Four-component quantum teleportation network system and construction method thereof

Abstract

The invention discloses a four-component quantum teleportation network system and a construction method thereof, belonging to the technical field of quantum communication devices between continuous variable multiple users; the technical problem to be solved is: to provide an improvement on the structure of a four-component quantum teleportation network system; the technical scheme adopted to solve the above technical problem is: comprising a generation device of continuous variable four-component quantum resources and four spatially separated quantum nodes, the four quantum nodes are respectively set as sending nodes, receiving nodes and control nodes in the quantum teleportation network, the four quantum nodes are used to realize the transmission process of participating in one quantum state or the transmission process of participating in two quantum states, and the four quantum nodes are all connected to the generation device of the continuous variable four-component quantum resources; the invention is applied to quantum teleportation.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum communication devices between continuous variables and multiple users, and specifically relates to a four-component quantum teleportation network system and a construction method thereof. Background Art

[0002] In recent years, quantum information networks have developed rapidly. The use of quantum resources to transmit and process information can break through the limits of classical information systems, such as speeding up the processing rate of information and improving the efficiency of information transmission. Quantum teleportation is a quantum communication technology that uses entangled resources to transmit unknown quantum states from one node to another through local operations and classical communications without the need for any information carriers. This technology has important application value in the establishment of quantum communication and quantum computing networks. At present, entangled particles in the field of separated variables and entangled light modes in the field of continuous variables can be used for quantum teleportation. Compared with quantum teleportation of separated variables, due to the approximate determinism of quantum teleportation of light modes, it is inevitable to study quantum teleportation network solutions in the field of continuous variables. Using two-component entangled light fields, it is possible to transmit an unknown quantum state from one quantum node to another. Because there are only two quantum nodes, the sender can only transmit information through a single classical channel. However, if multi-component quantum resources are used to realize quantum teleportation, on the one hand, the larger number of quantum nodes provides the sender with multiple selection channels when transmitting classical information. On the other hand, due to the mutual quantum correlation between the sub-modules of multiple quantum nodes, the sender and receiver need the assistance of a controller to successfully realize quantum teleportation. The existence of the controller makes the quantum teleportation network controllable. All of these provide a basis for building a more complex and practical quantum communication network in the future.

[0003] In 2004, Furusawa's group used three-component Greenberger–Horne–Zeilinger (GHZ) states to construct a three-node continuous variable quantum teleportation network. In this quantum network, any two nodes can transmit unknown quantum states, but only with the assistance of a third party can the receiver reconstruct a quantum state with a fidelity greater than 0.5. The paper "Demonstration of a quantum teleportation network for continuous variables" was published in the journal Nature. The continuous variable quantum teleportation network implemented in this article includes three quantum nodes, namely the sending node, the receiving node and the control node. Compared with the quantum teleportation of two users, the receiving node in this scheme can choose between the remaining two nodes, and because of the quantum correlation between the three submodules received by the three nodes, the receiving node must obtain the information of the control node at the same time as receiving the information of the sending node in order to successfully reconstruct the quantum teleportation with a fidelity greater than the classical limit of 0.5. The number of quantum nodes in this scheme should be further increased, and the characteristics of the quantum resources used in this scheme lead to the construction of only one form of quantum teleportation network, and the combination form is single. In addition, the quantum resource preparation method in this scheme uses more optical components such as optical cavities, which increases the difficulty of experimental operation.

[0004] Therefore, it is very necessary to propose a relatively simple and easy-to-operate scheme for constructing multi-component quantum resources and to propose an implementation plan for constructing multiple types of quantum teleportation networks using the same multi-component quantum resources. Summary of the invention

[0005] In order to overcome the deficiencies in the prior art, the present invention aims to solve the technical problem of providing an improvement in the hardware structure of a four-component quantum teleportation network system.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a four-component quantum teleportation network system, including a device for generating continuous variable four-component quantum resources and four spatially separated quantum nodes, the four quantum nodes are respectively set as sending nodes, receiving nodes, and control nodes in the quantum teleportation network, the four quantum nodes are used to participate in the transmission process of one quantum state or participate in the transmission process of two quantum states, and the four quantum nodes are all connected to the device for generating continuous variable four-component quantum resources.

[0007] The transmission process of the quantum state includes at least one sending node and at least one receiving node.

[0008] The four quantum nodes simultaneously participate in realizing a teleportation network for transmitting a quantum state, and the number of control nodes in the teleportation network for transmitting a quantum state is set to 2.

[0009] Two of the four quantum nodes are combined with each other to realize a teleportation network for transmitting two unknown quantum states, and the number of control nodes in the teleportation network for transmitting two unknown quantum states is set to 0.

[0010] The sending node is provided with a first Bell joint measurement system, the two control nodes are provided with a second Bell joint measurement system, and the receiving node is provided with a modulated optical path and a first optical beam splitter;

[0011] The sending node and one of the control nodes are both connected to the receiving node, and a classical feedforward device is arranged between the sending node and the receiving node, and between one of the control nodes and the receiving node.

[0012] The modulated optical path is obtained by loading an amplitude modulator and a phase modulator on an independent laser beam;

[0013] The first Bell joint measurement system and the second Bell joint measurement system both include a beam splitter with a beam splitting ratio of 1:1 and two balanced zero-beat detection systems;

[0014] The classical feedforward device comprises: a first classical feedforward device arranged between a sending node and a receiving node, and a second classical feedforward device arranged between one of the control nodes and the receiving node;

[0015] The first classical feedforward device and the second classical feedforward device both include an amplifier and an attenuator;

[0016] The amplifier and attenuator of the classical feedforward device are used to adjust the magnitude of the fed-back classical information gain factor.

[0017] The device for generating the continuous variable four-component quantum resource comprises a continuous variable dual-wavelength frequency-stabilized laser, a first mode cleaner, a second mode cleaner, at least one non-degenerate optical parametric amplifier, and two second optical beam splitters. The first mode cleaner and the second mode cleaner are connected in parallel and are located downstream of the optical path of the continuous variable dual-wavelength frequency-stabilized laser. The output light fields of the first mode cleaner and the second mode cleaner simultaneously enter a non-degenerate optical parametric amplifier or simultaneously enter two non-degenerate optical parametric amplifiers. The non-degenerate optical parametric amplifier outputs a pair of entangled state light fields. The second optical beam splitter is used to couple the two-component entangled state light fields with the two coherent state light fields or couple the two pairs of two-component entangled state light fields to obtain a four-component quantum resource with a certain quantum correlation.

[0018] A method for constructing a four-component quantum teleportation network system.

[0019] Step 1: A four-component quantum resource having a certain quantum correlation is obtained by coupling two-component entangled state light fields and two coherent state light fields or by coupling two pairs of two-component entangled state light fields through a continuous variable four-component quantum resource generation device;

[0020] Step 2: Distribute the four sub-modes generated in step 1 to four spatially separated quantum nodes respectively;

[0021] Step 3: Start quantum teleportation: the unknown quantum state being transmitted enters the sending node, and the unknown quantum state being transmitted and the sub-mode received by the sending node are subjected to Bell joint measurement through the first Bell joint measurement system. The amplitude component information and phase component information after measurement are respectively sent to the receiving node through the first classical feedforward device. At the same time, the two control nodes perform Bell joint measurement on the sub-modes they receive through the second Bell joint measurement system, and the amplitude component information and phase component information after measurement are also respectively sent to the receiving node through the second classical feedforward device.

[0022] Step 4: The receiving node loads the received amplitude component information and phase component information onto the modulated light beam through the amplitude modulator and phase modulator respectively, and then uses the beam splitter to couple its own sub-mode with the modulated light beam, so that its own sub-mode performs a translation operation, thereby obtaining the recovered unknown quantum state.

[0023] In the step 3, the beam splitter of the first Bell joint measurement system is used to couple the unknown coherent state light field and the sub-mode owned by the sending node, and the two coupled output light fields are respectively measured by two sets of balanced zero-beat detection systems of the Bell joint measurement system to obtain information on the amplitude component and the phase component;

[0024] The beam splitter of the second Bell joint measurement system in step three is used to couple the sub-modes owned by the two control nodes. The two coupled output light fields are respectively measured by two balanced zero-beat detection systems of the Bell joint measurement system to obtain amplitude component information and phase component information.

[0025] The beneficial effects of the present invention compared with the prior art are as follows:

[0026] 1) The four-component quantum resource used in the present invention requires a relatively small number of optical elements such as an optical parametric oscillator cavity and an optical beam splitter during the preparation process, and the experimental device is simple and easy to operate, which greatly improves the efficiency of the experimental operation.

[0027] 2) The invention proposes to use the coupling method of EPR entangled state light field and coherent state light field to prepare quantum resources used for quantum teleportation. The four light field sub-modes outputted by the invention have certain quantum correlations, and there are cases where two sub-modes are correlated with each other. According to the quantum correlation characteristics between them, two completely different types of quantum teleportation networks can be constructed. The two networks each have their own advantages and characteristics. In practical applications, they can be selected according to specific needs. This provides a certain reference for improving the practicality of quantum communication networks.

[0028] 3) The present invention proposes a further improvement plan for quantum resources, replacing the coherent state light field with the EPR entangled state light field. Without changing the original quantum teleportation network construction method, the fidelity of each quantum teleportation process is improved, and the information transmission efficiency of the entire quantum system is improved. This provides a strong reference for improving the fidelity of quantum teleportation in the future.

[0029] 4) The preparation and optimization methods of quantum resources for quantum teleportation proposed in the present invention can be easily extended to more components, making the types of constructible quantum teleportation networks more diverse, and providing certain requirements for the complexity and diversity of quantum information networks in practical applications.

[0030] 5) The optical parametric amplifier used in the present invention has a triple resonance structure, requires low pump light power, has a high degree of entanglement in the output light field, and is simple to operate. By using the same laser to simultaneously pump multiple optical parametric amplifiers, the experimental device can be expanded to more components, thereby establishing a more complex quantum information network.

[0031] In summary, the present invention first provides the first experimental scheme for offline preparation of four-component quantum resources for quantum teleportation networks. Using this quantum resource, we can build two quantum teleportation networks with their own characteristics. In addition to the flexible selection of classical information channels for transmitting quantum states, the number of quantum states that can be transmitted can also be flexibly selected. This provides a certain foundation for the flexibility and selectivity required for building more quantum nodes and more complex quantum networks in the future. Then, the present invention proposes an experimental scheme for optimizing quantum resources. Under the premise of not changing the first quantum network construction form, the fidelity of quantum teleportation is greatly improved, providing a certain reference for improving fidelity in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be further described below in conjunction with the accompanying drawings:

[0033] Figure 1 This is a schematic diagram of the structure of the four-component quantum resource prepared offline in the present invention.

[0034] Figure 2It is a schematic diagram of the structure of four quantum nodes participating in the same quantum teleportation network of the present invention.

[0035] Figure 3 This is a schematic diagram of the structure of a quantum teleportation network for simultaneously transmitting two unknown quantum states according to the present invention.

[0036] Figure 4 It is a schematic diagram of the structure of the improved four-component quantum resource preparation device of the present invention.

[0037] Figure 5 The following is a theoretical analysis diagram of the relationship between the fidelity of the four-component quantum teleportation network and the gain factor in two cases of the present invention.

[0038] Figure 6 This is a theoretical analysis diagram of the relationship between the fidelity of the two-component quantum teleportation network and the change of compression parameters in two cases of the present invention.

[0039] In the figure: 1 is a continuous variable dual-wavelength intracavity frequency-doubling and frequency-stabilizing laser, 6 is a continuous variable four-component quantum resource generating device, 7 is a control node, 8 is a sending node, 10 is a receiving node, 11 is a first optical beam splitter, 12 is an amplitude modulator, 13 is a phase modulator, 14 is a transmitted unknown quantum state, 15 is a recovered unknown quantum state, 16 is a second optical beam splitter, 21 is a first mode cleaner, 22 is a second mode cleaner, 23 is a two-color beam splitter lens, 31 is a first non-degenerate optical parametric amplifier, 32 is a second non-degenerate optical parametric amplifier, 91 is a first classical feedforward device, and 92 is a second classical feedforward device. DETAILED DESCRIPTION

[0040] like Figures 1 to 6 As shown, the four-component quantum teleportation network system of the present invention includes a four-component quantum resource prepared offline, including four spatially separated quantum nodes; the four quantum nodes can play the roles of a sending node 8, a receiving node 10 and a control node 7 in the quantum teleportation network. The four quantum nodes can participate in the transmission process of one quantum state at the same time, or two of them can be combined to participate in the transmission process of two quantum states.

[0041] The four-component quantum resource prepared offline includes two construction methods. The first is to couple two-component entangled light fields with two coherent light fields. The second is to couple two pairs of two-component entangled light fields. The coupling method refers to interfering the two light fields on a 50:50 beam splitter and locking the relative phase difference of the two interfering light fields at 0 degrees.

[0042] The four sub-modules are interrelated. In addition, there is also a situation where two sub-modules are interrelated.

[0043] The quantum resources prepared by the two methods can construct the same type of quantum teleportation network, but the second method is a further improvement of the first method, and the fidelity of teleportation is significantly improved.

[0044] The transmission process of the quantum state includes at least one sending node 8 and one receiving node 10. The number of the control nodes 7 is 0 or 2. When the number of the control nodes 7 is 0, a teleportation network for transmitting two unknown quantum states can be constructed, and when the number of the control nodes 7 is 2, the fidelity of transmitting an unknown quantum state can be maximized.

[0045] The sending node 8, the receiving node 10 and the control node 7 are all connected to a device 6 for generating a continuous variable four-component quantum resource; the sending node 8 is provided with a first Bell joint measurement system, the two control nodes 7 are provided with a second Bell joint measurement system, and the receiving node 10 is provided with a modulated optical path and a first optical beam splitter 11; the sending node 8 and one of the control nodes 7 are connected to the receiving node 10, and a classical feedforward device is provided between the sending node 8 and the receiving node 10, and between one of the control nodes 7 and the receiving node 10.

[0046] Furthermore, the modulated optical path is obtained by loading an amplitude modulator 12 and a phase modulator 13 on an independent laser beam; the positions of the amplitude modulator 12 and the phase modulator 13 can be interchanged.

[0047] Furthermore, the first Bell combined measurement system and the second Bell combined measurement system each include a beam splitter with a beam splitting ratio of 1:1 and two sets of balanced zero-beat detection systems.

[0048] Further, the classical feedforward device includes: a first classical feedforward device 91 arranged between the sending node 8 and the receiving node 10, and a second classical feedforward device 92 arranged between one of the control nodes 7 and the receiving node 10; the first classical feedforward device 91 and the second classical feedforward device 92 both include an amplifier and an attenuator. Further, the amplifier and attenuator of the classical feedforward device are used to adjust the magnitude of the feedback information gain factor, and all gain factors need to be adjusted simultaneously to maximize the fidelity.

[0049] The construction method of the four-component quantum teleportation network system first couples two-component entangled light fields with two coherent light fields or couples two pairs of two-component entangled light fields to obtain a four-component light field mode with certain quantum correlation. Then, the four sub-modes are distributed to four quantum nodes separated in space. Next, quantum teleportation begins: the transmitted unknown quantum state enters the sending node 8, and the transmitted unknown quantum state and the sub-mode received by the sending node 8 are bell-jointly measured through the first Bell joint measurement system. The measured amplitude component information and phase component information are respectively sent to the receiving node 10 through the first classical feedforward device 91. At the same time, the two control nodes 7 also bell-jointly measure the sub-modes they receive through the second Bell joint measurement system. The measured amplitude component information and phase component information are also sent to the receiving node 10 through the second classical feedforward device 92. The receiving node 10 loads the received amplitude component information and phase component information on the modulated light beam through the amplitude modulator 12 and the phase modulator 13, respectively, and then uses the beam splitter to couple its own sub-mode with the modulated light beam, so that its own sub-mode performs a translation operation, thereby obtaining the recovered unknown quantum state.

[0050] Furthermore, the beam splitter of the first Bell joint measurement system is used to couple the unknown coherent state light field and the sub-mode owned by the sending node. The two coupled output light fields are respectively measured by two balanced zero-beat detection systems of the Bell joint measurement system to obtain amplitude component information and phase component information.

[0051] Furthermore, the beam splitter of the second Bell joint measurement system is used to couple the sub-modes owned by the two control nodes 7, and the two coupled output light fields are respectively measured by two sets of balanced zero-beat detection systems of the second Bell joint measurement system to obtain amplitude component information and phase component information;

[0052] Furthermore, there is a certain quantum correlation between the four sub-modules, which can construct a quantum teleportation network. There is also a certain quantum correlation between two sub-modules, which can construct another quantum teleportation network.

[0053] Using the same quantum resource, different types of quantum teleportation networks can be constructed, providing a basis for flexible selectivity in the construction of quantum information networks in the future. It should be noted that no matter what the compression parameters of the initial two-component entangled resources are, two types of quantum teleportation networks can be established, which means that the types of quantum networks that can be constructed are not limited by the compression degree of the quantum resources used.

[0054] The improved method described above greatly improves the fidelity of teleportation without changing the network construction characteristics, and provides a certain basis for improving the fidelity in the future.

[0055] The specific implementation method of the four-component quantum teleportation network device is as follows: first, use Figure 1 The scheme shown prepares quantum resources for quantum teleportation network. Before transmitting the unknown quantum state, four submodules with certain quantum correlation are distributed to four quantum nodes separated in space, Alice, Bob, Claire and David, referred to as A, B, C, D. In addition to the quantum correlation between the submodules received by the four nodes, there is also a quantum correlation between the submodules received by node A (B) and node C (D). We can use the quantum correlation between the four submodules to construct a quantum teleportation network, such as Figure 2 As shown, the quantum correlation between two submodules can also be used to construct a quantum teleportation network, such as Figure 3 As shown, the two different types of quantum networks have their own characteristics.

[0056] A complete quantum teleportation process includes a sending node 8 and a receiving node 10, and the other quantum nodes participating in the process are called control nodes 7. Figure 2 The specific transmission and reconstruction process of the quantum state shown is as follows: the transmitted unknown quantum state enters the sending node 8, and the transmitted unknown quantum state 14 is subjected to bell joint measurement with the sub-mode received by the sending node 8, and the amplitude component information and phase component information after measurement are loaded onto the amplitude modulator 12 and the phase modulator 13 of the receiving node 10 respectively through the classical feedforward device; at the same time, the two control nodes 7 also perform bell joint measurement on the sub-modes they receive, and the amplitude component information and phase component information after measurement are also loaded onto the amplitude modulator 12 and the phase modulator 13 of the receiving node 10 respectively through the classical feedforward device; the receiving node 10 couples the sub-mode it receives with the modulated light beam containing the amplitude modulator 12 and the phase modulator 13 through the first optical beam splitter 11, and implements a translation operation to obtain the recovered unknown quantum state 15.

[0057] The schematic diagram of the structure of the four-component quantum resource prepared offline is as follows Figure 1 As shown, it specifically includes a low-noise high-power continuous variable dual-wavelength frequency-stabilized laser 1, a first mode cleaner 21, a second mode cleaner 22, a non-degenerate optical parametric amplifier, and two 50:50 second optical beam splitters 16. The first mode cleaner 21 and the second mode cleaner 22 are connected in parallel and located downstream of the optical path of the low-noise high-power frequency-stabilized laser 1. The output light fields of the first mode cleaner 21 and the second mode cleaner 22 simultaneously enter the first non-degenerate optical parametric amplifier 31, and the first non-degenerate optical parametric amplifier 31 outputs a pair of entangled state light fields. Light Field and coherent state light field The light field is coupled to the second optical beam splitter 16 at a ratio of 50:50. and coherent state light field It is also coupled to another 50:50 second optical beam splitter 16, and four sub-modes are obtained after coupling. It can be expressed as:

[0058]

[0059] Entangled light field The relationship between the output of the first non-degenerate optical parametric amplifier 31 operating in the parametric anti-amplification state and the amplitude component and phase component of the input coherent state light field can be expressed as:

[0060]

[0061] In the above formula, r represents the compression factor, r' represents the anti-compression factor, and They represent the amplitude (phase) components of the signal light field and the idle light field of the NOPA input respectively. Combining formulas (1) and (2), we can get four sub-modes: The expression of quantum correlation noise between amplitude component and phase component is:

[0062]

[0063] It can be seen that the quantum correlation noise between the four sub-modes is less than the shot noise benchmark 4, and there is a certain quantum correlation between them. Figure 1 The device shown is obviously a sub-module and And sub-module and There is no correlation between them. We consider the quantum correlation between the other two submodules. Combining formulas (1) and (2), we can get the two submodules and Quantum correlation between amplitude and phase components:

[0064]

[0065] It can be seen from formula 4 that the two submodules and The quantum correlation noise between them is also less than the corresponding shot noise baseline value of 2, and they are entangled with each other. The special quantum correlation between these four sub-modules provides a good quantum resource for the construction of quantum teleportation network.

[0066] The low-noise, high-power, continuously variable dual-wavelength frequency-stabilized laser 1 is separated by a dual-color beam splitter 23 (DBS) downstream of the laser. The dual-color beam splitter 23 (DBS) coating is highly reflective to the 540nm light field and highly transparent to the 1080nm light field. A green light with a wavelength of 540nm and a power of 4W is obtained. p , a 1080nm wavelength, 1W power infrared laser 0 .

[0067] The first mode cleaner 21 and the second mode cleaner 22 both adopt a three-mirror annular cavity structure, and their functions are to respectively 0 and a p Noise filtering and spatial transverse mode shaping are performed. The optimized light field a 0 A part of it is used as seed light to enter the non-degenerate optical parametric amplifier 31, a part of it is used as a coherent state light field to couple with the entangled state light field output by the non-degenerate optical parametric amplifier 31, and a part of it is used as the background oscillation light field of the balanced zero-beat detection system in the quantum teleportation network and the coherent state light field such as the modulated laser beam. p As a pump light field, it enters the non-degenerate optical parametric amplifier 31.

[0068] The non-degenerate optical parametric amplifier is composed of a nonlinear optical crystal with a wedge angle and an output mirror. By adjusting the position of the crystal, the signal light field, the idle light field and the pump light field in the cavity can resonate in the cavity at the same time, thereby increasing the entanglement of the output light field and reducing the pump light threshold of the optical cavity. It is convenient to use the same laser to pump multiple non-degenerate optical parametric amplifiers at the same time to obtain more and higher quality multi-component entangled state light fields.

[0069] The light field and coherent state light field When coupled on the second optical beam splitter 16 with a ratio of 50:50, the relative phase difference between the two light fields is locked at 0 degrees. and coherent state light field It is also coupled to another 50:50 second optical beam splitter 16, and the relative phase difference between the two light fields is also locked at 0 degrees.

[0070] The Bell joint measurement system includes a beam splitter with a beam splitting ratio of 1:1 and two balanced zero-beat detection systems. The beam splitter of the first Bell joint measurement system is used to couple the unknown coherent state light field and the sub-mode owned by the transmitting node. The two coupled output light fields are respectively measured by the two balanced zero-beat detection systems of the Bell joint measurement system to obtain information on the amplitude component and the phase component. The output modes of the beam splitter are respectively expressed as The beam splitter of the second Bell joint measurement system is used to couple the sub-modes owned by the two control nodes. The two coupled output light fields are respectively measured by two sets of balanced zero-beat detection systems of the second Bell joint measurement system to obtain information on the amplitude component and the phase component. Figure 2 The output modes of the beam splitter are respectively expressed as

[0071] The receiving node 10 loads the received classical information onto an independent laser beam through a modulator, and then couples the laser with the sub-mode received by itself through a first optical beam splitter 11 with a splitting ratio of 1:99 to reconstruct the quantum state, instead of directly loading the received classical information onto the sub-mode received by itself through a modulator, thereby reducing the additional loss of the sub-mode received by itself.

[0072] The modulated optical path is obtained by loading an amplitude modulator 12 and a phase modulator 13 onto an independent laser beam.

[0073] The classical feedforward device includes: a first classical feedforward device 91 set between the sending node 8 and the receiving node 10, and a second classical feedforward device 92 set between one of the control nodes 7 and the receiving node 10; the amplifier and attenuator of the classical feedforward device are used to adjust the size of the feedback information gain factor, and all gain factors are continuously adjusted during network construction to maximize the fidelity.

[0074] The first classical feedforward device 91 and the second classical feedforward device 92 both include an amplifier and an attenuator.

[0075] Figure 2 The number of control nodes described in the device shown is 2. This is because the quantum correlation between the four users is the strongest. Obtaining the classical information of the two control nodes can greatly improve the fidelity of teleportation. If one control node is reduced, the fidelity of teleportation is reduced. Therefore, in the construction of the multi-user quantum teleportation network, only the case of four users participating at the same time is considered, and the case of only three users participating at the same time is not considered. If two control nodes are reduced, although the fidelity is reduced, the advantage is that two quantum states can be transmitted at the same time. A detailed solution is given in another implementation case.

[0076] The fidelity is an important indicator to measure the similarity between the input state and the output state in the process of quantum teleportation. In the ideal case, that is, under infinite compression, the fidelity is 1, which can perfectly reproduce the transmitted quantum state. In practice, due to the limitation of imperfect quantum resources, the fidelity is usually less than 1. The calculation formula of the fidelity of coherent state teleportation is: They represent the quantum noise of the orthogonal amplitude component and phase component of the reconstructed quantum state respectively. Figure 2 For the quantum teleportation scheme shown in the figure, the expressions of the orthogonal amplitude component and phase component of the output quantum state can be written as:

[0077]

[0078] in are the gain factors of the classical signals fed back from each station. In an ideal situation, when the compression parameter r approaches infinity, if the classical feedback gain factors are all set to 1, according to the quantum correlation between the four sub-modes, Then the reconstructed quantum state can be expressed as At this point, the output state and the input state are completely consistent, and the fidelity is 1. However, usually, r is a finite value, and the output state is not completely equal to the input state. At this time, we need to adjust the size of the gain factor to make the characteristics of the output state as close to the input state as possible and make the fidelity as large as possible. The size of the fidelity is mainly affected by the compression parameter and the gain factor. In order to ensure the consistency of the reconstructed quantum state and the input quantum state, Two gain factors take unity gain 1, and the other gain factors Take the same value of g.

[0079] The result of the joint measurement of the submodule bells of the two control nodes is the addition of the amplitude component operator and the subtraction of the phase component operator. In order to successfully reconstruct the unknown quantum state, that is, the expression of the final output mode corresponds to the quantum correlation between the four-component submodules, the control node cannot be A and B at the same time, nor can it be C and D at the same time. Any other combination can construct a four-component quantum teleportation network, and because of the symmetry of the quantum resource preparation device, the final effects of different combinations are equal.

[0080] Since the two submodules and They are also entangled with each other. Therefore, the process of quantum teleportation can be established between node A (B) and node C (D), and the final fidelity of different combinations is the same. Figure 3 The figure shows a schematic diagram of the structure of a quantum teleportation network that transmits two quantum states simultaneously. In the figure, nodes A and C serve as the sending node and receiving node of one teleportation process, and nodes C and D serve as the sending node and receiving node of another teleportation process.

[0081] Figure 3 In the device shown, before transmitting the quantum state, four submodules with certain quantum correlations are first It is sent to four quantum nodes A, B, C, and D separated in space. The sending node A transmits an unknown quantum state to the receiving node C, and the sending node B transmits an unknown quantum state to the receiving node D. The network can transmit two quantum states at the same time. The specific process of each teleportation is as follows: the unknown quantum state being transmitted enters the sending node 8, and the sender performs a bell joint measurement on the unknown quantum state 14 being transmitted and its own sub-module. The measured amplitude component information and phase component information are respectively sent to the receiving node 10 through the first classical feedforward device 91. The receiving node 10 loads the received amplitude component information and phase component information onto the modulated light beam through the amplitude modulator 12 and the phase modulator 13, respectively, and then couples the modulated light beam with its own sub-module in the first optical beam splitter 11 with a beam splitting ratio of 1:99 to achieve a translation operation, that is, to restore the transmitted quantum state 15.

[0082] The present invention proposes to use a special method for preparing four-component quantum resources to obtain four light field modes with certain quantum correlations. At the same time, there is also a certain quantum correlation between two of the four sub-modes. Using quantum resources to perform quantum teleportation can break through the classical limit of teleportation. The present invention uses the four-component quantum resources to construct two different types of quantum teleportation networks. Their characteristics are that one can transmit an unknown quantum state with high fidelity, and the other can transmit two unknown quantum states at the same time. The flexibility of this network construction provides more options for the construction of quantum information networks in the future, and the preparation method of the four-component quantum resources is simple and easy to operate, and it is very easy to expand to more components.

[0083] according to Figure 1 If the quantum noise of the coherent state light field is further reduced, can the fidelity of teleportation be further improved? Therefore, the invention proposes improvement measures on this basis. The coherent state light field is replaced with a two-component entangled state light field to prepare a four-component quantum resource. Figure 4 The figure shows a schematic diagram of the structure of the improved four-component quantum resource preparation device. Specifically, it includes a low-noise high-power continuous variable dual-wavelength frequency-stabilized laser 1, a first mode cleaner 21, a second mode cleaner 22, a first non-degenerate optical parametric amplifier 31 and a second non-degenerate optical parametric amplifier 32, and two 50:50 second optical beam splitters 16. The first mode cleaner 21 and the second mode cleaner 22 are connected in parallel and located downstream of the optical path of the low-noise high-power frequency-stabilized laser 1. The output light fields of the first mode cleaner 21 and the second mode cleaner 22 enter the first non-degenerate optical parametric amplifier 31 and the second non-degenerate optical parametric amplifier 32 at the same time. The first non-degenerate optical parametric amplifier 31 outputs a pair of entangled state light fields. The second non-degenerate optical parametric amplifier 32 outputs a pair of entangled state light fields Light Field and light field The light field is coupled to the second optical beam splitter 16 at a ratio of 50:50. and light field Also coupled to another 50:50 second optical beam splitter 16. The device only Figure 1 The coherent state light field in the device shown is replaced, and the other devices are exactly the same.

[0084] The first non-degenerate optical parametric amplifier 31 and the second non-degenerate optical parametric amplifier 32 have the same structure, so the compression parameters and anti-compression parameters of the generated entangled light field are the same.

[0085] After coupling, four sub-modes are obtained. It can be expressed as:

[0086]

[0087] The improved device only improves the preparation method of the four-component quantum resources, and the scheme of the quantum teleportation network that can be constructed has not changed. By comparison, we have obtained a curve comparison diagram of the theoretical calculation fidelity size with the gain factor in two ways, with nodes A (B) and C (D) as sending nodes 8 or receiving nodes 10, and the other two nodes as control nodes 7, as shown in the figure. Figure 5 As shown. Curves L1, L2, and L3 correspond to the improved teleportation results, and curves M1, M2, and M3 correspond to the teleportation results using coherent state coupling. Curves L1 and M1 correspond to the case where the compression parameter is 0.5, curves L2 and M2 correspond to the case where the compression parameter is 0.8, and curves L3 and M3 correspond to the case where the compression parameter is 1.5. By comparing the cases with the same compression parameters, it is obvious that when the gain factor has the same value, the use of the entangled state coupling method can further improve the teleportation fidelity of the four users.

[0088] At the same time, we also obtained the comparison of the fidelity curves with the compression parameters in the two cases when only nodes A (B) and C (D) participate in quantum teleportation, as shown in the figure. Figure 6 Curve H1 represents the coupling between the EPR entangled state light field and the coherent state light field, and curve H2 represents the coupling between two pairs of EPR entangled state light fields. Obviously, the fidelity of teleportation between the two users after improvement has been greatly improved.

[0089] The present invention utilizes a relatively simple method of constructing four-component quantum resources to obtain four light field modes for quantum teleportation. On the one hand, the number of quantum nodes is increased. On the other hand, due to the special correlation characteristics of quantum resources, various types of quantum teleportation network construction schemes can be realized. The present invention also proposes a practical solution to further improve the fidelity of quantum teleportation. These provide more options for the future establishment of larger-scale and more complex quantum information networks, and accelerate the pace of practical application of quantum information.

[0090] What needs to be explained about the specific structure of the present invention is that the connection relationship between the various component modules adopted in the present invention is definite and feasible. Except for the special instructions in the embodiments, the specific connection relationship can bring about the corresponding technical effects, and solve the technical problems raised by the present invention without relying on the execution of the corresponding software program. Except for the specific instructions, the models and connection methods of the components, modules and specific components appearing in the present invention belong to the existing technologies such as published patents, published journal articles, or common knowledge that can be obtained by technical personnel in this field before the application date, and there is no need to elaborate, so that the technical solution provided in this case is clear, complete and feasible, and the corresponding physical products can be reproduced or obtained according to the technical means.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A four-component quantum teleportation network system, characterized in that: It comprises a device for generating a continuous variable four-component quantum resource (6) and four spatially separated quantum nodes, wherein the four quantum nodes are respectively set as a sending node (8), a receiving node (10), and a control node (7) in a quantum teleportation network, and the four quantum nodes are used to participate in the transmission process of one quantum state or participate in the transmission process of two quantum states, and the four quantum nodes are all connected to the device for generating a continuous variable four-component quantum resource (6); The continuous variable four-component quantum resource generation device (6) comprises a continuous variable dual-wavelength frequency-stabilized laser (1), a first mode cleaner (21), a second mode cleaner (22), at least one non-degenerate optical parametric amplifier, and two second optical beam splitters (16), wherein the first mode cleaner (21) and the second mode cleaner (22) are connected in parallel and located downstream of the optical path of the continuous variable dual-wavelength frequency-stabilized laser (1), the output light fields of the first mode cleaner (21) and the second mode cleaner (22) simultaneously enter a non-degenerate optical parametric amplifier or simultaneously enter two non-degenerate optical parametric amplifiers, the non-degenerate optical parametric amplifier outputs a pair of entangled state light fields, and the second optical beam splitter (16) is used to couple the two-component entangled state light fields with two beams of coherent state light fields or to couple two pairs of two-component entangled state light fields to obtain a four-component light field mode with certain quantum correlation; The non-degenerate optical parametric amplifier is composed of a nonlinear optical crystal with a wedge angle and an output mirror.

2. The four-component quantum teleportation network system according to claim 1, characterized in that: The quantum state transmission process includes at least one sending node (8) and at least one receiving node (10).

3. The four-component quantum teleportation network system according to claim 2, characterized in that: The four quantum nodes simultaneously participate in realizing a teleportation network for transmitting a quantum state, and the number of control nodes (7) in the teleportation network for transmitting a quantum state is set to 2.

4. The four-component quantum teleportation network system according to claim 2, characterized in that: Two of the four quantum nodes are combined with each other to realize a teleportation network for transmitting two unknown quantum states, and the number of control nodes (7) in the teleportation network for transmitting two unknown quantum states is set to 0.

5. The four-component quantum teleportation network system according to claim 3 or 4, characterized in that: The sending node (8) is provided with a first Bell joint measurement system, the two control nodes (7) are provided with a second Bell joint measurement system, and the receiving node (10) is provided with a modulation optical path and a first optical beam splitter (11); The sending node (8), one of the control nodes (7) and the receiving node (10) are connected, and a classical feedforward device is provided between the sending node (8) and the receiving node (10), and between one of the control nodes (7) and the receiving node (10).

6. The four-component quantum teleportation network system according to claim 5, characterized in that: The modulated optical path is obtained by loading an amplitude modulator (12) and a phase modulator (13) on an independent laser beam; The first Bell joint measurement system and the second Bell joint measurement system both include a beam splitter with a beam splitting ratio of 1:1 and two sets of balanced zero-beat detection systems.

7. The four-component quantum teleportation network system according to claim 6, characterized in that: The classical feedforward device comprises: a first classical feedforward device (91) arranged between a sending node (8) and a receiving node (10), and a second classical feedforward device (92) arranged between one of the control nodes (7) and the receiving node (10); The first classical feedforward device (91) and the second classical feedforward device (92) both include an amplifier and an attenuator; The amplifier and attenuator of the classical feedforward device are used to adjust the magnitude of the fed-back classical information gain factor.

8. A method for constructing a four-component quantum teleportation network system, characterized in that: Step 1: using a continuous variable four-component quantum resource generation device (6) to couple a two-component entangled state light field with two coherent state light fields or to couple two pairs of two-component entangled state light fields to obtain a four-component light field pattern with certain quantum correlation; Step 2: Distribute the four sub-modes generated in step 1 to four spatially separated quantum nodes respectively; Step 3: Start quantum teleportation: the unknown quantum state being transmitted enters the sending node (8), the unknown quantum state being transmitted and the sub-mode received by the sending node (8) are subjected to Bell joint measurement through the first Bell joint measurement system, and the amplitude component information and phase component information after measurement are respectively sent to the receiving node (10) through the first classical feedforward device (91), and at the same time, the two control nodes (7) perform Bell joint measurement on the sub-modes they receive through the second Bell joint measurement system, and the amplitude component information and phase component information after measurement are also respectively sent to the receiving node (10) through the second classical feedforward device (92); Step 4: The receiving node (10) loads the received amplitude component information and phase component information onto the modulated light beam through the amplitude modulator (12) and the phase modulator (13), respectively, and then uses the beam splitter to couple its own sub-mode with the modulated light beam, so that its own sub-mode performs a translation operation, thereby obtaining the recovered unknown quantum state.

9. The method for constructing a four-component quantum teleportation network system according to claim 8, characterized in that: In the step 3, the beam splitter of the first Bell joint measurement system is used to couple the unknown coherent state light field and the sub-mode owned by the transmitting node (8), and the two coupled output light fields are respectively measured by two sets of balanced zero-beat detection systems of the Bell joint measurement system to obtain information on the amplitude component and the phase component; The beam splitter of the second Bell joint measurement system in step 3 is used to couple the sub-modes owned by the two control nodes (7). The two coupled output light fields are respectively measured by two sets of balanced zero-beat detection systems of the second Bell joint measurement system to obtain amplitude component information and phase component information.

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