Polarization state adjustment method and device for quantum light and quantum communication satellite

Abstract

The application relates to the technical field of quantum communication, and discloses a polarization state adjustment method and device of quantum light and a quantum communication satellite. The quantum communication satellite measures the polarization state of emitted quantum light, the quantum light is generated and emitted by a light source in the quantum communication satellite, a change vector of the polarization state of the quantum light relative to a preset polarization state of the quantum light is determined, and the polarization state of the quantum light generated and emitted by the light source is adjusted according to the change vector. The quantum communication satellite uses the quantum light as a base vector optical signal for polarization compensation. The light source considers the change of the polarization state when emitting the quantum light, so that the polarization state of the emitted quantum light is always maintained at the preset polarization state, high polarization contrast of the quantum light is achieved, the polarization error rate of the quantum light is reduced, no additional hardware device is needed, hardware cost is saved, polarization state compensation can be realized through the quantum communication satellite, the workload of ground station staff is reduced, and the experience of the ground station staff is improved.

Description

Technical Field

[0001] This application relates to the field of quantum communication technology, and in particular to a method, device and quantum communication satellite for adjusting the polarization state of quantum light. Background Technology

[0002] In free-space quantum key distribution, quantum key distribution and quantum key relay can be achieved by satellite-to-ground docking between quantum communication satellites and ground stations. Quantum communication satellites move continuously in low Earth orbit. The continuous angular changes between the satellite's flight direction and the direction of the payload's optical axis, as well as the single-mode fiber used for quantum light emission, all lead to changes in polarization state. Compensation is required to achieve high polarization contrast and reduce the polarization error rate of quantum light.

[0003] In existing technologies, additional lasers need to be added to quantum communication satellites as the basis vector signals for polarization compensation, which results in high hardware costs. Furthermore, it requires the joint efforts of personnel from both the quantum communication satellite and the ground station to achieve polarization compensation. This not only requires improvements to the quantum communication satellite but also necessitates continuous manual operation of the ground station, leading to a poor user experience for the ground station personnel. Summary of the Invention

[0004] The purpose of this application is to provide a method, device, and quantum communication satellite for adjusting the polarization state of quantum light, so as to reduce hardware costs and improve the experience of ground station staff.

[0005] To address the aforementioned technical problems, embodiments of this application provide a method for adjusting the polarization state of quantum light, applied to a quantum communication satellite, comprising: measuring the polarization state of emitted quantum light; wherein the quantum light is generated and emitted by a light source in the quantum communication satellite; determining a change vector of the polarization state of the quantum light relative to a preset polarization state of the quantum light; and adjusting the polarization state of the quantum light generated and emitted by the light source according to the change vector.

[0006] An embodiment of this application also provides a method for adjusting the polarization state of quantum light, which further includes determining the preset polarization state of the quantum light before determining the change vector of the polarization state of the quantum light relative to a preset polarization state of the quantum light.

[0007] An embodiment of this application also provides a method for adjusting the polarization state of quantum light, wherein determining the preset polarization state of the quantum light includes: performing a unitary transformation on the polarization state of the quantum light using a waveplate to obtain the preset polarization state of the quantum light.

[0008] Embodiments of this application also provide a method for adjusting the polarization state of quantum light. The waveplate includes a first quarter-wave plate, a second quarter-wave plate, and a half-wave plate. The method involves performing a unitary transformation on the polarization state of the quantum light using the three waveplates to obtain a preset polarization state of the quantum light. This includes: the first quarter-wave plate transforming the R-ray of the quantum light to obtain a first transformed quantum light; the second quarter-wave plate transforming the H-ray of the first transformed quantum light to obtain a second transformed quantum light; and the half-wave plate transforming the H-ray of the second transformed quantum light to obtain the preset polarization state of the quantum light.

[0009] An embodiment of this application also provides a method for adjusting the polarization state of quantum light, wherein there are multiple polarization states of the emitted quantum light, and the multiple polarization states correspond to multiple change vectors; the method for adjusting the polarization state of the quantum light generated and emitted by the light source according to the multiple change vectors includes: determining a target change vector according to the multiple change vectors; and adjusting the polarization state of the quantum light generated and emitted by the light source based on the target change vector.

[0010] Embodiments of this application also provide a method for adjusting the polarization state of quantum light, wherein determining a target change vector based on multiple change vectors includes: performing maximum likelihood estimation on the multiple change vectors to determine the target change vector.

[0011] Embodiments of this application also provide a method for adjusting the polarization state of quantum light, wherein adjusting the polarization state of quantum light generated and emitted by the light source based on the target change vector includes: adjusting a polarization control element in the light source according to the target change vector to adjust the polarization state of quantum light generated and emitted by the light source.

[0012] An embodiment of this application also provides a method for adjusting the polarization state of quantum light, wherein measuring the polarization state of emitted quantum light includes: sampling emitted quantum light in real time and measuring the polarization state of emitted quantum light using a single-track continuous sampling method.

[0013] An embodiment of this application also provides a device for adjusting the polarization state of quantum light, comprising: a measurement module for measuring the polarization state of emitted quantum light; wherein the quantum light is generated and emitted by a light source in the quantum communication satellite; a determination module for determining a change vector of the polarization state of the quantum light relative to a preset polarization state of the quantum light; and an adjustment module for adjusting the polarization state of the quantum light generated and emitted by the light source according to the change vector.

[0014] Embodiments of this application also provide a quantum communication satellite, comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the above-described quantum light polarization state adjustment method.

[0015] In this application, the quantum communication satellite directly utilizes quantum light as the basis vector signal for polarization compensation. Based on the change vector of polarization state, the polarization state of the quantum light generated and emitted by the light source is adjusted. This application ensures that the light source in the quantum communication satellite takes into account the change of polarization state when emitting quantum light, so that the polarization state of the quantum light emitted by the light source always remains in the preset polarization state, reducing the change of polarization state, thereby achieving high polarization contrast and reducing the polarization bit error rate of quantum light. This application does not require additional hardware equipment, which can save hardware costs. Polarization state compensation can be achieved through the quantum communication satellite. The compensation process does not require the participation of ground station and ground station personnel, reducing the workload of ground station personnel and improving their experience. Attached Figure Description

[0016] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, and these illustrative descriptions do not constitute a limitation on the embodiments.

[0017] Figure 1 This is a schematic diagram of a satellite-to-ground quantum key distribution provided in an embodiment of this application;

[0018] Figure 2 This is a flowchart of a method for adjusting the polarization state of quantum light provided in an embodiment of this application;

[0019] Figure 3 This is a schematic diagram of a Poincaré sphere provided in an embodiment of this application;

[0020] Figure 4 This is a schematic diagram illustrating the polarization state relationship on a Bonga sphere provided in an embodiment of this application;

[0021] Figure 5 This is a schematic diagram of a unitary transformation provided in an embodiment of this application;

[0022] Figure 6 This is a schematic diagram of the structure of a quantum light polarization state adjustment device provided in an embodiment of this application;

[0023] Figure 7 This is a schematic diagram of the structure of a quantum communication satellite provided in an embodiment of this application. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the various embodiments of this application will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the various embodiments of this application to help readers better understand this application. However, the technical solutions claimed in this application can be implemented even without these technical details and various changes and modifications based on the following embodiments. The division of the various embodiments below is for the convenience of description and should not constitute any limitation on the specific implementation of this application. The various embodiments can be combined with and referenced by each other without contradiction.

[0025] In quantum communication, quantum key distribution (QKD) uses quantum systems to prepare, transmit, receive, and purify information to obtain a secure symmetric key that cannot be stolen in terms of physical principles. This process ensures that the keys obtained by the two communicating parties are completely consistent, and no third party can obtain any information about the key.

[0026] Quantum key distribution (QKD) can transmit quantum optical signals using fiber optic channels and free-space (atmospheric) channels. Fiber optic QKD's transceiver system maintains a stable connection for extended periods, resulting in continuous and stable key output characteristics. Free-space QKD can utilize satellite-to-ground connections between quantum communication satellites and ground stations for both QKD and QK relay. However, because quantum communication satellites typically orbit at low altitudes below 1000km, communication is only possible when they are within the line of sight of a ground station. Furthermore, the satellite-to-ground distance constantly changes during communication, leading to unstable channel attenuation. Factors such as weather, environmental obstructions, and visibility time also need to be considered, resulting in discontinuous and unstable key output characteristics in satellite-to-ground QKD.

[0027] Figure 1 This is a schematic diagram of a satellite-to-ground quantum key distribution provided in an embodiment of this application, as shown below. Figure 1As shown, by combining the satellite platform attitude pointing and the Autonomous Targeting Payload (ATP) system with the quantum key distribution ground terminal, a quantum channel is established between the ground station and the quantum communication satellite. Based on this, satellite-to-ground quantum key distribution is performed, and online key extraction is achieved using a laser communication channel, establishing a shared key between the ground terminal and the satellite. When the quantum communication satellite is operating in a single orbit, the satellite-to-ground quantum key distribution process includes three stages: initial pointing and acquisition, tracking and aiming, and quantum communication. Below the horizon, the quantum key distribution terminal of the quantum communication satellite receives instructions from the ground station and begins initialization, preparing to point at the ground station. The satellite payload completes self-checking before the quantum communication satellite reaches an elevation angle of 5° above the horizon. Between 5° and 15°, the ground station opens the loop to point at the quantum communication satellite based on orbit prediction, ensuring the beacon light covers the satellite, and the satellite payload captures the ground beacon light. Between 15° and 25°, a two-way tracking link is established. Based on this, the satellite payload transmits quantum signal light, which is detected and received by the ground station for quantum key distribution.

[0028] In single-track satellite-to-ground quantum key distribution, continuous angular changes between the satellite's flight direction (perpendicular to the Earth's sphere) and the payload's optical axis direction (coarse tracking direction, pointing towards the ground station) cause alterations in the polarization state, requiring continuous compensation. Simultaneously, in quantum communication satellites, the quantum light emission between the payload quantum unit and the optical transmission optical engine uses single-mode fiber, which also introduces polarization state changes, such as arbitrary unitary transformations, requiring compensation as well. Polarization state compensation is essential to achieve high polarization contrast and reduce the polarization error rate of quantum light. Furthermore, in satellite-to-ground quantum key distribution, due to the high fidelity of atmospheric polarization state preservation, polarization coding is also used as an encoding method. For a polarization-coded satellite-to-ground quantum key distribution system, factors such as unitary transformations introduced by single-mode fiber, relative rotation of the optical axis introduced by the telescope rotation mechanism, and basis vector changes introduced by the relative motion of the satellite and ground station cause polarization state degradation, affecting system performance and even preventing code generation, necessitating compensation.

[0029] Existing quantum satellites employ a scheme using multiple lasers and passive polarization encoding with free-space crystals. This adds an extra laser as the basis light signal for polarization compensation, resulting in high hardware costs. Furthermore, achieving polarization state compensation requires close cooperation between the quantum communication satellite and ground station personnel. This necessitates improvements to the quantum communication satellite and continuous manual operation of the ground station, leading to a poor user experience for ground station staff. To address the technical problems of existing quantum satellites, embodiments of this application provide a method for adjusting the polarization state of quantum light. Figure 2This is a flowchart of a method for adjusting the polarization state of quantum light provided in an embodiment of this application, as shown below. Figure 2 As shown, this method for adjusting the polarization state of quantum light can be applied to quantum communication satellites, and specifically includes the following steps.

[0030] Step 201: Measure the polarization state of the emitted quantum light.

[0031] Quantum light is generated and emitted by a light source in a quantum communication satellite.

[0032] In quantum communication satellites, the light source is a key device for generating quantum light and can be located in the satellite's payload area. The light source generates quantum photons, i.e., quantum light, through specific quantum physics processes.

[0033] After the light source in the quantum communication satellite generates and emits quantum light, the polarization state of the quantum light will change due to the continuous angular changes between the satellite's flight direction and the direction of the payload's optical axis, as well as the single-mode fiber used for quantum light emission. Therefore, it is necessary to measure the actual polarization state of the quantum light after the polarization state has changed, that is, to measure the polarization state of the emitted quantum light.

[0034] Quantum communication satellites measure the polarization state of emitted quantum light primarily by selecting appropriate polarization detectors or polarization measurement bases and using optical components such as polarizers and photon counters for precise measurement. Because the polarization state of quantum light undergoes wave function collapse during measurement, quantum communication satellites need to determine the photon's polarization state through probability statistics. They also need to consider errors and interference, employing error correction techniques to ensure reliable measurement of quantum information.

[0035] Step 202: Determine the change vector of the polarization state of the quantum light relative to the preset polarization state of the quantum light.

[0036] Among them, the preset polarization state of quantum light can be the polarization state when the quantum light has not changed its polarization state, the polarization state that the ground station and the quantum communication satellite can match, and the preset polarization state is the condition for satellite-ground docking.

[0037] In the embodiments of this application, quantum communication systems typically require that the polarization state of quantum light must meet certain conditions (quantum communication satellites and ground stations need to ensure that the polarization state of the quantum light emitted by their light sources is compatible with the polarization detector of the receiving equipment, which requires minimizing changes in polarization state during signal transmission) in order to ensure secure data transmission, system stability, and minimize errors.

[0038] In this embodiment, the change vector is the difference between the polarization state of the emitted quantum light as measured and the polarization state of the quantum light when the polarization state has not changed.

[0039] For example, the overlap of polarization states can be described by the inner product of the polarization state of quantum light and the preset polarization state of quantum light. Then, the angle between the polarization state of quantum light and the preset polarization state can be calculated by the inner product, thereby quantifying the change. Finally, the change and rotation of quantum polarization state can be described by a rotation matrix.

[0040] Step 203: Adjust the polarization state of the quantum light generated and emitted by the light source according to the change vector.

[0041] Once the change vector of polarization state is known, the output of the light source can be adjusted based on this change vector.

[0042] Optionally, waveplates, liquid crystal polarizers, etc., can be used to precisely control the polarization state of light. Adjusting the waveplate to an angle related to the change vector can achieve precise rotation of the polarization direction; setting the electric field in the liquid crystal polarizer according to the required angle can precisely adjust the polarization state of light.

[0043] After adjusting the polarization state of the quantum light generated and emitted by the light source according to the change vector, the polarization state of the quantum light emitted by the quantum communication satellite will remain near the preset polarization state after it is emitted, reducing the change of polarization state, achieving high polarization contrast of quantum light, reducing the polarization bit error rate of quantum light, and meeting the conditions for satellite-to-ground docking.

[0044] In this embodiment, the quantum communication satellite directly utilizes quantum light as the basis vector signal for polarization compensation. Based on the change vector of polarization state, the polarization state of the quantum light generated and emitted by the light source is adjusted. This embodiment ensures that the light source in the quantum communication satellite takes into account the change in polarization state when emitting quantum light, so that the polarization state of the quantum light emitted by the light source always remains in a preset polarization state, reducing the change in polarization state, thereby achieving high polarization contrast and reducing the polarization bit error rate of quantum light. This embodiment does not require additional hardware equipment, which can save hardware costs. Polarization state compensation can be achieved through the quantum communication satellite without the need for ground station and ground station personnel, reducing the workload of ground station personnel and improving their experience.

[0045] In the above Figure 2 Based on the method for adjusting the polarization state of quantum light shown, this application embodiment also provides another method for adjusting the polarization state of quantum light. Before step 202, which determines the change vector of the polarization state of quantum light relative to the preset polarization state of quantum light, the method further includes: determining the preset polarization state of quantum light.

[0046] In one case, the preset polarization state of quantum light can be pre-set; in another case, the preset polarization state can be obtained through calculation.

[0047] When the preset polarization state of quantum light is pre-set, factors such as communication protocols and equipment compatibility need to be considered. For example, it is necessary to select an appropriate polarization base, ensure the polarization compatibility of quantum communication satellites and ground station equipment, and select the polarization state according to the requirements of the quantum key distribution protocol to ensure that the preset polarization state can meet the reliability and security requirements of the satellite-to-ground quantum communication system.

[0048] When the preset polarization state is obtained by calculation, the preset polarization state of quantum light is determined, including: performing a unitary transformation on the polarization state of quantum light through a waveplate to obtain the preset polarization state of quantum light.

[0049] The static polarization compensation scheme is designed for quantum channels using ordinary single-mode fiber as the transmission route from the entanglement source to the quantum transmitter. Due to imperfections in the drawing of ordinary single-mode fiber, a slight birefringence effect occurs, preventing the fiber from maintaining the polarization of light. However, the effect of ordinary single-mode fiber on light polarization can be approximated as a unitary transformation when the fiber is not particularly long. Therefore, in this embodiment, the quantum communication satellite can use a unitary transformation to change the polarization state of quantum light back to a preset polarization state.

[0050] Optionally, the unitary transformation of the polarization state of quantum light can be achieved through quantum gates, interferometers, modulators, rotation matrices, etc.

[0051] To describe the polarization state of light, three waveplates (using a combination of two quarter-wave plates and one half-wave plate) can achieve arbitrary unitary transformations. Therefore, in this embodiment, the polarization state of quantum light is transformed using waveplates. The waveplates include a first quarter-wave plate, a second quarter-wave plate, and a half-wave plate. In this case, the unitary transformation of the polarization state of quantum light is performed using waveplates to obtain a preset polarization state of quantum light. This includes: the first quarter-wave plate transforms the R-ray of the quantum light to obtain a first transformed quantum light; the second quarter-wave plate transforms the H-ray of the first transformed quantum light to obtain a second transformed quantum light; and the half-wave plate transforms the H-ray of the second transformed quantum light to obtain the preset polarization state of quantum light.

[0052] To vividly describe the polarization state of light and its changes, and considering that any elliptically polarized light only needs two azimuth angles to completely determine its polarization state, and that a point on a sphere can be represented by two parameters, longitude and latitude, a sphere with a radius of 1 is used to describe the polarization state of light, i.e., by using a Bonga sphere.

[0053] Figure 3 This is a schematic diagram of a Poincaré sphere provided in an embodiment of this application, as shown below. Figure 3As shown, points on the Bonga sphere correspond one-to-one with light of different polarization states. For example, the upper and lower poles of the Bonga sphere correspond to right-handed and left-handed circularly polarized light, respectively; points on the equator represent linearly polarized light; the intersection of the x-axis and the sphere represents H-state polarized light; and the intersection of the y-axis and the sphere represents +-state polarized light. Under the influence of a waveplate with an azimuth angle of θ and a phase delay of Δ, the polarization state will rotate around any axis within the equatorial plane of the Bonga sphere (corresponding one-to-one with the azimuth angle), with the rotation angle being the waveplate delay Δ. Using the Bonga sphere, the principle of polarization control achieved by three waveplates can be described more vividly.

[0054] Figure 4 This is a schematic diagram illustrating the polarization state relationship on a Bonga sphere according to an embodiment of this application, as shown below. Figure 4 As shown, the effect of optical fiber on the polarization of quantum light can be viewed as a unitary transformation. On the Bonga sphere, the absolute positions of the corresponding points of the quantum light's H (horizontal polarization), D (diagonal polarization), and R (right-hand circular polarization) rays will change, becoming H', D', and R' respectively. However, the relative positions of the corresponding points of the quantum light's H, D, and R rays will not change (the relative positions of H', D', and R' are the same as those of H, D, and R). Since the unitary transformation is linear, if a unitary transformation U exists that returns the three points H, D, and R on the Bonga sphere to their original positions, then this unitary transformation completely cancels out the effect of the optical fiber on the polarization of the light. The optical fiber, combined with a system capable of performing this unitary transformation U in real time, constitutes a system that preserves polarization for all polarizations.

[0055] In this embodiment, the unitary transformation of the polarization state of quantum light is achieved through a first quarter-wave plate, a second quarter-wave plate, and a half-wave plate. Figure 5 This is a schematic diagram of a unitary transformation provided in an embodiment of this application, as shown below. Figure 5 As shown, the first quarter-wave plate will project the R-light after fiber transformation onto the corresponding point on the Poincaré sphere (e.g., ...). Figure 5 (1) Transform the R' point in the middle to the equatorial plane of the Bonga sphere (e.g., Figure 5 (2) As shown), at this time, the D light and the H light (corresponding to) Figure 5 (2) Points D' and H' will appear on a single meridian. The second quarter-wave plate will pass through the optical fiber and the H-point transformed by the first quarter-wave plate. Figure 5 (2) Transform point H' in the middle to the equatorial plane (e.g., point H' in the middle) to Figure 5 (3) shown); at this time R (corresponding to Figure 5(3) Point R' will be at the pole position. The last half-wave plate will transform the H light (corresponding to the optical fiber and the first two wave plates) after it has been transformed by the optical fiber and the first two wave plates. Figure 5 (4) When the H' point is transformed to the H point, due to the characteristics of the half-wave plate, R and D will return to their original positions (corresponding to) Figure 5 (4) As shown, point R' coincides with point R, and point D' coincides with point D. Thus, the three waveplates realize the unitary transformation U mentioned above. It can also be seen that rotating the three waveplates can realize the polarization control of the optical fiber.

[0056] By performing a unitary transformation U on the polarization state of quantum light using three waveplates, the preset polarization state of quantum light can be obtained.

[0057] In this embodiment of the application, before determining the change vector of the polarization state of quantum light relative to the preset polarization state of quantum light, the quantum communication satellite performs a unitary transformation on the polarization state of quantum light to accurately determine the preset polarization state of quantum light, thereby making the adjustment of the light source more precise.

[0058] In the above Figure 2 Based on the method for adjusting the polarization state of quantum light shown in the previous embodiment, this application also provides another method for adjusting the polarization state of quantum light. The quantum light emitted by the light source in a quantum communication satellite can be one or more beams. To improve system reliability, anti-interference capability, achieve quantum key distribution, improve information transmission efficiency, and enhance security, the light source in the quantum communication satellite can generate multiple beams, each with a different polarization state.

[0059] When the light source in a quantum communication satellite can generate multiple light beams, in step 201, the polarization state of the emitted quantum light is measured. Multiple polarization states exist, and correspondingly, multiple polarization states correspond to multiple change vectors. Then, in step 203, the polarization state of the quantum light generated and emitted by the light source is adjusted based on the change vectors. This includes: determining a target change vector based on the multiple change vectors; and adjusting the polarization state of the quantum light generated and emitted by the light source based on the target change vector.

[0060] Photons used in quantum communication carry quantum information, which is typically encoded through polarization states. In practical applications, the receiver needs to measure the received light beam. To simplify and streamline the measurement process, the polarization states of all beams are usually unified to a specific basis (e.g., horizontal / vertical basis, diagonal / anti-diagonal basis). This allows the receiver to use a unified algorithm and hardware for signal processing, rather than processing each polarization state individually. Therefore, in this embodiment, multiple change vectors are unified so that the polarization states of multiple beams in the quantum light generated by the adjusted light source are unified to a specific basis.

[0061] When determining the target change vector based on multiple change vectors, the target change vector can be determined by performing maximum likelihood estimation on the multiple change vectors. Of course, other methods such as averaging can also be used to unify the multiple change vectors. No specific limitations are made in the embodiments of this application.

[0062] When adjusting the polarization state of quantum light generated and emitted by a light source based on a target change vector, the polarization control elements in the light source can be adjusted according to the target change vector to change the polarization state of the quantum light generated and emitted by the light source. These polarization control elements can include polarizers, waveplates, optical rotators, etc., and their parameters are adjusted to change the polarization state of the quantum light. For example, the parameters of a waveplate can be adjusted according to the target change vector.

[0063] In this embodiment, after adjusting the polarization state of each beam of quantum light generated and emitted by the light source according to the target change vector, the polarization state of each beam of quantum light emitted by the quantum communication satellite will remain near the preset polarization state after being emitted, reducing the change of polarization state, achieving high polarization contrast of quantum light, reducing the polarization bit error rate of quantum light, and meeting the conditions for satellite-to-ground docking.

[0064] In the above Figure 2 Based on the method for adjusting the polarization state of quantum light shown, this application embodiment also provides another method for adjusting the polarization state of quantum light. Step 201, measuring the polarization state of the emitted quantum light, includes: sampling the emitted quantum light in real time and measuring the polarization state of the emitted quantum light using a single-track continuous sampling method.

[0065] The single-track continuous sampling method in quantum optics involves continuously measuring and sampling quantum light (such as single photons, entangled light, etc.) along a single optical track. By monitoring the quantum state changes of each or multiple photons in real time, their polarization states can be analyzed in real time, and the polarization state of the quantum light generated and emitted by the light source can be adjusted in real time.

[0066] Optionally, during sampling and measurement, single-photon detectors, polarization analyzers, and other methods can be used to detect and measure quantum light.

[0067] In this embodiment of the application, the measurement of the polarization state of the emitted quantum light is performed in real time, the determination of the change vector of the polarization state of the quantum light relative to the preset polarization state of the quantum light is also performed in real time, and the adjustment of the polarization state of the quantum light generated and emitted by the light source according to the change vector is also performed in real time.

[0068] In this embodiment of the application, the polarization state of the quantum light generated and emitted by the light source is adjusted in real time through real-time sampling and measurement processing, so that the polarization state of the quantum light emitted by the light source is kept near the preset polarization state in real time.

[0069] This application utilizes quantum light to achieve dynamic polarization control, directly using quantum light as the basis light signal for polarization compensation, simplifying system design and improving integration. Simultaneously, addressing the characteristics of low photon number and large fluctuations in the satellite-to-ground link, a dynamic scanning measurement method for polarization measurement is extracted, exhibiting strong resistance to link disturbances and high robustness. Specifically, the dynamic polarization control, under conditions of relative basis changes between satellite and ground without compensation, directly performs satellite-to-ground joint polarization control under equivalent dynamic conditions through continuous single-track data acquisition (collecting polarization states) combined with maximum likelihood estimation.

[0070] The quantum optical dynamic polarization compensation proposed in this application is a key technology in satellite-to-ground quantum key distribution. This scheme can effectively solve the problems of relative basis vector changes during satellite-to-ground docking and the increase in bit error rate caused by unitary transformation introduced by single-mode fiber, thereby significantly increasing the key generation rate of satellite-to-ground quantum key distribution, and can be applied to the development and experimentation of quantum micro / nano satellites.

[0071] Compared to static polarization compensation technology, this application has much lower requirements for the stability of the space-to-ground free-space link, and the requirements for the number of photons and fluctuations in measurement and calibration are also much lower, making it easier to implement. This application can directly perform space-to-ground joint polarization control under equivalent dynamic conditions by continuously sampling data from a single track and combining it with the maximum likelihood estimation method, even when there are relative basis vector changes between space and ground and no compensation is performed.

[0072] Current technical solutions are mostly geared towards quantum key distribution systems using fiber optic channels. In fiber optic systems, due to link stability and low polarization state change rates, polarization state measurement and compensation can be carried out relatively easily, ultimately achieving high-performance polarization control of the system. However, unlike fiber optic systems, achieving highly stable quantum links in satellite-to-ground quantum key distribution systems is extremely difficult. The received quantum light signals are small and inevitably exhibit large fluctuations, posing a severe challenge to satellite-to-ground polarization control. The applicant proposes using quantum light to achieve dynamic polarization control, which not only simplifies the need for additional polarization compensation basis light signals and improves integration, but also effectively suppresses the drawbacks of low photon count and large fluctuations in satellite-to-ground links using a dynamic scanning measurement method. This method has strong resistance to link disturbances and robustness, providing a feasible solution for future applications requiring miniaturized, low-cost micro / nano quantum communication constellations.

[0073] The steps of the various methods described above are only for clarity. In practice, they can be combined into one step or some steps can be split into multiple steps. As long as they include the same logical relationship, they are all within the scope of protection of this patent. Adding insignificant modifications or introducing insignificant designs to the algorithm or process, but without changing the core design of the algorithm and process, are also within the scope of protection of this patent.

[0074] This application relates to a device for adjusting the polarization state of quantum light. Figure 6 This is a schematic diagram of a quantum light polarization state adjustment device provided in an embodiment of this application. The specific structure of the device is as follows: Figure 6 As shown, the quantum light polarization state adjustment device specifically includes: a measurement module 601, a determination module 602, and an adjustment module 603.

[0075] Measurement module 601 is used to measure the polarization state of the emitted quantum light; wherein the quantum light is generated and emitted by a light source in the quantum communication satellite;

[0076] The determining module 602 is used to determine the change vector of the polarization state of quantum light relative to the preset polarization state of quantum light;

[0077] The adjustment module 603 is used to adjust the polarization state of the quantum light generated and emitted by the light source according to the change vector.

[0078] Optionally, before determining the change vector of the polarization state of the quantum light relative to the preset polarization state of the quantum light, the determining module 602 further includes: determining the preset polarization state of the quantum light.

[0079] Optionally, the determining module 602 is also used to determine the preset polarization state of the quantum light, including: performing a unitary transformation on the polarization state of the quantum light through a waveplate to obtain the preset polarization state of the quantum light.

[0080] Optionally, the determining module 602 is further configured to use waveplates including: a first quarter-wave plate, a second quarter-wave plate, and a half-wave plate; to perform unitary transformation on the polarization state of quantum light through the three waveplates to obtain a preset polarization state of quantum light, including: the first quarter-wave plate transforms the R-ray of quantum light to obtain a first transformed quantum light; the second quarter-wave plate transforms the H-ray of the first transformed quantum light to obtain a second transformed quantum light; and the half-wave plate transforms the H-ray of the second transformed quantum light to obtain the preset polarization state of quantum light.

[0081] Optionally, the adjustment module 603 is also used to measure that there are multiple polarization states of the emitted quantum light, and the multiple polarization states correspond to multiple change vectors; and to adjust the polarization state of the quantum light generated and emitted by the light source according to the multiple change vectors, including: determining a target change vector according to the multiple change vectors; and adjusting the polarization state of the quantum light generated and emitted by the light source based on the target change vector.

[0082] Optionally, the determining module 602 is further configured to determine a target change vector based on multiple change vectors, including: performing maximum likelihood estimation on the multiple change vectors to determine the target change vector.

[0083] Optionally, the adjustment module 603 is also used to adjust the polarization state of the quantum light generated and emitted by the light source based on the target change vector, including: adjusting the polarization control element in the light source according to the target change vector to adjust the polarization state of the quantum light generated and emitted by the light source.

[0084] Optionally, the adjustment module 603 is also used to measure the polarization state of the emitted quantum light, including: sampling the emitted quantum light in real time and measuring the polarization state of the emitted quantum light using a single-track continuous sampling method.

[0085] It is worth mentioning that all modules involved in this embodiment are logical modules. In practical applications, a logical unit can be a physical unit, a part of a physical unit, or a combination of multiple physical units. Furthermore, to highlight the innovative aspects of this invention, this embodiment does not introduce units that are not closely related to solving the technical problem proposed by this invention; however, this does not mean that other units are absent from this embodiment.

[0086] This application relates to a quantum communication satellite. Figure 7 This is a schematic diagram of the structure of a quantum communication satellite provided in an embodiment of this application, as shown below. Figure 7 As shown, it includes: at least one processor 701; and a memory 702 communicatively connected to at least one processor 701; wherein the memory 702 stores instructions executable by at least one processor 701, the instructions being executed by at least one processor 701 to enable at least one processor 701 to perform the quantum light polarization state adjustment method in the above embodiments.

[0087] The memory 702 and the processor 701 are connected by a bus, which can include any number of interconnected buses and bridges, and connect various circuits of one or more processors and the memory together.

[0088] This application relates to a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, it implements the method embodiments described above.

[0089] That is, those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. This program is stored in a storage medium and includes several instructions to cause a device (which may be a microcontroller, chip, etc.) or processor to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0090] This application relates to a computer program product storing a computer program. When the computer program is executed by a processor, it implements the method embodiments described above.

[0091] Those skilled in the art will understand that the above embodiments are specific embodiments for implementing this application, and in practical applications, various changes can be made to them in form and detail without departing from the spirit and scope of this application.

Claims

1. A method for adjusting the polarization state of quantum light, characterized in that, The method, applied to quantum communication satellites, includes: The polarization state of emitted quantum light is measured; wherein the quantum light is generated and emitted by a light source in the quantum communication satellite; Determine the vector change in the polarization state of the quantum light relative to a preset polarization state of the quantum light; The polarization state of the quantum light generated and emitted by the light source is adjusted according to the change vector.

2. The method for adjusting the polarization state of quantum light according to claim 1, characterized in that, Before determining the change vector of the polarization state of the quantum light relative to the preset polarization state of the quantum light, the method further includes: Determine the preset polarization state of the quantum light.

3. The method for adjusting the polarization state of quantum light according to claim 2, characterized in that, Determining the preset polarization state of the quantum light includes: The preset polarization state of the quantum light is obtained by performing a unitary transformation on the polarization state of the quantum light using a waveplate.

4. The method for adjusting the polarization state of quantum light according to claim 3, characterized in that, The waveplates include: a first quarter-wave plate, a second quarter-wave plate, and a half-wave plate; the polarization state of the quantum light is subjected to a unitary transformation through the three waveplates to obtain a preset polarization state of the quantum light, including: The first quarter-wave plate transforms the R-beam of the quantum light to obtain the first transformed quantum light; The second quarter-wave plate transforms the H-light of the first transformed quantum light to obtain the second transformed quantum light; The half-wave plate transforms the H-light of the second transformed quantum light to obtain the preset polarization state of the quantum light.

5. The method for adjusting the polarization state of quantum light according to claim 1, characterized in that, The measured emitted quantum light has multiple polarization states, and these multiple polarization states correspond to multiple change vectors. Adjusting the polarization state of the quantum light generated and emitted by the light source according to these multiple change vectors includes: Determine the target change vector based on multiple change vectors; Based on the target change vector, the polarization state of the quantum light generated and emitted by the light source is adjusted.

6. The method for adjusting the polarization state of quantum light according to claim 5, characterized in that, The step of determining the target change vector based on multiple change vectors includes: The target change vector is determined by performing maximum likelihood estimation on the multiple change vectors.

7. The method for adjusting the polarization state of quantum light according to claim 5, characterized in that, The step of adjusting the polarization state of the quantum light generated and emitted by the light source based on the target change vector includes: According to the target change vector, the polarization control element in the light source is adjusted to adjust the polarization state of the quantum light generated and emitted by the light source.

8. The method for adjusting the polarization state of quantum light according to claim 1, characterized in that, The measurement of the polarization state of the emitted quantum light includes: The emitted quantum light is sampled in real time and its polarization state is measured using a single-track continuous sampling method.

9. A device for adjusting the polarization state of quantum light, characterized in that, include: A measurement module is used to measure the polarization state of emitted quantum light; wherein the quantum light is generated and emitted by a light source in the quantum communication satellite; The determining module is used to determine the change vector of the polarization state of the quantum light relative to a preset polarization state of the quantum light; An adjustment module is used to adjust the polarization state of the quantum light generated and emitted by the light source according to the change vector.

10. A quantum communication satellite, characterized in that, include: At least one processor; And, a memory communicatively connected to the at least one processor; The memory stores instructions that can be executed by the at least one processor, which, when executed by the at least one processor, enables the at least one processor to perform the quantum light polarization state adjustment method according to any one of claims 1 to 8.

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