Quantum communication system, method and device

Abstract

The invention provides a quantum communication system, method and device, and is applied to the technical field of quantum communication. The quantum communication system comprises a first device and a second device which are connected through an optical fiber link, the first device generates an initial optical signal and a local oscillation optical signal, sends the initial optical signal to the second device, receives a quantum optical signal from the second device, and sends the quantum optical signal to the second device. Performing coherent detection and demodulation based on the local oscillator optical signal and the quantum optical signal to generate a quantum key, monitoring a preset parameter in the coherent detection and demodulation process, and adjusting the local oscillator optical signal to enable the preset parameter to reach a preset value; and the second equipment receives the initial optical signal, performs quantum state modulation on the initial optical signal to form a quantum optical signal, and sends the quantum optical signal to the first equipment. According to the embodiment of the invention, the deployment cost of the quantum communication system can be reduced, and the optimization of equipment power consumption and detection efficiency in the key distribution process is realized.

Description

Technical Field

[0001] The present disclosure relates to the field of quantum communication technology, and in particular, to a quantum communication system, method and device. Background Art

[0002] QKD (Quantum Key Distribution) is the product of the combination of cryptography and quantum mechanics. It uses quantum states as information carriers and, based on the uncertainty relation and quantum no-cloning theorem of quantum mechanics, enables the communicating sender and receiver to share keys through quantum channels.

[0003] In the process of quantum key distribution, the two devices, the sender and the receiver, need to negotiate to determine the quantum key. Generally speaking, the sender generates an initial optical signal and modulates the initial optical signal in a quantum state, and sends the modulated quantum optical signal to the receiver through an optical fiber link (also called a quantum channel). After receiving the quantum optical signal, the receiver uses the local oscillator optical signal generated by itself to perform coherent detection and demodulation on the quantum optical signal, and then performs post-processing information interaction with the sender through a classical channel to determine the quantum key.

[0004] This key negotiation method requires light source equipment to be installed on both the transmitter and the receiver, and requires additional frequency locking and phase synchronization, which is costly and hinders the layout of large-scale quantum communication systems.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0006] The purpose of the present disclosure is to provide a quantum communication system, method and device for reducing the layout cost of the quantum communication system.

[0007] According to a first aspect of an embodiment of the present disclosure, a quantum communication system is provided, comprising a first device and a second device connected via an optical fiber link, wherein the first device generates an initial optical signal and a local oscillator optical signal, and sends the initial optical signal to the second device, and receives a quantum optical signal from the second device, performs coherent detection and demodulation based on the local oscillator optical signal and the quantum optical signal to generate a quantum key, monitors preset parameters during the coherent detection and demodulation process, and adjusts the local oscillator optical signal so that the preset parameters reach preset values; the second device receives the initial optical signal, performs quantum state modulation on the initial optical signal to form the quantum optical signal, and sends the quantum optical signal to the first device.

[0008] According to a second aspect of an embodiment of the present disclosure, a quantum communication method is provided, which is applied to the quantum communication system as described above, including: generating an initial light signal and a local oscillator light signal by a first device; sending the initial light signal from the first device to the second device; performing quantum state modulation on the initial light signal by the second device to form a quantum light signal; sending the quantum light signal from the second device to the first device; performing coherent detection and demodulation on the first device based on the local oscillator light signal and the quantum light signal to generate a quantum key, monitoring preset parameters in the coherent detection and demodulation process, and adjusting the local oscillator light signal so that the preset parameters reach preset values.

[0009] According to a third aspect of an embodiment of the present disclosure, a quantum communication device is provided, including: a light source module, used to generate an initial light signal and a local oscillator light signal; a coherent detection and demodulation module, used to receive the local oscillator light signal and the quantum light signal, and perform coherent detection and demodulation on the quantum light signal based on the local oscillator light signal to generate the quantum key; a first monitoring module, used to adjust the power of the initial light signal, and send the adjusted initial light signal to a second device; a first control module, connected to the coherent detection and demodulation module and the light source module, used to monitor preset parameters in the coherent detection and demodulation process of the coherent detection and demodulation module, and adjust the local oscillator light signal sent by the light source module according to the preset parameters so that the preset parameters reach preset values.

[0010] According to a fourth aspect of an embodiment of the present disclosure, a quantum communication device is provided, comprising: a quantum state modulation module, used to perform quantum state modulation on an initial optical signal from a first device to form a quantum optical signal; a second monitoring module, used to receive the initial optical signal from the first device, adjust the power of the initial optical signal, and send the adjusted initial optical signal to the quantum state modulation module, and receive the quantum optical signal from the quantum state modulation module, adjust the power of the quantum optical signal, and send the adjusted quantum optical signal to the first device.

[0011] The disclosed embodiment uses a light source to generate an initial optical signal and a local oscillator optical signal, and respectively sets the light source and quantum state modulation functions on a first device and a second device, thereby breaking through the traditional functional definition of a transmitting end and a receiving end, and can greatly save the cost of the second device. It also allows the local oscillator optical signal to be adjusted in real time during coherent detection and demodulation, thereby optimizing the coherent detection and demodulation effects, and optimizing the device power consumption and detection efficiency.

[0012] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification are used to explain the principles of the present disclosure. Obviously, the accompanying drawings described below are only some embodiments of the present disclosure, and for ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0014] Figure 1 is a schematic diagram of a quantum communication system in an exemplary embodiment of the present disclosure.

[0015] Figure 2 Schematic diagram of the structure of the first device 1 and the second device 2 in an exemplary embodiment of the present disclosure.

[0016] Figure 3 Schematic diagram of the interaction of various modules in the quantum communication system 100 in the exemplary embodiment of the present disclosure.

[0017] Figure 4 It is a flow chart of the quantum communication method in the embodiment of the present disclosure.

[0018] Figure 5 It is a schematic diagram of a quantum communication device in an embodiment of the present disclosure.

[0019] Figure 6 It is a schematic diagram of a quantum communication device in an embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in a variety of forms and should not be construed as being limited to the examples set forth herein; on the contrary, these embodiments are provided so that the present disclosure will be more comprehensive and complete, and the concepts of the example embodiments are fully conveyed to those skilled in the art. The described features, structures, or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be practiced while omitting one or more of the specific details, or other methods, components, devices, steps, etc. may be adopted. In other cases, known technical solutions are not shown or described in detail to avoid obscuring various aspects of the present disclosure.

[0021] In addition, the accompanying drawings are only schematic diagrams of the present disclosure, and the same reference numerals in the drawings represent the same or similar parts, so their repeated description will be omitted. Some of the block diagrams shown in the accompanying drawings are functional entities, which do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented in software form, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontroller devices.

[0022] The exemplary embodiments of the present disclosure are described in detail below with reference to the accompanying drawings.

[0023] Figure 1 is a schematic diagram of a quantum communication system in an exemplary embodiment of the present disclosure.

[0024] refer to Figure 1 , the quantum communication system 100 may include:

[0025] The first device 1 generates an initial optical signal and a local oscillator optical signal, and sends the initial optical signal to the second device 2, and receives a quantum optical signal from the second device 2, performs coherent detection and demodulation based on the local oscillator optical signal and the quantum optical signal to generate a quantum key, monitors a preset parameter in the coherent detection and demodulation process, and adjusts the local oscillator optical signal so that the preset parameter reaches a preset value;

[0026] The second device 2 receives the initial optical signal, performs quantum state modulation on the initial optical signal to form a quantum optical signal, and sends the quantum optical signal to the first device 1.

[0027] The first device 1 and the second device 2 are both quantum communication devices, connected by an optical fiber link, which includes a quantum channel and a classical channel. The first device 1 and the second device 2 transmit an initial optical signal and a quantum optical signal through the quantum channel, and perform post-processing negotiation through the classical channel to determine the quantum key.

[0028] The quantum communication system provided by the embodiments of the present disclosure can be used to implement both the traditional QKD system and the CV-QKD (Continuous Variable QKD) system. Compared with the traditional QKD system, CV-QKD not only has a higher key rate, but also has better compatibility with traditional coherent optical communications. The Hilbert space where the quantum state used for encoding by the CV-QKD protocol is infinite-dimensional and continuous, usually a Gaussian random number that satisfies the continuous distribution, and the carrier of information is no longer the polarization or phase of a single photon, but the canonical component of the light field state ("position" and "momentum" in the phase space).

[0029] Whether it is a traditional QKD system or a CV-QKD system, the initial optical signal is used to perform quantum state modulation to form a quantum optical signal. For example, the initial optical signal can be modulated by a modulator, such as changing the polarization state or phase of the light, so as to load quantum information. Different systems have different quantum state modulation methods, which will not be described in detail here.

[0030] The local oscillator light signal is used for coherent detection and demodulation of quantum light signals. In this process, the frequency and phase of the local oscillator light signal need to be precisely controlled to ensure efficient coherent detection with the quantum light signal. During the coherent detection process, the local oscillator light signal interferes with the received quantum light signal in the detector, converting the weak quantum light signal information into detectable electrical signal changes.

[0031] Finally, according to the demodulation result, the first device 1 and the second device 2 perform processing negotiation through the classical channel to determine the quantum key.

[0032] In the traditional QKD system, the post-processing negotiation content transmitted through the classical channel includes: signal measurement results, error correction information, key extraction algorithm, etc. After a certain post-processing step, both parties generate a quantum key based on the quantum key distribution protocol (such as the BB84 protocol or other quantum key distribution protocols). In order to further improve the reliability of the key, the first device 1 and the second device 2 can use the classical channel to exchange error checking information, and perform error correction and error correction processing on the preliminary key information obtained based on operations such as quantum optical signal measurement.

[0033] In the CV-QKD system, the post-processing negotiation content transmitted through the classical channel includes: statistical information of the canonical components of the light field (such as orthogonal amplitude and orthogonal phase) measured by the first device 1 and the second device 2, including data such as mean, variance and covariance. Based on this information, both parties will perform parameter estimation to determine the noise and loss introduced by the quantum channel. Afterwards, a series of complex error correction algorithms are used to coordinate the differences in the data of both parties, because during the signal transmission process, due to factors such as channel noise and device non-ideality, there will be deviations between the canonical components of the light field measured by the receiving end and those prepared by the sending end. After completing the error correction, a privacy amplification operation is also required to remove information that may be obtained by eavesdroppers, thereby generating a secure quantum key. In order to ensure the security and effectiveness of the entire process, the two parties may also exchange some verification information about the data processing process and parameter information of specific algorithms to ensure the consistency and accuracy of the key generation process between the two parties, so that the quantum key finally generated can meet the high requirements of confidential communication.

[0034] The above introduction to the quantum key generation process is only an example. In practical applications, the embodiments of the present disclosure can also be used to form QKD systems composed of other principles, which are not listed here one by one.

[0035] In some embodiments, the first device 1 is set in the operator's own machine room (for easy management and maintenance), and the second device 2 is set in the user's machine room (not easy to enter), so as to achieve centralized deployment and maintenance of the first device 1 and simplify the cost and maintenance of the second device 2. Since the second device 2 does not have a light source and is only used for modulation, the deployment and maintenance cost of the second device 2 is low, which can greatly reduce the deployment cost when deploying a large-scale quantum communication system.

[0036] Right now, Figure 1 The illustrated embodiment places the light source and the coherent detection and demodulation functions on the same side, and places the quantum state modulation function on the other side to achieve the distribution of quantum keys, thereby realizing the reuse of the light source. While maintaining the efficiency of coherent detection and demodulation, it allows the device at one end of the system to not need to be equipped with a light source, thereby reducing the setup cost and maintenance cost of the device at one end that is difficult to maintain, especially when deploying large-scale quantum communication systems, which can greatly reduce the deployment cost of the quantum communication system.

[0037] Next, exemplary structures of the first device 1 and the second device 2 are introduced.

[0038] Figure 2 is a schematic diagram of the structure of the first device 1 and the second device 2 in the exemplary embodiment of the present disclosure. It should be noted that, Figure 2 The structure shown is only an example. In actual application, the structure of the first device 1 and the second device 2 can be realized as long as Figure 1 The functions of the first device 1 and the second device 2 of the illustrated embodiment are sufficient.

[0039] refer to Figure 2 In some embodiments, the first device 1 may include:

[0040] The light source module 11 is used to generate an initial light signal S1 and a local oscillator light signal S0;

[0041] A coherent detection and demodulation module 12, used to receive the local oscillator light signal S0 and the quantum light signal S2, and perform coherent detection and demodulation on the quantum light signal S2 based on the local oscillator light signal S0 to generate a quantum key;

[0042] A first monitoring module 13, configured to adjust the power of the initial optical signal S1, and send the adjusted initial optical signal S1 to the second device 2;

[0043] The first control module 14 is connected to the coherent detection and demodulation module 12 and the light source module 11, and is used to monitor the preset parameters in the coherent detection and demodulation process of the coherent detection and demodulation module 12, and adjust the local oscillator light signal S0 sent by the light source module according to the preset parameters so that the preset parameters reach the preset values.

[0044] The second device 2 may include:

[0045] The quantum state modulation module 21 is used to perform quantum state modulation on the initial optical signal S1 to form a quantum optical signal S2;

[0046] The second monitoring module 22 is used to receive the initial optical signal S1 from the first device 1, adjust the power of the initial optical signal S1, and send the adjusted initial optical signal S1 to the quantum state modulation module 21, and receive the quantum optical signal S2 from the quantum state modulation module 21, adjust the power of the quantum optical signal S2, and send the adjusted quantum optical signal S2 to the first device 1.

[0047] It should be noted that in order to control and coordinate the operation of the quantum state modulation module 21 and the second monitoring module 22, the second device 2 may also be provided with a second control module (not shown) so that the quantum state modulation module 21 and the second monitoring module 22 can operate in coordination.

[0048] Exemplarily, since the light source module 1 needs to be able to generate an initial light signal and a local oscillator light signal, the light source module 1 may be a tunable laser light source or an optical parametric oscillator (OPO) light source.

[0049] Tunable laser light sources are a feasible light source. For example, by using an external cavity diode laser (ECDL), a narrow line width and a relatively stable output frequency can be provided to generate an initial optical signal. For the generation of local oscillator optical signals, a portion of light can be separated from the main optical path by a splitter (such as a fiber coupler), and then this portion of light can be made into a suitable local oscillator light by adjusting the optical path length (such as using a fiber delay line) or changing the frequency of the light (such as using an acousto-optic modulator).

[0050] An optical parametric oscillator (OPO) light source is a nonlinear optical device that can convert pump light into quantum light signals and idle light. Under certain conditions, the quantum light signal can be used as the initial light signal for loading quantum information, and the idle light can be used as the local oscillator light after appropriate processing (such as frequency adjustment, power amplification or attenuation, etc.). For example, by adjusting the pump power of the OPO and the parameters of the crystal, the frequency, power and other characteristics of the quantum light signal and the idle light can be controlled to meet the requirements of the initial light signal and the local oscillator light signal in the QKD system.

[0051] The coherent detection and demodulation module 12 performs coherent detection and demodulation on the quantum light signal based on the local oscillator light signal. In an exemplary embodiment, the coherent detection and demodulation module 12 may include a detector, a balanced mixer, and a local oscillator. The detector usually adopts a highly sensitive photodetector, such as a superconducting nanowire detector or an avalanche photodiode detector, which can quickly and accurately convert the optical signal into an electrical signal for subsequent signal processing. The balanced mixer plays a key role in the entire system. It mixes the received quantum light signal with the local oscillator light generated by the local oscillator. The local oscillator is responsible for providing a stable and frequency-accurately adjustable local oscillator light, whose frequency matches the frequency of the quantum light signal. By adjusting the parameters of the local oscillator, the mixing effect can be optimized, thereby effectively extracting information from the quantum light signal. During the signal processing process, the electrical signal output from the detector will generate an intermediate frequency signal containing quantum state information after the mixing operation of the balanced mixer. The intermediate frequency signal will be further transmitted to the subsequent signal processing circuit for a series of operations such as filtering, amplification, and digitization to remove noise interference and extract valuable key information-related data, providing strong support for the final generation of secure and reliable quantum keys.

[0052] In short, during the coherent detection process, the local oscillator light signal and the quantum light signal interfere with each other in the detector of the coherent detection and demodulation module 12, and the signal information of the weak quantum light signal is converted into a detectable electrical signal change. Those skilled in the art can use general methods to implement the coherent detection and demodulation functions, and the present disclosure does not impose any special restrictions on this.

[0053] Compared with the QKD device in the related technology, the initial optical signal of the embodiment of the present disclosure is not modulated in the local device that generates the initial optical signal, but is sent to the other end for modulation. Therefore, a first monitoring module 13 is set to detect the initial optical signal to ensure that when the initial optical signal reaches the second device 2, the minimum modulation optical power requirement of the second device 2 is met, thereby reducing the power consumption of the light source, that is, satisfying the first preset condition.

[0054] In an exemplary embodiment, the first preset condition includes that the power of the initial optical signal is greater than or equal to the third power, and the light source module 11 adjusts the power of the initial optical signal including: according to the power detection result of the initial optical signal by the first monitoring module 13, adjusting the light source module 11 so that the power of the initial optical signal reaches the first power, wherein the optical attenuation power of the optical fiber link from the first device 1 to the second device 2 is the second power, the sum of the minimum modulated optical power of the second device 2 and the second power is the third power, the first power is greater than or equal to the third power, and the difference between the first power and the third power is less than the preset value.

[0055] In this embodiment, the optical attenuation power of the optical fiber link can be measured experimentally, and different types of quantum communication systems and different device distances correspond to different optical attenuation powers of the optical fiber link between the first device 1 and the second device 2. When setting the first device 1, the minimum modulated optical power required by the second device 2 (mainly the quantum state modulation module 21) can be obtained first, and then the optical attenuation power of the optical fiber link between the first device 1 and the second device 2 can be obtained (which can be measured in advance), and finally the sum of the two is set as the third power.

[0056] In the process of generating the initial optical signal, the light source module 11 can be directly set to send an initial optical signal with an optical power slightly greater than the third power, and obtain feedback from the second device 2. If the second device 2 successfully receives the initial optical signal and determines that it meets the minimum modulated optical power, the optical power of the initial optical signal can continue to be reduced until the critical point at which the initial optical signal reaching the second device 2 does not meet the minimum modulated optical power of the second device 2 is found, and the optical power of the minimum initial optical signal that can meet the minimum modulated optical power of the second device 2 is set as the optical power of the initial optical signal corresponding to this key distribution process.

[0057] The process of adjusting the optical power of the initial optical signal generated by the light source module 11 according to the requirement of the quantum state modulation module 21 of the second device 2 for the input optical power can be carried out by adjusting the first monitoring module 13 and the light source module 11 through the first control module 14, and the first control module 14 can also communicate with the second device 2 to determine whether the initial optical signal sent meets the minimum modulated optical power of the second device 2, or can be implemented by the first monitoring module 13 and the light source module 11 in coordination with each other to realize feedback control inside the first device 1.

[0058] Corresponding to the first monitoring module 13 , a second monitoring module 22 is also provided in the second device 2 .

[0059] In the second device 2, the quantum state modulation module 21 is used to modulate the received initial optical signal. Different types of quantum modulation systems have different modulation methods, which will not be described in detail in the present disclosure.

[0060] The second monitoring module 22 is used to detect the initial optical signal from the first device 1. Only when the initial optical signal meets the input optical power requirement of the quantum state modulation module 21, that is, meets the second preset condition, the initial optical signal is transparently transmitted to the quantum state modulation module 21, otherwise, the information of insufficient power of the initial optical signal is fed back to the first device 1. In an exemplary embodiment, the second preset condition at least includes that the power of the initial optical signal is greater than the minimum modulated optical power of the quantum state modulation module 21.

[0061] In some embodiments, if an optical power enhancement device is provided in the second device 2, such as the second monitoring module 22, the second monitoring module 22 may also directly call the optical power enhancement device to enhance the initial optical signal to meet the second preset condition when detecting that the initial optical signal does not meet the second preset condition. This can reduce the cost of the first device 1, but increase the cost of the second device 2, and those skilled in the art may make a choice according to actual working conditions.

[0062] In addition, the second monitoring module 22 is also responsible for sending the quantum light signal modulated by the quantum state modulation module 21 to the first device 1 .

[0063] In an exemplary embodiment of the present disclosure, before the second device 2 sends the quantum light signal to the first device 1, the second device 2 attenuates the quantum light signal and sends the attenuated quantum light signal to the first device 1. Figure 2 In the illustrated embodiment, the second monitoring module 22 may be responsible for attenuating the quantum light signal, or the second control module may control the second monitoring module 22 to attenuate the quantum light signal.

[0064] The reason why quantum light signals need to be attenuated is that in some quantum key distribution (QKD) protocols (such as the single-photon-based BB84 protocol), the ideal situation is to send one photon at a time to carry quantum information. If attenuation is not performed, the light source may produce light pulses containing multiple photons. When there are multi-photon pulses, the eavesdropper (Eve) can use a photon number separation (PNS) attack. Eve can separate one photon in the multi-photon pulse for measurement, while allowing the remaining photons to continue to be transmitted to the receiving end, so that Eve can obtain part of the key information without being easily discovered. By attenuating the quantum light signal to make it as close to the single-photon level as possible, this attack can be effectively resisted and the security of the system can be improved.

[0065] In addition, the detector of the first device 1 has a suitable working range. If the intensity of the quantum light signal is too high, the detector may be saturated and unable to accurately distinguish the number and state of photons. For example, the avalanche multiplication process of the avalanche photodiode detector will be out of control under excessive light intensity, causing the detector to lose its normal response characteristics, resulting in detector failure or inability to effectively extract quantum information. At the same time, the attenuated quantum light signal can better adapt to the transmission characteristics of the channel and reduce the damage to quantum information caused by factors such as channel nonlinearity.

[0066] Finally, in the CV-QKD system, the quantum light signal that enters the line optical fiber after modulation is required to have less than 100 photons per pulse and an average optical power of less than -70dBm. Therefore, for the CV-QKD system, a large optical signal attenuation is required before the quantum light signal enters the line optical fiber.

[0067] The above-mentioned attenuation process can be achieved, for example, by providing an adjustable optical attenuator in the second monitoring module 22, and the present disclosure does not impose any special limitation on this.

[0068] Therefore, in the embodiment of the present disclosure, the second device 2 has only two functions of modulation and attenuation, with simple functions and structure, and low deployment and maintenance costs, which can greatly reduce the deployment cost and maintenance cost of large-scale quantum communication systems.

[0069] In some embodiments, the first monitoring module 13 is further used to receive the quantum light signal S2 from the second device 2, detect the power of the quantum light signal S2, and send the quantum light signal S2 to the coherent detection and demodulation module 12. In an exemplary embodiment, after the second device 2 sends the quantum light signal to the first device 1, the first monitoring module 13 in the first device 1 can detect the optical power of the quantum light signal to ensure that the quantum light signal does not damage the detector of the coherent detection and demodulation module 12.

[0070] If the optical power of the quantum light signal meets the optical power requirement of the detector, the first monitoring module 13 can directly send the quantum light signal to the coherent detection and demodulation module 12, or send a signal to the first control module 14, indicating that the current quantum light signal is within a power range that can be processed normally, allowing the data processing process to continue.

[0071] If the optical power of the quantum light signal does not meet the optical power requirement of the detector, for example, the optical power of the quantum light signal is too large and will damage the detector of the coherent detection and demodulation module 12, or the optical power of the quantum light signal is too small, the first monitoring module 13 can trigger the feedback adjustment mechanism.

[0072] In some embodiments, the first monitoring module 13 also includes an optical power enhancement unit, which is used to enhance the initial optical signal. Since reducing the optical power of the initial optical signal is to reduce the power of the light source module 11, the optical power of the initial optical signal is reduced only in the light source module 11, and the first monitoring module 13 does not attenuate the initial optical signal. However, in some embodiments, when the power cost of enhancing the initial optical signal by the light source module 11 is greater than the power cost of enhancing the initial optical signal by the optical power enhancement unit, the optical power enhancement unit of the first monitoring module 13 can enhance the initial optical signal, thereby further reducing the power of the light source module 11 and saving energy consumption.

[0073] By setting the first monitoring module 13 to detect and control the optical power of the initial optical signal and to detect the optical power of the quantum optical signal, the stable operation of the quantum communication system 100 can be ensured and the system reliability can be enhanced.

[0074] After the first monitoring module 13 outputs the quantum light signal, the coherent detection and demodulation module 12 can accurately perform coherent detection operations on the quantum light signal, mix the light signal with the local oscillator light, and convert the interference result into an electrical signal output. These electrical signals carry key information of the quantum light signal, such as changes in quantum state information such as the phase and amplitude of the light field.

[0075] During this process, the embodiment of the present disclosure monitors the coherent detection process and adjusts the local oscillator light signal through the first control module 14 and the light source module 11 to optimize the detection efficiency and the coding rate.

[0076] In the process of coherent detection and demodulation, the quantum light signal and the local oscillator light signal are coupled into the two input ports of the detector. Inside the detector, they interfere with each other, and the light intensity difference after interference is converted into an electrical signal. This electrical signal is related to the orthogonal amplitude and orthogonal phase difference between the quantum light signal and the local oscillator light.

[0077] The power of the local oscillator light signal is crucial to the coherent detection and demodulation process. If the power is too low, the signal strength after interference with the quantum light signal may be insufficient, making it difficult to be accurately captured by the detector, thereby affecting the detection efficiency; if the power is too high, it may cause detector saturation and nonlinear optical effects, introduce additional noise and interfere with the accurate extraction of information carried by the quantum light signal. Therefore, the embodiment of the present disclosure sets a feedback adjustment mechanism to dynamically adjust the power of the local oscillator light signal according to the actual detection situation, so as to maintain the coherent detection and demodulation process in an optimal working range.

[0078] In an exemplary embodiment, the preset parameters include coherent detection efficiency, and adjusting the local oscillator light signal so that the preset parameters reach preset values ​​includes: monitoring the coherent detection efficiency during coherent detection and demodulation, and adjusting the local oscillator light signal so that the detection efficiency reaches the preset detection efficiency.

[0079] The coherent detection efficiency can be monitored by counting the response counts of photodetectors (such as superconducting nanowire detectors or avalanche photodiode detectors) to the mixture of quantum light signals and local oscillator light. For example, the ratio of the number of photons actually detected to the number of photons that should be detected theoretically. The theoretical number of photons can be calculated based on parameters such as the power and frequency of the quantum light signal and local oscillator light, as well as the quantum efficiency of the detector. In addition, when monitoring the coherent detection efficiency, it is necessary to consider the losses of optical elements (such as beam splitters, optical fibers, etc.) that the quantum light signal and local oscillator light pass through during transmission. The losses can be calculated by measuring the changes in the intensity of light before and after each element, and then the impact of these losses on the detection efficiency can be evaluated.

[0080] After monitoring the coherent detection efficiency, the light source power and / or light attenuation of the local oscillator light signal can be adjusted to make the preset parameter (coherent detection efficiency) reach a preset value, such as a calculated better coherent detection efficiency value.

[0081] The detection efficiency is closely related to the light source power of the local oscillator light. Generally speaking, within a certain range, increasing the power of the local oscillator light can improve the detection efficiency. This is because the stronger local oscillator light can enhance the signal intensity after mixing when coherently detecting with the quantum light signal (such as heterodyne detection or homodyne detection), so that the detector can detect the signal more easily. For example, in the process of optical mixing, the quantum light signal interacts with the electric field of the local oscillator light to produce a beat signal. The higher the power of the local oscillator light, the higher the intensity of the beat signal will be to a certain extent, which is conducive to the detector response. Therefore, a variable current source or a variable voltage source can be used to control the working current or voltage of the light source module 11, so as to adjust the power of the local oscillator light signal, and find the best power setting by gradually increasing the power of the local oscillator light signal and observing the change in the detection efficiency. In this process, the feedback system can be used to monitor the detection efficiency or the response signal intensity of the detector in real time. According to the feedback signal, the light source power of the local oscillator light is automatically adjusted. For example, if the detection efficiency decreases or the detector response signal weakens, the power of the local oscillator light can be increased by the feedback control system until a satisfactory detection efficiency is achieved.

[0082] In addition, light attenuation will reduce the intensity of the local oscillator light. If the local oscillator light has a large light attenuation during the transmission process, its intensity will decrease when it reaches the position where the detector mixes with the quantum light signal, which will lead to a decrease in detection efficiency. Because the local oscillator light after light attenuation may not be able to effectively enhance the mixed signal intensity of the quantum light signal, it is difficult for the detector to distinguish the signal, especially for weak quantum light signals, the impact of light attenuation is more obvious. Therefore, equipment such as optical amplifiers can be used to compensate for light attenuation. For example, an erbium-doped fiber amplifier (EDFA) is added to the optical path of the local oscillator light signal (between the light source module 11 and the coherent detection and demodulation module 12) to amplify the optical signal and offset part of the light attenuation. However, it should be noted that the optical amplifier may introduce additional noise, and it is necessary to reasonably set parameters such as the gain of the amplifier to balance the relationship between light attenuation compensation and noise increase.

[0083] In some embodiments, the preset parameters include a coding rate, and adjusting the local oscillator light signal so that the preset parameters reach a preset value includes: monitoring the coding rate during coherent detection and demodulation, and adjusting the local oscillator light signal so that the coding rate reaches a preset coding rate.

[0084] The coding rate refers to the number of valid key bits successfully generated per unit time. In the QKD system, the coding rate is calculated by counting the number of valid key bits finally generated after a series of steps such as key screening, error correction and privacy amplification within a period of time (such as per second).

[0085] When monitoring the coding rate, the transmission time, coherent detection time, and signal processing time (including demodulation, key screening, and other processes) of the quantum light signal can be analyzed to determine the processing speed of the entire system, thereby calculating the coding rate. For example, if the total period of quantum light signal transmission and processing is T, and N valid key bits are generated during this period, then the coding rate R = N / T. In addition, the noise and error rate in the quantum channel will affect the coding rate. High noise will lead to more signal errors and require more time for error correction, thereby reducing the coding rate. The impact of noise level on the coding rate can be analyzed by measuring the noise level (such as by detecting the noise spectrum of the photocurrent).

[0086] After the coding rate is monitored, the light source power and / or light attenuation of the local oscillator optical signal can be adjusted to make the preset parameter (coding rate) reach a preset value, such as a calculated better coding rate.

[0087] When it is found that the coding rate is lower than the preset value, if the low coding rate is caused by insufficient local oscillator light power, then the light source power of the local oscillator light signal can be appropriately increased. With the increase of local oscillator light power, the intensity of the beat frequency signal after the signal light and the local oscillator light are mixed will increase during the coherent detection process, which will help improve the detector's ability to capture signals, thereby increasing the number of effective signals extracted and thus improving the coding rate. However, when increasing the local oscillator light power, it is necessary to pay close attention to the working state of the detector to prevent the detector from being saturated or nonlinear optical effects caused by excessive power, resulting in signal distortion or the introduction of additional noise.

[0088] If the code rate is affected because of excessive light attenuation of the local oscillator light during transmission, measures can be taken to reduce the light attenuation. For example, check the optical components in the optical path, such as optical fibers and beam splitters, to see if they are damaged or have degraded performance, and replace the problematic components in time to reduce the light attenuation. Alternatively, use an optical amplifier to compensate for the amplification of the local oscillator light, but pay attention to setting the gain of the optical amplifier reasonably to avoid the problem of increased noise caused by excessive amplification. By accurately adjusting the light source power and light attenuation of the local oscillator light, the code rate is continuously optimized to make it as close to or reach the preset better code rate as possible while ensuring the stable operation of the system, so as to meet the requirements of the quantum key distribution system for efficient and stable key generation and ensure the security and reliability of quantum communication.

[0089] In the above embodiment, by detecting the attenuation of the optical fiber link between devices and adjusting the light source power and light attenuation, the device power consumption and detection efficiency can be optimized. By adjusting the light power of the light source module 11 and monitoring the detection efficiency or key coding rate of the coherent detection and demodulation module 12, the system performance can be optimized.

[0090] In the disclosed embodiment, other preset parameters may be set and other methods may be used to adjust the local oscillator light signal to optimize the coherent detection and demodulation process and ensure the smooth progress of the quantum key distribution process.

[0091] By using the first control module 14 to monitor the coherent detection and demodulation process, adjust the light source module 11 in real time, and adjust the light source module 11 in real time to adjust the initial optical power, the power of the light source can be optimized and adjusted, while achieving a reduction in system power consumption and an improvement in detection efficiency.

[0092] Figure 3 Schematic diagram of the interaction of various modules in the quantum communication system 100 in the exemplary embodiment of the present disclosure.

[0093] refer to Figure 3 In combination with the above embodiments, the quantum key distribution process of the quantum communication system 100 may include:

[0094] In step S301 , the light source device 11 of the first device 1 generates an initial light signal and sends the initial light signal to the first monitoring module 13 .

[0095] In step S302 , the first monitoring module 13 detects the optical power of the initial optical signal and feeds back the power to the first control module 14 .

[0096] In step S303, the first control module 14 determines whether the initial optical power is greater than the third power, and according to the determination result, in step S304, the light source module 11 is adjusted to adjust the initial optical power so that the initial optical power meets the requirement.

[0097] When the first monitoring module 13 detects that the initial optical power meets the requirement, the process goes to step S305 to send the initial optical signal to the second monitoring module 22 of the second device 2 .

[0098] In step S306, the second monitoring module 22 performs optical power detection on the initial optical signal after transmission. If the received initial optical signal meets the minimum modulation power requirement of the quantum state modulation module 21, it enters step S307 and sends the initial optical signal to the quantum state modulation module 21. If it does not meet the requirement, it can be fed back to the first device 1 to enhance the optical power of the initial light, or the initial optical power can be enhanced locally (this function requires the setting of an optical enhancement device in the second device 2).

[0099] In step S308 , the quantum state modulation module 21 modulates the initial optical signal to form a quantum optical signal, and in step S309 , sends the quantum optical signal to the second monitoring module 22 .

[0100] In step S310, the second monitoring module 22 detects the optical power of the quantum optical signal and attenuates it to make it meet the safety standard. Then, the process proceeds to step S311, where the quantum optical signal is sent to the first device 1.

[0101] In step S312, after receiving the quantum light signal, the first monitoring module 13 performs optical power detection on the quantum light signal. When the optical power of the quantum light signal meets the requirements, the process proceeds to step S313 to send the quantum light signal to the coherent detection and demodulation module 12. It should be noted that, since the optical power of the quantum light signal entering the optical fiber link is relatively small, in order to prevent the detection from causing attenuation of the quantum light signal and resulting in the failure of the detector detection, in some embodiments, step S312 may not be set and step S313 may be directly entered.

[0102] In step S314 , the light source module 11 generates and sends a local oscillator light signal to the coherent detection and demodulation module 12 .

[0103] In step S315 , the coherent detection and demodulation module 12 processes and coherently detects the received quantum light signal and the local oscillation light signal, and feeds back the preset parameters to the first control module 14 in step S316 .

[0104] In step S317 , the first control module 14 sends an adjustment instruction to the light source module 11 according to the preset parameters to adjust the local oscillator light power so that the preset parameters reach the preset values.

[0105] Through loop control, the disclosed embodiment can not only provide a second device with low deployment and maintenance costs, thereby reducing the deployment cost of the quantum communication system, but also achieve the dual effects of reducing device power consumption and improving detection efficiency, thereby greatly optimizing the working performance of the quantum communication system.

[0106] According to another aspect of an embodiment of the present disclosure, a quantum communication method is provided.

[0107] Figure 4 It is a flow chart of the quantum communication method in the embodiment of the present disclosure.

[0108] refer to Figure 4 , Figure 4 The quantum communication method 400 is applied to a quantum communication system in any of the above embodiments, including:

[0109] Step S1, generating an initial optical signal by a first device, and sending the initial optical signal from the first device to a second device;

[0110] Step S2, performing quantum state modulation on the initial optical signal by a second device to form a quantum optical signal;

[0111] Step S3, sending the quantum light signal from the second device to the first device;

[0112] Step S4, generating a local oscillator light signal through the first device, performing coherent detection and demodulation on the first device based on the local oscillator light signal and the quantum light signal to generate a quantum key, monitoring preset parameters in the coherent detection and demodulation process, and adjusting the local oscillator light signal so that the preset parameters reach preset values.

[0113] The relevant explanation of the quantum communication method 400 has been described in detail in the above-mentioned system embodiment and will not be repeated here.

[0114] According to another aspect of the embodiments of the present disclosure, a quantum communication device is provided, which is used to implement the above-mentioned quantum communication system and the above-mentioned quantum communication method.

[0115] Figure 5 It is a schematic diagram of a quantum communication device in an embodiment of the present disclosure.

[0116] refer to Figure 5 , the quantum communication device 500 may be the first device 1 in the quantum communication system 100, and the quantum communication device 500 may include:

[0117] The light source module 11 is used to generate an initial light signal and a local oscillator light signal;

[0118] A coherent detection and demodulation module 12, used to receive a local oscillator light signal and a quantum light signal, and to perform coherent detection and demodulation on the quantum light signal based on the local oscillator light signal to generate a quantum key;

[0119] A first monitoring module 13, configured to adjust the power of the initial optical signal and send the adjusted initial optical signal to the second device;

[0120] The first control module 14 is connected to the light source module 11, the coherent detection and demodulation module 12, and the first monitoring module 13, and is used to monitor the preset parameters in the coherent detection and demodulation process of the coherent detection and demodulation module, adjust the local oscillator light signal sent by the light source module according to the preset parameters so that the preset parameters reach the preset values, and control the light source module 11 to adjust the initial light power according to the optical power detection result of the initial light signal by the first monitoring module 13.

[0121] The relevant explanation of the quantum communication device 500 has been described in detail in the introduction of the first device 1 in the above system embodiment, and will not be repeated here.

[0122] Figure 6 It is a schematic diagram of a quantum communication device in an embodiment of the present disclosure.

[0123] refer to Figure 6 , the quantum communication device 600 may be the second device 2 in the quantum communication system 100, and the quantum communication device 600 may include:

[0124] A quantum state modulation module 21, configured to perform quantum state modulation on an initial optical signal from a first device to form a quantum optical signal;

[0125] The second monitoring module 22 is used to receive the initial optical signal from the first device, adjust the power of the initial optical signal, and send the adjusted initial optical signal to the quantum state modulation module 21, and receive the quantum optical signal from the quantum state modulation module 21, adjust the power of the quantum optical signal, and send the adjusted quantum optical signal to the first device.

[0126] The relevant explanation of the quantum communication device 600 has been described in detail in the introduction of the second device 2 in the above system embodiment, and will not be repeated here.

[0127] It should be noted that, although several modules or units of the device for action execution are mentioned in the above detailed description, this division is not mandatory. In fact, according to the embodiments of the present disclosure, the features and functions of two or more modules or units described above can be embodied in one module or unit. On the contrary, the features and functions of one module or unit described above can be further divided into multiple modules or units to be embodied.

[0128] Those skilled in the art will readily appreciate other embodiments of the present disclosure after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include common knowledge or customary techniques in the art that are not disclosed in the present disclosure. The specification and examples are to be considered exemplary only, and the true scope and concept of the present disclosure are indicated by the claims.

Claims

1. A quantum communication system, characterized in that: The invention comprises a first device and a second device connected by an optical fiber link, wherein: The first device generates an initial optical signal and a local oscillator optical signal, and sends the initial optical signal to the second device, and receives a quantum optical signal from the second device, performs coherent detection and demodulation based on the local oscillator optical signal and the quantum optical signal to generate a quantum key, monitors a preset parameter in the coherent detection and demodulation process, and adjusts the local oscillator optical signal so that the preset parameter reaches a preset value; The second device receives the initial optical signal, performs quantum state modulation on the initial optical signal to form the quantum optical signal, and sends the quantum optical signal to the first device.

2. The quantum communication system according to claim 1, characterized in that Adjusting the local oscillator light signal so that the preset parameter reaches a preset value includes: The light source power and / or light attenuation of the local oscillator light signal are adjusted so that the preset parameter reaches a preset value.

3. The quantum communication system according to claim 1 or 2, characterized in that: The preset parameters include coherent detection efficiency and / or coding rate, the preset parameters in the monitoring coherent detection and demodulation process, and adjusting the local oscillator light signal so that the preset parameters reach preset values. Adjusting the local oscillator light signal so that the preset parameters reach preset values ​​includes at least one of the following: Monitoring the coherent detection efficiency during the coherent detection and demodulation process, and adjusting the local oscillator light signal so that the detection efficiency reaches a preset detection efficiency; The coding rate in the coherent detection and demodulation process is monitored, and the local oscillator optical signal is adjusted so that the coding rate reaches a preset coding rate.

4. The quantum communication system according to claim 1, characterized in that The second device sending the quantum light signal to the first device includes: The second device attenuates the quantum light signal, and sends the attenuated quantum light signal to the first device.

5. The quantum communication system according to claim 1, characterized in that: The first device comprises: A light source module, used for generating the initial light signal and the local oscillator light signal; A coherent detection and demodulation module, used for receiving the local oscillator light signal and the quantum light signal, and performing coherent detection and demodulation on the quantum light signal based on the local oscillator light signal to generate the quantum key; a first monitoring module, configured to detect the power of the initial optical signal, so that when the initial optical signal does not meet the first preset condition, the light source module adjusts the initial optical signal according to the detection result, and sends the initial optical signal that meets the first preset condition to the second device; The first control module is connected to the light source module and the coherent detection and demodulation module, and is used to monitor the preset parameters in the coherent detection and demodulation process of the coherent detection and demodulation module, and adjust the local oscillator light signal sent by the light source module according to the preset parameters so that the preset parameters reach the preset values.

6. The quantum communication system according to claim 5, characterized in that: The first preset condition includes that the power of the initial optical signal is greater than or equal to the third power, and the light source module adjusts the initial optical signal according to the detection result, including: The power of the initial optical signal is adjusted to reach a first power, wherein the optical attenuation power of the optical fiber link from the first device to the second device is a second power, the sum of the minimum modulated optical power of the second device and the second power is a third power, the first power is greater than or equal to the third power, and the difference between the first power and the third power is less than a preset value.

7. The quantum communication system according to claim 1, characterized in that The second device comprises: A quantum state modulation module, used for performing quantum state modulation on the initial optical signal to form the quantum optical signal; A second monitoring module is used to receive the initial optical signal from the first device, detect the power of the initial optical signal, and send the initial optical signal that meets a second preset condition to the quantum state modulation module, wherein the second preset condition includes that the power of the initial optical signal is greater than the minimum modulated optical power of the quantum state modulation module; and receive the quantum optical signal from the quantum state modulation module, adjust the power of the quantum optical signal, and send the adjusted quantum optical signal to the first device.

8. A quantum communication method, characterized in that: A quantum communication system as claimed in any one of claims 1 to 7, comprising: generating an initial optical signal by a first device, and sending the initial optical signal from the first device to the second device; Performing quantum state modulation on the initial optical signal by a second device to form a quantum optical signal; sending the quantum light signal from the second device to the first device; A local oscillator light signal is generated by the first device, and coherent detection and demodulation are performed on the first device based on the local oscillator light signal and the quantum light signal to generate a quantum key, preset parameters in the coherent detection and demodulation process are monitored, and the local oscillator light signal is adjusted so that the preset parameters reach preset values.

9. A quantum communication device, characterized in that: include: A light source module, used for generating an initial light signal and a local oscillator light signal; A coherent detection and demodulation module, used for receiving the local oscillator light signal and the quantum light signal, and performing coherent detection and demodulation on the quantum light signal based on the local oscillator light signal to generate the quantum key; a first monitoring module, configured to detect the power of the initial optical signal, so that when the initial optical signal does not meet the first preset condition, the light source module adjusts the initial optical signal according to the detection result, and sends the initial optical signal that meets the first preset condition to the second device; The first control module is connected to the light source module and the coherent detection and demodulation module, and is used to monitor the preset parameters in the coherent detection and demodulation process of the coherent detection and demodulation module, and adjust the local oscillator light signal sent by the light source module according to the preset parameters so that the preset parameters reach the preset values.

10. A quantum communication device, characterized in that: include: A quantum state modulation module, used for performing quantum state modulation on the initial optical signal to form the quantum optical signal; A second monitoring module is used to receive the initial optical signal from the first device, detect the power of the initial optical signal, and send the initial optical signal that meets a second preset condition to the quantum state modulation module, wherein the second preset condition includes that the power of the initial optical signal is greater than the minimum modulated optical power of the quantum state modulation module; and receive the quantum optical signal from the quantum state modulation module, adjust the power of the quantum optical signal, and send the adjusted quantum optical signal to the first device.

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