tunable optical add / drop filter is:
It has an optical circulator and a wavelength tunable Bragg reflector,
The light input to the first port of the optical circulator is output from the second port, the light input to the second port is output from the third port,
The wavelength tunable Bragg reflector is connected to the second port of the optical circulator, and out of the light output from the second port of the optical circulator, the wavelength component that matches the Bragg wavelength of the wavelength tunable Bragg reflector Is Bragg-reflected and input again to the second port of the optical circulator and output as drop light from the third port.
The multi-terminal quantum key distribution system according to claim 1 or 2, wherein components other than the Bragg wavelength are transmitted as the through light through the wavelength tunable Bragg reflector. The quantum key receiving device includes:
Half mirror, 1/2 wavelength plate, 1st polarization separation circuit, 2nd polarization separation circuit, 1st single photon detector, 2nd single photon detector, 3rd single photon detector, 4th single photon Equipped with a detector,
Photons arriving at the quantum key receiving device are stochastically divided into two paths by the half mirror, one path is guided to the first polarization separation circuit, and the other path passes through the half-wave plate. And led to the second polarization separation circuit,
The first polarization separation circuit separates photons that have passed through one path into polarization components that are stochastically orthogonal to each other, and inputs them to the first single photon detector and the second single photon detector, respectively. ,
The second polarization separation circuit separates photons guided to the other path and passed through the half-wave plate into polarization components that are probabilistically orthogonal to each other, and the third single-photon detector, the fourth Each input to a single photon detector,
5. The photon is detected by the first single photon detector, the second single photon detector, the third single photon detector, and the fourth single photon detector. The multi-terminal quantum key distribution system according to any one of the above. N is an integer of 2 or more, and f bit / s is the assumed maximum key generation rate of the quantum encryption key.
Quantum entangled light source that generates entangled photon pairs with optical frequency range of 2Nf Hz or higher, 1 × 2 optical coupler that splits into two by accepting the output of the entangled light source, and 2N bidirectional types with different drop wavelengths A closed loop quantum key distribution transmission system including a transmission and reception terminal, and a control unit;
Each of the 2N bidirectional transmission / reception terminals includes first and second optical circulators, a first tunable optical add / drop filter whose drop wavelength can be changed, and a first quantum key receiving device. A block, a second wavelength variable optical add / drop filter whose drop wavelength can be changed, and a second light receiving / transfer block including a second quantum key receiving device,
The closed-loop quantum key distribution transmission system is formed as a closed loop including the 1 × 2 optical coupler and 2N bidirectional transmission / reception terminals,
The first and second quantum key receivers provided by 2N bidirectional bidirectional transmission / reception terminals accept photons detected from adjacent bidirectional transmission / reception terminals or the 1 × 2 optical coupler and perform photon detection. And a signal processing circuit for transmitting measurement base information for generating a quantum encryption key, receiving measurement base information from another bidirectional transmission / reception terminal, and further executing an error correction and secret amplification function. Including each
The control unit selects a drop wavelength of the first and second tunable optical add / drop filters respectively provided in 2N of the bidirectional transmission / reception terminals, and is output from 2N of the bidirectional transmission / reception terminals. Receive the measurement base information and transfer it to the corresponding other bidirectional transmission / reception terminal,
Quantum key distribution between any two bidirectional transmission / reception terminals of the 2N bidirectional transmission / reception terminals, and simultaneous quantum key distribution between a plurality of two bidirectional transmission / reception terminals, Multi-terminal quantum key distribution system. The bidirectional transmission / reception terminal is:
The first optical circulator, the second optical circulator, the first light receiving transfer block, the second light receiving transfer block,
The first light receiving and transferring block includes the first quantum key receiving device and the first wavelength variable optical add / drop filter, and the second light receiving and transferring block includes the second quantum key receiving device and the second wavelength variable light. It has an add / drop filter,
A first port of the first optical circulator is coupled to a through port of the first tunable optical add / drop filter, a third port is coupled to an input port of the second tunable optical add / drop filter,
The first port of the second optical circulator is coupled to the through port of the second wavelength tunable optical add / drop filter, the third port is coupled to the input port of the first wavelength tunable optical add / drop filter,
The first quantum key receiver is connected to a drop port of the first wavelength tunable optical add / drop filter, and the second quantum key receiver is connected to a drop port of the second wavelength tunable optical add / drop filter. And
The closed loop quantum key distribution transmission system is:
The first optical input / output end of the 1 × 2 optical coupler and the second port of the first optical circulator of the first bidirectional transceiver terminal are connected by an optical transmission path for propagating quantum entangled light. A second port of the second optical circulator of the bidirectional transmission / reception terminal is connected to a second port of the first optical circulator of the second bidirectional transmission / reception terminal, and sequentially the (2N-1) th bidirectional Connected to the second port of the second optical circulator of the second-type transmission / reception terminal and the second port of the first optical circulator of the 2N-th bidirectional transmission / reception terminal, The second port is connected to the second optical input / output terminal of the 1 × 2 optical coupler, and is formed as a closed loop including the 1 × 2 optical coupler and 2N bidirectional transmission / reception terminals. The multi-terminal quantum key distribution system according to claim 6. The first and second wavelength tunable optical add / drop filters are:
The multi-terminal quantum according to claim 6 or 7, comprising a dielectric multilayer filter, wherein the transmitted light output of the dielectric multilayer filter is output as through light, and the reflected light output is output as drop light. Key distribution system. The first and second wavelength tunable optical add / drop filters are:
It has an optical circulator and a wavelength tunable Bragg reflector,
The light input to the first port of the optical circulator is output from the second port, the light input to the second port is output from the third port,
The wavelength tunable Bragg reflector is connected to the second port of the optical circulator, and out of the light output from the second port of the optical circulator, the wavelength component that matches the Bragg wavelength of the wavelength tunable Bragg reflector Is Bragg-reflected and input again to the second port of the optical circulator and output as drop light from the third port.
The multi-terminal quantum key distribution system according to claim 6 or 7, wherein components other than the Bragg wavelength are transmitted through the wavelength tunable Bragg reflector and output as through light. The first and second quantum key receiving devices,
Half mirror, 1/2 wavelength plate, 1st polarization separation circuit, 2nd polarization separation circuit, 1st single photon detector, 2nd single photon detector, 3rd single photon detector, 4th single photon Equipped with a detector,
Photons arriving at the quantum key receiving device are stochastically divided into two paths by the half mirror, one path is guided to the first polarization separation circuit, and the other path passes through the half-wave plate. And led to the second polarization separation circuit,
The first polarization separation circuit separates photons that have passed through one path into polarization components that are stochastically orthogonal to each other, and inputs them to the first single photon detector and the second single photon detector, respectively. ,
The second polarization separation circuit also separates photons that have been guided to the other path and passed through the half-wave plate into polarization components that are probabilistically orthogonal to each other, and the third single-photon detector, the fourth Each input to a single photon detector,
10. The photon is detected by the first single photon detector, the second single photon detector, the third single photon detector, and the fourth single photon detector. The multi-terminal quantum key distribution system according to any one of the above. The quantum entangled light source is
A wavelength division multiplexing filter, a polarization separation / synthesis circuit, a second-order nonlinear optical medium, a 90-degree polarization plane rotation and optical phase adjustment unit, and a low-pass optical filter,
A Sagnac type optical interferometer is composed of the polarization separation / synthesis circuit, the second-order nonlinear optical medium, the 90-degree polarization plane rotation, and the optical phase adjustment unit,
The input excitation light to the quantum entangled light source passes through the wavelength division multiplex filter, becomes 45 degree polarized excitation light, and is input to the polarization separation / combination circuit,
In the polarization separation / combination circuit, the 45-degree polarized excitation light is branched into p-polarized light and s-polarized light that rotate clockwise around the Sagnac optical interferometer, and circulates around the Sagnac optical interferometer,
The signal light and idler light generated in the second-order nonlinear optical medium are reflected by the wavelength division multiplex filter, and the wavelength component of the input excitation light is removed by the low-pass optical filter, so that the signal light and idler light are entangled. It outputs as a photon pair, The multi-terminal quantum key distribution system as described in any one of Claims 1-10 characterized by the above-mentioned.