CN108650088B - Quantum communication device and method comprising at least three parties - Google Patents
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Abstract
本发明提供了一种包含至少三方的量子通信装置及方法，所述至少三方包括至少两个用户和至少一个中继点，其中，该装置包括：控制器，用于确定至少两个用户的待发送信号的信号态光强和至少一个诱导态光强的比例、以及信号态光强和诱导态光强的强度参数；调制器，与所述控制器连接，用于根据所述比例和强度参数，调制所述待发送信号，并将调整后的待发送信号发送至至少一个中继点。本发明适用于非对称信道和对称信道，尤其是当不同用户使用非对称信道传输信息时，不需在一侧信道添加损耗，只需通过调节光强的比例和强度参数即可补偿信道的损失，完成通信的过程。
The present invention provides a quantum communication device and method including at least three parties, the at least three parties including at least two users and at least one relay point, wherein the device includes: a controller for determining at least two users to be The ratio of the signal state light intensity and at least one induced state light intensity of the transmitted signal, and the intensity parameters of the signal state light intensity and the induced state light intensity; a modulator, connected to the controller, for controlling the ratio and the intensity parameter according to the ratio , modulate the signal to be sent, and send the adjusted signal to be sent to at least one relay point. The invention is suitable for asymmetric channels and symmetric channels. Especially when different users use asymmetric channels to transmit information, there is no need to add losses to one side of the channel. The loss of the channel can be compensated by simply adjusting the ratio and intensity parameters of light intensity. , complete the communication process.
Description
Technical Field
The invention relates to the field of quantum communication, in particular to a quantum communication device and method comprising at least three parties.
Background
Quantum Key Distribution (QKD) systems allow two users to share a random pair of keys through one quantum channel. In the BB84 protocol proposed by Bennett and Branguard ("Quantum cryptography: public key distribution and coin tossing" by C Bennett, G Branguard, international Conference on Computer System and Signal Processing, IEEE (1984)), a user prepares and transmits a quantum signal randomly in one of two non-orthogonal basis vectors. The other user also randomly selects one of the two basis vectors and measures the received quantum signal. They screen out events that both select the same set of basis vectors and, after communication over a published classical channel, perform error-correction and privacy amplification (privacy amplification), ultimately obtaining a pair of keys.
Examples of algorithms for error correction and privacy amplification are low density parity check codes (LDPC), an error correction code that is highly resistant to noise, and random global hash (random universal hashing) functions, which are typically implemented with Toeplitz matrix hash functions, for example using LDPC and Toeplitz hashes for error correction and privacy amplification.
An induced state quantum key distribution network generally uses attenuated laser pulses of greater utility to encode information, also known as weak coherent pulsed light Sources (WCPs). The encoding of the information may employ polarization encoding, time-bin encoding, or phase encoding. The user randomly selects one light intensity from several light intensities (called induced light intensity and signal light intensity) to encode. The user may then error correct the portion of the data transmitted using the signal intensity to generate the original key. Meanwhile, a user can know how much privacy amplification is needed to be carried out on the original key by analyzing the induced state data. In this way, the user can use the WCP light source while guaranteeing the security of the protocol.
Measuring device independent quantum key distribution networks (MDI-QKD) involve three parties: two users, and a third party relay. Two users are each connected to a third party through one quantum channel. They each prepare and send signals over an independent quantum channel and have them interfere with each other at a third party. The third party then measures the result of the intervention and announces it publicly. Two users can generate a pair of keys by analyzing these disclosures without requiring trust of the third party relay (i.e., the measurement device) by both.
Measurement device independent quantum key distribution networks are commonly used with inducible states. In existing systems, two users will choose the same set of induced light intensities (this set may be three or four) and the ratio of these light intensities to be transmitted in the experiment.
In the existing experiments of the measuring equipment independent quantum key distribution network, two quantum channels are required to have similar (namely 'symmetrical') loss, and if the two quantum channels are asymmetric, the code rate of the system can be greatly reduced, and even the system cannot code. Thus, existing systems are either limited to the case where the channel is approximately symmetrical or have to deliberately add loss in one side channel in exchange for higher channel symmetry, i.e. add extra fiber in one side channel to increase loss in exchange for higher symmetry.
Disclosure of Invention
First, the technical problem to be solved
The present invention is directed to a quantum communication device and method including at least three parties, so as to solve at least one of the above-mentioned problems.
(II) technical scheme
In one aspect of the invention, a quantum communication device is provided comprising at least three parties including at least two users and at least one relay point, wherein the device comprises:
the controller is used for determining the ratio of the signal state light intensity and at least one induced state light intensity of signals to be transmitted by at least two users and the intensity parameters of the signal state light intensity and the induced state light intensity;
and the modulator is connected with the controller and used for modulating the signal to be transmitted according to the proportion and the intensity parameter and transmitting the adjusted signal to be transmitted to at least one relay point.
In some embodiments of the present invention, the at least two users send the modulated signal to be sent through an asymmetric channel, and the signal state light intensity and the induced state light intensity of the users are different, and the controller is further configured to determine the ratio of the signal state light intensity and the at least one induced state light intensity of the signal to be sent and the intensity parameters of the signal state light intensity and the induced state light intensity of the at least two users through a local search algorithm or a global optimization algorithm; preferably, the local search algorithm includes a coordinate descent method and a gradient descent method; the global optimization algorithm comprises a genetic algorithm; and/or
The modulator further comprises: the optical power system comprises an optical intensity modulator, a phase modulator, an acousto-optic modulator and a polarization modulator, wherein the optical intensity modulator, the phase modulator, the acousto-optic modulator and the polarization modulator are used for modulating the signal to be transmitted according to the proportion and the intensity parameter and transmitting the signal to be transmitted to at least one relay point; and/or
The apparatus further comprises: the test unit is used for carrying out exchange test or Bell state test on the first user and the second user which are communicated with the relay point by the relay point, so that the measurement device-independent quantum key distribution protocol or the double-field quantum key distribution protocol is realized, and the tested result is sent to the first user and the second user.
In some embodiments of the invention, the at least two usesThe user comprises a first user and a second user, the at least one induced state light intensity comprises two non-vacuum induced state light intensities and one vacuum induced state light intensity, and the signal state light intensity of the signal to be sent by the first user, the two non-vacuum induced state light intensities and the one vacuum induced state light intensity are expressed as s by the intensity parameters A ，μ A ，ν A Omega, the ratio of the intensity of the signal state of the signal to be sent by the first user and the intensity of the two non-vacuum induced states is expressed asThe intensity parameters of the signal state light intensity, the two non-vacuum induced state light intensities and the vacuum induced state light intensity of the signal to be sent by the second user are expressed as s B ，μ B ，v B Omega, the ratio of the intensity of the signal state of the signal to be transmitted by the second user and the intensity of the two non-vacuum induced states is expressed as +.> wherein ,/>The probability of the signal state light intensity and the two non-vacuum induced state light intensities of the first user, respectively, +.>The probability of the signal state light intensity and the probability of the two non-vacuum induced state light intensities of the second user are respectively indicated, and the signal state light intensity and the induced state light intensity are orthogonal basis vectors.
In some embodiments of the invention, the controller is further configured to control the step of A ，μ A ，v A ，s B ，μ B ，v B And converting into polar coordinate parameters to obtain:
θ s ＝tan -1 (s A /s B )，
θ μ ＝tan -1 (μ A /μ B )，
θ v ＝tan -1 (v A /v B), wherein ,θμ ＝θ v 。
In another aspect of the present invention, there is also provided a quantum communication method including at least three parties including at least two users and at least one relay point, wherein the method includes:
determining the ratio of the signal state light intensity and at least one induced state light intensity of signals to be transmitted of at least two users and the intensity parameters of the signal state light intensity and the induced state light intensity;
and modulating the signal to be transmitted according to the proportion and the intensity parameter, and transmitting the modulated signal to be transmitted to at least one relay point.
In some embodiments of the present invention, the at least two users send the modulated signal to be sent through an asymmetric channel, and the signal state light intensity and the induced state light intensity of the users are different, and the ratio of the signal state light intensity and the at least one induced state light intensity of the signal to be sent of the at least two users and the intensity parameters of the signal state light intensity and the induced state light intensity are determined through a local search algorithm or a global optimization algorithm.
In some embodiments of the invention, the local search algorithm includes a coordinate descent method and a gradient descent method; the global optimization algorithm includes a genetic algorithm.
In some embodiments of the present invention, the at least two users include a first user and a second user, the at least one induced light intensity includes two non-vacuum induced light intensities and one vacuum induced light intensity, and the intensity parameters of the signal state light intensity, the two non-vacuum induced light intensities and the one vacuum induced light intensity of the signal to be sent by the first user are denoted as s A ，μ A ，v A Omega, the ratio of the intensity of the signal state of the signal to be sent by the first user and the intensity of the two non-vacuum induced states is expressed asThe intensity parameters of the signal state light intensity, the two non-vacuum induced state light intensities and the vacuum induced state light intensity of the signal to be sent by the second user are expressed as s B ，μ B ，v B Omega, the ratio of the intensity of the signal state of the signal to be transmitted by the second user and the intensity of the two non-vacuum induced states is expressed as +.> wherein ,/>The probability of the signal state light intensity and the two non-vacuum induced state light intensities of the first user, respectively, +.>The probability of the signal state light intensity and the probability of the two non-vacuum induced state light intensities of the second user are respectively indicated, and the signal state light intensity and the induced state light intensity are orthogonal basis vectors.
In some embodiments of the invention, s will be A ，μ A ，v A ，s B ，μ B ，v B And converting into polar coordinate parameters to obtain:
θ s ＝tan -1 (s A /s B )，
θ μ ＝tan -1 (μ A /μ B )，
θ v ＝tan -1 (ν A /ν B), wherein ,θμ ＝θ v 。
In some embodiments of the invention, further comprising: the relay point performs exchange test or Bell state test on the first user and the second user which are communicated with the relay point, so that a measurement device-independent quantum key distribution protocol or a double-field quantum key distribution protocol is realized, and the tested result is sent to the first user and the second user.
(III) beneficial effects
Compared with the prior art, the quantum communication device and method comprising at least three parties have the following advantages:
1. the invention is suitable for asymmetric channels and symmetric channels, and especially when different users use the asymmetric channels to transmit information, the loss of the channels can be compensated by adjusting the proportion of light intensity and the intensity parameter without adding loss on one side of the channels, and the communication process is completed. Therefore, the invention does not need to additionally introduce hardware facilities such as optical fibers and the like as the traditional method, simplifies the structure and the method, and simultaneously can improve the code rate and expand the safety distance of key distribution.
2. The method is suitable for different quantum communication protocols and has good universality.
Drawings
FIG. 1 is a schematic diagram of a prior art symmetric measurement device independent quantum key distribution network;
FIG. 2 is a schematic diagram of a portion of a prior art measurement device independent quantum key distribution network;
FIG. 3 is a schematic diagram of asymmetric quantum communication;
fig. 4A is a schematic structural diagram of a quantum communication device including at least three parties according to an embodiment of the present invention;
fig. 4B is an application scenario diagram of a quantum communication device including at least three parties according to a first embodiment of the present invention;
FIG. 5 is a schematic diagram showing a comparison of a conventional protocol and a seven-state protocol according to the present invention;
FIG. 6 is a schematic diagram of variables requiring optimization in a seven-state protocol of the present invention;
FIG. 7 is a schematic diagram of variable optimization using a coordinate descent method according to an embodiment of the present invention;
FIG. 8 is a schematic diagram of variable optimization using iterative search according to an embodiment of the present invention
FIG. 9 is a diagram showing the comparison of the code rates of the prior art protocol and the seven-state protocol of the present invention;
FIG. 10 is a schematic diagram of a quantum communication device comprising at least three parties according to a first embodiment of the present invention applied to a quantum key distribution network comprising a single relay point;
FIG. 11 is a schematic diagram of a quantum communication device including at least three parties applied to another quantum key distribution network including a plurality of relay points according to a second embodiment of the present invention;
FIG. 12 is a schematic diagram of an embodiment of the invention in which a quantum communication device comprising at least three parties is applied to a ship-to-ship free-space based quantum key distribution network;
FIG. 13 is a schematic diagram of a free space based quantum key distribution network for satellite-terrestrial applications for a quantum communication device comprising at least three parties according to an embodiment of the present invention;
FIG. 14 is a schematic diagram of a free space based quantum key distribution network for satellite-terrestrial applications for a quantum communication device comprising at least three parties according to an embodiment of the present invention;
FIG. 15 is a schematic diagram of two users connected to a relay point through a free space channel and a fiber channel, respectively, according to an embodiment of the present invention;
FIG. 16 is a schematic diagram of a quantum key distribution network in a single arm scenario of an embodiment of the present invention;
fig. 17 is a schematic diagram illustrating steps of a quantum communication method including at least three parties according to an embodiment of the present invention.
Detailed Description
Fig. 1 is a schematic diagram of a prior art symmetric measurement device independent quantum key distribution network, as shown in fig. 1, where users 100 and 102 are connected to a third party relay point 108 via quantum channels 104, 106, which have the same (or similar) losses in the channels.
Fig. 2 is a schematic diagram of a portion of a prior art measurement device independent quantum key distribution network, shown in fig. 2, with laboratories for a first user (user 1) and a second user (user 2) being denoted by 200 and 202 in the figure. User 1 (user 2) causes laser light to be emitted from light source 214 (216), attenuated to a single photon level using attenuator 218 (220), modulated to pulses using light intensity modulator 234 (236), randomized to phase using phase modulator 226 (228), modulated to different induced light intensities using acousto-optic modulator 230 (232), and encoded into qubits using polarization modulator 234 (236).
In fig. 2, polarization encoding is used, but the encoding method is not limited to polarization encoding. For example, here 234 and 236 may be replaced by an asymmetric Mach-Zehnder interferometer (AMZI) and a phase modulator to implement time-phase encoding (time-bin phase encoding). All instruments follow 238 (240) control logic. The control logic here comprises a classical computer, a random number generator, and a control circuit. Quantum signals 208 and 210 (in the form of weak coherent pulses) are transmitted to third party relay points 212 via quantum channels 204 and 206, respectively. Specific details of the measurement device in 212 are omitted herein.
Fig. 3 is a schematic diagram of prior art asymmetric quantum communications, where users 300 and 310 are connected to a relay 308 through quantum channels 304 and 306, but with different degrees of loss of their channels, as shown in fig. 3. Because the rate of the measurement device independent quantum key distribution network is dependent on the symmetry between the quantum channels, user 2 may choose to deliberately add some loss (such as a length of optical fiber) 314, i.e. move from position 310 to position 312. Here, items 310, 312, 314 are all located in user 2's laboratory 302 and are fully controlled by user 2. While such a system design can increase symmetry, the design is still very low in code rate and can only be used with low channel loss.
It can be seen that in the experiments of the existing quantum communication system, two quantum channels are required to have similar (i.e. "symmetrical") loss, if the two quantum channels are asymmetric, loss is added in one side channel to change higher channel symmetry, so that the quantum communication system has complex structure and weak practicability. In view of this, the present invention provides a quantum communication device and method including at least three parties, which is suitable for asymmetric channels and symmetric channels, and especially when different users use the asymmetric channels to transmit information, the loss of the channels can be compensated only by adjusting the proportion of light intensity and the intensity parameter without adding loss to the channels at one side, so as to complete the communication process.
The present invention will be further described in detail below with reference to specific embodiments and with reference to the accompanying drawings, in order to make the objects, technical solutions and advantages of the present invention more apparent.
In one aspect of the embodiments of the present invention, there is provided a quantum communication device including at least three parties including at least two users and at least one relay point, as shown in fig. 4A, the device including:
a controller 41 for determining the ratio of the signal state light intensity and at least one induced state light intensity of the signals to be transmitted by at least two users, and the intensity parameters of the signal state light intensity and the induced state light intensity;
and the modulator 42 is connected with the controller and is used for modulating the signal to be transmitted according to the proportion and the intensity parameter and transmitting the adjusted signal to be transmitted to at least one relay point. The modulator further comprises: the optical power system comprises an optical intensity modulator, a phase modulator, an acousto-optic modulator and a polarization modulator, wherein the optical intensity modulator, the phase modulator, the acousto-optic modulator and the polarization modulator are used for modulating the signal to be transmitted according to the proportion and the intensity parameter and transmitting the signal to be transmitted to at least one relay point.
The relay point and at least two users can be located in different devices, and at the moment, two channels exist between the three parties; the relay may also be located in the same facility as one of the subscribers, in which case in practice the apparatus/method may comprise only two ends: one user, and the other user who is simultaneously controlling the relay point. There is only one channel between the two ends.
In the device, each user has a pair of a controller and a modulator. Each controller is connected to a modulator of a corresponding user. The controllers of the users can be connected through classical channels, and the proportion of the signal state light intensity and at least one induced state light intensity of signals to be transmitted by all the users and the intensity parameters of the signal state light intensity and the induced state light intensity can be determined together.
The apparatus may further include: the test unit is used for carrying out exchange test or Bell state test on the first user and the second user which are communicated with the relay point by the relay point, so that the measurement device-independent quantum key distribution protocol or the double-field quantum key distribution protocol is realized, and the tested result is sent to the first user and the second user.
It should also be noted that the present invention may be applied not only to measurement device independent quantum key distribution protocols and two-field quantum key distribution protocols, but also to other quantum key distribution protocols, such as bit commitment (bit commit), covert transmission (oblivious transfer), coin tossing (spin-down), quantum latent transmission (quantum report), or blind quantum computation (blind quantum computing). Although the preferred embodiment herein involves only three parties (users and relay points), the present invention is applicable to any generalized quantum network, including global quantum networks.
As shown in fig. 4B, the loss of channels 404 and 406 may be any value. The controller performs parameter optimization and selects the best two sets of induced light intensities for the two users' light intensity modulators. For channels with higher losses, the optimum light intensity will typically be stronger (and their specific optimum values can be obtained by numerical optimization) as will the relationship between channel 404 and signal pulse 410 in the figure and channel 406 and signal pulse 412 in the figure. The optimal rate of formation is achieved by optimizing the intensity of the induced states without the need to add any additional loss to the channel.
As shown in fig. 5, a four-state measurement device independent quantum key distribution protocol is exemplified. In the four-state protocol (existing protocol), each user encodes information using four light intensities (s, μ, ν, ω), where s is the signal state light intensity and is encoded in the Z-basis vector only, and μ, ν, ω is the induced state light intensity, including two non-vacuum induced state light intensities μ, v and one vacuum induced state light intensity ω and is encoded in the X-basis vector only. By encoding the quantum signals in these light intensities, the user can achieve measurement device independent quantum key distribution. It is noted that this protocol only considers the case where two users use the same set of light intensities.
It should be noted that the present invention may be applied to more or fewer induced states, such as one signal state+two induced states. In the present invention, each user is allowed to use a different light intensity, i.e. the first user (user 1) uses (s A ，μ A ，v A ω), while the second user (user 2) uses(s) B ，μ B ，v B ω) to form a new protocol, the "seven-state protocol", where the ω light intensity of both users is referred to as the vacuum state and is therefore the same. The different light intensities can effectively compensate for the asymmetry of the channel loss. This enables the seven-state protocol to be much more adaptable to asymmetric channels, and can be used in any asymmetric situation.
To implement this protocol and get a Gao Cheng code rate, it is necessary to find the best light intensities and the proportions at which they are transmitted. Here, fig. 6 lists the variables that need to be optimized. In particular, for this embodiment of a seven-state protocol, there are 12 parameters that need to be optimized:
wherein the ratio of the signal state light intensity of the signal to be transmitted by the user to the two non-vacuum induced state light intensities is expressed as(i.e., probability of signal state light intensity and two non-vacuum induced state light intensities of user 1), the ratio of signal state light intensity of the signal to be transmitted by user 2 and two non-vacuum induced state light intensities is expressed as +.>(i.e., the probability of the second user's signal state light intensity and two non-vacuum induced state light intensities).
In practical application, to increase the stability of parameter search, 6 light intensity parameters should be represented in polar coordinates:
θ s ＝tan -1 (s A /s B )，/>θ μ ＝tan -1 (μ A /μ B )，θ v ＝tan -1 (v A /v B )。
meanwhile, for seven-state protocols, θ can be defined here μ ＝θ v Bind to the same variable and search them simultaneously (because the optimal values of the two variables are always equal in a seven-state protocol). Therefore, when using a seven-state protocol, there are 11 parameters that actually need to be optimized.
As shown in fig. 7, the light intensity and the light intensity ratio may be optimized by a local search algorithm of the coordinate descent method (coordinate descent). The algorithm is able to quickly search a large number of parameters, one-dimensional search along each axis in turn (i.e. search one variable at a time, keeping the other constant).
As shown in fig. 8, the one-dimensional search for each variable by the iterative search method can be further accelerated by using an adaptive search resolution. First, an initial step size is determined, from which the algorithm traverses the search range at low resolution (this step can be effectively implemented in parallel). Thereafter, the search range can be redefined to be the position one step to the left and right of the optimum value obtained by the previous search, the new search step is reduced, and the search is performed at a higher resolution within the new range. This process may iterate until the maximum iteration depth is reached.
At the same time, the coordinate descent method and the iterative search method are combined, so that the optimization can be performed with very high speed and accuracy (the process only needs less than 0.1 seconds on a common computer). Such high optimization speeds can also allow real-time optimization of the controller in the field.
It should be noted that the coordinate descent method and the iterative search method are not unique local search algorithms, and that the local search is not the only optimization algorithm that can be used here. For example, the gradient descent method (another local search algorithm) may be used instead of the coordinate descent method, as shown by the broken line in fig. 7. In addition, a global optimization algorithm, such as a genetic algorithm (genetic algorithm), may also be used for parameter optimization in the present invention, and will not be described herein.
As shown in fig. 9, four contours of the bit rate (the number of key bits that can be obtained per pulse transmitted) are shown. The simulation here takes into account the finite length effects (fine-size effects) and uses a smaller data length n=10 11 And the following experimental parameters were used: dark count rate (dark count rate) of detector 8×10 -7 (per pulse) detector efficiency 65%, base vector calibration error (misalignment) 0.5%, and error correction efficiency 1.16. It can be seen that the existing protocols can only provide high bit-rate at the location where the channels are approximately symmetric, whereas the seven-state protocols are almost completely unaffected by the symmetry of the two user channels, and can provide high bit-rate at any combination of channels.
At point a (100 km,0 km), only seven-state protocols can generate non-zero code rate: 6.59X10 per pulse -10 Whereas existing four-state protocols cannot generate any security keys. At point BAt (50 km,0 km), the seven-state protocol can achieve an encoded rate of up to 1585% times that of the four-state protocol. Similarly, even at locations with only moderate asymmetry, such as point C (60 km,30 km), point D (50 km,20 km), and point E (40 km,10 km), the resultant rate for the seven-state protocol is 301%,219%,177% times that for the four-state protocol, respectively. At the same time, if the channel of user 1 is fixed at 0km, and a minimum bit rate of 10 is required, taking the maximum distance in the standard fiber as a standard -8 In the mean time, the maximum distance of the channel of user 2 can be increased up to 37.5km (from 58km to 95.5 km) using the seven-state protocol. This demonstrates the great advantage of the seven-state protocol over the existing protocols in case of channel asymmetry. Compared with the existing protocol, the new protocol can greatly expand the scenes to which the measurement device independent quantum key distribution can be applied.
The device of the invention also considers the finite length effect at the same time, and can still obtain good bit rate under the condition of smaller data length. As one embodiment, a seven-state protocol is capable of communicating at a high rate of bit-rate with both small data lengths and highly asymmetric channels. (in fig. 9, all the bit rates are at a smaller data length n=10 11 Obtained below). Importantly, the designs presented herein are not limited to the number of light intensities used, but the software optimization algorithm described above can be efficiently applied to quantum key distribution networks using any number of induced states.
A quantum key distribution network refers to a generalized quantum key distribution system in which two or more users (and possibly one or more relay points) are involved.
As shown in fig. 10, in a first embodiment, the network consists of users 1000, 1002, 1004, 1006 and one relay 1008 responsible for the measurements. Importantly, the relay point herein does not have to be trusted by the user. Users 1,2,3,4 are connected to relay 1 through channels 1010, 1012, 1014, 1016. All channel losses may be different. By using the device of the invention, a quantum communication connection with high bit rate can be established between any pair of users 1-2,1-3,1-4,2-3,2-4,3-4, thereby forming a quantum network 1018 which is completely connected with the users 1,2,3, 4. And, each pair of users' connections can be optimized independently so that the addition/deletion of new users does not affect existing connections.
The quantum key distribution network may comprise a number of relay points connecting different users and forming a number of sub-networks. As shown in fig. 11, in the second embodiment, here the users 1100, 1102, 1104 are connected to a first relay point 1108, and the users 1102, 1106 are connected to a second relay point 1110. Thus, users 1,2,3 form one fully connected subnetwork 1122, while users 2 and 4 form another subnetwork 1124. In other embodiments, the number of relay points may be greater than 2, and may be specifically selected according to the user requirement, which is not described herein.
As shown in fig. 12, a ship-to-ship free space based quantum key distribution network is illustrated. Items 1200, 1202, 1204, 1206, 1208 are defined herein as items 100, 102, 104, 106, 108 in fig. 1. Quantum channels 1204 and 1206 may vary over time and have any degree of asymmetry, while a seven-state protocol may be suitable for all situations herein.
A free space based quantum key distribution network between satellite and ground is shown in fig. 13. Items 1300, 1302, 1304, 1306, 1308 are the same as items 100, 102, 104, 106, 108 in fig. 1. Two ground base stations transmit quantum signals as users, while satellites act as relay points that may not be trusted. Similarly, quantum channels 1304 and 1306 may change over time and have any degree of asymmetry.
As shown in fig. 14, another satellite-ground free space based quantum key distribution network is illustrated. The two satellites 1404 and 1406 may each act as subscribers to transmit downstream signals over the quantum channels 1404 and 1406 to the ground base station 1408. Here the ground base station acts as a relay point that may not be trusted. This situation is also asymmetric quantum key distribution, while seven-state protocols are equally applicable.
The apparatus of the present invention may also be adapted to situations where one of the channels changes over time (where the symmetry of the channel also changes over time). As shown in fig. 15, two users 1500 and 1502 are shown connected to a relay point through a free space channel 1504 and a fiber channel 1506, respectively.
As shown in fig. 16, a quantum key distribution network in a single arm situation is illustrated. Here, the user 1600 and the relay 1608 are located in the same laboratory 1610, and the channel loss between the two is set to be as small as possible. Another user 1602 may communicate with the laboratory of the previous user over a quantum channel 1606. This situation has a high degree of asymmetry (where the loss of one channel is close to a minimum). A seven-state protocol is used, in which case a high rate of formation can also be achieved.
The single arm quantum key distribution system described above is also within the scope of this invention, as in practice there is a relay point in the system that is located in the same laboratory as a user. At this point, from a laboratory perspective, the system actually contains only the communication between the two ends.
The single arm design described above can still allow two users to communicate when it is inconvenient to set up a relay point in a quantum channel (e.g., a free space channel). In this way, two users can communicate over a certain critical single channel, but still maintain the security of the measurement device independent quantum key distribution or the two-field quantum key distribution. The single arm design described above can also be applied to ship-to-ship or satellite-to-ground communications.
In free space based quantum communications, atmospheric turbulence effects can affect losses in the channel in real time. At this time, the asymmetric system and post-selection (post-selection) method set forth herein may also be combined. The selection method can greatly improve the performance of the quantum communication system when the turbulence is strong. The apparatus and method of the present invention are also compatible with the post-selection method described above when the system contains one or more free space channels.
Depending on whether the test unit at the relay point performs the exchange test or the bell state test, the above-described quantum key distribution network may be based on either measurement device independent quantum key distribution or on double field quantum key distribution.
The invention is applicable not only to free space channels and fibre channels, but also to any other channel, including in-water channels. In the foregoing description, the invention has been described in the context of unconditional security, but the invention may also be used with other cryptographic assumptions, such as a finite storage model (bounded storage models). While the invention has been described as a preferred embodiment for its application in an induced state based measurement device independent quantum key distribution network based on a weakly coherent pulsed light source, the invention may also be used for other quantum light sources, such as an induced state based spontaneous parametric down-conversion (spontaneous parametric down conversion) light source.
In another aspect of the embodiment of the present invention, there is further provided a quantum communication method including at least three parties including at least two users and at least one relay point, as shown in fig. 17, the method including the steps of:
s1, determining the ratio of signal state light intensity and at least one induced state light intensity of signals to be transmitted of at least two users and the intensity parameters of the signal state light intensity and the induced state light intensity;
s2, modulating the signal to be transmitted according to the proportion and the intensity parameter, and transmitting the modulated signal to be transmitted to at least one relay point.
In step S1, when two users (user 1 and user 2) communicate each time, because the channel for transmitting information by the two users has two conditions of symmetry and asymmetry, when the channel is a symmetric channel, the light intensity (signal state light intensity and induced state light intensity) of the signals to be transmitted by the two users is the same, and the proportion and the intensity parameter of the light intensity do not need to be adjusted, and the signals are directly transmitted; when the channel is a symmetric channel, the ratio of the signal state light intensity and at least one induced state light intensity of the signals to be transmitted by the user 1 and the user 2 and the intensity parameters of the signal state light intensity and the induced state light intensity are required to be adjusted.
More specifically, the two users send the modulated signals to be sent through asymmetric channels, and the signal state light intensity and the induced state light intensity of the users are different, at this time, the ratio of the signal state light intensity and at least one induced state light intensity of the signals to be sent of the at least two users and the intensity parameters of the signal state light intensity and the induced state light intensity can be determined through a local search algorithm or a global optimization algorithm. In some embodiments of the invention, the local search algorithm includes a coordinate descent method and a gradient descent method; the global optimization algorithm includes a genetic algorithm.
The at least one induced state light intensity comprises two non-vacuum induced state light intensities and one vacuum induced state light intensity, and the signal state light intensity, the two non-vacuum induced state light intensities and the one vacuum induced state light intensity of the signal to be sent by the first user are expressed as s by the intensity parameters A ，μ A ，v A Omega, the ratio of the intensity of the signal state of the signal to be sent by the first user and the intensity of the two non-vacuum induced states is expressed asThe intensity parameters of the signal state light intensity, the two non-vacuum induced state light intensities and the vacuum induced state light intensity of the signal to be sent by the second user are expressed as s B ，μ B ，ν B Omega, the ratio of the intensity of the signal state of the signal to be transmitted by the second user and the intensity of the two non-vacuum induced states is expressed as +.> wherein ,/>The probability of the signal state light intensity and the two non-vacuum induced state light intensities of the first user, respectively, +.>The probability of the signal state light intensity and the probability of the two non-vacuum induced state light intensities of the second user are respectively indicated, and the signal state light intensity and the induced state light intensity are orthogonal basis vectors.
To increase the stability of the parameter search, 6 parameters s can be used A ，μ A ，v A ，s B ，μ B ，v B And converting into polar coordinate parameters to obtain:
θ s ＝tan -1 (s A /s B )，
θ μ ＝tan -1 (μ A /μ B )，
θ v ＝tan -1 (ν A /ν B), wherein ,θμ ＝θ v 。
In step S2, the relay point may further perform a switching test or a bell state test on the first user and the second user in communication with the relay point, so as to implement a measurement device independent quantum key distribution protocol or a two-field quantum key distribution protocol, and send the tested result to the first user and the second user. In addition, the present invention is also applicable to some other quantum communication protocols, and will not be described herein.
In summary, the invention is suitable for asymmetric channels and symmetric channels, and especially when different users use the asymmetric channels to transmit information, the loss of the channels can be compensated by adjusting the proportion of light intensity and the intensity parameter without adding loss on one side of the channels, and the communication process is completed. Therefore, the invention does not need to additionally introduce hardware facilities such as optical fibers and the like as the traditional method, simplifies the structure and the method, and simultaneously can improve the code rate and expand the safety distance of key distribution.
Unless otherwise known, the numerical parameters in this specification and the attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present disclosure. In particular, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". In general, the meaning of expression is meant to include a variation of + -10% in some embodiments, a variation of + -5% in some embodiments, a variation of + -1% in some embodiments, and a variation of + -0.5% in some embodiments by a particular amount.
Furthermore, "comprising" does not exclude the presence of elements or steps not listed in a claim. The singular reference of "a", "an", and "the" preceding an element does not exclude the plural reference of such elements.
The use of ordinal numbers such as "first," "second," "third," etc., in the description and the claims to modify a corresponding element does not by itself connote any ordinal number of elements or the order of manufacturing or use of the ordinal numbers in a particular claim, merely for enabling an element having a particular name to be clearly distinguished from another element having the same name.
While the foregoing is directed to embodiments of the present invention, other and further details of the invention may be had by the present invention, it should be understood that the foregoing description is merely illustrative of the present invention and that no limitations are intended to the scope of the invention, except insofar as modifications, equivalents, improvements or modifications are within the spirit and principles of the invention.
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| CN110380824A (en) * | 2019-07-19 | 2019-10-25 | 哈尔滨工业大学 | Quantum Error Correcting Codes preparation method towards fault-tolerant blind quantum calculation |
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| CN113141252B (en) * | 2020-01-20 | 2022-11-25 | 阿里巴巴集团控股有限公司 | Quantum key distribution method, quantum communication method, device and system |
| US11646803B2 (en) | 2020-04-09 | 2023-05-09 | Psiquantum, Corp. | Expanded photonic bell state generators |
| CN111431601B (en) * | 2020-05-12 | 2021-04-06 | 南京邮电大学 | Method for improving system channel utilization rate |
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| CN113438076B (en) * | 2021-07-08 | 2022-12-27 | 南京大学 | Side-channel-free quantum key distribution method and system |
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