A multi-qubit entangled state generating device and a generating method

Abstract

This application discloses a device and method for generating multi-qubit entangled states, including an entangled state preparation module, a multi-layer quantum coding module, a detection module, and a control module. The multi-layer quantum coding module comprises an n-layer measurement coding structure. The control module sets the measurement basis and codes the paths of photons input through different paths using path coding units. This allows photons representing different n-qubit ground states to exit from different path coding units and enter corresponding single-photon detectors after passing through different paths. After multiple cycles of measurement coding, the detection results of all single-photon detectors in the detection module are statistically analyzed to obtain an n-qubit entangled state with r ground states. The construction process of the multi-qubit state is transformed into a multi-layer quantum measurement process, reducing the number of interference units, space requirements, and control signals needed, thereby reducing the complexity and cost of the quantum computing measurement and control system.

Description

Technical Field

[0001] This application belongs to the field of quantum computing technology, and more specifically, relates to a technology for generating quantum entangled state resources. Background Technology

[0002] Quantum computing, leveraging properties such as quantum superposition and entanglement, holds the promise of significantly surpassing classical computing capabilities for specific problems. Among numerous quantum computing implementation schemes, two physically rich and experimentally feasible models have attracted considerable attention: one is the quantum gate circuit model based on unitary evolution operations, and the other is the measurement-based quantum computation (MBQC) model, which relies on pre-prepared large-scale multi-qubit entangled states (such as cluster states) as general-purpose computing resources, and its computation process is realized through single-qubit measurement sequences. Among various physical platforms, optical quantum computing, with its advantages of room-temperature operation, low decoherence rate, high-fidelity manipulation, and natural suitability for long-distance quantum communication, has become one of the important technical routes for realizing scalable quantum information processing and has shown strong development momentum in recent years. Encoding multi-qubit entangled states using photons (including single-photons and multi-photons) is theoretically feasible, not only easily realizing high-dimensional entanglement and parallel operations, but also compatible with existing optical communication infrastructure.

[0003] The preparation and generation of multiphoton entangled states require significant overhead in quantum devices and control signals, resulting in high costs for quantum computing chips or quantum computers. In recent years, a feasible approach to reducing the overhead of entangled state preparation has been to encode as much information as possible into each photon, such as through high-dimensional encoding techniques. However, high-dimensional encoding typically requires up to 2... n To construct a 2-dimensional Hilbert space (where n is the number of qubits), the photon path needs to be extended step by step through a beam-splitting network. n The quantum computing measurement and control system first considers the dimensions of quantum computing, and then uses a large-scale general-purpose interference network to construct several quantum logic gates to perform qubit operations on different dimensions. The measurement is then converged through a beam splitting network. This brings huge resource challenges, including a sharp increase in the number of optical quantum devices and an increase in chip area. The number of optical quantum devices also leads to an increase in the number of signal channels that need to be controlled simultaneously, which brings greater scale and accuracy challenges to the quantum computing measurement and control system. Summary of the Invention

[0004] To address the resource consumption problem of high-dimensional quantum encoding, this application provides a multi-qubit entangled state generation device and a method for generating multi-qubit entangled states. The specific scheme is as follows:

[0005] This application discloses a multi-qubit entangled state generation device, including an entangled state preparation module, a multi-layer quantum coding module, a detection module, and a control module.

[0006] The entangled state preparation module is used to generate a photon in a superposition state in each cycle and output it from any one of the r paths.

[0007] The multilayer quantum coding module includes an n-layer measurement coding structure, and the detection module includes multiple single-photon detectors, where n and r are both integers greater than 1. n ≥r≥2.

[0008] The first-layer measurement coding structure includes m path coding units arranged in parallel, where m is an integer greater than 1, and r ≥ m ≥ 2. The photons output by the entangled state preparation module are transmitted to the m path coding units of the first-layer measurement coding structure via any one of the r paths. The second-layer measurement coding structure includes (m / 2) path coding units arranged in parallel, and so on, until the i-th layer includes 2 path coding units. The i-th to (n-1)-th layers each include 2 path coding units, where i is an integer greater than 1, and n-1 > i > 1. The n-th layer includes 1 path coding unit. Each path coding unit includes two input ports and two output ports. The path coding units of the 1-n-th layers are cascaded in a cross-connected manner. One output port of each path coding unit in the 1-(n-1)-th layers connects to the next layer of measurement coding structure, and the other output port connects to a single-photon detector in the detection module. The path coding unit of the n-th layer measurement coding structure connects to two single-photon detectors.

[0009] The control module is used to program and control each path coding unit in the measurement coding structure of each layer. In this way, the path coding unit performs measurement basis setting and path coding for photons with different path inputs, so that photons with different path inputs and representing different n-qubit ground states are output from different path coding units and enter the corresponding single-photon detectors after passing through different routes.

[0010] The control module is also used to perform statistical analysis on the detection results of all single-photon detectors in the detection module after multiple cycles of measurement encoding, complete the photon measurement encoding, and obtain an n-qubit entangled state with r ground states.

[0011] Preferably, the entangled state preparation module includes:

[0012] A 1xN beam splitter is used to split an externally input laser pulse into an equal beam and output it from its N output ports respectively;

[0013] N 50:50 beam splitters are connected to the N output ports of the 1xN beam splitter. Each 50:50 beam splitter will split the input laser pulse into an average beam and output it from its two output ports respectively.

[0014] N photon source pairs, including two photon source pairs connected to the two outputs of each 50:50 beam splitter, are used to generate entangled two photons with different wavelengths (l1, l2);

[0015] N photon separation unit groups, including two photon separation units connected to the output end of the photon pair source, are used to output each pair of entangled two photons according to their wavelengths from their upper output port and lower output port respectively;

[0016] N first fusion and exchange modules are used to exchange the paths of photons output by different photon separation units in the same photon separation unit group;

[0017] (N-1) second fusion and exchange modules are used to exchange the paths of photons output by different photon separation unit groups to generate a multi-photon entangled state composed of 2N photons.

[0018] There are 2N output terminal groups, each of which is used to output one photon in a multi-photon entangled state.

[0019] Optionally, when the number of sub-ports in each output group of the entangled state preparation module is less than r, the entangled state preparation module further includes 2N path extension units, which are respectively connected to 2N output groups, and are used to extend the photon output path of each output group to r.

[0020] Optionally, the path coding unit is an MZ interferometer (Mach-Zehnder interferometer) or a multimode interferometer.

[0021] Optionally, the photon pair source is one of a spiral waveguide coil, a silicon nitride microring structure, or a periodically polarized crystal waveguide.

[0022] Optionally, the first fusion switching module and the second fusion switching module are cross waveguides.

[0023] Optionally, all devices in the entangled state preparation module and the multilayer quantum coding module are integrated on the same semiconductor substrate and formed in one piece through a monolithic integration process.

[0024] This application also discloses a method for generating multi-qubit entangled states, applied to the aforementioned multi-qubit entangled state generation device. The multi-qubit entangled state generation device includes an entangled state preparation module, a multi-layer quantum coding module, and a detection module. The method includes:

[0025] During each cycle, the entangled state preparation module generates a photon in a superposition state;

[0026] The photons output by the entangled state preparation module are transmitted to multiple path coding units of the first-layer measurement coding structure via any one of the r paths;

[0027] The multi-layer quantum coding module is based on the programming control of the control module. It sets the measurement basis and codes the path for photons input through different paths through the path coding unit, so that photons with different paths and representing different n-qubit ground states are output from different path coding units and enter the corresponding single-photon detectors after passing through different routes.

[0028] After multiple cycles of measurement encoding, the control module performs statistical analysis on the detection results of all single-photon detectors in the detection module, completes the photon measurement encoding, and obtains the n-qubit entangled state.

[0029] Optionally, the entangled state preparation module includes a 1xN beam splitter, N 50:50 beam splitters, N photon pair source groups, N photon separation unit groups, N first fusion switching modules, (N-1) second fusion switching modules, and 2N output terminal groups. The method includes:

[0030] The 1xN beam splitter receives externally input laser pulses, divides them into N equal parts, and outputs them to N 50:50 beam splitters through N output ports.

[0031] Each 50:50 beam splitter splits the input laser pulse into an average beam and outputs it from its two output ports respectively;

[0032] Each photon pair source group is pumped and excited by a laser pulse, generating entangled two photons with different wavelengths (l1, l2);

[0033] Each photon separation unit group outputs the received pair of entangled photons according to their wavelengths through its upper and lower output ports respectively;

[0034] Each first fusion and exchange module performs path exchange on the photons output by different photon separation units in the same photon separation unit group;

[0035] Each second fusion and exchange module swaps the paths of photons output from different photon separation unit groups to generate a multi-photon entangled state consisting of 2N photons.

[0036] Each output group outputs one photon in a multi-photon entangled state.

[0037] Optionally, when the number of sub-ports in each output group of the entangled state preparation module is less than r, the entangled state preparation module also includes 2N path extension units, which are respectively connected to 2N output groups. The path extension units extend the photon output paths of each output group to m.

[0038] In summary, compared with the prior art, the above-described technical solutions conceived in this application can achieve the following beneficial effects:

[0039] This application provides a resource-efficient scheme for generating multi-qubit quantum states using a single photon. By combining preliminary quantum state generation and state measurement, layer-by-layer qubit encoding is achieved. The process of constructing multi-qubit states using multiple photons is replaced by a direct single-photon multi-layer quantum measurement process. By combining quantum state generation and state measurement, the construction process of multi-qubit states is transformed into a multi-layer quantum measurement process, eliminating the need for a general-purpose interference network, reducing the number and space required for interference units, saving optical quantum devices, and freeing up more space for chip wiring by reducing the number of control signals. This also reduces the requirements for the scale and accuracy of the control signals provided by the control module, thereby reducing the complexity and cost of the quantum computing measurement and control system, making the preparation of large-scale optical quantum entangled states and quantum computing easier to implement and apply. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in this embodiment or the prior art, the drawings used in the description of the embodiment or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 A schematic diagram of a multi-qubit entangled state generation device provided in this application;

[0042] Figure 2 A schematic diagram of a multilayer quantum coding module provided in this application;

[0043] Figure 3 A schematic diagram of yet another multilayer quantum coding module provided in this application;

[0044] Figure 4 A schematic diagram of another multilayer quantum coding module provided in this application;

[0045] Figure 5 The m=2 provided for this application n A schematic diagram of a multi-layer quantum coding module under certain conditions;

[0046] Figure 6 A schematic diagram of a module for preparing entangled states that can generate multiphoton quantum entangled states;

[0047] Figure 7 A schematic diagram of a 4qubit multilayer quantum coding module used to encode GHZ state photons;

[0048] Figure 8 A schematic diagram of expanding a 4-qubit GHZ state into a 16-qubit graphical state;

[0049] Figure 9 A schematic diagram of a multilayer quantum coding module when m=3;

[0050] Figure 10 A schematic diagram of a module for preparing an entangled state when N=3;

[0051] Figure 11 This is a schematic diagram of a path extension unit in one embodiment of this application;

[0052] Figure 12 This is a schematic diagram of an on-chip MZ interferometer;

[0053] Figure 13 A flowchart illustrating a method for generating multi-qubit entangled states provided in an embodiment of this application. Detailed Implementation

[0054] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the embodiments of this application will be further described in detail below with reference to the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0055] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0056] Currently, the generation of multi-photon entangled states requires a large amount of quantum devices and control signals, resulting in high costs for quantum computing chips or quantum computers. Therefore, this invention proposes a multi-qubit entangled state generation device and method, which simplifies the generation process of large-scale multi-qubit entangled states by implementing multi-qubit encoding through layer-by-layer measurement and coding.

[0057] The following detailed description of the multi-qubit entangled state generation device and method provided in this application, with reference to specific embodiments, provides a detailed explanation.

[0058] like Figure 1 As shown, this application provides a multi-qubit entangled state generation device, including an entangled state preparation module 1, a multi-layer quantum coding module 2, a detection module 3, and a control module 4.

[0059] The entanglement preparation module generates a photon in a superposition state within each cycle and outputs it from any of the r paths, or in other words, expands it to any of the r paths. This photon is in a path superposition state, meaning it appears on any of the r paths with equal probability. This expansion can be seen as a preliminary encoding, encoding the single photon onto the r paths; physically, the single photon may be located on any of these r paths. The photon to be encoded before expansion can be a photon that has not undergone quantum operations, or a photon that has undergone preliminary quantum operations and is in a certain quantum state or entangled state. Here, we will take a single photon that has not undergone quantum operations before expansion as an example.

[0060] The multi-layer quantum coding module 2 includes an n-layer measurement coding structure 21, used to further encode the input photon into an n-qubit entangled state with r ground states (probability amplitudes not zero) based on the programming control of the control module 4, where n and r are both integers greater than 1. n For a cluster state with ≥r≥2, such as a four-qubit cluster, the expression is as follows:

[0061]

[0062] The cluster states of this four qubit have four four-qubit ground states: |0000>, |0011>, |1100>, and |1111>. The coefficients of the other ground states of the four qubits (such as |0101>, |1010>, etc.) are all zero.

[0063] The detection module 3 includes multiple single-photon detectors 31. The multiple single-photon detectors 31 can be combined into one or more multi-channel single-photon detectors.

[0064] The first-layer measurement coding structure (hereinafter referred to as Layer 1) includes m path coding units 22 arranged in parallel, where m is an integer greater than 1, and r ≥ m ≥ 2. The photons output by the entangled state preparation module are transmitted to the m path coding units of the first-layer measurement coding structure via any one of the r paths. Here, the photons may be transmitted to the first-layer measurement coding structure via any one of the r paths.

[0065] The second layer of the measurement coding structure includes (m / 2) path coding units arranged in parallel, taking the entire path coding unit upwards. This continues, with each subsequent layer reducing the number of path coding units by half. When the number of path coding units is an odd number H, the number of path coding units in the next layer is (H+1) / 2, until the i-th layer contains 2 path coding units, layers i to (n-1) each contain 2 path coding units, and the n-th layer contains 1 path coding unit, where i is an integer greater than 1, and n-1 > i > 1. There are some special cases where only one layer of the measurement coding structure has 2 path coding units. For example, when m=2 and n=2, Layer1 contains 2 path coding units, and Layer2 contains 1 path coding unit. Figure 2 As shown, this is the most simplified coding structure, which requires only four single-photon detectors 31. For example, when m=4 and n=3, Layer 1 includes four path coding units, Layer 2 includes two path coding units, and Layer 3 includes one path coding unit.

[0066] When m=2, n=3, Layer 1 includes 2 path coding units, Layer 2 includes 2 path coding units, and Layer 3 includes 1 path coding unit, corresponding to 6 single-photon detectors 31 (D1~D6), as follows. Figure 3 As shown. When m=4, n=4, Layer 1 includes 4 path coding units, Layer 2 includes 2 path coding units, Layer 3 includes 2 path coding units, and Layer 4 includes 1 path coding unit, corresponding to 10 single-photon detectors 31, as shown. Figure 4 As shown.

[0067] Each path coding unit 22 includes two input ports and two output ports. The path coding units of layers 1 to n are sequentially cascaded to form a tree-like cascaded network, such as... Figure 1 As shown, in layers 1 to (n-1), one output port of each path coding unit connects to the next layer's measurement coding structure 21, and the other output port connects to a single-photon detector. The path coding unit of the nth layer's measurement coding structure connects to two single-photon detectors. Furthermore, since each path coding unit includes two input ports, the number of input paths r satisfies: m ≤ r ≤ 2m. The number of input paths r can be odd or even, and the number of input paths m only needs to satisfy m ≥ r / 2, meaning that all input paths have corresponding input ports of path coding units.

[0068] The control module is used to program and control each path coding unit in the measurement coding structure of each layer. The path coding unit sets the measurement basis and encodes the photons input by different paths, so that photons with different paths and representing different n-qubit ground states are output from different path coding units and enter the corresponding single-photon detectors after passing through different routes. The path coding units at the end of the path of photons with different input paths are also different.

[0069] The control module is also used to statistically analyze the detection results of all single-photon detectors within the total time of all cycles in the detection module after multiple cycles of measurement encoding, completing the photon measurement encoding and obtaining an n-qubit entangled state with r ground states. In actual quantum computing operations, the above process is typically run for 10 cycles. 4 ~10 8 The operation time can range from milliseconds to tens of seconds, with cycles lasting several cycles or even longer. After a sufficient number of cycles, if the statistical detection results are statistically significant, then the statistical results can be considered to approximate or represent the calculated results.

[0070] Photons input through different paths are combined through different path encoding units and then enter the single-photon detector connected to the path encoding unit at the end of the combination. This completes the projection measurement of n qubits, generating an n-qubit entangled state with r non-zero ground states. The end of this specific path encoding unit combination is not necessarily the nth layer measurement encoding structure; it can be any other layer measurement encoding structure. This is because multi-layer quantum encoding modules can perform projection measurements at any layer, and the end of this specific path encoding unit combination may be located at any layer measurement encoding structure. The specific layer depends on the number of qubits to be projected. However, regardless of which layer of path encoding unit the photon outputs from and ultimately enters the detection module 3, all single-photon detectors 31 in the detection module 3 must simultaneously perform single-photon detection and simultaneously feed back the detection results of all single-photon detectors 31 to the control module. This determines which single-photon detectors detected photons and which did not, so that the control module can comprehensively judge the encoded quantum state. In addition, the control module's programming control of each path encoding unit ensures that photons input through different paths enter different single-photon detectors, and the routes of photons input through different paths are different.

[0071] The following is combined Figure 1 and Figure 4The process of generating a multi-qubit entangled state is described in detail below. Here, r=4, m=4, and n=4. The input photon enters the multi-layer quantum coding module (here, 4-qubit coding) via four paths: |0000>, |0011>, |1100>, and |1111>. Note that this refers to inputting only one single photon at a time. This photon is in a superposition or entangled state. This single photon enters from any path with a 1 / 4 probability. Path coding allows photons input via different paths to exit from different path coding units and enter the corresponding single-photon detectors. When a specific single-photon detector detects the single photon, the coding is successful. This process constitutes one cycle. The control module performs multiple cycles of measurement coding and detection. Different single-photon detectors may respond to photons in different cycles, corresponding to different ground states. Then, the counts of all single-photon detectors in the detection module over the total time of multiple cycles are counted, and the quantum state coding result is obtained through analysis.

[0072] When it is necessary to encode the input photon into a |0011> quantum state, and this is done through measurement in Layer 1, the control module controls the encoding of the path encoding unit M2 in the first layer of the measurement encoding structure of Layer 1. This causes the photon (representing the |0011> quantum state) input to the path encoding unit M2 to be output from its upper output and enter the single-photon detector D2. The single-photon detector D2 detects the photon and feeds the signal back to the control module, indicating that the input photon has been successfully encoded into the |0011> quantum state. Of course, for a complete determination of successful encoding of the |0011> quantum state, other single-photon detectors must not detect the photon. For example, if single-photon detector D2 detects the photon and outputs 1, while other single-photon detectors do not detect the photon and all output 0. Of course, in actual operation, photons may also enter the first layer of measurement coding structure (Layer 1) from path coding units M4, M5, and M7, and then enter other single-photon detectors via other path coding units. The system will also record the responses of other single-photon detectors, but will define them as non-|0011>. Only when they enter path coding unit M2 and are detected by D2 are they considered to have successfully encoded the |0011> quantum state. This method is also called post-selection, which is a commonly used statistical method in optical quantum computing. It retains the measurement results of the required quantum state and discards the detector responses of the unnecessary ones. Therefore, successfully encoding the target quantum state is actually a certain probabilistic behavior. However, when the measurement coding period or number of times is large enough, such as when millions or tens of millions of photons enter the single-photon detector through multiple layers of quantum coding modules in a single quantum computing operation, and the frequency of the light source is usually sufficient to support the generation of millions of single photons per second, then the number of successfully encoded target quantum states is also large enough to complete the required quantum computing and obtain the target result.

[0073] It's also important to clarify that layer 1 here refers to the measurement of the last bit (|1>) in the n-qubit sequence |0011>. However, the quantum state of the photon is already determined to be the |0011> state, so there's no need to measure the other qubits in |0011> to complete the encoding of the |0011> quantum state. In actual quantum computing, the choice of which qubit (i.e., which layer of the measurement and encoding structure) to measure is determined by the overall quantum algorithm or the target quantum state. Any qubit can be selected for measurement to encode the quantum state, based on the needs of the overall algorithm. Furthermore, only one qubit can be selected for measurement to encode the quantum state in each computation; multiple qubits cannot be measured simultaneously.

[0074] In addition, projection measurement is performed on layer 1, which corresponds to the measurement of the last qubit. Projection measurement is performed on layer n of the encoding structure, which corresponds to the measurement of the first qubit. That is, the order of the layers and the order of the qubits are reversed.

[0075] When it is necessary to encode the input photon into a quantum state, and this is done by measuring in Layer 2, the control module controls the path encoding units M2 and M3 in the first and second layer measurement encoding structures to encode the photon (representing the quantum state) input to the path encoding unit M2. The photon is output from its lower output end, enters the path encoding unit M3, and then enters the single-photon detector D3. The single-photon detector D3 detects the photon and feeds the signal back to the control module, indicating that the input photon has been successfully encoded into a quantum state.

[0076] When it is necessary to encode the input photon into a quantum state (|0011>) via measurement at Layer n, the control module controls the path encoding units M2, M3, M1, and M9 in the measurement encoding structure of layers 1 to n. This ensures that the photon (representing the quantum state) input to path encoding unit M2 is output from its lower output, passes through M3, M1, and M9, and then enters the single-photon detector D9. The single-photon detector D9 detects the photon and feeds the signal back to the control module, indicating successful encoding of the input photon into a quantum state. Simultaneously, the control module must also control other path encoding units to prevent photons entering the multi-layer quantum encoding module via other paths from entering M9, or to redirect them to other single-photon detectors.

[0077] The above describes the projection measurement encoding of the quantum state (4-qubit entangled state) at Layer 1, Layer 2, and Layer n, respectively. The path encoding unit of each layer's measurement encoding structure sets the measurement basis (also called the Z-basis) for photons, which is reflected in the photon's path selection as either direct passage or reflection within the path encoding unit. When measuring a particle using the Z-basis, if a photon outputs from a specific path encoding unit and enters a specific single-photon detector, the measurement result is 1, equivalent to performing a Pauli-Z gate operation on all neighboring particles of that particle. If no photon enters the single-photon detector, the measurement result is 0, and there is no effect. In other embodiments of this application, depending on the algorithmic requirements of the actual overall quantum computing, projection measurements of single photons can be performed simultaneously through a multi-layer measurement-coding structure. This allows photons to be output from several preset path encoding units with different probabilities and appear at several preset ports. For example, photons along the |0011> path may be output from any of the Layer 1, Layer 2, or Layer n measurement-coding structures with different probabilities and enter different single-photon detectors. By statistically analyzing the probabilities of photons output from different ports, different multi-qubit entangled states can be generated. In this implementation, the measurement basis of each path encoding unit is no longer the computation basis (|0> and |1>), but a preset, specific basis, such as the X basis (|+> and |->). Each path encoding unit is set to a Hada code transformation, which is equivalent to performing an H-gate (single-qubit logic gate) operation. A single photon can only be output from one path encoding unit at a time, while multiple photons will be output from different path encoding units. For example, through programming control of M2, M3, and M1, photons in the |0011> path can enter D2, D3, and D1 with probabilities of P / 2, P / 4, and P / 4, respectively, or enter D2, D3, D1, and D9 with probabilities of P / 2, P / 6, P / 6, and P / 6, where P is the overall probability of photons in the |0011> path. By statistically analyzing the probabilities of photons output from different ports, different multi-qubit entangled states can be generated.

[0078] Similarly, when it is necessary to encode the input photon into a |1100> quantum state and perform measurements at Layer n, the control module controls the encoding of path encoding units M7, M6, M8, and M9 in the measurement encoding structure of layers 1 to n. This causes the photon (representing the |1100> quantum state) input to path encoding unit M7 to be output from its upper output, pass through M6, M8, and M9, and then enter the single-photon detector D9. The single-photon detector D9 detects the photon and feeds the signal back to the control module, indicating that the input photon has been successfully encoded into the |1100> quantum state. The encoding methods for the other two quantum states |0000> and |1111> are similar to the above process and will not be described in detail here.

[0079] In the actual operation of quantum computing, photons enter the multi-layer quantum coding module in any of the following states or paths: |0000>, |0011>, |1100>, and |1111>. By simultaneously programming and controlling all path coding units in the first-layer measurement coding structure, the four ground states |0000>, |0011>, |1100>, and |1111> can be encoded through projection measurement in layer 1, thereby generating a single-photon four-qubit entangled state (all single-photon detectors connected to the measurement coding structures of all layers need to be in working condition and provide detection results). By simultaneously programming and controlling all path coding units in the measurement coding structures of layers 1 to n, a single-photon four-qubit entangled state can be generated through any layer of measurement coding structure. Of course, regardless of which ground state of the four-qubit entangled state is encoded, all single-photon detectors need to detect simultaneously and collaboratively determine whether the measurement coding was successfully performed, that is, whether the target quantum state was successfully generated. Therefore, the multi-qubit entangled state generation device and its operation process provided in this application are not pattern preparation in the traditional sense. Instead, the photon is guided by a specific setting through the measurement device module. As long as it is detected at a specific node (other nodes do not detect it), it means that the generation is successful and the initial application of the pattern is completed at the same time.

[0080] In the examples above, the measurement of different qubits is achieved through the detection responses of single-photon detectors corresponding to different path encoding units. Theoretically, the system can be simplified to only setting a single-photon detector at the output of the path encoding unit M9, that is, only performing qubit measurements on layer n to encode the four ground states |0000>, |0011>, |1100>, and |1111>. This method is the most energy-efficient in terms of photonic quantum devices and has the smallest chip area, but it places the highest demands and load on the single-photon detector D9. The detection frequency of the single-photon detector D9 needs to be greater than the frequency of the input photon (here, the pulse frequency, not the wavelength frequency), and the single-photon detector D9 needs to operate at full capacity, leaving little time for periodic calibration or reset operations. In addition, the control of the path encoding unit needs to be adjusted multiple times to switch the paths of photons input from different paths in order to encode different ground states, increasing the complexity of quantum measurement and control.

[0081] Figure 4 The path coding unit and single-photon detector depicted by the dashed line are photonic quantum devices that can be omitted when generating multi-qubit entangled states using measurement coding, relative to a complete tree-shaped path coding network. Since the encoded multi-qubits are entangled states, the input path does not need to be configured with 2-1. nInstead of setting a single line, r lines are sufficient. Furthermore, each path encoding unit is connected to a control module, which provides one control signal to each path encoding unit. This saves on optical quantum devices, and the reduction in the number of control signals also frees up more space for chip wiring, reducing wiring difficulty. It also lowers the requirements for the scale and precision of the control signals provided by the control module, thus reducing the complexity and cost of the quantum computing measurement and control system. This makes the generation of large-scale optical quantum entangled states and quantum computing easier to implement and put into practical use.

[0082] Furthermore, it's important to note that the projection measurement operation on the qubits in this embodiment is both a process of generating entangled quantum states and a quantum computing process. The measurement-based quantum computing model is characterized by the local measurement of multi-qubit entangled states such as cluster states or graph states. This local measurement causes the original overall quantum state to collapse onto the remaining qubits, altering their entangled states, which is equivalent to applying quantum logic gates to them. In this embodiment, the measurement operation on any qubit, i.e., the local projection measurement of cluster states or graph states, is equivalent to applying quantum logic gates. This can be understood as the multi-layer quantum coding module simultaneously generating and measuring multi-qubit entangled states while measuring and encoding photons, which is equivalent to simultaneously performing quantum logic gate operations, i.e., simultaneously completing some quantum computing steps. Overall, it integrates multi-qubit entangled states (cluster states, graph states, etc.) with local measurements within the same subsystem, thereby saving on optical quantum devices and control signal resources.

[0083] The following is based on Figure 5 Taking a complete tree-structured path coding network as an example, this paper introduces the process of generating an n-qubit entangled state. Figure 5 In this case, m=4 and n=3, which is also the case where m has the largest value, i.e., m=2. n And r=2m=8. There are 8 paths for photon input, corresponding to |000>, |001>, |010>, |011>, |100>, |101>, |110>, and |111> respectively. The target quantum entangled state is:

[0084]

[0085] Each time a photon enters through one of the paths, the control module measures and sets the encoding units for each path. When a photon from the |010> path is detected by single-photon detector D1, and other single-photon detectors show no response, it means the |010> ground state is encoded. Similarly, a photon from the |011> path enters single-photon detector D1 after passing through layers 1 and 2, and other single-photon detectors show no response, indicating the |011> ground state is encoded. The same applies to photons from other paths. Each single-photon detector's response corresponds to a ground state. All layers of the measurement and encoding structure maintain preset settings, applying photon splitting ratios or photon allocation ratios to photons from different input ends, ensuring that photons from different input paths all enter a single-photon detector, achieving simultaneous encoding of all ground states, i.e., completing the input of an n-qubit entangled state. In this embodiment, complete encoding of all ground states requires the simultaneous participation of all layers of measurement and encoding structures and all single-photon detections. Each path encoding unit essentially sets a computational basis for the photon, and each input path photon has a corresponding single-photon detector response. When the algorithm based on overall quantum computing requires that each ground state correspond to the photon response of multiple single-photon detectors, the measurement basis of each path encoding unit can be set to other types, such as the X basis mentioned above. Then, after passing through multiple quantum encoding modules, the photon of each input path may be output from multiple path encoding units to different single-photon detectors with different probabilities (e.g., the |011> photon may enter D1, D2, and D4 with probabilities of P / 4, P / 4, and P / 2, respectively, and the |100> photon may enter D8, D7, and D5 with probabilities of P / 4, P / 4, and P / 2, respectively), to obtain the photon response. Then, the generated quantum state is confirmed by the statistical analysis of the control module.

[0086] In different embodiments of the present invention, the measurement basis setting of the path encoding unit can be a computational basis or other types of measurement basis (such as the X basis). It can be selected and pre-set according to the needs of the actual quantum algorithm, and the measurement basis is not switched during the calculation process. Choosing computational basis (|0> and |1>) as the measurement basis is characterized by its simplicity and high determinism, making it suitable for verification and entanglement witnessing of quantum state encoding. Choosing other types of measurement basis is suitable for applying this measurement encoding method to practical quantum algorithms such as Grover's search, Shor's factorization, and quantum Fourier transform, thereby achieving practical quantum acceleration.

[0087] In one embodiment of multi-qubit entangled state preparation, the multi-qubit entangled state prepared in the above manner is used in the Grover search algorithm. The algorithm needs to find marked elements in an unsorted database and map all elements in the database to all states in the multi-qubit entangled state. First, oracle encoding is required to mark the marked elements as specific qubits, such as marking the marked elements as |0>. Then, a diffusion operation and the final projection measurement and output are performed. The final output |0> indicates a successful search. In this application, the projection measurement operation for a certain layer or a certain qubit can be applied to the oracle encoding operation in the Grover algorithm. That is, the projection measurement operation for a certain layer or a certain qubit realizes the required multi-qubit entangled state (mapping database elements) and also realizes the oracle encoding operation in the Grover algorithm. Combined with the subsequent operations of the Grover algorithm, the complete Grover search is completed through single-vector quantum computation.

[0088] In some other embodiments, the detection module may also include photon processing devices such as a single-photon counter and a time-to-digital converter, which are used to count the number of photons detected during the calculation process, the time, and other information, and transmit the information to the control module to assist the control module in confirming whether the target quantum state has been successfully generated.

[0089] In traditional high-dimensional encoding methods for single photons, a tree-like interferometer network is first used to encode the photon into 2D. n One path, then through a 2 n Universal interferometric network of the model (requires 2) n *2 n-1 The process involves performing various single-qubit quantum gate operations using interferometers and control signals, followed by measurement through a tree-like interferometer network. This process requires a significant number of quantum devices and control signals. The multi-qubit entangled state generation device provided in this application eliminates the need for a general-purpose interferometer network, reducing the number of required interferometer units and space. While saving on optical quantum devices, the reduced number of control signals also provides more space for chip wiring, reducing wiring difficulty and the required number of chip signal ports. The size of the control signal ports is much larger than that of the optical quantum devices. Too many control signal ports on the chip surface increase packaging difficulty, reduce packaging stability, and increase signal fluctuations and crosstalk. Saving on the number of control signals improves packaging stability and signal stability. Furthermore, the reduced number of required control signals also lowers the requirements for the scale and precision of the control signals provided by the control module, thus reducing the complexity and cost of the quantum computing measurement and control system, making the generation of large-scale optical quantum entangled states and quantum computing easier to implement and practically apply.

[0090] A tree-like interferometer network requires 2 n *2 n-1 By cascading two interferometers, the number of measurement nodes can be further reduced when encoding specific multi-qubit entangled states. For example, when encoding an n-qubit GHZ state, only O(n) measurement nodes are needed, where O(n) represents a function of n. Figure 3 Only 2n measurement nodes are needed. When encoding an n-qubit W state, the W state has n ground states and n input paths, requiring n*(n-1) / 2 measurement nodes, which means only O(n* ... 2 ) measurement nodes, O(n 2 ) represents about n 2 The function. Figure 3 The path coding unit and single-photon detector depicted by the dashed line are photonic quantum devices that can be omitted when generating multi-qubit entangled states using measurement coding, relative to a complete tree-shaped path coding network.

[0091] The multi-qubit entangled state generation device provided in this application generates multi-qubit entangled states through a multi-layer quantum encoding module. The process of constructing multi-qubit states using multiple photons is replaced by a direct single-photon multi-layer quantum measurement process. By combining quantum state generation and state measurement, the construction process of multi-qubit states is transformed into a multi-layer quantum measurement process. In this way, each photon in the multi-photon quantum state can be distributedly encoded with multiple qubits, thus constructing larger entangled states.

[0092] In another embodiment of the application, a basic multiphoton quantum entangled state is first generated through an entangled state preparation module, such as... Figure 6 As shown, each photon output is in a fundamental quantum entangled state. Each photon enters a multi-layer quantum coding module, thus expanding the fundamental quantum entangled state into a larger-scale multi-qubit entangled state, such as... Figure 8 . Figure 6 The entangled state preparation module generates a 4-qubit entangled state consisting of 4 photons. Each photon enters a multi-qubit entangled state generation device. Through measurement and encoding operations on the photons by the multi-qubit entangled state generation device, the initial 4-qubit entangled state can be expanded into a 16-qubit entangled state. If a 16-qubit entangled state is generated using conventional methods, it would require 2... 16 The entangled state preparation module requires a large number of optical quantum devices, including an interferometer or tunable beam splitter, as well as subsequent single-qubit gates and complex projection measurements, which are difficult to wire. The structure and operation of the entangled state preparation module are described in detail below.

[0093] The entangled state preparation module includes one 1xN beam splitter 11, N 50:50 beam splitters 12, N photon pair source groups 13, N photon separation unit groups 14, N first fusion and exchange modules 15, (N-1) second fusion and exchange modules 16, and 2N output terminal groups 17.

[0094] Figure 6 Taking N=2 as an example. A 1xN beamsplitter is used to evenly split the externally input laser pulse and output it from its N output ports. N 50:50 beamsplitters are connected to the N output ports of the 1xN beamsplitter. Each 50:50 beamsplitter evenly splits the input laser pulse and outputs it from its two output ports. N photon pair source groups include two photon pair sources connected to the two output ports of each 50:50 beamsplitter, used to generate entangled two-photons with different wavelengths (l1, l2). N photon separation unit groups include two photon separation units connected to the output ports of the photon pair sources, used to output each pair of entangled two-photons according to their wavelengths from their upper and lower output ports respectively. N first fusion and exchange modules are used to exchange the paths of photons output from different photon separation units within the same photon separation unit group. (N-1) second fusion and exchange modules are used to exchange the paths of photons output from different photon separation unit groups, generating a multi-photon entangled state composed of 2N photons. There are 2N output terminal groups, each of which is used to output one photon in a multi-photon entangled state.

[0095] An externally input pulsed laser pulse is split into N beams by a 1xN beamsplitter, each beam entering one of N 50:50 beamsplitters. Each 50:50 beamsplitter splits the input laser pulse into two beams, which are then output from their two output ports to two photon source pairs in the corresponding photon source pair group. Both photon source pairs can generate a pair of entangled photons (wavelengths l1 and l2). Since the generation of entangled photons by photon source pairs is probabilistic, the probability of both photon source pairs generating a pair of entangled photons simultaneously is even smaller, and this can be filtered out using post-selection. Therefore, only the case where one of the two photon source pairs generates a pair of entangled photons is considered. Thus, each photon source pair group generates a pair of entangled photons, which then enter the corresponding photon separation unit group. The photon separation unit receiving the entangled photons separates them to two different output ports. Here, we take... Figure 6 For example, the entangled two photons generated by the first photon pair source group 131 are separated by the first photon separation unit 141 and denoted as follows: and The entangled two photons generated by the second photon pair source group 132 are separated by the second photon separation unit 142 and denoted as follows: and The entangled two photons generated by the third photon pair source group 133 are separated by the third photon separation unit 143 and denoted as follows: and The entangled two photons generated by the fourth photon pair source group 134 are separated by the fourth photon separation unit 144 and denoted as follows: and .

[0096] After the source group of 4 photons generates two pairs of entangled two-photons, the initial quantum state is denoted as:

[0097]

[0098] After the two first fusion exchange modules 15, the quantum state evolves as follows:

[0099]

[0100] After one second fusion exchange module 16, the quantum state evolves as follows:

[0101]

[0102] Where j is a normalized state, representing two photons simultaneously outputting from a set of waveguide transmission paths, which are filtered out in the subsequent selection process and are considered invalid outputs; this case is not considered in this application. Therefore, the final four-photon quantum entangled state output by the entangled state preparation module is:

[0103]

[0104] Will ~ Redefining, |1> λ1 |4> λ1 |3> λ2 |6> λ2 Defined as |0000>, |0> λ1 |2> λ2 |5> λ1 |7> λ2 Defined as |1111>, the four-photon quantum entangled state ultimately output by the entanglement preparation module is actually a four-qubit GHZ state:

[0105]

[0106] Each output terminal group 17 includes two sub-ports. Each output terminal group 17 outputs a photon. The photon is output from either sub-port. The two sub-ports also correspond to the single photon being in one of the 0s in |0000> or one of the 1s in |1111>. It can also be considered that the single photon is in a superposition of 0 and 1.

[0107] Figure 6Each photon generated by the entangled state preparation module shown can be input into a multi-layer quantum coding module, such as a 4-qubit multi-layer quantum coding module. Figure 7 As shown, a four-qubit GHZ state can be extended into a 16-qubit graphical state, as follows. Figure 8 As shown, the entangled state preparation module generates a T-shaped basic pattern, which is then transformed into a 16-qubit entangled pattern through a multi-layer quantum encoding module. Figure 7 The path coding unit and single-photon detector depicted by the dashed line are photonic quantum devices that can be omitted when generating multi-qubit entangled states using measurement coding, relative to a complete tree-shaped path coding network.

[0108] Figure 8 It includes four multi-layer quantum coding modules. When one or more of these modules are not working or are not performing coding operations, the four-qubit GHZ state expands into 4-qubit, 7-qubit, 10-qubit, and 13-qubit graphical states. Compared to the traditional method of generating a 16-qubit entangled state, which requires 2... 16 This embodiment provides a solution that seamlessly integrates a basic quantum entangled state generation module with a multi-qubit entangled state generation device, utilizing hundreds of quantum optical devices to accomplish what was previously required 2 16 The generation of quantum states, which previously required a network of devices, reduces the computational resources needed for large-scale graph state generation and measurement-based quantum computing, thereby lowering the cost of quantum computing and improving the feasibility of measurement-based quantum computing of large-scale graph entangled states. Figure 3 , Figure 4 , Figure 7 All of them have m as an even number (m=2 or m=4). Figure 9 The architecture of a multi-layer quantum coding module with m=3 and n=4 is presented. The second-layer measurement coding structure includes two path coding units arranged in parallel (3+1) / 2=2. This multi-layer quantum coding module architecture with m=3 and n=4 can directly encode a photon in a 3-qubit W state. Note that this is the quantum state before multi-layer measurement coding. Each photon, after 4 qubits of measurement coding, can be expanded into a 12-qubit graph state. Similarly, Figure 9 The path coding unit and single-photon detector depicted by the dashed line are photonic quantum devices that can be omitted when generating multi-qubit entangled states using measurement coding, relative to a complete tree-shaped path coding network.

[0109] Figure 10The architecture of the entangled state preparation module is shown in the case of N=3 (an example where N is an odd number), i.e., a 1xN beam splitter is a 1x3 beam splitter. This structure outputs a six-photon entangled state. Each photon output is fed to a multi-layer quantum coding module with "n=4", which ultimately expands the six-photon entangled state into a 24-qubit graph state.

[0110] When the number of sub-ports in each output group of the entangled state preparation module is less than r, the entangled state preparation module also includes 2N path extension units 18, each corresponding to one of the 2N output groups, used to extend the photon output paths of each output group to r. Taking a sub-port count of 2 and m=4 as an example, as follows... Figure 11 As shown, the two sub-ports of each output group 17 are expanded into four ports by two 50:50 beam splitters, corresponding to m=4, and input to the subsequent multi-layer quantum coding module.

[0111] In some embodiments of this application, the path coding unit is an MZ interferometer or a multimode interferometer. Figure 12 A schematic diagram of a commonly used on-chip MZ interferometer is shown. The MZ interferometer mainly consists of two directional couplers 51, two interferometer arms, and a phase modulator 50 mounted on one of the interferometer arms. The control module adjusts the output path of the photons by regulating the phase of the phase modulator 50. The control module's programming control of the path encoding unit is specifically manifested in the programming control of its phase modulator 50, creating a specific phase difference between the two interferometer arms, thereby controlling the splitting ratio of the photon MZ interferometer. In the case of a single photon, this manifests as the probability of the photon being output from each of the two output ports. In quantum processing, the regulation of the splitting ratio is equivalent to operating an H-gate, or setting an X-measurement basis. Setting or programming the measurement basis through a multimode interferometer is similar to changing the splitting ratio through phase modulation, producing an operation equivalent to an H-gate on the photons.

[0112] In other embodiments of this application, the photon source employs one of the following: a helical waveguide coil, a silicon nitride microring structure, or a periodically polarized crystal waveguide. The helical waveguide coil can be directly fabricated using currently mature silicon-based optoelectronic processes, offering stable performance and low manufacturing costs. The silicon nitride microring structure or the periodically polarized crystal waveguide exhibits superior nonlinear performance compared to the helical waveguide coil, resulting in a higher rate of entangled two-photon generation. Furthermore, the photon separation unit is a wavelength demultiplexer or an optical filter, its primary function being to separate the entangled two photons according to wavelength.

[0113] In some other embodiments of this application, the first fusion switching module and the second fusion switching module are cross waveguides.

[0114] When all devices in the entangled state preparation module and the multilayer quantum coding module are on-chip devices, all devices are integrated on the same semiconductor substrate and formed as a single piece through monolithic integration technology.

[0115] Based on the multi-qubit entangled state generation device provided in this application, this application also provides a method for generating multi-qubit entangled states, which is applied to, for example... Figure 1 The diagram shows a multi-qubit entangled state generation device. For details, refer to... Figure 13 The method for generating multi-qubit entangled states includes the following steps:

[0116] S1. In each cycle, the entangled state preparation module generates a photon in a superposition state;

[0117] S2. The photons output by the entangled state preparation module are transmitted to the m path coding units of the first layer measurement coding structure via any one of the r paths;

[0118] S3. The multi-layer quantum coding module is based on the programming control of the control module. The path coding unit performs measurement basis setting and path coding for photons input through different paths, so that photons input through different paths and representing different n-qubit ground states are output from different path coding units and enter the corresponding single-photon detectors after passing through different routes.

[0119] S4. After multiple cycles of measurement encoding, the control module performs statistical analysis on the detection results of all single-photon detectors in the detection module, completes the photon measurement encoding, and obtains the n-qubit entangled state.

[0120] In other embodiments of this application, a small-scale or basic graph state can be combined with the above-mentioned multi-qubit entangled state generation method. First, a basic multi-photon quantum entangled state is generated through the entangled state preparation module. Each photon output is in a basic quantum entangled state. Each photon enters a multi-layer quantum coding module, thereby expanding the basic quantum entangled state into a larger-scale multi-qubit entangled state.

[0121] The entangled state preparation module includes a 1xN beam splitter, N 50:50 beam splitters, N photon pair source groups, N photon separation unit groups, N first fusion and switching modules, (N-1) second fusion and switching modules, and 2N output terminal groups. The method includes:

[0122] The 1xN beam splitter receives externally input laser pulses, divides them into N equal parts, and outputs them to N 50:50 beam splitters through N output ports.

[0123] Each 50:50 beam splitter splits the input laser pulse into an average beam and outputs it from its two output ports respectively;

[0124] Each photon pair source group is pumped and excited by a laser pulse, generating entangled two photons with different wavelengths (l1, l2);

[0125] Each photon separation unit group outputs the received pair of entangled photons according to their wavelengths through its upper and lower output ports respectively;

[0126] Each first fusion and exchange module performs path exchange on the photons output by different photon separation units in the same photon separation unit group;

[0127] Each second fusion and exchange module swaps the paths of photons output from different photon separation unit groups to generate a multi-photon entangled state consisting of 2N photons.

[0128] Each output group outputs one photon in a multi-photon entangled state.

[0129] In other embodiments of this application, when the number of sub-ports in each output group of the entangled state preparation module is less than r, the entangled state preparation module further includes 2N path extension units, each corresponding to one of the 2N output groups, used to extend the photon output path of each output group to r paths. Taking a sub-port count of 2 and m=4 as an example, as... Figure 10 As shown, the two sub-ports of each output group 17 are expanded into four ports by two 50:50 beam splitters, corresponding to m=4, and input to the subsequent multi-layer quantum coding module.

[0130] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or apparatus that includes the aforementioned element.

[0131] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multi-qubit entangled state generation device, characterized in that, It includes an entangled state preparation module, a multi-layer quantum coding module, a detection module, and a control module; The entangled state preparation module is used to generate a photon in a superposition state in each cycle and output it from any one of the r paths; The multilayer quantum coding module includes an n-layer measurement coding structure, and the detection module includes multiple single-photon detectors, where n and r are both integers greater than 1. n ≥r≥2; The first layer measurement coding structure includes m path coding units arranged in parallel, where m is an integer greater than 1, and r ≥ m ≥ 2. The photons output by the entangled state preparation module are transmitted to the m path coding units of the first layer measurement coding structure via any one of the r paths. The second layer measurement coding structure includes (m / 2) path coding units arranged in parallel, and so on, until the i-th layer includes 2 path coding units. The i-th to (n-1)-th layers each include 2 path coding units, where i is an integer greater than 1, and n-1 > i > 1. The n-th layer includes 1 path coding unit. Each path coding unit includes two input ports and two output ports. The path coding units of the 1-n-th layers are cascaded in a cross-connected manner. One output port of each path coding unit in the 1-(n-1)-th layers connects to the next layer measurement coding structure, and the other output port connects to a single-photon detector in the detection module. The path coding unit of the n-th layer measurement coding structure connects to two single-photon detectors. The control module is used to program and control each path coding unit in the measurement coding structure of each layer, thereby setting the measurement basis and coding the path of photons input by different paths through the path coding unit, so that photons input by different paths, representing different n-qubit ground states, are output from different path coding units and enter the corresponding single-photon detectors after passing through different routes. The control module is also used to perform statistical analysis on the detection results of all single-photon detectors in the detection module after multiple cycles of measurement encoding, complete the photon measurement encoding, and obtain an n-qubit entangled state with r ground states.

2. The multi-qubit entangled state generation device according to claim 1, characterized in that, The entangled state preparation module includes: A 1xN beam splitter is used to split an externally input laser pulse into an equal beam and output it from its N output ports respectively; N 50:50 beam splitters are connected to the N output ports of the 1xN beam splitter. Each 50:50 beam splitter will split the input laser pulse into an average beam and output it from its two output ports respectively. N photon source pairs, including two photon source pairs connected to the two outputs of each 50:50 beam splitter, are used to generate entangled two photons with different wavelengths (l1, l2); N photon separation unit groups, including two photon separation units connected to the output end of the photon pair source, are used to output each pair of entangled two photons according to their wavelengths from their upper output port and lower output port respectively; N first fusion and exchange modules are used to exchange the paths of photons output by different photon separation units in the same photon separation unit group; (N-1) second fusion and exchange modules are used to exchange the paths of photons output by different photon separation unit groups to generate a multi-photon entangled state composed of 2N photons. There are 2N output terminal groups, each of which is used to output one photon in a multi-photon entangled state.

3. The multi-qubit entangled state generation device according to claim 2, characterized in that, When the number of sub-ports in each output group of the entangled state preparation module is less than r, the entangled state preparation module also includes 2N path extension units, which are respectively connected to 2N output groups to extend the photon output path of each output group to r.

4. The multi-qubit entangled state generation device according to claim 1, characterized in that, The path coding unit is an MZ interferometer or a multimode interferometer.

5. The multi-qubit entangled state generation device according to claim 2, characterized in that, The photon pair source is one of the following: a spiral waveguide coil, a silicon nitride microring structure, or a periodically polarized crystal waveguide.

6. The multi-qubit entangled state generation device according to claim 2, characterized in that, The first and second fusion switching modules are cross-waveguides.

7. The multi-qubit entangled state generation device according to claim 1, characterized in that, All devices in the entangled state preparation module and the multilayer quantum coding module are integrated on the same semiconductor substrate and formed in one piece through monolithic integration technology.

8. A method for generating multi-qubit entangled states, characterized in that, The method, applicable to the multi-qubit entangled state generation device according to any one of claims 1-7, wherein the multi-qubit entangled state generation device comprises an entangled state preparation module, a multi-layer quantum coding module, and a detection module, comprises: During each cycle, the entangled state preparation module generates a photon in a superposition state; The photons output by the entangled state preparation module are transmitted to the m path coding units of the first layer measurement coding structure via any one of the r paths; The multi-layer quantum coding module is based on the programming control of the control module. It sets the measurement basis and codes the path for photons input through different paths through the path coding unit, so that photons with different paths and representing different n-qubit ground states are output from different path coding units and enter the corresponding single-photon detectors after passing through different routes. After multiple cycles of measurement encoding, the control module performs statistical analysis on the detection results of all single-photon detectors in the detection module, completes the photon measurement encoding, and obtains the n-qubit entangled state.

9. The method for generating multi-qubit entangled states according to claim 8, characterized in that, The entangled state preparation module includes a 1xN beam splitter, N 50:50 beam splitters, N photon pair source groups, N photon separation unit groups, N first fusion and switching modules, (N-1) second fusion and switching modules, and 2N output terminal groups. The method includes: The 1xN beam splitter receives externally input laser pulses, divides them into N equal parts, and outputs them to N 50:50 beam splitters through N output ports. Each 50:50 beam splitter splits the input laser pulse into an average beam and outputs it from its two output ports respectively; Each photon pair source group is pumped and excited by a laser pulse, generating entangled two photons with different wavelengths (l1, l2); Each photon separation unit group outputs the received pair of entangled photons according to their wavelengths through its upper and lower output ports respectively; Each first fusion and exchange module performs path exchange on the photons output by different photon separation units in the same photon separation unit group; Each second fusion and exchange module swaps the paths of photons output from different photon separation unit groups to generate a multi-photon entangled state consisting of 2N photons. Each output group outputs one photon in a multi-photon entangled state.

10. The method for generating multi-qubit entangled states according to claim 9, characterized in that, When the number of sub-ports in each output group of the entangled state preparation module is less than r, the entangled state preparation module also includes 2N path extension units, which are respectively connected to 2N output groups. The path extension unit extends the photon output path of each output group to m.

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