JP4632203B2 - Quantum key generation system and quantum key generation method - Google Patents

Description

  The present invention relates to a quantum key distribution system and a quantum key generation method.

  In recent years, research on quantum cryptography systems that can perform cryptographic communication with physically secured security by utilizing the uncertainty principle of quantum mechanics has been underway. Quantum cryptography is a mechanism for sharing an encryption key for encrypting and decrypting information communication between two distant parties, also called quantum key distribution, and various methods have been proposed so far. (For example, refer to Patent Document 1).

JP 2004-187268 A

  However, the conventional quantum key distribution realizes key distribution between two nodes. Therefore, in order to share a common encryption key among three or more nodes, there is a problem that it is necessary to construct a complex system in which two or more quantum encryption systems are combined.

  The present invention has been made in view of such a problem, and an object of the present invention is to securely encrypt a common encryption among two, three, or three or more of three or more nodes. An object is to provide a quantum key distribution system and a quantum key generation method for sharing a key.

In order to achieve such an object, the present invention provides a quantum key generation for generating a quantum key that is an encryption key for encrypting or decrypting data transmitted and received between nodes. A first and second polarization entangled photon pair generating means for generating a photon pair in a quantum entangled state with respect to polarization, an auxiliary node, and first, second, third and fourth The auxiliary node includes a first input port for inputting one photon of the photon pair output from the first polarization entangled photon pair generating means, and the second polarization entangled photon. A second input port for inputting one photon of the photon pair output from the pair generating means, and one axial photon of the photon pair input from the first input port can be transmitted in the axial direction. A first half-wave plate and the second input Transmitting one of photons of the photon pair which is input from over preparative, organic and a second half-wave plate in a rotatable, first, second, third, and fourth ports axial A polarization beam splitter, which is input from one photon of the pair of vertically polarized photons transmitted through the first half-wave plate input from the first port and the second port. One photon of the pair of horizontally polarized photons transmitted through the second half-wave plate is branched and coupled to the third port, and the first 2 input from the first port. One photon of the horizontally polarized photon pair transmitted through the half-wave plate and the vertically polarized photon pair transmitted through the second half-wave plate input from the second port A polarization beam splitter for branching and coupling one photon to the fourth port, and the third port A third half-wave plate that can rotate in the axial direction and transmits one photon of the photon pair output from the fourth port, and one photon of the photon pair output from the fourth port. A first half-wave plate capable of rotating in the axial direction, a first output port that outputs one photon of the pair of photons transmitted through the third half-wave plate, and And a second output port that outputs one photon of the photon pair that has passed through the fourth half-wave plate, and the first node is connected to the first polarization entangled photon pair generating means. The other photon of the photon pair is input, the measurement to determine whether the photon is longitudinally polarized wave or transversely polarized wave, and whether it is +45 degree polarized wave or -45 degree polarized wave One of the measurements to be discriminated is selected at random, and the bias of the other photon in the input photon pair is selected. First polarization discriminating means for discriminating a wave, and the second node inputs the other photon of the photon pair from the second polarization entangled photon pair generating means, and for the photon, Either the measurement for discriminating whether it is longitudinal polarization or transverse polarization and the measurement for discriminating whether it is +45 degree polarization or -45 degree polarization are selected at random and input 2nd polarization discriminating means for discriminating the polarization of the other photon of the photon pair is provided, and the third node inputs one photon of the photon pair output from the first output port. Randomly select one of the measurement to determine whether the photon is longitudinally polarized wave or transversely polarized wave, and the measurement to determine whether it is +45 degree polarized wave or -45 degree polarized wave. And determining the polarization of one photon of the input photon pair Polarization determining means is provided, and the fourth node inputs one photon of the photon pair output from the second output port, and the photon is either longitudinally polarized or transversely polarized. One of a measurement for discriminating whether or not +45 degree polarization or -45 degree polarization is selected at random, and the polarization of one photon of the input photon pair is selected. A fourth polarization discriminating unit for discriminating, and each of the first, second, third and fourth nodes is selected at the time when the polarization discriminating unit of the own node receives the photon. The measurement type and the polarization of the determined photon is recorded, and the time and the measurement type selected at the time are transmitted to the auxiliary node and all nodes other than the self, The auxiliary nodes are the first, second, third, and The time at which two or more of the fourth nodes simultaneously receive photons and the angle of the crystal axes of the first, second, third, and fourth half-wave plates at the time are Means for transmitting to the first, second, third and fourth nodes, each of the first, second, third and fourth nodes comprising the first, second, third, And at least two of the fourth nodes simultaneously detect photons, and the polarization discrimination type used for the detection of the photons, the first, second, third and fourth 2 Means for allocating and storing a predetermined bit to the detected photon when the combination of angles of crystal axes of the half-wave plate is coincident; The encryption key is shared with the detected node .

The invention according to claim 2 is characterized in that in the quantum key generation system, the auxiliary node and the third or fourth node are integrated.

The invention according to claim 3 is a quantum key generation system that generates a quantum key that is an encryption key for encrypting or decrypting data transmitted and received between nodes, and is in a quantum entangled state with respect to polarization. First and second polarization entangled photon pair generating means for generating a pair of photons and first, second and third nodes, wherein the first node is the first polarization entangled photon One photon of the photon pair from the pair generating means is input, a measurement for determining whether the photon is longitudinally polarized wave or transversely polarized wave, and +45 degree polarized wave or −45 degree polarized wave A first polarization discriminating unit that randomly selects one of the measurements for discriminating between the two photons and discriminates the polarization of one photon of the input photon pair; and the second node includes: It said light from said second polarization entangled photon pair generating means Measurement that inputs one photon of a pair and determines whether the photon is longitudinally polarized wave or transversely polarized wave, and whether it is +45 degree polarized wave or -45 degree polarized wave And a second polarization discriminating unit that discriminates the polarization of one photon of the input photon pair, and the third node includes the first polarization. A first input port for inputting the other photon of the photon pair output from the entangled photon pair generating means, and a first input port for inputting the other photon of the photon pair output from the second polarization entangled photon pair generating means. Two input ports, an axially rotatable first half-wave plate that transmits the other photon of the photon pair input from the first input port, and the second input port and it transmits the other photon of the photon pair which is input from the axial And the rolling possible second half-wave plate, the first, second, third, and a polarization beam splitter that have a fourth port, said first input from said first port The second photon of the vertically polarized photon pair transmitted through the half-wave plate and the horizontally polarized photon transmitted through the second half-wave plate input from the second port. Branching and coupling the other photon of the pair to the third port, and passing through the first half-wave plate inputted from the first port, the other photon of the horizontally polarized photon pair and A polarization beam splitter for branching and coupling the other photon of the pair of vertically polarized photons transmitted through the second half-wave plate inputted from the second port to the fourth port; Photon detection means for detecting the other photon of the photon pair output from the third port; The other photon of the photon pair output from the fourth port is input, the measurement to determine whether the photon is longitudinally polarized wave or transversely polarized wave, and +45 degree polarized wave or −45 one of the measurement to determine whether it is in degrees polarization randomly select, and a third polarization discriminating means for discriminating the polarization of the other photon of the photon pair which is input, wherein the Each of the first, second, and third nodes records the time at which the polarization discriminating unit of the node receives the photon, the type of measurement selected at the time, and the discriminated polarization of the photon, Means for transmitting the time and the type of measurement selected at the time to all nodes other than the auxiliary node and the self, wherein the third node comprises the first, second and third Two or more of the nodes receive photons simultaneously And a means for transmitting the first and second nodes to the first and second half-wave plate angles at the time and the first and second half-wave plates at the time, the first, second and third Each of the first, second, and third nodes has photons detected simultaneously by two or more of the first, second, and third nodes, and the polarization discrimination type used to detect the photons, and the first Means for allocating and storing predetermined bits to the detected photons when the combination of crystal axis angles of the first and second half-wave plates coincides; The bit is used as an encryption key shared with a node that simultaneously detects photons .

The invention according to claim 4 is a quantum key generation method for generating a quantum key which is an encryption key for encrypting or decrypting data transmitted and received between nodes , wherein the quantum key is in a quantum entangled state with respect to polarization. First and second polarization entangled photon pair generating means for generating a pair of photons, an auxiliary node, and first, second, third and fourth nodes, wherein the auxiliary node includes the first and second nodes. A first input port for inputting one photon of the photon pair output from the polarization entangled photon pair generating means, and one photon of the photon pair output from the second polarization entangled photon pair generating means. An input second input port; an axially rotatable first half-wave plate that transmits one photon of the pair of photons input from the first input port; and the second One photon of the photon pair input from the input port is transmitted through. Let a second half wave plate that can be rotated axially, first, second, a polarization beam splitter that have the third and fourth ports, the input from the first port Horizontally transmitted through one photon of the vertically polarized photon pair transmitted through the first half-wave plate and the second half-wave plate input from the second port. One photon of the polarized photon pair is branched and coupled to the third port, and the horizontally polarized photon pair transmitted through the first half-wave plate input from the first port Polarized light for branching and coupling one photon of the pair of vertically polarized photons transmitted through the second half-wave plate input from the second port and the second port to the fourth port Transmits one photon of the photon pair output from the beam splitter and the third port. A third half-wave plate capable of rotating in the axial direction and a fourth half-portable in the axial direction that transmits one photon of the photon pair output from the fourth port. A first output port that outputs one photon of the photon pair that has passed through the third half-wave plate, and the fourth wave plate that has passed through the fourth half-wave plate. A second output port for outputting one photon of the photon pair, and the first node inputs the other photon of the photon pair from the first polarization entangled photon pair generating means , and Select either the measurement to determine whether the photon is longitudinally polarized wave or transversely polarized wave, and the measurement to determine whether it is +45 degree polarized wave or -45 degree polarized wave. A first polarization discriminating means for discriminating the polarization of the other photon of the photon pair, wherein the second node is: , A measurement of inputting the other photon of the photon pair from the second polarization entangled photon pair generating means and determining whether the photon is longitudinally polarized wave or transversely polarized wave, and +45 degrees Second polarization discriminating means is provided for selecting either of the measurements for discriminating between the polarization and the -45 degree polarization and discriminating the polarization of the other photon of the inputted photon pair. The third node receives one photon of the photon pair output from the first output port, and determines whether the photon is longitudinally polarized or transversely polarized. And a third polarization discrimination that discriminates the polarization of one photon of the input photon pair by selecting one of the measurements for discriminating whether the polarization is +45 degree polarization or -45 degree polarization. And the fourth node is output from the second output port. One photon of a pair of photons is input, measurement for determining whether the photon is longitudinally polarized wave or transversely polarized wave, and whether it is +45 degree polarized wave or -45 degree polarized wave And a fourth polarization discriminating means for discriminating the polarization of one photon of the inputted photon pair, wherein the auxiliary node has the first, The angles of the crystal axes of the second, third, and fourth half-wave plates are randomly 0 °, 0 °, 0 °, and 0 °, 22.5 °, 22 for each unit time. .0 degrees, 0 degrees, 0 degrees, and 0 degrees, -22.5 degrees, -22.5 degrees, -22.5 degrees, one of .5 degrees, 22.5 degrees, and 22.5 degrees and a step of setting one of -22.5 degrees, said first, second, each of the third and fourth nodes, randomly for each of the unit time The vertical polarization or measured to determine whether it is a horizontally polarized wave, and select one of the measurement to determine whether it is of the + 45 ° polarization or -45 degrees polarized input light record the step of determining the polarization of the child, the time that has received photon in the step of determining the polarization of the photon, the type of selected measurement in the time, and the polarization of the discriminated said photons, the time, and transmitting the type of selected measurement at the time to all the nodes other than the auxiliary node and self, the auxiliary node, said first, second, third, and fourth node Of the first, second, third, and fourth half-wave plates at the time at which two or more of the nodes simultaneously receive photons, and the first, second, Sent to the second, third, and fourth nodes And each of the first, second, third, and fourth nodes causes photons to be simultaneously emitted by two or more of the first, second, third, and fourth nodes. The polarization discrimination type detected and used for detecting the photon coincides with the combination of the crystal axis angles of the first, second, third and fourth half-wave plates. A predetermined bit is allocated to the detected photon and stored, and the allocated predetermined bit is used as an encryption key shared with a node that simultaneously detects the photon. To do.

The invention according to claim 5 is a quantum key generation method for generating a quantum key that is an encryption key for encrypting or decrypting data transmitted and received between nodes , wherein the quantum key is in a quantum entangled state with respect to polarization. First and second polarization entangled photon pair generating means for generating a pair of photons and first, second and third nodes, wherein the first node is the first polarization entangled photon One photon of the photon pair from the pair generating means is input, a measurement for determining whether the photon is longitudinally polarized wave or transversely polarized wave, and +45 degree polarized wave or −45 degree polarized wave A first polarization discriminating unit that selects one of the measurements for discriminating between the two photons and discriminates the polarization of one photon of the input photon pair, and the second node includes the first node 2 of one of the light of the photon pairs from the polarization entangled photon pair generating means And select either measurement to determine whether the photon is longitudinally polarized or transversely polarized, and measurement to determine whether it is +45 degree polarized wave or -45 degree polarized wave And second polarization discriminating means for discriminating the polarization of one photon of the input photon pair, and the third node outputs from the first polarization entangled photon pair generating means A first input port for inputting the other photon of the photon pair generated, a second input port for inputting the other photon of the photon pair output from the second polarization entangled photon pair generating means, An axially rotatable first half-wave plate that transmits the other photon of the photon pair input from the first input port, and the photon pair input from the second input port and it transmits the other photon, 1 of the second-half rotatable axial And elongated plate, first, second, third, and a polarization beam splitter that have a fourth port, passed through the first said inputted from the port of the first half wave plate of The other photon of the horizontally polarized photon pair that has passed through the other half photon of the vertically polarized photon pair and the second half-wave plate input from the second port is the third photon. Branched and coupled to a port, and the other photon of the horizontally polarized photon pair that has passed through the first half-wave plate input from the first port and the input from the second port A polarization beam splitter for branching and coupling the other photon of the vertically polarized photon pair transmitted through the second half-wave plate to the fourth port, and the photon output from the third port The photon detection means for detecting the other photon of the pair and the fourth port output The other photon of the photon pair is input, the measurement to determine whether the photon is longitudinally polarized wave or transversely polarized wave, and whether it is +45 degree polarized wave or -45 degree polarized wave one of the measurement to determine selected at random, and a third polarization discriminating means for discriminating the polarization of the other photon of the photon pair which is input, the method, the third node The angles of the crystal axes of the first and second half-wave plates are randomly set to one of 0 degrees and 22.5 degrees, or 0 degrees and -22.5 degrees, every unit time. The step of setting to one of the following, and a measurement for determining whether each of the first, second, and third nodes is the longitudinally polarized wave or the transversely polarized wave at random for each unit time, And any one of the measurements for determining whether the polarization is +45 degree polarization or -45 degree polarization. And-option, the step of determining the polarization of the input photon, time of receiving photons in the step of determining the polarization of the optical element, the type of selected measurement in the time, and discriminated the photon the polarization recording, and transmitting the time, and the type of measurement selected in the time to all the nodes other than the self, the third node, said first, second, and third two or more nodes the first and second half of the first and second node the angle of the crystal axis of the wave plate at the time and the time of receiving photons simultaneously of the three nodes Transmitting , each of the first, second, and third nodes detecting photons simultaneously by two or more of the first, second, and third nodes, and Polarization discrimination used for photon detection And another, the first, if the combination of the angle of the crystal axis of the second and third half-wave plate of matches, stores assigning a predetermined bit in the detected photon And using the assigned predetermined bit as an encryption key shared with a node that simultaneously detects photons .

  As described above, according to the present invention, a quantum key distribution system for securely sharing a common encryption key between two, three, or three or more of three or more nodes, and A quantum key generation method can be provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings described below, components having the same function are denoted by the same reference numerals, and repeated description thereof is omitted.
(First embodiment)
FIG. 1 shows a first embodiment of a quantum key distribution system according to the present invention. The quantum key distribution system 100 includes a polarization entangled light source 101 and a polarization entangled light source 102 that respectively output a photon pair composed of a signal photon and an idler photon, and a node to which an idler photon output from the polarization entangled light source 101 is input. 111, the node 112 to which the idler photon output from the polarization entangled light source 102 is input, the signal photon output from the polarization entangled light source 101 and the signal photon output from the polarization entangled light source 102 are the auxiliary node 130. Nodes 113 and 114 input via.

  The polarization entangled light source 101 and the polarization entangled light source 102 generate a polarization entangled photon pair having the quantum state shown in the equation (1).

Here, | V> indicates the vertically polarized quantum state, | H> indicates the laterally polarized quantum state, and the subscripts s and i indicate the signal and idler photon.

  The auxiliary node 130 has an input port 131 to which the signal photon output from the polarization entangled light source 101 is input, an input port 132 to which the signal photon output from the polarization entangled light source 102 is input, and an input from the input port 131. A half wave plate (HWP) 151 that rotates the polarization of the signal photons, a HWP 152 that rotates the polarization of the signal photons input from the input port 132, and ports 161, 162, and 163. 164, the vertically polarized signal light transmitted through the HWP 151 input from the port 161 and the horizontally polarized signal photon transmitted through the HWP 152 from the port 162 are branched and coupled to the port 163. Horizontally polarized signal photons transmitted through the input HWP 151 and input from the port 162 Polarization beam splitter (PBS) 160 for branching and coupling vertically polarized signal photons transmitted through the HWP 152 to the port 164, and HWP 153 for rotating the polarization of the signal photons output from the port 163 of the PBS 160 An HWP 154 that rotates the polarization of the signal photons output from the port 164 of the PBS 160, an output port 141 that outputs the signal photons that have passed through the HWP 153, and an output port 142 that outputs the signal photons that have passed through the HWP 154. Is provided. Signal photons output from the output port 141 and the output port 142 are input to the nodes 113 and 114, respectively.

  Each of the HWPs 151, 152, 153, and 154 includes a mechanism that rotates the crystal axis of the HWP in either the vertical direction (from 0 degree) or +22.5 degrees from the vertical direction every unit time. That is, when the crystal axis of the HWP is set to 0 degrees from the vertical direction, the polarization of the photon transmitted through the HWP rotates by π. When the crystal axis of the HWP is rotated 22.5 degrees from the vertical direction, the polarization of the photon transmitted through the HWP rotates by 45 degrees. The combinations of angles of crystal axes of HWP 151, 152, 153, and 154 are (0 degree, 0 degree, 0 degree, 0 degree) and (22.5 degree, 22.5 degree, 22.5 degree, 22.5 degree). Is selected at random for each unit time.

  Each of the nodes 1 to 4 has a measurement (hereinafter referred to as {V, H} measurement) for determining whether the input photon is vertical (V) or horizontal (H) polarized wave, and +45 Is selected at random for each unit time to measure whether the polarization is a positive polarization or -45 degree polarization (hereinafter referred to as {+45, -45} measurement). Photon detection means 121, 122, 123, 124 having a polarization discrimination function for discriminating between

Next, the operation of the quantum key distribution system 100 having the above configuration will be described.
The signal photon output from the polarization entangled light source 101 is input to the HWP 151 via the input port 131 of the auxiliary node 130. Similarly, the signal photon output from the polarization entangled light source 102 is input to the HWP 152 via the input port 132 of the auxiliary node 130.

  The HWP 151 and the HWP 152 each rotate the crystal axis of the HWP randomly at 0 ° from the vertical direction and + 22.5 ° from the vertical direction at every unit time, and the polarization of the transmitted signal photon is 180 degrees. Rotate (π rad) or 45 degrees (π / 4 rad).

  Horizontally polarized wave (polarized wave 0 rad or π rad) signal photon input to PBS 160 via port 161 and vertical polarization wave (polarized wave π / 2 rad or −π / 2 rad) input to PBS 160 via port 162. Are coupled to the port 163, and the vertically polarized signal photons input to the PBS 160 via the port 161 and the horizontally polarized signal photons input to the PBS 160 via the port 162 are branched and coupled to the port 164. Is done.

  The HWP 153 and the HWP 154 are each rotated at 0 degree from the vertical direction and 22.5 degrees from the vertical direction at random, and the polarization of the transmitted signal photon is 0 degree respectively. Or rotate 45 degrees (π / 4 rad). As described above, when the angle of the crystal axes of HWP 151 and HWP 152 is 0 degrees, the angle of the crystal axes of HWP 153 and HWP 154 is also set to 0 degrees, and when the angle of the crystal axes of HWP 151 and HWP 152 is 22.5 degrees, HWP 153 The angle of the crystal axis of HWP154 is set to 22.5 degrees. Signal photons transmitted through the HWP 153 and the HWP 154 are input to the node 113 and the node 114 via the output port 141 and the output port 142, respectively.

  The photon detection means 121, 122, 123, 124 provided in each node randomly selects one of {V, H} measurement and {+45, −45} measurement for each unit time, and inputs photons Determine the polarization. The photon detection means 121 and the photon detection means 122 discriminate the polarization of idler photons from the polarization entangled light source 101 and the polarization entangled light source 102, respectively. The photon detection means 123 and the photon detection means 124 respectively determine the polarization of the signal photons from the output port 141 and the output port 142 of the auxiliary node.

  When the entire state (of 4 photons) including the polarization entangled light source 101 and the polarization entangled light source 102 is represented by | Φ>, it can be expressed as Expression (2).

The subscripts s1 and i1 represent the signal and idler photon from the polarization entangled light source 101, and the subscripts s2 and i2 represent the signal and idler photon from the polarization entangled light source 102. Further, in Equation (2), the normalization coefficient is omitted.

Here, when a longitudinally polarized idler photon from the polarization entangled light source 101 is input to the node 111, | V> _i1 is converted to | V> ₁ , and a longitudinally polarized signal from the polarization entangled light source 101 is obtained. When a photon is input to node 113, | V> _s1 is converted to | V> ₃ , and when a horizontally polarized idler photon from polarization entangled light source 101 is input to node 111, | H> _i1 is When | H> ₁ is converted and the horizontally polarized idler photon from the polarization entangled light source 101 is input to the node 114, | H> _s1 is converted to | H> ₄ . Similarly, when the longitudinally polarized idler photon from the polarization entangled light source 102 is input to the node 112, | V> _i2 is converted to | V> ₂ , and the longitudinally polarized idler from the polarization entangled light source 102 is converted. When a photon is input to node 114, | V> _s2 is converted to | V> ₄ , and when a horizontally polarized idler photon from polarization entangled light source 102 is input to node 112, | H> _i2 is It is assumed that | H> _s2 is converted to | V> ₃ when | H> ₂ and longitudinally polarized idler photons from the polarization entangled light source 102 are input to the node 113.

  Using these transformations, equation (2) can be rewritten into equation (3). Note that in Equation (3), the normalization coefficient is omitted.

  Here, in the auxiliary node 130, the crystal axes of all the HWPs (151, 152, 153, 154) are set to 0 degrees with respect to the vertical direction, and the photon detection means (121, 122, 123, 124) of all the nodes Let us consider a case where {V, H} measurement is performed in FIG. At this time, the photons input to the HWPs 151 and 152 are output with the V polarized wave remaining as the V polarized wave and the H polarized wave remaining as the H polarized wave. In this situation, it is assumed that reception of photons is simultaneously observed in the nodes 111 to 114. At this time, the photon detected at the node 113 is either (1) a V-polarized photon from the polarization entangled light source 101 or (2) an H-polarized photon from the polarization entangled light source 102. If (1), due to the nature of the polarization entangled photon pair, the node 111 receives the V polarization photon from the polarization entangled light source 101 and is observed at the node 112 and the node 114. Are V-polarized photons from the polarization entangled light source 102. On the other hand, if (2), the node 112 receives the H polarization photon from the polarization entangled light source 102 and the nodes 111 and 114 observe the polarization entangled light source 101. H-polarized photons.

  The third term of Equation (3) represents the case where no photon is input to the node 114, and the fourth term of Equation (3) represents the case where no photon is input to the node 113. It is expressed as the following formula (4).

Here, subscripts 1 to 4 represent quantum states observed at the nodes 111 to 114.

  Next, in the auxiliary node 130, the HWP 151 and the HWP 152 are set to rotate the polarization of the input photon by +45 degrees, and the HWP 153 and the HWP 4 are set to rotate the polarization of the input photon by +45 degrees. Consider a case where {+45, −45} measurement is performed in the photon detection means of all nodes. In this situation, it is assumed that reception of photons is simultaneously observed in the nodes 111 to 114. The photons detected at this time are either (1) a +45 degree polarized photon from the polarization entangled light source 101 or (2) a −45 degree polarized photon from the polarization entangled light source 102. If (1), due to the nature of the polarization entangled photon pair, the node 111 receives +45 degree polarization photons from the polarization entangled light source 101 and is observed at the nodes 102 and 104. Is a +45 degree polarized photon from the polarization entangled light source 102. On the other hand, in the case of (2), the node 112 receives the -45 degree polarized photon from the polarization entangled light source 102, and the nodes 111 and 114 observe the polarization entangled light source. -45 degree polarized photons from 101.

  Here, | H> input to HWP 151 and HWP 152 is converted to | +45>, | V> is converted to | −45>, and | H> input to HWP 153 and HWP 154 is | -45>, and | V> is converted to | +45>. Also, | +45> is represented as | V> + | H>, and | −45> is represented as − | V> + | H>.

According to the above conversion, the state of photons input to the node 113 and the node 114 is converted from | V> _s1 to − | −45> ₃ + | +45> ₄ and | H> _s1 is | −45> _3. + | _+45> are converted to _4, | _{V> s2} is _- | is converted _+45> to _{3, | | -45> 4 +} H> s2 is _| is converted into _{+45> 3} | -45> 4 +. In addition, | V> _i1 is | +45> ₁ − | −45> ₁ and | H> _i1 is | +45> ₁ + | −45> ₁ and | V> _i2 is | +45> ₂ − | −45>. ₂ and | H> _i2 is represented as | +45> ₂ + | −45> ₂ .
| −45> _s2 and | −45> _s2 can be expressed as | +45> ₃ + | −45> ₄ and − | V> _s1 + | H> _s1 .

  Using these, equation (2) can be rewritten as equation (5). Note that in Equation (5), the normalization coefficient is omitted.

  The third term of Equation (5) represents the case where no photon is input to the node 113, and the fourth term of Equation (5) represents the case where no photon is input to the node 114. It is expressed as equation (6).

Here, | +45> represents the quantum state of a +45 degree polarized photon, and | −45> represents the quantum state of a −45 degree polarized photon.

  As described above, when the angle setting of each HWP of the auxiliary node 130 matches the polarization discrimination method of each node, the measurement result of each node has a correlation represented by the equations (4) and (6). That is, for example, when the crystal axis of each HWP of the auxiliary node 130 is set to 0 degree and {V, H} measurement is performed at all the nodes 111 to 114, the measurement results of the nodes 111 to 114 are all V or All become H. Further, for example, the crystal axes of each HWP of the auxiliary node 130 are set to 0 degree, {V, H} measurement is performed at the nodes 111 and 112, and {+45, −45} measurement is performed at the nodes 113 and 114. In this case, the measurement results of the nodes 111 and 112 have a correlation, and the measurement results of the nodes 113 and 114 have no correlation. Using these properties, an encryption key can be generated between nodes according to the following procedure.

  1. The auxiliary node 130 sets the angle combinations of the crystal axes of the HWPs 151, 152, 153, and 154 to (0 degrees, 0 degrees, 0 degrees, 0 degrees) and (22.5 degrees, 22.5) every certain unit time. (Degrees, 22.5 degrees, 22.5 degrees) is selected at random and set to the selected angle.

  2. Each node (111, 112, 113, 114) selects one of {V, H} measurement and {+45, −45} measurement at random for each unit time, and the polarization of the input photon. To determine. Each node records the time when the photon is received (measured) and the measured polarization of the photon as data.

  3. Each node publishes to the auxiliary node 130 and all nodes the time at which the photon was received and the type of measurement used at that time.

  4). The auxiliary node exposes to all nodes the time at which two or more nodes received photons simultaneously and the angle of the crystal axis of each HWP at that time. The above 3. And 4. Publication in can be performed using known communication means.

  5. Each node leaves only data when two or more nodes detect photons at the same time, and the combination of the polarization discrimination type used and the angle of the crystal axis of each HWP of the auxiliary node is the same. Discard the data. That is, each node has the above 2. The data whose photon reception time does not coincide with the time disclosed by the auxiliary node is deleted from the data recorded in (1). Further, at each time, each node has (1) when the angle of the crystal axes of the auxiliary nodes HWP 151 to HWP 154 is set to 0 degree and {V, H} measurement is selected by the photon detection means (2 ) Delete the other data except the data when the angle of the crystal axes of the auxiliary nodes HWP151 to HWP154 is set to 45 degrees and {+45, −45} measurement is selected by the photon detection means.

  6). Each node generates a key using the remaining data. For example, “0” bit for V polarization measured using {V, H} measurement, “1” bit for H polarization, and “0” for +45 degree polarization measured using {+45, −45} measurement. "1" bit is assigned to "bit, -45 degree polarization".

FIG. And the data recorded by each node in the above 3. A part of the data to be disclosed in. For example, the node 111 indicates that, among the recorded data, the measurement types at times t ₀ and t _{2 to} t ₈ and times t ₀ and t _{2 to} t ₈ are disclosed to the auxiliary node and all nodes.

FIG. 5 shows the time when the auxiliary node 130 opens to each node and the angle of the crystal axis of each HWP at that time. For example, the auxiliary node determines the angle of the crystal axis of each HWP at times t ₀ , t _{2 to} t ₅ , t ₇ , and t ₈ , and at times t ₀ , t ₃ , t ₅ , t ₇ , and t ₈ . Indicates that it will be made public.

FIG. And 6. Shows the data remaining in each node and the bits allocated to the data. The node 111 uses the bit “101” assigned to the photons measured at times t ₀ , t ₇ , and t ₈ as an encryption key shared among the nodes 112, 113, and 114. The node 112 uses the bit “0” assigned to the photon measured at time t ₃ as an encryption key shared with the node 114.

  As described above, it is possible to share different encryption keys between any two nodes, three nodes, and all nodes between the nodes 1 to 4.

  In the present embodiment, the combinations of angles of crystal axes of HWP 151, 152, 153, and 154 are (0 degrees, 0 degrees, 0 degrees, 0 degrees) and (22.5 degrees, 22.5 degrees, 22 .5 degrees, 22.5 degrees) is selected, but (0 degrees, 0 degrees, 0 degrees, 0 degrees) and (-22.5 degrees, -22.5 degrees, -22.5) are described. Degree, -22.5 degrees).

(Second Embodiment)
FIG. 5 shows a second embodiment of the quantum key distribution system according to the present invention. The quantum key distribution system 200 of this embodiment is different from the quantum key distribution system 100 of the first embodiment in that it includes a node 213 in which the auxiliary node 130 and the node 113 in the first embodiment are integrated.

  The quantum key distribution system 200 includes a polarization entangled light source 101 and a polarization entangled light source 102, a node 111 to which an idler photon output from the polarization entangled light source 101 is input, and an idler photon output from the polarization entangled light source 102. , The node 112 to which the signal photon output from the polarization entangled light source 101 and the signal photon output from the polarization entangled light source 102 are input via the auxiliary node 130, and the polarization entangled light source The signal photon output from 101 and the signal photon output from the polarization entangled light source 102 are input via the node 213.

  The node 213 is input from the input port 131 to which the signal photon output from the polarization entangled light source 101 is input, the input port 132 to which the signal photon output from the polarization entangled light source 102 is input, and the input port 131. HWP 151 that rotates the polarization of the signal photon, HWP 152 that rotates the polarization of the signal photon input from the input port 132, and ports 161, 162, 163, and 164, and the HWP 151 that is input from the port 161. The vertically polarized signal light and the horizontally polarized signal photon transmitted through the HWP 152 input from the port 162 are branched and coupled to the port 163, and the horizontally polarized signal photon transmitted through the HWP 151 input from the port 161 and Vertical transmission through HWP 152 input from port 162 PBS 160 for branching and coupling wave signal photons to port 164, HWP 153 for rotating the polarization of signal photons output from port 163 of PBS 160, and HWP 154 for rotating the polarization of signal photons output from port 164 of PBS 160 And a photon detection means 123 to which signal photons transmitted through the HWP 153 are input, and an output port 142 from which signal photons transmitted through the HWP 154 are output. The signal photon output from the output port 142 is input to 114.

  The node 213 randomly sets the crystal axis of each HWP to either 0 degree and 22.5 degrees, or to 0 degree and -22.5 degrees every unit time. The node 213 selects either the {V, H} measurement or the {+45, −45} measurement, and receives the photons assigned to the node 213. Thereby, 1. of the first embodiment. To 6. It is possible to share different encryption keys among any two nodes, three nodes, and all of the nodes 111, 112, 114, and 213 by the same procedure as the above. However, the combination including the node 213 is overwhelmingly large.

(Third embodiment)
FIG. 6 shows a third embodiment of the quantum key distribution system according to the present invention. The quantum key distribution system 300 according to the present embodiment shares a common encryption key between two or three of the three nodes.

  The quantum key distribution system 300 includes a polarization entangled light source 101 and a polarization entangled light source 102, a node 111 to which an idler photon output from the polarization entangled light source 101 is input, and an idler photon output from the polarization entangled light source 102. And a node 313 to which a signal photon output from the polarization entangled light source 101 and a signal photon output from the polarization entangled light source 102 are input.

  The node 313 is input from the input port 131 to which the signal photon output from the polarization entangled light source 101 is input, the input port 132 to which the signal photon output from the polarization entangled light source 102 is input, and the input port 131. HWP 151 that rotates the polarization of the signal photon, HWP 152 that rotates the polarization of the signal photon input from the input port 132, and ports 161, 162, 163, and 164, and the HWP 151 that is input from the port 161. The vertically polarized signal light and the horizontally polarized signal photon transmitted through the HWP 152 input from the port 162 are branched and coupled to the port 163, and the horizontally polarized signal photon transmitted through the HWP 151 input from the port 161 and Vertical transmission through HWP 152 input from port 162 PBS 160 for branching and coupling wave signal photons to port 164, photon detector 323 to which signal photons output from port 163 of PBS 160 are input, and photon detection to which signal photons output from port 164 of PBS 160 are input Means 124.

  The polarization entangled light source 101 and the polarization entangled light source 102 output the polarization entangled photon pair shown in the above equation (1). The idler photon from the polarization entangled light source 101 is input to the node 111, and the idler photon from the polarization entangled light source 102 is input to the node 112. Signal photons output from the polarization entangled light source 101 and the polarization entangled light source 102 are input to the node 313 from the input ports 131 and 132, respectively.

  Signal photons from the input port 131 of the node 313 are input from the port 161 of the PBS 160 after passing through the HPW 151. Similarly, signal photons from the input port 132 are input from the port 162 of the PBS 160 after passing through the HWP 122. Photons output from the port 163 of the PBS 160 are detected by the photon detector 323. Photons output from the port 164 of the PBS 160 are detected by the photon detection means 124 having a polarization discrimination function. On the other hand, the photons input to the node 111 and the node 2 are detected by the photon detection means 121 and the photon detection means 122 having a polarization discrimination function, respectively.

  In the above configuration, as in the case of the first embodiment, the result of each node is obtained only when the combination of the HWP angle and polarization discrimination method at the node 3 matches the polarization discrimination method at the other nodes. Correlation occurs. Thereby, an encryption key can be generated between the nodes according to the following procedure.

  1. The node 313 randomly selects a combination of angles of crystal axes of the HWP 151 and the HWP 152 from one of (0 degree, 0 degree) and (22.5 degree, 22.5 degree) every certain unit time, Set to the selected angle.

  2. For each node, (111, 112, 313) is a random selection of one of {V, H} measurement and {+45, −45} measurement for each unit time, and polarization of input photons. To determine. Each node records the time when the photon is received (measured) and the measured polarization of the photon as data.

  3. Each node discloses the time when the photon is received and the type of measurement used at that time to all nodes.

  4). The node 313 discloses the time at which two or more nodes simultaneously receive photons and the angle of the crystal axis of each HWP at that time to all nodes.

  5. For each node, two or more nodes detect photons at the same time, and leave only the data when the combination of the polarization discrimination type used and each HWP angle of the node 313 matches, and discard other data. . That is, each node has the above 2. In the data recorded in the step 1, data whose photon reception time does not match the time disclosed by the node 313 is deleted. Further, at each time, each node (1) When the angle of the crystal axes of the HWP 151 and HWP 152 of the node 313 is set to 0 degree and {V, H} measurement is selected by the photon detection means, (2 ) The crystal axis angle of the HWP 151 and the HWP 152 at the node 313 is set to 45 degrees and {+45, −45} measurement is selected by the photon detection means, leaving other data and deleting other data.

  6). Each node generates a key using the remaining data. For example, “0” bit for V polarization measured using {V, H} measurement, “1” bit for H polarization, and “0” for +45 degree polarization measured using {+45, −45} measurement. "1" bit is assigned to "bit, -45 degree polarization".

  As described above, it is possible to share different encryption keys between any two nodes and three nodes among the nodes 111, 112, and 313.

  In the present embodiment, the case where the combination of the crystal axis angles of the HWP 151 and the HWP 152 is selected from (0 degrees, 0 degrees) and (22.5 degrees, 22.5 degrees) has been described. (Degrees, 0 degrees) and (-22.5 degrees, -22.5 degrees) may be selected.

It is a block diagram which shows the quantum key distribution system concerning the 1st Embodiment of this invention. It is a figure which shows a part of the data which each node recorded, and the data disclosed. It is a figure which shows the angle which the auxiliary node discloses to each node, and the angle of the crystal axis of each HWP at that time. It is a figure which shows the data remaining at each node, and the bit allocated to the data. It is a block diagram which shows the quantum key distribution system concerning the 2nd Embodiment of this invention. It is a block diagram which shows the quantum key distribution system concerning the 3rd Embodiment of this invention.

Explanation of symbols

100, 200, 300 Quantum key distribution system 101, 102 Polarized light source 111, 112, 113, 114, 213, 313 Node 121, 122, 123, 124 Photodetector with polarization discrimination function 130 Auxiliary node 131, 132 Input Port 133, 134 Output port 151, 152, 153, 154 Half-wave plate (HWP)
160 Polarized beam splitter (PBS)
161, 162, 163, 164 port 323 photon detector

Claims (5)

A quantum key generation system that generates a quantum key that is an encryption key for encrypting or decrypting data transmitted and received between nodes,
First and second polarization entangled photon pair generating means for generating a photon pair in a quantum entangled state with respect to polarization;
An auxiliary node;
Comprising first, second, third and fourth nodes;
The auxiliary node is
A first input port for inputting one photon of the photon pair output from the first polarization entangled photon pair generating means;
A second input port for inputting one photon of the photon pair output from the second polarization entangled photon pair generating means;
A first half-wave plate capable of rotating in the axial direction that transmits one photon of the photon pair input from the first input port;
An axially rotatable second half-wave plate that transmits one photon of the photon pair input from the second input port; and
First, second, a polarization beam splitter that have the third and fourth ports, the vertically polarized transmitted through the first said inputted from the port of the first half wave plate of One photon of the photon pair and one photon of the horizontally polarized photon pair transmitted through the second half-wave plate inputted from the second port are branched and coupled to the third port. And one second photon of the pair of horizontally polarized photons transmitted through the first half-wave plate inputted from the first port and the second 2 inputted from the second port. A polarization beam splitter for branching and coupling one photon of the pair of vertically polarized photons transmitted through the half-wave plate to the fourth port;
A third half-wave plate capable of rotating in the axial direction that transmits one photon of the photon pair output from the third port;
A fourth half-wave plate capable of rotating in the axial direction that transmits one photon of the photon pair output from the fourth port;
A first output port for outputting one photon of the photon pair transmitted through the third half-wave plate;
A second output port for outputting one photon of the pair of photons transmitted through the fourth half-wave plate;
The first node is:
The other photon of the photon pair from the first polarization entangled photon pair generating means is input, the measurement to determine whether the photon is longitudinally polarized wave or transversely polarized wave, and +45 degree polarization 1st polarization discriminating means for discriminating the polarization of the other photon of the inputted photon pair by randomly selecting either of the measurement for discriminating between the wave and the −45 degree polarization. ,
The second node is
The other photon of the photon pair from the second polarization entangled photon pair generating unit is input, and a measurement to determine whether the photon is longitudinal polarization or transverse polarization, and +45 degree polarization Second polarization discriminating means for discriminating the polarization of the other photon of the inputted photon pair by randomly selecting one of the measurements for discriminating between the wave and the −45 degree polarization. Prepared,
The third node receives one photon of the photon pair output from the first output port, and determines whether the photon is longitudinally polarized or transversely polarized, And a third polarization for discriminating the polarization of one photon of the input photon pair by randomly selecting one of the measurements for discriminating between +45 degree polarization and -45 degree polarization. With a discrimination means,
The fourth node receives one photon of the photon pair output from the second output port, and determines whether the photon is longitudinally polarized or transversely polarized, And a fourth polarization for discriminating the polarization of one photon of the input photon pair by randomly selecting one of the measurements for discriminating between +45 degree polarization and -45 degree polarization. With a discrimination means ,
Each of the first, second, third, and fourth nodes includes the time at which the polarization discriminating unit of the node receives the photon, the type of measurement selected at the time, and the deviation of the discriminated photon. Means for recording a wave and transmitting the time and the type of measurement selected at the time to each node other than the auxiliary node and the self;
The auxiliary node includes a time at which two or more of the first, second, third, and fourth nodes simultaneously receive photons and the first, second, third, and Means for transmitting the angle of the crystal axis of the fourth half-wave plate to the first, second, third and fourth nodes;
Each of the first, second, third, and fourth nodes has a photon detected simultaneously by two or more of the first, second, third, and fourth nodes; and When the polarization discrimination type used for detection of the photon and the combination of the angles of the crystal axes of the first, second, third, and fourth half-wave plates match, comprising a means for storing assigning predetermined bits of the detected photons, a predetermined bit of the allocated, quantum key generation, characterized in that the encryption key shared with the node that detects the photons simultaneously system. In the quantum key generation system,
The quantum key generation system according to claim 1, wherein the auxiliary node and the third or fourth node are integrated. A quantum key generation system that generates a quantum key that is an encryption key for encrypting or decrypting data transmitted and received between nodes,
First and second polarization entangled photon pair generating means for generating a photon pair in a quantum entangled state with respect to polarization;
Comprising first, second and third nodes;
The first node is:
One photon of the photon pair from the first polarization entangled photon pair generating means is input, measurement to determine whether the photon is longitudinally polarized wave or transversely polarized wave, and +45 degree polarization 1st polarization discriminating means for discriminating the polarization of one photon of the inputted photon pair by randomly selecting one of the measurements for discriminating between the wave and the −45 degree polarization. ,
The second node is
One photon of the photon pair from the second polarization entangled photon pair generating means is input, a measurement to determine whether the photon is longitudinally polarized or transversely polarized, and +45 degree polarization A second polarization discriminating means for discriminating one of the photons of the input photon pair by randomly selecting one of the measurements for discriminating between the wave and the −45 degree polarization. Prepared,
The third node is
A first input port for inputting the other photon of the photon pair output from the first polarization entangled photon pair generating means;
A second input port for inputting the other photon of the photon pair output from the second polarization entangled photon pair generating means;
A first half-wave plate capable of rotating in the axial direction and transmitting the other photon of the photon pair input from the first input port;
An axially rotatable second half-wave plate that transmits the other photon of the photon pair input from the second input port;
First, second, a polarization beam splitter that have the third and fourth ports, the vertically polarized transmitted through the first said inputted from the port of the first half wave plate of The other photon of the horizontally polarized photon pair transmitted through the second half-wave plate inputted from the other photon of the photon pair and the second port is branched and coupled to the third port. The second photon input from the second port and the other photon of the pair of horizontally polarized photons transmitted through the first half-wave plate input from the first port. A polarization beam splitter that branches and couples the other photon of the pair of vertically polarized photons transmitted through the half-wave plate to the fourth port;
Photon detection means for detecting the other photon of the photon pair output from the third port ;
The other photon of the photon pair output from the fourth port is input, and the measurement to determine whether the photon is longitudinally polarized wave or transversely polarized wave, and +45 degree polarized wave or −45 A third polarization discriminating means for randomly selecting one of the measurements for discriminating which degree of polarization is present, and discriminating the polarization of the other photon of the input photon pair ;
Each of the first, second, and third nodes records the time at which the polarization discriminating unit of the local node receives the photon, the type of measurement selected at the time, and the polarization of the discriminated photon. And means for transmitting the time and the type of measurement selected at the time to each node other than the auxiliary node and the self,
The third node includes a time at which two or more of the first, second, and third nodes simultaneously receive photons and the first and second half wavelengths at the time. Means for transmitting the angle of the crystal axis of the plate to the first and second nodes;
In each of the first, second, and third nodes, photons are simultaneously detected by two or more of the first, second, and third nodes, and are used to detect the photons. If the detected polarization discrimination type matches the combination of the crystal axis angles of the first and second half-wave plates, a predetermined bit is assigned to the detected photon and stored. A quantum key generation system , wherein the assigned predetermined bit is used as an encryption key shared with a node that simultaneously detects photons . A quantum key generation method for generating a quantum key that is an encryption key for encrypting or decrypting data transmitted and received between nodes,
First and second polarization entangled photon pair generating means for generating a photon pair in a quantum entangled state with respect to polarization, an auxiliary node, and first, second, third and fourth nodes ,
The auxiliary node outputs a first input port for inputting one photon of the photon pair output from the first polarization entangled photon pair generation unit, and is output from the second polarization entangled photon pair generation unit. A second input port for inputting one photon of the photon pair and a first half of the photon pair input from the first input port and transmitting the one photon of the photon pair and capable of rotating in the axial direction. A one-wave plate, a second half-wave plate capable of rotating in the axial direction that transmits one photon of the pair of photons input from the second input port, and first, second, second 3, and a polarization beam splitter that have a fourth port, the photon pairs one photon of the first said inputted from the port of the first vertical polarization transmitted through the half wave plate And transmitted through the second half-wave plate inputted from the second port. One photon of the horizontally polarized photon pair is branched and coupled to the third port, and the horizontally polarized photon transmitted through the first half-wave plate input from the first port One of the photons in the pair and one photon in the vertically polarized photon pair transmitted through the second half-wave plate inputted from the second port are branched and coupled to the fourth port. A wave beam splitter, a third half-wave plate capable of rotating in the axial direction that transmits one photon of the photon pair output from the third port, and an output from the fourth port A fourth half-wave plate capable of rotating in the axial direction, which transmits one photon of the photon pair, and one photon of the photon pair transmitted through the third half-wave plate. A first output port for outputting, and the photon transmitted through the fourth half-wave plate And a second output port for outputting one of the photons, the first node receives the other photon of the photon pair from said first polarization entangled photon pair generating means, to the photon On the other hand, either the measurement for discriminating whether it is longitudinal polarization or transverse polarization and the measurement for discriminating whether it is +45 degree polarization or -45 degree polarization are selected and inputted. First polarization discriminating means for discriminating the polarization of the other photon of the photon pair, and the second node detects the other photon of the photon pair from the second polarization entangled photon pair generating means. Input and select either measurement to determine whether the photon is longitudinally polarized or transversely polarized and measurement to determine whether it is +45 degree polarized wave or -45 degree polarized wave The second polarization for determining the polarization of the other photon of the input photon pair Wave detection means, and the third node inputs one photon of the photon pair output from the first output port, and is either longitudinally polarized or transversely polarized with respect to the photon. A measurement for discriminating between them and a measurement for discriminating between +45 degree polarization and -45 degree polarization, and the polarization of one photon of the inputted photon pair is discriminated. 3 polarization discriminating means, wherein the fourth node inputs one photon of the photon pair output from the second output port, and the photon is either longitudinally polarized or transversely polarized. Select one of the measurement to determine which is the +45 degree polarization or the −45 degree polarization to determine the polarization of one photon of the input photon pair. And a fourth polarization discriminating means for discriminating, the method comprising:
The auxiliary node is
The crystal axis angles of the first, second, third, and fourth half-wave plates are randomly set to 0 degree, 0 degree, 0 degree, and 0 degree, respectively, for each unit time. One of 5 degrees, 22.5 degrees, 22.5 degrees, and 22.5 degrees, or 0 degrees, 0 degrees, 0 degrees, and 0 degrees, -22.5 degrees, -22.5 degrees, -22 . Setting one of 5 degrees and -22.5 degrees;
Each of the first, second, third, and fourth nodes is
Any one of the measurement for determining whether the polarization is the longitudinal polarization or the transverse polarization, and the measurement for determining whether the +45 degree polarization or the −45 degree polarization is randomly performed at each unit time. a step of selecting, to determine the polarization of the input photon,
Time of receiving photons in the step of determining the polarization of the optical element, the type of selected measurement in the time, and record the polarization discriminated the photon, the time, and the measurement selected in the time transmitting a type to all the nodes other than the auxiliary node and self,
The auxiliary node is
The time at which two or more of the first, second, third, and fourth nodes simultaneously receive photons and the first, second, third, and fourth minutes at the time. Transmitting the angle of the crystal axis of the one-wave plate to the first, second, third, and fourth nodes;
Each of the first, second, third, and fourth nodes is
Two or more of the first, second, third, and fourth nodes detect photons at the same time, and the polarization discrimination type used to detect the photons, and the first, first, When the combination of the crystal axis angles of the second, third, and fourth half-wave plates coincides, a predetermined bit is allocated and stored in the detected photon, and the allocated predetermined A method for generating a quantum key, comprising the step of: using a bit as a cryptographic key shared with a node that simultaneously detects photons . A quantum key generation method for generating a quantum key that is an encryption key for encrypting or decrypting data transmitted and received between nodes,
First and second polarization entangled photon pair generating means for generating a photon pair in a quantum entangled state with respect to polarization, and first, second and third nodes,
The first node inputs one photon of the photon pair from the first polarization entangled photon pair generating means , and determines whether the photon is longitudinally polarized or transversely polarized The first polarization for discriminating the polarization of one photon of the input photon pair is selected. Wave detection means, and the second node inputs one photon of the photon pair from the second polarization entangled photon pair generation means, and the photon is either vertically polarized or transversely polarized. Select one of the measurement to determine which is the +45 degree polarization or the −45 degree polarization to determine the polarization of one photon of the input photon pair. A second polarization discriminating means for discriminating, wherein the third node comprises the first polarization A first input port for inputting the other photon of the photon pair output from the wave entangled photon pair generating means, and the other photon of the photon pair output from the second polarization entangled photon pair generating means are input. A second input port, a first half-wave plate capable of rotating in the axial direction and transmitting the other photon of the photon pair input from the first input port, and the second input and it transmits the other photon of the photon pair which is input from the port and chromatic 1 and half-wave plate rotatable second axial direction, the first, second, third, and fourth ports A polarization beam splitter, which is input from the other photon of the pair of vertically polarized photons transmitted through the first half-wave plate input from the first port and the second port The other of the horizontally polarized photon pairs transmitted through the second half-wave plate Branching and coupling a photon to the third port, the other photon of the horizontally polarized photon pair transmitted through the first half-wave plate input from the first port, and the second A polarization beam splitter that branches and couples the other photon of the pair of vertically polarized photons transmitted through the second half-wave plate input from the port to the fourth port; and the third port The photon detection means for detecting the other photon of the photon pair output from the photon and the other photon of the photon pair output from the fourth port are input, and longitudinal polarization or transverse polarization is applied to the photon. Of the other photon of the input photon pair is selected by randomly selecting one of the measurement for determining whether the photon is +45 degree polarization or the −45 degree polarization. A third polarization discriminating means for discriminating the polarization; The method
The third node is
The angles of the crystal axes of the first and second half-wave plates are randomly set to one of 0 degree and 22.5 degrees, or 0 degree and -22.5 degrees, every unit time. One step to set,
Each of the first, second, and third nodes is
Any one of the measurement for determining whether the polarization is the longitudinal polarization or the transverse polarization, and the measurement for determining whether the +45 degree polarization or the −45 degree polarization is randomly performed at each unit time. a step of selecting, to determine the polarization of the input photon,
Time of receiving photons in the step of determining the polarization of the optical element, the type of selected measurement in the time, and record the polarization discriminated the photon, the time, and the measurement selected in the time Sending the type of each to all nodes other than self ,
The third node is
The time at which two or more of the first, second, and third nodes simultaneously receive photons and the angle of the crystal axes of the first and second half-wave plates at that time. Transmitting to the first and second nodes;
Each of the first, second, and third nodes is
The photon is simultaneously detected by two or more of the first, second, and third nodes, and the polarization discrimination type used to detect the photon, and the first, second, and If the combination of angles of crystal axes of the third half-wave plate is coincident, a predetermined bit is allocated and stored in the detected photon, and the allocated predetermined bit is stored as a photon. A quantum key generation method comprising: a cryptographic key shared with nodes detected at the same time .

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