Satellite quantum communication system and method based on hour-level quantum storage

Abstract

The application discloses a satellite quantum communication system and method based on hour-level quantum storage, wherein the system comprises: a quantum communication satellite payload end for generating entangled photon pairs, which are independently sent to corresponding satellite ground stations; two satellite ground stations for obtaining symmetric keys from the entangled photon pairs, and performing information encryption and quantum communication by using the symmetric keys; specifically, the weather is monitored, and it is judged whether the entangled photons can effectively pass through; if yes, the transit satellite is tracked, the entangled photons are received and measured by a measurement module to obtain the symmetric keys; if not, a UAV is started, the entangled photons are received and stored in the hour-level quantum storage module, after the satellite transits, the UAV returns to the satellite ground station, the entangled information in the quantum storage is read and measured to obtain the symmetric keys. The application can effectively improve the real-time performance and security of quantum key distribution.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of quantum communication, in particular to a satellite quantum communication system and method based on hour-level quantum storage. BACKGROUND

[0002] Quantum communication can provide a new way of distributing keys, generally based on the quantum entanglement or superposition of photons, and quantum communication ensures that the key is not deciphered in the transmission channel. According to the difference of quantum optical transmission channel, it can be generally divided into fiber quantum communication and satellite quantum communication. Since the fiber has a fixed link attenuation of about 0.2 dB / km, there will also be additional attenuation at the fiber welding site, and for long-distance quantum communication, satellite quantum communication is generally used.

[0003] According to the difference of communication protocol, satellite quantum communication can use BB84 protocol based on decoy state and BBM92 protocol based on entangled light source. For two ground stations to share keys, the BB84 protocol based on decoy state needs to distribute keys with one of the stations through the satellite first, then distribute keys with the other station, and then use the XOR method to enable the two ground stations to share secure keys, which requires the satellite to be a secure and trusted relay. At present, many intercontinental quantum key distribution adopts this way. Based on the BBM92 quantum key distribution protocol, the satellite simultaneously distributes entangled light to two ground stations, and the two ground stations measure after receiving the photons to obtain symmetric keys. This way does not require the satellite to be a trusted relay, so it is more secure. However, since this way requires both satellite ground stations to be sunny, it to some extent limits the application of this protocol. Some solutions propose to equip quantum storage devices at satellite ground stations, which can use sunny days to distribute entanglement and store it for later measurement. This way requires long-term quantum storage, which is not available at the current stage. SUMMARY

[0004] The main purpose of the present application is to provide a satellite quantum communication system and method based on hour-level quantum storage, which can realize quantum key distribution under different weather conditions and effectively improve the real-time performance and security of quantum key distribution.

[0005] The technical solution adopted by the present application is:

[0006] A satellite quantum communication system based on hour-level quantum storage is provided, comprising:

[0007] The quantum communication satellite payload end comprises an entangled light source and two transmitting telescopes. The entangled light source is started according to the satellite transit time and trajectory to generate entangled photon pairs. The two transmitting telescopes independently send the entangled photon pairs to the corresponding satellite ground stations through pointing and tracking.

[0008] Two satellite ground stations are used to obtain symmetric keys from entangled photon pairs, and information is encrypted by symmetric keys before classical communication; the satellite ground station comprises a weather monitoring module, a receiving telescope, a measurement module, a quantum storage module of hour level and a UAV; wherein the weather monitoring module is used to monitor the weather and determine whether the entangled photons can effectively pass through each satellite ground station, if yes, the transit satellite is tracked by turning on the pointing and tracking mode of the receiving telescope, the entangled photon pairs are received and measured by the measurement module to obtain the symmetric keys; if not, the satellite ground station starts the UAV, carries the receiving telescope and the quantum storage module of hour level, flies to the appropriate position above the cloud layer according to the satellite orbit and pointing, receives the entangled photons through the receiving telescope and stores them into the quantum storage module of hour level, after the satellite transits, the UAV returns to the satellite ground station, reads the entangled information in the quantum storage module and measures it by the measurement module, and then the symmetric keys are obtained by the data processing module.

[0009] According to the above technical solution, the two satellite ground stations send corresponding communication instructions to the quantum communication satellite payload in advance before quantum communication.

[0010] According to the above technical solution, the quantum storage module of hour level comprises a quantum storage medium, which is a solid-state quantum storage medium based on rare earth ion doping, quantum dots or cold atomic groups.

[0011] According to the above technical solution, the quantum storage module of hour level further comprises a control pulse module and a timing control module, wherein the control pulse module is used to control laser, microwave or radio frequency pulses to initialize and manipulate quantum states; and the timing control module is used for clock synchronization.

[0012] According to the above technical solution, if the entangled photons are received by the receiving telescope carried by the UAV, the quantum information is stored first, and then read out and measured after the aircraft lands on the ground; if the entangled photons are directly received by the receiving telescope on the ground, they are directly measured.

[0013] The application also provides a satellite quantum communication method based on quantum storage of hour level, comprising the following steps:

[0014] The quantum communication satellite payload starts an entangled light source according to the satellite transit time and trajectory, the entangled light source generates entangled photon pairs, and the entangled photon pairs are independently sent to the corresponding satellite ground station through the pointing and tracking of two transmitting telescopes;

[0015] The satellite ground station monitors the weather and judges whether the entangled photon pairs can pass through effectively, if yes, the overflight satellite is tracked to receive the entangled photons, and the entangled photons are measured to obtain the symmetric key, if no, the unmanned aerial vehicle is started to carry the receiving telescope and the quantum storage module of the hour level, flies to the appropriate position above the cloud layer according to the satellite orbit and direction, receives the entangled photon pairs through the receiving telescope and stores them into the quantum storage module of the hour level, after the satellite overflight ends, the unmanned aerial vehicle returns to the satellite ground station, reads the entangled information in the quantum storage and measures, and then obtains the symmetric key through data processing.

[0016] The satellite ground station encrypts information by using the symmetric key and then performs classical communication with other satellite ground stations.

[0017] According to the above technical scheme, before quantum communication, the two satellite ground stations send corresponding communication instructions to the quantum communication satellite payload, and the quantum communication satellite payload sends the entangled photons to the corresponding satellite ground stations according to the communication instructions.

[0018] According to the above technical scheme, if the entangled photons are received by the unmanned aerial vehicle carrying the receiving telescope, data transmission is performed through the classical channel, and if the entangled photons are directly received by the receiving telescope on the ground, data transmission is performed through classical communication or laser communication.

[0019] According to the above technical scheme, the quantum communication satellite payload and the two satellite ground stations perform quantum key distribution based on the BBM92 protocol.

[0020] According to the above technical scheme, the entangled light source directly generates single photons, and the polarization entanglement principle is used for encoding.

[0021] The present application has the advantages that the satellite quantum communication system based on the quantum storage of the hour level can take off by the unmanned aerial vehicle carrying the quantum storage device and the receiving telescope when the weather is bad and the quantum light cannot penetrate the cloud layer, receive and store the quantum light, and then return to the ground station to complete the reading and measurement of the quantum light. The present application can effectively solve the practical difficulty that the two satellite ground stations cannot guarantee good weather at the same time in the satellite quantum key distribution, and improve the real-time performance and security of the quantum key distribution.

[0022] Of course, any product implementing the present application does not necessarily need to achieve all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required by the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0024] Figure 1 is a structural schematic diagram of a satellite quantum communication system based on hour-level quantum storage according to an embodiment of the present application;

[0025] Figure 2 is a complete satellite quantum communication flowchart according to an embodiment of the present application. DETAILED DESCRIPTION

[0026] In order to make the objects, technical solutions and advantages of the present application clearer, the following will further describe the present application in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0027] It should be noted that the diagrams provided in the embodiments of the present application only illustrate the basic concept of the present application in a schematic manner, and therefore only the components related to the present application are shown in the diagrams, not the number, shape and size of the components when actually implemented. The actual implementation of each component can be arbitrarily changed in shape, number and proportion, and the layout pattern of the components can also be more complex.

[0028] In the present application, it should also be noted that, if terms such as "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like appear, the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, if the terms "first" and "second" appear, they are only for description and distinction purposes and cannot be understood as indicating or implying relative importance.

[0029] In addition, it should also be noted that the features of various embodiments of the present application can be combined or integrated partially or entirely, and as understood by those skilled in the art, can interact and operate in different ways. Each embodiment can be realized independently of each other, or in an associated relationship.

[0030] The present application proposes a satellite quantum communication system based on quantum storage, which only needs to achieve hour-level storage time, that is, to complete the quantum key distribution of the two-station BBM92 protocol when the weather is bad. The hour-level quantum storage device has been completed in the laboratory.

[0031] Unlike the BB84 light source, the entangled light source directly generates single photons, and uses a BBO crystal or a PPLN crystal to generate entangled photon pairs through parametric down-conversion. The crystal is composed of two thin crystals with perpendicular optical axes and is used to generate a type I parametric down-conversion process. Under the condition of satisfying phase matching, one e light photon will split into two o light photons, i.e., one horizontally (vertically) polarized photon splits into two vertically (horizontally) polarized photons. The BB84 light source directly attenuates coherent light, while the entangled light source directly generates single photons.

[0032] Unlike the ground entangled source, the ground entangled source does not have too much requirement on the generation rate and wavelength, while the satellite payload end needs to generate high rate and wavelength in the atmospheric window due to atmospheric attenuation and other factors. Here, the entangled source with high single photon generation rate and entangled light wavelength in the 1500ns-1580nm band can be selected. After the pulsed light enters the crystal to generate entangled light, the entangled light enters the coupler connected to the polarization maintaining optical fiber to ensure that the polarization does not change. The polarization maintaining optical fiber is connected to the telescope, the distance of the optical element is controlled, and the length of the optical fiber is controlled to ensure that the time of the entangled photon pair reaching the two telescopes is substantially the same, and appropriate elements are selected to ensure that the optical efficiency of the two light reaching the telescope is consistent. The telescopes can be selected to have consistent size, consistent optical efficiency, highest transmission efficiency in the 1550nm-1580nm band, and can be independently pointed. As in the sending end, the aircraft end and the detection end need to maintain the same optical efficiency of the quantum storage module and the ground reading and measuring module.

[0033] Since the quantum storage module and the measuring module need accurate time synchronization, the satellite and the two aircrafts and the two ground stations need to maintain accurate clock synchronization, and the clock synchronization accuracy is high. Among them, the satellite and the aircraft use the beacon light to emit classical light pulses to perform clock synchronization, while the aircraft and the ground need to use light pulses or more accurate atomic clocks to synchronize their clocks in advance. At this time, the relative clock accuracy of each module can meet the requirements, but the absolute time accuracy of the two ground data processing modules is not determined.

[0034] Since coincidence counting is required in the entanglement experiment (i.e., selecting appropriate photons from the entangled photons received by the two satellite ground stations to form entangled photon pairs), the present application adopts a post-processing method to synchronize the relative time of the two sites.

[0035] Quantum storage module stores quantum state and can read out the stored quantum state after a period of time. In the past decade, quantum storage has been studied in various storage schemes. The quantum storage schemes include: electromagnetically induced transparency, Duan-Lukin-Cirac-Zoller (DLCZ) storage scheme, Faraday interaction, reversible inhomogeneous broadening, atomic frequency comb, Raman storage, and ladder storage. The above storage schemes are essentially the evolution and recovery of light and matter interaction, internal state interference of matter, or phase relationship.

[0036] An embodiment of the present application is based on the satellite quantum communication of BBM92 protocol, which generally requires that the weather of two stations is fine at the same time, or there is a long-time quantum storage device. The satellite quantum communication system based on the hour-level quantum storage can effectively solve the problem of quantum key generation when the weather of two stations is not good.

[0037] The satellite quantum communication system based on the hour-level quantum storage includes the following parts: a satellite quantum communication payload end and two satellite ground station ends. The satellite quantum communication payload end is mainly used for generating entangled photons and transmitting quantum light to two ground stations; the two satellite ground stations are used for receiving and measuring the entangled photons transmitted by the satellite, wherein each ground station includes an unmanned aerial vehicle receiving terminal carrying a quantum storage module.

[0038] When the weather is not good and the quantum light cannot penetrate the cloud layer, the unmanned aerial vehicle carrying the quantum storage module and the receiving telescope can be launched to receive and store the quantum light, and then return to the ground station to complete the reading out and measurement of the quantum light. The system can effectively solve the practical difficulty that the two satellite ground stations cannot guarantee good weather at the same time based on the satellite quantum key distribution of BBM92 protocol, and effectively improve the real-time performance and security of quantum key distribution.

[0039] Specifically, as shown in Figure 1 The quantum communication satellite payload includes a quantum satellite entangled light source A for generating entangled photon pairs and two independently pointing and tracking transmitting telescopes A1 and A2. The entangled photon pairs are generated by the quantum satellite entangled light source A and independently transmitted to the ground receiving station by the two transmitting telescopes. The satellite payload end generally needs to be configured with corresponding power supply and electronic devices to ensure the normal operation of the satellite. All parts of the satellite payload need to adapt to the space environment.

[0040] The two satellite ground stations are mainly used for obtaining symmetric keys from the entangled photon pairs, and performing information encryption and quantum communication using the symmetric keys. As shown in Figure 1As shown, the satellite ground station of the present application comprises a weather monitoring module, a receiving telescope, a measurement module, a data processing module, a quantum storage module of the order of hours and a UAV; wherein the weather monitoring module is used to monitor the weather and determine whether the entangled photons can pass through effectively, if yes, the pointing and tracking mode is opened through the receiving telescope to track the passing satellite, receive the entangled photons and measure them through the measurement module to obtain the symmetric key; if not, the UAV is started to carry the receiving telescope and the quantum storage module of the order of hours, fly to the appropriate position above the cloud layer according to the satellite orbit and pointing, receive the entangled photons through the receiving telescope and store them into the quantum storage module of the order of hours, after the satellite passes, the UAV returns to the satellite ground station, reads the entangled information in the quantum storage and measures it through the measurement module, and then processes the symmetric key through the data processing module.

[0041] Among them, the quantum storage module includes quantum storage medium, such as using solid-state quantum storage medium based on rare earth ion doping, quantum dots, cold atom groups, etc.; control pulse module; laser, microwave or radio frequency pulse, used for initialization, manipulation of quantum state; and timing control module: electronic device for accurate synchronization of quantum operation.

[0042] The satellite ground station can receive the entangled photons transmitted by the satellite and measure them, and through the assistance of classical communication, a group of keys can be shared between two different satellite ground stations. At the same time, the UAV with quantum storage of the order of hours is configured in the satellite ground station, which takes off when the weather is bad, crosses the cloud layer, and reaches the stratosphere and above. The measurement module of the satellite ground station can be divided into a measurement module that only needs to measure the polarization entanglement information, and a reading and measurement module that first reads the information in the quantum storage module and then measures it. The UAV part can not be configured with a measurement module and a data processing module, and part of the data can be multiplexed through the ground fixed module.

[0043] As shown in Figure 2 A complete satellite quantum communication process is as follows:

[0044] S1, determine that two ground stations need to carry out quantum communication experiment, and send relevant instructions to satellite payload and satellite ground station.

[0045] S2, the satellite payload starts the quantum light source to generate entangled photon pairs in time according to the satellite passing time and trajectory, and points two emission telescopes to two satellite ground stations to be connected.

[0046] S3, the satellite ground station monitors the weather through the weather monitoring module at the site, and determines whether the entangled photons can pass through each satellite ground station effectively.

[0047] S4, if the judgment can be, through the ground fixed end of receiving telescope open pointing, tracking mode, tracking the transit satellite, receiving entangled photons and through the measurement module for direct measurement, through the data processing module data processing, between the two ground stations to produce symmetric key.

[0048] S5, if the judgment is not, the satellite ground station starts the unmanned aerial vehicle, carries the receiving telescope and quantum storage module, according to the satellite orbit and pointing, flies to the appropriate position above the cloud layer, receives the entangled photons through the receiving telescope, and stores them into the quantum storage module. After the satellite transits, the unmanned aerial vehicle returns to the ground station, and the photons in the quantum storage module are read out and measured through the reading and measuring module, and the symmetric key is obtained. Generally, the transit time of low-orbit satellite is about 10 minutes, and the quantum storage of hours is enough to complete the landing of the unmanned aerial vehicle and the time required for reading and measuring the photons.

[0049] S6, two satellite ground stations use the obtained symmetric key to encrypt information.

[0050] The satellite quantum communication method based on the quantum storage of hours mainly includes the following steps:

[0051] The quantum communication satellite payload starts the entangled light source according to the satellite transit time and trajectory, the entangled light source generates entangled photon pairs, and the entangled photon pairs are independently sent to the corresponding satellite ground station through the pointing and tracking of the two transmitting telescopes;

[0052] The satellite ground station monitors the weather and judges whether the entangled photon pairs can pass through each satellite ground station effectively. If yes, the transit satellite is tracked, the entangled photons are received, and the entangled photons are measured to obtain the symmetric key. If not, the satellite ground station starts the unmanned aerial vehicle, carries the receiving telescope and the quantum storage module of hours, flies to the appropriate position above the cloud layer according to the satellite orbit and pointing, receives the entangled photons through the receiving telescope, and stores them into the quantum storage module of hours. After the satellite transits, the unmanned aerial vehicle returns to the satellite ground station, and the entangled photon pairs in the quantum storage module are read out and measured through the measuring module, and the symmetric key is obtained.

[0053] The satellite ground station uses the symmetric key to encrypt information and then performs classical communication with other satellite ground stations.

[0054] Further, the two satellite ground stations send corresponding communication instructions to the quantum communication satellite payload before quantum communication, and the quantum communication satellite payload sends the entangled photons to the corresponding satellite ground station according to the communication instructions.

[0055] If the entangled photon pair is received by the receiving telescope carried by the unmanned aerial vehicle, data transmission is performed through the classical channel; if the entangled photon pair is directly received by the receiving telescope on the ground, data transmission is performed through classical communication or laser communication.

[0056] Quantum key distribution is performed between the payload end of the quantum communication satellite and the two satellite ground stations based on the BBM92 protocol.

[0057] In this embodiment, the entangled light source directly generates single photons, and the single photon generation rate is high.

[0058] It should be noted that, according to the needs of implementation, each step / component described in the present application can be split into more steps / components, or two or more steps / components or part of the operation of the steps / components can be combined into a new step / component, so as to achieve the purpose of the present application.

[0059] The size of the serial number of each step in the above embodiment does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0060] It should be understood that, for those skilled in the art, improvements or changes can be made according to the above description, and all these improvements and changes shall fall within the protection scope of the appended claims of the present application.

Claims

1. A satellite quantum communication system based on hour-level quantum storage, characterized in that, include: The quantum communication satellite payload includes an entangled light source and two transmitting telescopes. The entangled light source is activated according to the satellite's transit time and trajectory to generate entangled photon pairs. The two transmitting telescopes independently transmit the entangled photon pairs to their respective satellite ground stations through pointing and tracking. Two satellite ground stations are used to obtain symmetric keys from entangled photon pairs, encrypt information using these keys, and then conduct classical communication. Each satellite ground station includes a weather monitoring module, a receiving telescope, a measurement module, a data processing module, an hourly quantum storage module, and a drone. The weather monitoring module monitors the weather and determines whether entangled photons can effectively pass through each satellite ground station. If so, it uses the receiving telescope to activate pointing and tracking mode to track the passing satellite, receive the entangled photons, and measure them using the measurement module to obtain the symmetric key. If not, the satellite ground station launches a drone carrying the receiving telescope and the hourly quantum storage module. Following the satellite's orbit and pointing direction, the drone flies to a suitable position above the clouds, receives the entangled photons through the receiving telescope, and stores them in the hourly quantum storage module. After the satellite passes over the satellite, the drone returns to the satellite ground station, reads and measures the entangled information in the quantum storage using the measurement module, and then processes the data using the data processing module to obtain the symmetric key.

2. The satellite quantum communication system based on hour-level quantum storage according to claim 1, characterized in that, Before quantum communication, the two satellite ground stations send the corresponding communication commands to the quantum communication satellite payload in advance.

3. The satellite quantum communication system based on hour-level quantum storage according to claim 1, characterized in that, Hourly quantum storage modules include quantum storage media, which utilize solid-state quantum storage media based on rare-earth ion doping, quantum dots, or cold atom clusters.

4. The satellite quantum communication system based on hour-level quantum storage according to claim 1, characterized in that, The hour-level quantum storage module also includes a control pulse module and a timing control module. The control pulse module is used to control laser, microwave or radio frequency pulses to initialize and manipulate quantum states; the timing control module is used for clock synchronization.

5. The satellite quantum communication system based on hour-level quantum storage according to claim 1, characterized in that, If entangled photons are received using a drone carrying a receiving telescope, the quantum information must first be stored, and then read and measured after the drone lands on the ground; if the receiving telescope is used directly on the ground, the measurement can be performed directly.

6. A satellite quantum communication method based on hour-level quantum storage, characterized in that, Includes the following steps: The quantum communication satellite payload activates an entangled light source based on the satellite's transit time and trajectory. The entangled light source generates entangled photon pairs, which are then independently transmitted to the corresponding satellite ground stations via two transmitting telescopes for pointing and tracking. The satellite ground station monitors the weather and determines whether entangled photons can pass effectively. If so, it tracks the passing satellite, receives the entangled photons, and measures them to obtain the symmetric key. If not, it launches a drone carrying a receiving telescope and an hourly quantum storage module. Following the satellite's orbit and direction, the drone flies to a suitable position above the clouds, receives the entangled photons through the receiving telescope, and stores them in the hourly quantum storage module. After the satellite passes over, the drone returns to the satellite ground station, reads and measures the entanglement information in the quantum memory through the measurement module, and then obtains the symmetric key through data processing. Satellite ground stations use symmetric keys to encrypt information before communicating with other satellite ground stations.

7. The satellite quantum communication method based on hour-level quantum storage according to claim 6, characterized in that, Before quantum communication, the two satellite ground stations send the corresponding communication commands to the quantum communication satellite payload in advance. The quantum communication satellite payload then sends entangled photons to the corresponding satellite ground station according to the communication commands.

8. The satellite quantum communication method based on hour-level quantum storage according to claim 6, characterized in that, If entangled photons are received via a drone carrying a receiving telescope, data transmission is performed through a classical channel; if the data is received directly via a ground-based receiving telescope, classical communication or laser communication is used for data transmission.

9. The satellite quantum communication method based on hour-level quantum storage according to claim 6, characterized in that, Quantum key distribution between the quantum communication satellite payload and two satellite ground stations is based on the BBM92 protocol.

10. The satellite quantum communication method based on hour-level quantum storage according to any one of claims 6-9, characterized in that, Entangled light sources directly generate single photons and encode them using the principle of polarization entanglement.

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