A Downlink Continuous-Variable Quantum Key Distribution Access Network Method

Abstract

The present invention discloses a method for downlink continuous variable quantum key distribution access network, belonging to the field of continuous variable quantum key distribution. Specifically, first, for the downlink access network, the transmitting end of the continuous variable quantum key distribution prepares the signal light by using the local local oscillator scheme or the accompanying local oscillator scheme, and sends it to the optical splitter to be evenly divided into n paths; every two different receiving ends are randomly grouped, and the respective local oscillator lights are obtained according to different local oscillator light schemes; then, the two receiving ends in each group respectively randomly select or use the shared random number to select the quadrature component of the homodyne measurement as the basis of the homodyne detector; each receiving end inputs its own local oscillator light and one randomly selected from the n paths of signal lights into the homodyne detector together, and outputs the differential current of each receiving end; finally, the detection results of the two receiving ends with different bases are selected and discarded, and the key information is obtained after post-processing; the retention ratio and efficiency of the key information of the present invention are 1.5-2 times that of the existing downlink access network.

Description

Technical Field

[0001] The present invention belongs to the field of continuous variable quantum key distribution, and particularly relates to a method for a downlink continuous variable quantum key distribution access network. Background Art

[0002] Continuous variable quantum key distribution uses the canonical components of an optical field as the carrier of key information. The Hilbert space where the quantum state for encoding is located is infinite-dimensional and continuous. Its advantages include the ability to use mature commercial fiber optic communication devices, having a series of advantages such as low cost, high reliability, and a relatively high security bit rate within metropolitan distances. Currently, continuous variable quantum key distribution is rapidly moving into the application stage. As the connection between the backbone network and user terminals, the access network plays an important role in network construction.

[0003] In the current downlink access network scheme for continuous variable quantum key distribution, a quantum signal containing key information is sent by a single transmitter, and multiple receivers can receive this signal. However, only one user at the receiver is allowed to retain the key, and other receivers need to discard the data to ensure the security of key distribution. This makes the downlink access network of continuous variable quantum key distribution inefficient and seriously wastes resources, which is not conducive to the implementation of a multi-user downlink access network in practical scenarios. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a method for a downlink continuous variable quantum key distribution access network, in which the receivers of continuous variable quantum key distribution are combined in pairs into a group, and the two receivers in each group randomly or according to a shared string of binary random numbers select homodyne detection bases to detect the signal light, and the key retention efficiency of the receivers is 1.5 - 2 times that of the prior art.

[0005] The method for a downlink continuous variable quantum key distribution access network described above includes the following steps:

[0006] Step 1: For the downlink access network, the transmitter of continuous variable quantum key distribution at the network node end prepares the signal light Q using a local oscillator scheme or a pilot tone oscillator scheme.

[0007] The transmitter signal light Q is signal light Q1 or signal light Q2, and the corresponding preparation schemes are the local oscillator scheme or the pilot tone oscillator scheme respectively.

[0008] The process for the local oscillator scheme is as follows:

[0009] First, the transmitter prepares a pulse signal through a laser or a combination of a laser and a modulator.

[0010] Then, modulate the pulse signal, modulate at least 50% of the pulse signal into quantum signal light, and modulate the remaining pulse signals into phase reference light; or modulate all the pulse signals into quantum signal light, and modulate the phase reference light at another frequency. During the modulation process, the modulator loads the key information into the quantum signal light;

[0011] Finally, couple the modulated quantum signal light and the phase reference light and pass them through an attenuator to attenuate them to a level that meets the security requirements and system performance requirements, obtaining the signal light Q1;

[0012] The process for the accompanying local oscillator scheme is as follows:

[0013] First, the transmitting end prepares a pulse signal through a laser, or a laser cooperating with an intensity modulator;

[0014] Subsequently, a beam splitter divides the pulse signal into quantum signal light and local oscillator light. Among them, the quantum signal light modulates the quantum state through a modulation module including an intensity modulator and a phase modulator, and prepares a continuous variable quantum signal pulse through an attenuator; during the modulation process, the modulator loads the key information into the quantum signal light;

[0015] Finally, couple the quantum signal light prepared by attenuation with the local oscillator light through a polarization combiner to obtain the signal light Q2;

[0016] Step 2: The transmitting end sends the prepared signal light Q to an optical splitter, which evenly decomposes it into n paths and then sends it to n receiving ends;

[0017] Step 3: Every two different receiving ends are randomly grouped into a pair, and according to the signal light prepared by different schemes, obtain the local oscillator light corresponding to each receiving end in this pair;

[0018] According to different local oscillator light schemes, the process for each receiving end to obtain the local oscillator light is different; specifically:

[0019] When the signal light prepared by the transmitting end is Q1, the two receiving ends respectively use local lasers, or lasers cooperating with modulators, to generate their respective corresponding local oscillator lights;

[0020] When the signal light prepared by the transmitting end is Q2, the two receiving ends respectively control the polarization through a dynamic polarization controller (DPC), and then separate the local oscillator light from the quantum signal light through a polarization beam splitter (PBS), thereby obtaining their respective local oscillator lights.

[0021] Step 4: For each pair of receiving ends, randomly select or use a shared random number to select the quadrature component of the homodyne measurement as the basis of the homodyne detector;

[0022] Each receiving end has a homodyne detector;

[0023] Randomly selecting a quadrature component means that both receiving ends A and B respectively and randomly select the x component or p component for homodyne detection;

[0024] Sharing a random number means that a string of random numbers of 0s and 1s is shared between the two receiving ends in each group, and the probabilities of 0 and 1 appearing in the random numbers are both 50%; for each bit in the random number, when the bit is 1, receiving end A measures the x component of homodyne detection, and the other receiving end B measures the p component of homodyne detection; when the bit is 0, the measurements of the two receiving ends are opposite to those when the random number is 1, that is, receiving end A measures the p component of homodyne detection, and the other receiving end B measures the x component of homodyne detection;

[0025] Step Five: For the two receiving ends in each group, the local oscillator light of each receiving end and a signal light randomly selected from n signal lights are input into their respective homodyne detectors together to obtain the differential current of each receiving end;

[0026] Specifically:

[0027] First, for receiving end A or B, the local oscillator light and a random signal light enter the 3dB coupler in the homodyne detector together for coupling;

[0028] Next, the phase difference between the local oscillator light and the signal light is controlled by a phase modulator: for the x component as the basis of homodyne detection at the receiving end, the phase difference between the local oscillator light and the signal light at this receiving end is modulated to 0 degrees; for the p component as the basis of homodyne detection at the receiving end, the phase difference between the local oscillator light and the signal light at this receiving end is modulated to 90 degrees;

[0029] Then, the 3dB coupler outputs two optical signals, which are converted into photocurrents by a photoelectric converter and subtracted to obtain the differential current containing key information corresponding to receiving end A or B, as the detection result of receiving end A or B;

[0030] Step Six: For the two cases of randomly selecting or using the shared random number to select the basis, the detection results of the two receiving ends in each group are selected and discarded, and the retained detection results are post-processed to obtain key information;

[0031] Specifically:

[0032] For the randomly selected homodyne detection basis, the two receiving ends announce their respective detection bases to each other and selectively retain the detection results: if the bases of the two receiving ends are different, the key information obtained by both is retained at the same time; if the bases of the two receiving ends are the same, according to the principle that the probability ratio of each side's selection and rejection is 1:1, the key information of one side to be discarded is selected; then, the sending end and the receiving end that retains the detection result extract the key information from the retained detection result through post-processing; therefore, the efficiency of the receiving end to retain key information is 1.5 times that of the existing downstream access network.

[0033] When using a shared random number to select the homodyne detection basis, two receiving ends respectively measure the x-component and p-component. The sending end and the receiving end that retains the detection result extract the key information from the retained detection result through post-processing. The key data is retained simultaneously, and there is no need to perform key selection. Therefore, the efficiency of the receiving end to retain the key information is twice that of the existing downlink access network.

[0034] The advantages of the present invention are as follows:

[0035] A downlink continuous variable quantum key distribution access network method combines two receiving ends into a group and all use homodyne detection. Compared with the prior art, when the sending end sends a quantum signal loaded with key information each time, the two receiving ends of each group can retain the key information at most simultaneously. The retention ratio and efficiency of the key information are 1.5 - 2 times that of the existing downlink access network. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic structural diagram of the downlink continuous variable quantum key distribution access network of the present invention;

[0037] Figure 2 It is a flowchart of a downlink continuous variable quantum key distribution access network method of the present invention;

[0038] Figure 3 It is a schematic structural diagram of the continuous variable quantum key distribution sending end of the present invention when using the local local oscillator scheme;

[0039] Figure 4 It is a schematic structural diagram of the receiving end of the present invention when randomly selecting the homodyne detection basis and performing detection when using the local local oscillator scheme;

[0040] Figure 5 It is a schematic structural diagram of the continuous variable quantum key distribution sending end of the present invention when using the along-path local oscillator scheme;

[0041] Figure 6 It is a schematic structural diagram of the receiving end of the present invention when randomly selecting the homodyne detection basis and performing detection when using the along-path local oscillator scheme;

[0042] Figure 7 It is a schematic structural diagram of the homodyne detector adopted by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0043] The following makes a specific description of the specific embodiments of the present invention according to the drawings.

[0044] It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made; these all belong to the protection scope of the present invention.

[0045] A method for downlink continuous variable quantum key distribution access network according to the present invention is as follows Figure 1 As shown, for the access network with a downlink structure, the transmitter of continuous variable quantum key distribution at the node end prepares the signal light loaded with key information, and evenly decomposes the signal light into n paths through an optical splitter, and sends the key to the receivers of continuous variable quantum key distribution of n user terminals. Every two receivers form a group, with a total of groups; the two receivers in each group randomly or according to a shared string of binary random numbers select the homodyne detection basis to detect the signal light, and the key retention efficiency of the receiver is 1.5 - 2 times that of the prior art.

[0046] The method for downlink continuous variable quantum key distribution access network as described above is as follows Figure 2 As shown, it includes the following steps:

[0047] Step 1: For the downlink access network, the transmitter of continuous variable quantum key distribution at the network node end prepares the signal light Q using the local local oscillator scheme or the accompanying local oscillator scheme;

[0048] The transmitter signal light Q is signal light Q1 or signal light Q2, and the corresponding preparation schemes are the local local oscillator scheme or the accompanying local oscillator scheme respectively;

[0049] The schematic diagram of the structure of the continuous variable quantum key distribution transmitter is as Figure 3 and Figure 5 shown;

[0050] As Figure 3 shown, the process for the local local oscillator scheme is as follows:

[0051] First, the transmitter prepares a pulse signal through a laser or a laser cooperating with an intensity modulator;

[0052] Then, the pulse signal is modulated, at least 50% of the pulse signals are modulated into quantum signal light, and the remaining pulse signals are modulated into phase reference light, or all the pulse signals are modulated into quantum signal light, and the phase reference light is modulated at another frequency. The modulator loads the key information into the quantum signal light during the modulation process;

[0053] Finally, the modulated quantum signal light and the phase reference light are coupled and passed through an attenuator, and attenuated to a level that meets the security requirements and system performance requirements to obtain the signal light Q1;

[0054] As Figure 5 shown, the process for the accompanying local oscillator scheme is as follows:

[0055] First, the transmitter prepares a pulse signal through a laser or a laser and an intensity modulator;

[0056] Subsequently, the beam splitter divides the pulsed signal into a quantum signal light and a local oscillator light. Among them, the quantum signal light modulates the quantum state through a modulation module including an intensity modulator and a phase modulator, and prepares a continuous variable quantum signal pulse through an attenuator; the modulation module loads the key information into the quantum signal light during the modulation process;

[0057] Finally, the quantum signal light prepared by attenuation is coupled with the local oscillator light through a polarization combiner to obtain the signal light Q2;

[0058] Step 2: The sending end sends the prepared signal light Q to an optical splitter, which is evenly decomposed into n paths and then sent to n receiving ends;

[0059] Step 3: Every two different receiving ends are randomly grouped into a pair. For each pair of receiving ends A and B, the local oscillator light corresponding to each receiving end in the pair is obtained according to the signal light prepared by different schemes;

[0060] The local oscillator light can be continuous light or pulsed light;

[0061] According to different local oscillator light schemes, the process for each receiving end to obtain the local oscillator light is different; specifically:

[0062] As Figure 4 shown, when the signal light prepared by the sending end is Q1, the two receiving ends respectively use local lasers, or lasers in cooperation with modulators, to generate their respective corresponding local oscillator lights;

[0063] As Figure 6 shown, when the signal light prepared by the sending end is Q2, the two receiving ends respectively control the polarization through a dynamic polarization controller (DPC), and then separate the local oscillator light from the quantum signal light through a polarization beam splitter (PBS), so as to obtain their respective local oscillator lights.

[0064] Step 4: For each pair of receiving ends, randomly select or use a shared random number to select the quadrature component of homodyne measurement as the basis of the homodyne detector;

[0065] Each receiving end corresponds to a homodyne detector;

[0066] Randomly selecting the quadrature component means that both receiving ends A and B respectively randomly select the x component or p component of homodyne detection; the probability of selecting the x component or p component each time is 50%.

[0067] The shared random number means that a string of random numbers of 0 and 1 bits is shared between each pair of receiving ends; the probability of 0 and 1 appearing in the random number is 50% each; the random number is used to control the measurement of the signal quadrature component by the homodyne detector.

[0068] For each bit in the random number, when the bit is 1, receiving end A measures the x component of homodyne detection, and the other receiving end B measures the p component of homodyne detection; when the bit is 0, the measurements of the two receiving ends are opposite to those when the random number is 1, that is, receiving end A measures the p component of homodyne detection, and the other receiving end B measures the x component of homodyne detection; the shared random number bit string is used to control the measurement of the signal regular component by the homodyne detector.

[0069] Step Five: For the two receiving ends in each group, the local oscillator light of each receiving end and a signal light randomly selected from n signal lights are input into their respective homodyne detectors together to obtain the differential current of each receiving end.

[0070] Specifically:

[0071] As Figure 6 and Figure 7 shown, first, the local oscillator light in receiving end A and a signal light randomly selected from n signal lights enter the 3dB coupler in the homodyne detector together for coupling.

[0072] Then, for different bases, the phase difference between the local oscillator light and the signal light is controlled by the phase modulator: for the base of the x component of homodyne detection at the receiving end, the phase difference between the local oscillator light and the signal light of this receiving end is modulated to 0 degrees; for the base of the p component of homodyne detection at the receiving end, the phase difference between the local oscillator light and the signal light of this receiving end is modulated to 90 degrees.

[0073] Next, the 3dB coupler outputs two optical signals, which are converted into photocurrents by the photoelectric converter and subtracted to obtain the differential current containing the key information corresponding to receiving end A as the detection result of receiving end A.

[0074] For receiving end B, the processing process is the same as that of receiving end A. Specifically: first, the local oscillator light and a signal light randomly selected from n signal lights enter the 3dB coupler in the homodyne detector together for coupling.

[0075] For different bases, the phase difference between the local oscillator light and the signal light is controlled by the phase modulator; for the base of the x component of homodyne detection at the receiving end, the phase difference between the local oscillator light and the signal light of this receiving end is modulated to 0 degrees; for the base of the p component of homodyne detection at the receiving end, the phase difference between the local oscillator light and the signal light of this receiving end is modulated to 90 degrees.

[0076] Next, the 3dB coupler outputs two optical signals, which are converted into photocurrents by the photoelectric converter and subtracted to obtain the differential current containing the key information corresponding to receiving end B as the detection result of receiving end B.

[0077] Further, a local laser or a local laser combined with an intensity modulator is used to generate a local oscillator optical pulse; according to the phase change of the reference light, the phase modulator compensates the phase difference to maintain the same frequency, the same polarization, and a constant phase difference between the signal light and the local oscillator light;

[0078] Step Six: For the two cases of randomly selecting or using a shared random number to select a basis, the detection results of the two receiving ends in each group are selected and discarded, and the retained detection results are normalized to obtain key information;

[0079] Specifically:

[0080] For the homodyne detection basis randomly selected, the two receiving ends announce the detection bases selected during their respective homodyne detections to each other, and selectively retain the detection results: If the homodyne detection bases of the two receiving ends are different, the detection results obtained by both are retained; if the bases of the two receiving ends are the same, according to the principle that the probability ratio of each side's selection and rejection is 1:1, the detection result of the rejected side is selected. For example: Only the first detection end retains the detection result during odd-numbered measurements, and only the second detection end retains the detection result during even-numbered measurements. Thereafter, the sending end and the receiving end that retains the detection result extract the key information from the retained detection results through post-processing steps. Therefore, the efficiency of the receiving end retaining the key information is 1.5 times that of the existing downlink access network.

[0081] For the case of using a shared random number to select the homodyne detection basis, the two receiving ends measure the x component and the p component respectively. Thereafter, the sending end and the receiving end that retains the detection result extract the key information from the retained detection results through post-processing steps. The key data is retained simultaneously, and there is no need to perform key selection and rejection. Therefore, the efficiency of the receiving end retaining the key information is 2 times that of the existing downlink access network.

[0082] Through the above measurement strategy, each time the sending end sends a quantum signal loaded with key information, at most two receiving ends can retain the key information, and the retention ratio and efficiency of the key information are at most twice as high as those of the existing downlink access network. The present invention lays a foundation for the large-scale practical application of the continuous variable quantum key distribution access network.

[0083] As can be seen from the above examples, the present invention uses mature commercial optical devices to implement a method for a downlink continuous variable quantum key distribution access network under room temperature conditions. Although the content of the present invention has been introduced in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present invention. After those skilled in the art have read the above content, various modifications and substitutions to the present invention will be obvious. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims

1. A method for a downlink continuous variable quantum key distribution access network, characterized in that Including the following steps: First, for the downlink access network, the transmitter of continuous variable quantum key distribution at the network node side prepares the signal light Q by using the local local oscillator scheme or the accompanying local oscillator scheme respectively, and sends the prepared signal light Q to the optical splitter. After being evenly decomposed into n paths, it is sent to n receivers; Then, every two different receivers are randomly grouped into a group. According to the signal light prepared by different methods, the local oscillator light corresponding to each receiver in this group is obtained respectively; for the two receivers in each group, the quadrature component of homodyne measurement is randomly selected or selected by using a shared random number as the basis of the homodyne detector; Specifically: Randomly selecting the quadrature component means that both receivers A and B randomly select the x component or the p component of homodyne detection respectively; The shared random number means that a string of random numbers of 0 and 1 bits is shared between the two receivers in each group, and the probabilities of 0 and 1 appearing in the random number are each 50%; for each bit in the random number, when the bit is 1, receiver A measures the x component of homodyne detection and the other receiver B measures the p component of homodyne detection; When the bit is 0, the measurements of the two receivers are opposite to those when the random number is 1, that is, receiver A measures the p component of homodyne detection and the other receiver B measures the x component of homodyne detection; Next, the local oscillator light of each receiver and one path randomly selected from the n paths of signal light are input into their respective homodyne detectors together, and the differential current of each receiver is obtained as the detection result; Finally, in the two cases of randomly selecting or using a shared random number to select the basis, the detection results of the two receivers in each group are selected and discarded, and the retained detection results are post-processed to obtain the key information; For the randomly selected homodyne detection basis, the two receivers announce their respective detection bases to each other and selectively retain the detection results: if the bases of the two receivers are different, the key information obtained by both is retained at the same time; if the bases of the two receivers are the same, according to the principle that the probability ratio of each party's selection and discard is 1:1, the key information of the discarded party is selected; the transmitter and the receiver retaining the detection result extract the key information from the retained detection result through post-processing; Therefore, the efficiency of the receiver retaining the key information is 1.5 times that of the existing downlink access network; When using a shared random number to select the homodyne detection basis, the two receivers measure the x component and the p component respectively. The transmitter and the receiver retaining the detection result extract the key information from the retained detection result through post-processing, and the key data is retained at the same time, and there is no need to perform key selection and discard. Therefore, the efficiency of the receiver retaining the key information is 2 times that of the existing downlink access network.

2. The downlink continuous variable quantum key distribution access network method according to claim 1, wherein The signal light Q is signal light Q1 or signal light Q2, and the corresponding preparation schemes are respectively: The process for the local local oscillator scheme is: First, the transmitter prepares a pulse signal through a laser or a laser combined with a modulator; Then, modulate the pulse signal, modulate at least 50% of the pulse signal into quantum signal light, and modulate the remaining pulse signal into phase reference light; or modulate all the pulse signals into quantum signal light, and modulate the phase reference light at another frequency. The modulator loads the key information into the quantum signal light during the modulation process; Finally, couple the modulated quantum signal light and the phase reference light and pass them through an attenuator to attenuate them to a level that meets the security requirements and system performance requirements, obtaining signal light Q1; The process for the accompanying local oscillator scheme is as follows: First, the transmitting end prepares a pulse signal through a laser, or a laser in cooperation with an intensity modulator; Subsequently, a beam splitter divides the pulse signal into quantum signal light and local oscillator light. Among them, the quantum signal light modulates the quantum state through a modulation module including an intensity modulator and a phase modulator, and prepares a continuous variable quantum signal pulse through an attenuator; The modulator loads the key information into the quantum signal light during the modulation process; Finally, couple the quantum signal light prepared by attenuation with the local oscillator light through a polarization combiner to obtain signal light Q2.

3. A downlink continuous variable quantum key distribution access network method according to claim 1, characterized in that For the signal light prepared by the different methods, the specific method for obtaining the local oscillator light of each receiving end is as follows: When the signal light prepared by the transmitting end is Q1, the two receiving ends respectively use local lasers, or lasers in cooperation with modulators, to generate their respective corresponding local oscillator lights; When the signal light prepared by the transmitting end is Q2, the two receiving ends respectively control the polarization through dynamic polarization controllers, and then separate the local oscillator light from the quantum signal light through a polarization beam splitter, thereby obtaining their respective local oscillator lights.

4. The downlink continuous variable quantum key distribution access network method according to claim 1, wherein Each of the receiving ends has a homodyne detector.

5. A method for a downlink continuous variable quantum key distribution access network according to claim 1, characterized in that The specific process for each group of two receiving ends to obtain the detection result is as follows: First, for receiving end A or B, the local oscillator light and a randomly selected path of signal light enter the 3dB coupler of the homodyne detector for coupling; Next, control the phase difference between the local oscillator light and the signal light through a phase modulator: for the x component as the basis of homodyne detection at the receiving end, modulate the phase difference between the local oscillator light and the signal light at this receiving end to 0 degrees; for the p component as the basis of homodyne detection at the receiving end, modulate the phase difference between the local oscillator light and the signal light at this receiving end to 90 degrees; Then, the 3dB coupler outputs two optical signals, which are converted into photocurrents by a photoelectric converter and subtracted to obtain the differential current containing the key information corresponding to receiving end A or B, as the detection result of receiving end A or B.

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