A quantum key distribution method and system in free space channel

Abstract

The present invention proposes a quantum key distribution method and system under a free-space channel. The transmitting device is used to control a first quantum state transmitter to transmit quantum light under the free-space channel according to a first transmitting-side random state basis; the receiving device is used to control an i-th quantum state receiver to receive quantum light according to an i-th receiving-side random state basis, wherein 1≤i≤N; the receiving device is used to transmit the i-th receiving-side random state basis to the transmitting device through a classical channel; after receiving the i-th receiving-side random state basis, the transmitting device is used to feed back the first transmitting-side random state basis to the receiving device through a classical channel; when the first transmitting-side random state basis is the same as the i-th receiving-side random state basis, the transmitting device is used to generate a current quantum key according to the quantum light emitted by the first quantum state transmitter, and the receiving device is used to generate a current quantum key according to the quantum light received by the i-th quantum state receiver, thereby increasing the key generation rate.

Description

Technical Field

[0001] The present invention relates to the field of quantum communication, and in particular to a quantum key distribution method and system under a free-space channel. Background Art

[0002] Quantum Key Distribution (QKD) is a confidential communication method that uses quantum systems as information carriers for transmission and then extracts shared security keys. For example, single photons are used as carriers, the transmitter loads encoded information, and the receiver detects the decoded information and then extracts the shared security key.

[0003] Quantum key distribution is an important branch of quantum information technology. The transmission channels of quantum key distribution equipment mainly include optical fiber channels and free-space channels. Quantum key distribution under free-space channels can be applied to scenarios such as satellites and drones. The information carrier of free-space quantum key distribution is mainly attenuated laser beams.

[0004] Currently, quantum key distribution devices in satellite and drone scenarios all use a single-transmit and single-receive method. However, since laser beams in free space inevitably diverge, not all photons at the transmitting end can be received, resulting in a lower key generation rate. Summary of the Invention

[0005] The object of the present invention is to provide a quantum key distribution method and system under a free-space channel to at least partially improve the above-mentioned problems.

[0006] In order to achieve the above objectives, the technical solutions adopted in the embodiments of the present invention are as follows:

[0007] In a first aspect, an embodiment of the present invention provides a quantum key distribution system in a free-space channel, the quantum key distribution system comprising a transmitting device and a receiving device, the transmitting device being provided with a first quantum state transmitter, and the receiving device being provided with N quantum state receivers;

[0008] The transmitting device is used to control the first quantum state transmitter to transmit quantum light in a free space channel according to the first transmitting-side random state basis;

[0009] The receiving device is used to control the i-th quantum state receiver to receive quantum light according to the i-th receiving side random state basis, where 1≤i≤N;

[0010] The receiving device is configured to transmit the i-th receiving-side random state basis to the transmitting device through a classical channel;

[0011] The transmitting device is configured to feed back the first transmitting side random state base to the receiving device through a classical channel after receiving the i-th receiving side random state base;

[0012] When the first transmitting side random state basis is the same as the i-th receiving side random state basis, the transmitting device is used to generate a current quantum key based on the quantum light emitted by the first quantum state transmitter, and the receiving device is used to generate a current quantum key based on the quantum light received by the i-th quantum state receiver.

[0013] Optionally, when the first transmitting side random state basis is the same as the i-th receiving side random state basis, the transmitting device is used to search for quantum light and key mapping information, and determine the quantum key that matches the quantum light emitted by the first quantum state transmitter as the current quantum key; the receiving device is used to search for quantum light and key mapping information, and determine the quantum key that matches the quantum light received by the i-th quantum state receiver as the current quantum key.

[0014] Optionally, when the first transmitting-side random state basis is different from all receiving-side random state basis, the transmitting device and the receiving device are configured to determine that basis matching has failed.

[0015] Optionally, the transmitting device is provided with M quantum state transmitters;

[0016] The transmitting device is used to control the j-th quantum state emitter to emit quantum light in a free space channel according to the j-th transmitting side random state basis within the j-th interval of the current quantum light emission cycle;

[0017] The receiving device is used to control the i-th quantum state receiver to receive quantum light according to the i-th receiving side random state basis within the j-th interval, where 1≤j≤M;

[0018] The receiving device is configured to transmit the i-th receiving-side random state basis corresponding to the j-th interval to the transmitting device through a classical channel;

[0019] After receiving the i-th receiving-side random state base corresponding to the j-th interval, the transmitting device feeds back the j-th transmitting-side random state base to the receiving device through the classical channel;

[0020] When the random state basis of the i-th receiving side corresponding to the j-th interval is the same as the random state basis of the j-th transmitting side, the transmitting device is used to generate the quantum key of the j-th interval based on the quantum light emitted by the j-th quantum state transmitter in the j-th interval; the receiving device is used to generate the quantum key of the j-th interval based on the quantum light received by the i-th quantum state receiver in the j-th interval.

[0021] Optionally, the transmitting device and the receiving device are used to sort multiple interval quantum keys generated in the current quantum light emission cycle, and call the interval quantum keys generated in the current quantum light emission cycle according to the sorting.

[0022] Optionally, the transmitting device includes a first controller and M quantum state transmitters, the first controller is connected to the M quantum state transmitters respectively, and the first controller is connected to the receiving device through a classical channel communication.

[0023] Optionally, the receiving device includes a second controller and N quantum state receivers, the second controller is connected to the N quantum state receivers respectively, and the second controller is connected to the transmitting device through a classical channel communication.

[0024] Optionally, the M quantum state transmitters and the N quantum state receivers are time synchronized at preset periodic intervals.

[0025] In a second aspect, an embodiment of the present invention provides a quantum key distribution method in a free-space channel, which is applied to the above-mentioned quantum key distribution system. The method includes:

[0026] The transmitting device controls the first quantum state transmitter to transmit quantum light in a free space channel according to the first transmitting side random state basis;

[0027] The receiving device controls the i-th quantum state receiver to receive quantum light according to the i-th receiving side random state basis, where 1≤i≤N;

[0028] The receiving device transmits the i-th receiving-side random state basis to the transmitting device through a classical channel;

[0029] After receiving the i-th receiving-side random state base, the transmitting device feeds back the first transmitting-side random state base to the receiving device through a classical channel;

[0030] When the first transmitting side random state basis is the same as the i-th receiving side random state basis, the transmitting device generates a current quantum key based on the quantum light emitted by the first quantum state transmitter, and the receiving device generates a current quantum key based on the quantum light received by the i-th quantum state receiver.

[0031] Optionally, the step of the transmitting device generating a current quantum key according to the quantum light emitted by the first quantum state transmitter, and the receiving device generating a current quantum key according to the quantum light received by the i-th quantum state receiver includes:

[0032] The transmitting device searches for quantum light and key mapping information, and determines a quantum key that matches the quantum light emitted by the first quantum state emitter as the current quantum key;

[0033] The receiving device searches for quantum light and key mapping information, and determines a quantum key that matches the quantum light received by the i-th quantum state receiver as the current quantum key.

[0034] Compared with the prior art, the embodiments of the present invention provide a quantum key distribution method and system under a free-space channel, wherein a transmitting device is used to control a first quantum state transmitter to transmit quantum light under a free-space channel according to a first transmitting-side random state basis; a receiving device is used to control an i-th quantum state receiver to receive quantum light according to an i-th receiving-side random state basis, where 1≤i≤N; the receiving device is used to transmit the i-th receiving-side random state basis to the transmitting device through a classical channel; the transmitting device is used to feed back the first transmitting-side random state basis to the receiving device through a classical channel after receiving the i-th receiving-side random state basis; when the first transmitting-side random state basis is the same as the i-th receiving-side random state basis, the transmitting device is used to generate a current quantum key based on the quantum light emitted by the first quantum state transmitter, and the receiving device is used to generate a current quantum key based on the quantum light received by the i-th quantum state receiver, thereby increasing the key generation rate.

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 This is one of the structural diagrams of the quantum key distribution system provided by an embodiment of the present invention.

[0038] Figure 2 This is the second structural diagram of the quantum key distribution system provided by an embodiment of the present invention.

[0039] Figure 3 The third structural diagram of the quantum key distribution system provided by an embodiment of the present invention.

[0040] Figure 4 A schematic diagram of the flow of a quantum key distribution method provided in an embodiment of the present invention.

[0041] In the figure: 10 - transmitting device; 20 - receiving device; 101 - quantum state transmitter; 102 - first controller; 201 - quantum state receiver; 202 - second controller. DETAILED DESCRIPTION

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0043] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0044] It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings. At the same time, in the description of the present invention, the terms "first", "second", etc. are used only to distinguish the description and should not be understood as indicating or implying relative importance.

[0045] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0046] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they should not be understood as limiting the present invention.

[0047] In the description of the present invention, it should also be noted that, unless otherwise expressly specified or limited, the terms "disposed" and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections, or electrical connections; direct connections, indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0048] The following embodiments of the present invention are described in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0049] In order to improve the key generation rate, the embodiment of the present invention provides a quantum key distribution system under a free space channel, please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of a quantum key distribution system provided by an embodiment of the present invention. The quantum key distribution system includes a transmitting device 10 and a receiving device 20. The transmitting device 10 is provided with one or more quantum state transmitters 101. Figure 1 In the example, the transmitting device 10 is provided with one quantum state transmitter 101, i.e., the first quantum state transmitter 101. When the transmitting device 10 is provided with M quantum state transmitters 101, it can be represented as the jth quantum state transmitter 101, where 1≤j≤M. The receiving device 20 is provided with N quantum state receivers 201, which can be represented as the i-th quantum state receiver 201, where 1≤i≤N.

[0050] The transmitting device 10 and the receiving device 20 are communicatively connected via a classical channel.

[0051] The transmitting device 10 is used to control the first quantum state transmitter 101 to transmit quantum light in a free space channel according to the first transmitting-side random state basis.

[0052] The quantum state transmitter 101 can be, but is not limited to, a telescope system of satellite-to-ground free-space QKD.

[0053] Optionally, the quantum key distribution system may, but is not limited to, adopt the polarization BB84 protocol. The polarization BB84 protocol corresponds to the Z basis {0 degrees, 90 degrees} and the X basis {45 degrees, 135 degrees}, with a total of four polarization states.

[0054] The first emission-side random state basis can be a Z basis or an X basis, and the first emission-side random state basis may change at different time points. When the first emission-side random state basis is a Z basis, the quantum light emitted by the first quantum state emitter 101 is quantum light with a 0-degree polarization state or a 90-degree polarization state; when the first emission-side random state basis is an X basis, the quantum light emitted by the first quantum state emitter 101 is quantum light with a 45-degree polarization state or a 135-degree polarization state.

[0055] The receiving device 20 is used to control the i-th quantum state receiver 201 to receive quantum light according to the i-th receiving-side random state basis, where 1≤i≤N.

[0056] The random state basis of the i-th receiving side may be a Z basis or an X basis. At different time points, the random state basis of the i-th receiving side may change.

[0057] The receiving device 20 is used to transmit the i-th receiving-side random state basis to the transmitting device 10 through a classical channel.

[0058] Optionally, the receiving device 20 transmits the i-th receiving-side random state basis in the current quantum light emission period to the transmitting device 10 through a classical channel.

[0059] The transmitting device 10 is configured to feed back the first transmitting side random state base to the receiving device 20 through a classical channel after receiving the i-th receiving side random state base.

[0060] Optionally, the transmitting device 10 feeds back the first transmitting-side random state basis in the current quantum light emission period to the receiving device 20 via a classical channel.

[0061] Transmitting device 10 and receiving device 20 can determine whether the first transmitting-side random state basis and the i-th receiving-side random state basis within the current quantum light emission cycle are identical. If they are identical, it indicates that the i-th quantum state receiver 201 has successfully and accurately acquired the quantum light emitted by the first quantum state transmitter 101 within the current quantum light emission cycle and can generate a quantum key based on this information. The specific process is as follows.

[0062] When the first transmitting side random state basis is the same as the i-th receiving side random state basis, the transmitting device 10 is used to generate the current quantum key based on the quantum light emitted by the first quantum state transmitter 101, and the receiving device 20 is used to generate the current quantum key based on the quantum light received by the i-th quantum state receiver 201.

[0063] Among them, the current quantum key is the quantum key corresponding to the quantum light in the current quantum light emission cycle.

[0064] Taking the polarization BB84 protocol as an example, assume that receiving device 20 is equipped with two quantum state receivers 201: the first quantum state receiver 201 and the second quantum state receiver 201. Let's name the first quantum state transmitter 101 Alice, the first quantum state receiver 201 Bob, and the second quantum state receiver 201 Charlie. During the current quantum light emission cycle, Alice, Bob, and Charlie each independently and randomly select either the X basis or the Z basis, with a probability of 50%.

[0065] According to the protocol rules, when the basis vector sent by Alice is the same as the measurement basis vector selected by Bob / Charlie, the basis matching is successful, and the key can be successfully generated. If the basis vector sent by Alice is different from that of Bob and Charlie, the basis matching fails, and the key cannot be generated. The specific basis selection is shown in Table 1 below:

[0066] Table 1

[0067] Alice Bob Charlie Can a key be generated? X X X Can X X Z Can X Z X Can X Z Z no Z X X no Z X Z Can Z Z X Can Z Z Z Can

[0068] As can be seen from Table 1, there are 8 base selection situations for Alice, Bob, and Charlie. The probability of these 8 situations occurring is the same. A total of 6 situations can successfully generate keys, so the probability of successfully generating keys is 75%.

[0069] For a single receiving end mechanism, the base situation is as follows Table 2:

[0070] Table 2

[0071] Alice Bob Can a key be generated? X X Can X Z no Z X no Z Z Can

[0072] As can be seen from Table 2, there are 4 base selection situations for Alice and Bob, and the probability of these 4 situations occurring is the same. There are 2 situations in total in which the key can be successfully generated, so the probability of successfully generating the key is 50%.

[0073] It can be seen from the above two tables that, assuming that the efficiency of multiple receiving ends is the same as that of a single receiving end, the base matching success rate of the single receiving end scheme is 50%, and the base matching success rate of the dual receiving end scheme is 75%. The dual receiving end scheme increases the key generation rate.

[0074] In an optional embodiment, when the random state basis on the first transmitting side is the same as the random state basis on the i-th receiving side, the transmitting device 10 is used to search for quantum light and key mapping information, and determine the quantum key that matches the quantum light emitted by the first quantum state transmitter 101 as the current quantum key; the receiving device 20 is used to search for quantum light and key mapping information, and determine the quantum key that matches the quantum light received by the i-th quantum state receiver 201 as the current quantum key.

[0075] Optionally, when the first transmitting-side random state basis is different from all receiving-side random state bases, the transmitting device 10 and the receiving device 20 fail to determine the basis, and the current quantum light emission cycle does not generate a quantum key.

[0076] In order to further improve the probability of generating quantum keys, the present invention also provides an optional implementation method, please refer to Figure 2 , Figure 2 This is a second structural diagram of a quantum key distribution system according to an embodiment of the present invention. The transmitting device 10 is provided with M quantum state transmitters 101.

[0077] The transmitting device 10 is used to control the jth quantum state transmitter 101 to transmit quantum light in a free space channel according to the jth transmitting side random state basis within the jth interval of the current quantum light emission cycle.

[0078] The current quantum light emission cycle is divided into M intervals. In the current quantum light emission cycle, the M quantum state emitters 101 are time-division multiplexed according to the intervals, and only one quantum state emitter 101 works in each interval.

[0079] The receiving device 20 is used to control the i-th quantum state receiver 201 to receive quantum light according to the i-th receiving side random state basis within the j-th interval, where 1≤j≤M.

[0080] In each interval, the N quantum state receivers 201 need to remain in working state.

[0081] The receiving device 20 is used to transmit the i-th receiving-side random state basis corresponding to the j-th interval to the transmitting device 10 through the classical channel.

[0082] After receiving the i-th receiving-side random state basis corresponding to the j-th interval, the transmitting device 10 feeds back the j-th transmitting-side random state basis to the receiving device 20 through the classical channel.

[0083] When the random state basis of the i-th receiving side corresponding to the j-th interval is the same as the random state basis of the j-th transmitting side, the transmitting device 10 is used to generate the quantum key of the j-th interval based on the quantum light emitted by the j-th quantum state transmitter 101 in the j-th interval; the receiving device 20 is used to generate the quantum key of the j-th interval based on the quantum light received by the i-th quantum state receiver 201 in the j-th interval.

[0084] Optionally, the transmitting device 10 and the receiving device 20 are used to sort multiple interval quantum keys generated in the current quantum light emission cycle, and call the interval quantum keys generated in the current quantum light emission cycle according to the sorting.

[0085] Please refer to Figure 3 , Figure 3 Figure 3 is a schematic diagram of the structure of a quantum key distribution system provided by an embodiment of the present invention. In an optional embodiment, the transmitting device 10 includes a first controller 102 and M quantum state transmitters 101. The first controller 102 is connected to each of the M quantum state transmitters 101. The first controller 102 is connected to the receiving device 20 via a classical channel communication.

[0086] Please continue to refer to Figure 3 The receiving device 20 includes a second controller 202 and N quantum state receivers 201. The second controller 202 is connected to the N quantum state receivers 201 respectively. The second controller 202 is connected to the transmitting device 10 through a classical channel communication.

[0087] Optionally, the second controller 202 is communicatively connected to the first controller 102 via a classical channel.

[0088] Optionally, the M quantum state transmitters 101 and the N quantum state receivers 201 are time synchronized according to a preset periodic interval.

[0089] The embodiment of the present invention further provides a quantum key distribution method under a free space channel, which can be applied to, but not limited to, the above-mentioned quantum key distribution system. Figure 4 , Figure 4 A schematic flow chart of a quantum key distribution method under a free-space channel provided by an embodiment of the present invention. The quantum key distribution method under a free-space channel includes: S310, S320, S330, S340, and S350, which are described in detail below.

[0090] S310: The transmitting device controls the first quantum state transmitter to transmit quantum light in a free space channel according to the first transmitting-side random state basis.

[0091] S320, the receiving device controls the i-th quantum state receiver to receive quantum light according to the i-th receiving-side random state basis.

[0092] Among them, 1≤i≤N.

[0093] S330: The receiving device transmits the i-th receiving-side random state basis to the transmitting device through a classical channel.

[0094] S340 , after receiving the i-th receiving-side random state base, the transmitting device feeds back the first transmitting-side random state base to the receiving device through the classical channel.

[0095] S350, when the random state basis of the first transmitting side is the same as the random state basis of the i-th receiving side, the transmitting device generates the current quantum key based on the quantum light emitted by the first quantum state transmitter, and the receiving device generates the current quantum key based on the quantum light received by the i-th quantum state receiver.

[0096] Optionally, the steps of the transmitting device generating a current quantum key based on the quantum light emitted by the first quantum state transmitter, and the receiving device generating a current quantum key based on the quantum light received by the i-th quantum state receiver include: S351 and S352, as follows.

[0097] S351, the transmitting device searches for the mapping information between quantum light and key, and determines the quantum key that matches the quantum light emitted by the first quantum state transmitter as the current quantum key.

[0098] S352: The receiving device searches for the mapping information between the quantum light and the key, and determines the quantum key that matches the quantum light received by the i-th quantum state receiver as the current quantum key.

[0099] It should be noted that the quantum key distribution method over a free-space channel provided in this embodiment can perform the functions and uses described in the aforementioned embodiment of a quantum key distribution system over a free-space channel, achieving the corresponding technical effects. For the sake of brevity, any details not mentioned in this embodiment are referenced to the corresponding content in the aforementioned embodiments.

[0100] In summary, an embodiment of the present invention provides a quantum key distribution method and system under a free space channel, wherein a transmitting device is used to control a first quantum state transmitter to transmit quantum light under a free space channel according to a first transmitting-side random state basis; a receiving device is used to control an i-th quantum state receiver to receive quantum light according to an i-th receiving-side random state basis, where 1≤i≤N; the receiving device is used to transmit the i-th receiving-side random state basis to the transmitting device through a classical channel; the transmitting device is used to feed back the first transmitting-side random state basis to the receiving device through a classical channel after receiving the i-th receiving-side random state basis; when the first transmitting-side random state basis is the same as the i-th receiving-side random state basis, the transmitting device is used to generate a current quantum key according to the quantum light emitted by the first quantum state transmitter, and the receiving device is used to generate a current quantum key according to the quantum light received by the i-th quantum state receiver, thereby increasing the key generation rate.

[0101] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

[0102] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A quantum key distribution system in a free-space channel, characterized in that: The quantum key distribution system includes a transmitting device and a receiving device, wherein the transmitting device is provided with a first quantum state transmitter, and the receiving device is provided with N quantum state receivers; The transmitting device is used to control the first quantum state transmitter to transmit quantum light in a free space channel according to the first transmitting-side random state basis; The receiving device is used to control the i-th quantum state receiver to receive quantum light according to the i-th receiving side random state basis, where 1≤i≤N; The receiving device is configured to transmit the i-th receiving-side random state basis to the transmitting device through a classical channel; The transmitting device is configured to feed back the first transmitting side random state base to the receiving device through a classical channel after receiving the i-th receiving side random state base; When the first transmitting side random state basis is the same as the i-th receiving side random state basis, the transmitting device is used to generate a current quantum key based on the quantum light emitted by the first quantum state transmitter, and the receiving device is used to generate a current quantum key based on the quantum light received by the i-th quantum state receiver.

2. The quantum key distribution system under a free space channel according to claim 1, characterized in that: When the first transmitting side random state basis is the same as the i-th receiving side random state basis, the transmitting device is used to search for quantum light and key mapping information, and determine the quantum key that matches the quantum light emitted by the first quantum state transmitter as the current quantum key; the receiving device is used to search for quantum light and key mapping information, and determine the quantum key that matches the quantum light received by the i-th quantum state receiver as the current quantum key.

3. The quantum key distribution system under a free space channel according to claim 1, characterized in that: In a case where the first transmitting-side random state basis is different from all receiving-side random state basis, the transmitting device and the receiving device are configured to determine that basis matching has failed.

4. The quantum key distribution system under a free space channel according to claim 1, characterized in that The transmitting device is provided with M quantum state transmitters; The transmitting device is used to control the jth quantum state emitter to emit quantum light in a free space channel according to the jth transmitting side random state basis within the jth interval of the current quantum light emission cycle; The receiving device is used to control the i-th quantum state receiver to receive quantum light according to the i-th receiving side random state basis within the j-th interval, where 1≤j≤M; The receiving device is configured to transmit the i-th receiving-side random state basis corresponding to the j-th interval to the transmitting device through a classical channel; After receiving the i-th receiving-side random state base corresponding to the j-th interval, the transmitting device feeds back the j-th transmitting-side random state base to the receiving device through the classical channel; When the random state basis of the i-th receiving side corresponding to the j-th interval is the same as the random state basis of the j-th transmitting side, the transmitting device is used to generate the quantum key of the j-th interval based on the quantum light emitted by the j-th quantum state transmitter in the j-th interval; the receiving device is used to generate the quantum key of the j-th interval based on the quantum light received by the i-th quantum state receiver in the j-th interval.

5. The quantum key distribution system under a free space channel according to claim 4, characterized in that: The transmitting device and the receiving device are used to sort multiple interval quantum keys generated in the current quantum light emission cycle, and call the interval quantum keys generated in the current quantum light emission cycle according to the sorting.

6. The quantum key distribution system under a free space channel according to claim 4, characterized in that: The transmitting device includes a first controller and M quantum state transmitters, the first controller is connected to the M quantum state transmitters respectively, and the first controller is connected to the receiving device through classical channel communication.

7. The quantum key distribution system under a free space channel according to any one of claims 1 to 6, characterized in that: The receiving device includes a second controller and N quantum state receivers, the second controller is connected to the N quantum state receivers respectively, and the second controller is connected to the transmitting device through a classical channel communication.

8. The quantum key distribution system under a free space channel according to claim 4, characterized in that: The M quantum state transmitters and the N quantum state receivers are time synchronized according to preset periodic intervals.

9. A quantum key distribution method in a free space channel, characterized in that: The quantum key distribution system according to any one of claims 1 to 8, wherein the method comprises: The transmitting device controls the first quantum state transmitter to transmit quantum light in a free space channel according to the first transmitting side random state basis; The receiving device controls the i-th quantum state receiver to receive quantum light according to the i-th receiving side random state basis, where 1≤i≤N; The receiving device transmits the i-th receiving-side random state basis to the transmitting device through a classical channel; After receiving the i-th receiving-side random state base, the transmitting device feeds back the first transmitting-side random state base to the receiving device through a classical channel; When the first transmitting side random state basis is the same as the i-th receiving side random state basis, the transmitting device generates a current quantum key based on the quantum light emitted by the first quantum state transmitter, and the receiving device generates a current quantum key based on the quantum light received by the i-th quantum state receiver.

10. The quantum key distribution method under a free space channel according to claim 9, characterized in that: The step of the transmitting device generating a current quantum key according to the quantum light emitted by the first quantum state transmitter, and the receiving device generating a current quantum key according to the quantum light received by the i-th quantum state receiver, comprises: The transmitting device searches for quantum light and key mapping information, and determines a quantum key that matches the quantum light emitted by the first quantum state emitter as the current quantum key; The receiving device searches for quantum light and key mapping information, and determines a quantum key that matches the quantum light received by the i-th quantum state receiver as the current quantum key.

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