An optical quantum chip based on graph theory

Abstract

The application discloses a kind of light quantum chips based on graph theory, it is characterized in that, including M group photon pair sources, N adjustable linear networks, a cross network and N path erasing units;Pump light source output end is connected with M group photon pair sources respectively, and a MZI is connected between pump light source and each group of photon pair sources;Each adjustable linear network is connected with the output end of a group of photon pair sources, for the photon generated by this group of photon pair sources is rearranged on path, corresponding with graph theory;The graph in graph theory includes N vertices, each vertex has M edges;Cross network is connected with the output end of each adjustable linear network, for selecting an output from the output of each adjustable linear network as the input of a path erasing unit;A phase shifter is connected between each output of adjustable linear network and the corresponding input of path erasing unit;The output end of each path erasing unit is connected with a single-photon detector.The application enables quantum experiment based on graph theory to be realized.

Description

Technical Field

[0001] This invention relates to the field of optical quantum physics, specifically to a corresponding graph theory optical quantum chip that utilizes integrated optical chip technology to ensure quantum indistinguishability, achieves the superposition of a large number of photon pairs from the source through interference, and further enables quantum entanglement, quantum computing, and quantum simulation. Background Technology

[0002] Currently, a close connection has been discovered between quantum experiments and graph theory. In quantum experiments, detectors and photon pairs correspond to sources, just as vertices and edges in graph theory exist. Furthermore, the intensity and phase of the source correspond one-to-one with the weight and phase of the edge, respectively. Utilizing graph theory to design preparation schemes for complex quantum states and calculating the Hafnian matrix through boson sampling are of great significance for quantum entanglement, quantum computing, and quantum simulation.

[0003] Traditional methods use a laser beam to sequentially pump multiple photon pairs to achieve quantum interference superposition. However, in practical experiments, due to losses, it is difficult to precisely control the pump intensity of each source, and the sequential pumping method also makes phase adjustment quite complex, making traditional methods difficult to implement. Summary of the Invention

[0004] To overcome the pump light loss problem caused by cascaded pumping in traditional schemes, this invention proposes a graph theory-based optical quantum chip. It adopts a novel scheme of simultaneously pumping all photon pairs, which can individually adjust the phase and intensity of each photon pair, achieving a direct correspondence with graph theory.

[0005] In traditional approaches, realizing a graph with N vertices, each with M edges, through quantum experiments requires N single-photon detectors and NM / 2 photon pair sources. These photon pair sources are arranged in M ​​layers, with N / 2 photons per layer, and are coherently pumped by N / 2 laser beams, such as... Figure 1 This pumping scheme results in the pump intensity and phase of each photon pair source being correlated with its preceding photon pair source. Furthermore, due to losses in the circuit, the pump intensity of the later photon pair source is weaker, making the traditional scheme unscalable.

[0006] This invention avoids the correlation of light sources caused by cascaded pumping interference by simultaneously pumping all photon pair sources. When a photon pair source is pumped by a laser, it can probabilistically generate a photon on each of two paths simultaneously. After the generated photon pairs are arranged through an adjustable linear network, the path matching advantage of integrated photonic devices is easily achieved. The path erasure unit composed of MZI is used to remove the path information of photons from different photon pair sources. The photon pairs output from all photon pair sources are superimposed by interference, thereby realizing the correspondence between quantum experiments and graph theory.

[0007] This invention simplifies the process of setting up quantum graphs, enabling parameters in quantum experiments to correspond precisely with graph theory, and the scheme has strong scalability.

[0008] The technical solution adopted by this invention to solve its technical problem is:

[0009] A graph theory-based optical quantum chip is characterized by comprising M sets of photon pair sources, N tunable linear networks, a cross network, and N path erasure units;

[0010] The output end of the pump source is connected to M groups of photon pair sources respectively, and is used to input the output pump laser into each group of photon pair sources respectively, and to coherently pump N / 2 photon pair sources in each group of photon pair sources; an MZI is connected between the pump source and each group of photon pair sources, and the MZI is used to adjust the intensity of the pump laser in the input photon source pair;

[0011] The photon pair source is used to probabilistically generate one photon simultaneously on each of two paths during laser pumping;

[0012] Each of the aforementioned tunable linear networks is connected to the output of a set of photon pair sources, and is used to rearrange the photons generated by the set of photon pair sources along the path, corresponding to graph theory; the graph in the graph theory includes N vertices, and each vertex has M edges;

[0013] The cross network is connected to the output of each of the adjustable linear networks and is used to select one output from the output of each of the adjustable linear networks as an input of one of the path erasure units; a phase shifter is connected between each output of the adjustable linear network and the corresponding input of the path erasure unit to adjust the phase of the photon.

[0014] The output of each path erasure unit is connected to a single-photon detector to guide the photons that erase the path information to the corresponding single-photon detector.

[0015] Furthermore, the cross-network is used to convert the M×N input paths into N×M output paths, that is, to convert the M groups of input, each with N waveguides, into N groups of output, each with M waveguides.

[0016] Furthermore, the loss and distance along each input-to-output path in the cross network are consistent.

[0017] Furthermore, the path erasure unit includes the N / 2, N / 4, ..., 1st MZI arranged in columns, which are used to merge single-photon interferences from different paths into one path.

[0018] Furthermore, the adjustable linear network is an N×N array consisting of cascaded MZI arrays and path-compensated waveguides, with the odd-numbered columns containing N / 2-1 MZIs and one path-compensated waveguide on each side, and the even-numbered columns containing N / 2 MZIs.

[0019] Furthermore, the phase of the transmission matrix corresponding to the MZI array is set to 0 or π, so that single photons generated by different photon pairs from the source do not interfere with each other when rerouting in the tunable linear network.

[0020] This invention has the following characteristics:

[0021] 1) The pump light is split into M groups of photon pair sources, and N / 2 photon pair sources in each group are coherently pumped, corresponding to one layer in the traditional scheme;

[0022] 2) By adjusting the phase of the MZI before the photon pair source, the proportion of pump light entering the photon pair source after passing through the MZI is controlled, thereby individually adjusting the pump intensity of each photon pair source, relative to... Figure 1 The traditional approach decouples the pump modulation of each photon pair from the source;

[0023] 3) After each group of N / 2 photon pairs, use as follows: Figure 1 (b) The tunable linear network in the diagram rearranges the path of a single photon, which corresponds to graph theory.

[0024] 4) Use a cross-network to guide each group of photons from step 3) to N groups of detectors;

[0025] 5) The single photons in front of each group of detectors are phase-adjusted, and the path information is erased by the path erasure unit before output and detection.

[0026] The advantages of this invention are as follows:

[0027] This invention employs simultaneous pumping, where the pump intensity and phase of each photon pair with the source do not affect each other, enabling graph-based quantum experiments. Compared to previous cascaded pumping methods, this reduces experimental difficulty, enhances the scalability of the scheme, and strengthens the one-to-one correspondence with graph theory. Attached Figure Description

[0028] Figure 1 It is a chip design diagram based on a traditional solution;

[0029] (a) The overall input-to-output scheme of the chip;

[0030] (b) An example of an adjustable linear network composed of MZI, with 8-path input and 8-path output;

[0031] (c) Legend of MZI and MZI transfer matrix.

[0032] Figure 2 This is a schematic diagram of the overall input-output scheme of the chip of the present invention.

[0033] Figure 3 This is a diagram showing the cross-connect network, where a 4x8 structure is converted to an 8x4 structure.

[0034] Figure 4 The structure diagram of the path erasure module composed of MZI with 8 path inputs. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0036] This invention employs a method of pumping multiple photon pairs in parallel. After the generated photon pairs are arranged through a tunable linear network, the superiority of path matching easily achieved by integrated photonic devices is utilized. Path erasure units remove the path information carried by photons from different photon pairs, and the photon pairs output from all photon pairs are superimposed through interference, thus realizing a quantum experimental scheme corresponding to graph theory. Compared to traditional schemes, this invention reduces the experimental difficulty, enhances the scalability of the scheme, and strengthens the one-to-one correspondence with graph theory.

[0037] This invention provides a chip design scheme for linking graph theory and quantum experiments, such as... Figure 2 As shown, the system includes an adjustable side-by-side pumped photon pair source, an adjustable linear network, a crossover network for group routing, and modules for adjusting phase and path erasure. The pump laser and single-photon detector are provided by off-chip instruments, while the remaining modules consist of various on-chip devices, including: optical waveguides, 50:50 beam splitters, single-photon pair sources, MZI, phase shifters, and crossovers, all fabricated using standard CMOS processes.

[0038] The CMOS process of integrated optics ensures that the waveguide lengths of each single photon during transmission are equal to achieve path matching, ensuring coherence in the spatial, temporal, and frequency domains. The path compensation part of all waveguides is not shown in the schematic diagram, and each path travels the same distance from the input end to the output end.

[0039] The photon pair source is coherently pumped along various paths. The pre-amplifier (MZI) consists of two 50:50 beam splitters and a phase shifter. By changing the phase applied by the phase shifter, the attenuation along the path can be altered, thereby adjusting the pump intensity. The output photon pairs are separated into two paths, such as... Figure 2 .

[0040] The tunable linear network consists of cascaded MZI arrays and path-compensated waveguides. For an N×N array, the odd-numbered columns contain N / 2-1 MZIs and one path-compensated waveguide on each side, while the even-numbered columns contain N / 2 MZIs, for a total of N-1 columns. The transmission matrix of the MZIs is set to phase 0 or π, ensuring that single photons from different sources do not interfere with each other during rerouting within the tunable linear network. Figure 1 (b)

[0041] The crossover network is responsible for guiding the M groups of waveguides (each group containing N waves) from the left input to the N groups of waveguides (each group containing M waves) from the right output in a fixed manner. That is, it selects one output from each adjustable linear network as an input to a path erasure unit, converting the M×N input paths into N×M output paths. The crossover network consists of crossover units and path-compensating waveguides, maintaining consistent loss and path length across all paths. Figure 3 There is a crossover device at each waveguide intersection in the diagram, while at non-intersecting waveguide locations, a combination of curved waveguides and crossover devices is used to ensure path and loss matching.

[0042] The characteristic of the phase adjustment and path erasure unit is that all paths first pass through a phase shifter. By changing the phase applied to the phase shifter, the phase of each edge of the reconstructed image can be adjusted. Then, it enters the path erasure unit composed of MZIs. N / 2, N / 4…1 MZIs are arranged in columns to sequentially merge single-photon interferences from different paths into a single path, thus merging the single-photon interferences output from N / 2 photon pairs from the same photon pair source into a single path. Figure 4 .

[0043] Figure 2 The scheme realizes the principle of correspondence between quantum experiments and graph theory: Pump lasers are generated by off-chip lasers and coupled into the chip (e.g., vertical coupling and edge coupling). The pump light is split into individual light sources by on-chip devices, and the pump intensity of each light source is adjusted by MZIs while ensuring coherence. Single photon pairs generated by each photon pair source enter tunable linear networks and cross networks. The tunable linear networks composed of MZIs control the path of each single photon pair generated by the light source, determining the two detectors it enters. This correspondence between photon pairs and two detectors corresponds to the correspondence between an edge and two vertices in graph theory. Finally, phase shifters adjust the phase of each single photon pair, and path erasure units interfere each pair of single photons to their respective detectors, allowing single photons from multiple photon pair sources to enter the same detector, completing the matching between the chip and the graph. The detection results of the single photon detectors are used to obtain the coincidence count of each channel through a coincidence counter. The coincidence count corresponds to the perfect matching in graph theory. Perfect matching can be used to solve some graph theory-related problems and realize some graph theory-related functions.

[0044] Although specific embodiments of the invention have been disclosed for illustrative purposes to aid in understanding and implementing the invention, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the content disclosed in the preferred embodiments, and the scope of protection claimed by the invention is defined by the claims.

Claims

1. A graph-based photonic quantum chip, characterized in that, It includes M sets of photon pair sources, N tunable linear networks, a cross network, and N path erasure units; The output end of the pump source is connected to M groups of photon pair sources respectively, and is used to input the output pump laser into each group of photon pair sources respectively, and to coherently pump N / 2 photon pair sources in each group of photon pair sources; an MZI is connected between the pump source and each group of photon pair sources, and the MZI is used to adjust the intensity of the pump laser in the input photon source pair; The photon pair source is used to probabilistically generate one photon simultaneously on each of two paths during laser pumping; Each of the aforementioned tunable linear networks is connected to the output of a set of photon pair sources, and is used to rearrange the photons generated by the set of photon pair sources along the path, corresponding to graph theory; the graph in the graph theory includes N vertices, and each vertex has M edges; The cross network is connected to the output of each of the adjustable linear networks and is used to select one output from the output of each of the adjustable linear networks as an input of one of the path erasure units; a phase shifter is connected between each output of the adjustable linear network and the corresponding input of the path erasure unit to adjust the phase of the photon. The output of each path erasure unit is connected to a single-photon detector to guide the photons that erase the path information to the corresponding single-photon detector.

2. The photonic quantum chip of claim 1, wherein, The cross-network is used to convert M×N input paths into N×M output paths, that is, to convert M groups of input, each with N waveguides, into N groups of output, each with M waveguides.

3. The optical quantum chip according to claim 2, characterized in that, In the cross-network, the loss and distance on each input-to-output path are the same.

4. The optical quantum chip according to claim 1, 2, or 3, characterized in that, The path erasure unit includes the N / 2, N / 4, ..., 1st MZI arranged in columns, which are used to merge single-photon interferences from different paths into one path.

5. The optical quantum chip according to claim 1, characterized in that, The adjustable linear network is an N×N array consisting of cascaded MZI arrays and path-compensated waveguides. The odd-numbered columns contain N / 2-1 MZIs and one path-compensated waveguide on each side, while the even-numbered columns contain N / 2 MZIs.

6. The optical quantum chip according to claim 5, characterized in that, The phase of the transmission matrix corresponding to the MZI array is set to 0 or π, so that single photons generated by different photon pairs from the source do not interfere with each other when rerouting in the tunable linear network.

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