Quantum device, quantum operation apparatus, and quantum operation method

Abstract

This quantum computing device comprises: three first optical waveguides by which qubits are to be connected; a second optical waveguide; a beam splitter; first optical switches that are provided to the respective three first optical waveguides and that conduct switching of optical connection and disconnection between the second optical waveguide and the first optical waveguides; and a second optical switch that conducts switching of optical connection and disconnection between the second optical waveguide and the beam splitter.

Description

[Technical field]

[0001] The present disclosure relates to a quantum device, a quantum processing apparatus, and a quantum processing method. [Background technology]

[0002] Research and development of quantum computers is being conducted as one of the next-generation computing technologies. The structure of quantum devices containing qubits used in quantum computers is a two-dimensional structure in which one qubit is connected to multiple qubits. In a two-dimensional structure, a direct connection between two adjacent qubits is possible, but a direct connection between two non-adjacent qubits is not possible. For this reason, when connecting two non-adjacent qubits, a swap operation is performed to relay quantum information using the qubit between them. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Pat. No. 10,622,536 [Patent Document 2] U.S. Patent No. 7,546,000 [Patent Document 3] US Patent Application Publication No. 2019 / 0325336 [Patent Document 4] U.S. Patent No. 7,529,437 [Non-patent literature]

[0004] [Non-Patent Document 1] A. Frank, et al., "Quantum supremacy using a programmable superconducting processor", Nature 574, 505 (2019) [Non-Patent Document 2] N. Kalb, et al., "Entanglement distillation between solid-state quantum network nodes", Science 356, 928 (2017) Summary of the Invention [Problem to be solved by the invention]

[0005] The more swap operations there are, the higher the quantum error rate becomes, and the more swap operations there are, the more time is spent swapping, reducing the number of quantum operations that can be performed in a coherent time.

[0006] An object of the present disclosure is to provide a quantum device, a quantum processing apparatus, and a quantum processing method that are capable of connecting quantum bits without performing a swap operation. [Means for solving the problem]

[0007] According to one embodiment of the present disclosure, there is provided a quantum device having three first optical waveguides to which quantum bits are connected, a second optical waveguide, a beam splitter, first optical switches provided in each of the three first optical waveguides for switching between optical connection and disconnection between the first optical waveguide and the second optical waveguide, and a second optical switch for switching between optical connection and disconnection between the second optical waveguide and the beam splitter. Effect of the Invention

[0008] According to the present disclosure, quantum bits can be connected without performing swap operations. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a quantum device according to the first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating a quantum device according to the second embodiment. [Diagram 3]FIG. 3 is a diagram illustrating a quantum device according to the third embodiment. [Figure 4] FIG. 4 is a diagram illustrating a quantum device according to the fourth embodiment. [Diagram 5] FIG. 5 is a diagram illustrating a quantum computer according to the fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configurations may be denoted by the same reference numerals to avoid repetitive explanation. In this disclosure, the X1-X2 direction and the Y1-Y2 direction are mutually orthogonal directions.

[0011] (First embodiment) First, a first embodiment will be described. The first embodiment relates to a quantum device. The quantum device according to the first embodiment is used in a quantum operation device such as a quantum computer. FIG. 1 is a diagram showing the quantum device according to the first embodiment.

[0012] As shown in FIG. 1, the quantum device 1 according to the first embodiment has three quantum bits 11, three first optical waveguides 12, one second optical waveguide 13, two beam splitters 14, six first optical switches 15, four second optical switches 16, and four photodetectors 17.

[0013] The three first optical waveguides 12 extend in the Y1-Y2 direction and are arranged side by side in the X1-X2 direction. The quantum bits 11 are directly connected to the Y2-side ends of the first optical waveguides 12 one by one. The quantum bits 11 include, for example, diamond color centers having a nanobeam structure. The diamond color centers emit photons when irradiated with light. The second optical waveguide 13 extends in the X1-X2 direction and is arranged in the vicinity of the Y1-side ends of the three first optical waveguides 12, away from the three first optical waveguides 12. The first optical waveguide 12 and the second optical waveguide 13 are, for example, diamond optical waveguides.

[0014] Two first optical switches 15 are arranged for each first optical waveguide 12 near the end of the first optical waveguide 12 on the Y1 side. One of the first optical switches 15 is arranged on the X1 side of the first optical waveguide 12, and the other is arranged on the X2 side of the first optical waveguide 12. The first optical switches 15 switch between optical connection and non-connection between the first optical waveguide 12 and the second optical waveguide 13. When the first optical switch 15 on the X1 side of the first optical waveguide 12 is turned on, light can propagate between the first optical waveguide 12 and a portion of the second optical waveguide 13 on the X1 side of the first optical waveguide 12. When the first optical switch 15 on the X2 side of the first optical waveguide 12 is turned on, light can propagate between the first optical waveguide 12 and a portion of the second optical waveguide 13 on the X2 side of the first optical waveguide 12. The first optical switch 15 includes, for example, a micro electro mechanical systems (MEMS) variable directional coupler.

[0015] The beam splitters 14 are disposed one by one between the contact points of the second optical waveguide 13 and the first optical waveguide 12. The beam splitters 14 use, for example, a diamond photonic crystal, a mirror, and a directional coupler.

[0016] Two second optical switches 16 are arranged near the second optical waveguide 13 for each beam splitter 14. One second optical switch 16 is arranged on the X1 side of the beam splitter 14, and the other is arranged on the X2 side of the beam splitter 14. The second optical switch 16 switches between optical connection and non-connection between the beam splitter 14 and the second optical waveguide 13. When the second optical switch 16 on the X1 side of the beam splitter 14 is turned on, light can propagate between the beam splitter 14 and a portion of the second optical waveguide 13 on the X1 side of the beam splitter 14. When the second optical switch 16 on the X2 side of the beam splitter 14 is turned on, light can propagate between the beam splitter 14 and a portion of the second optical waveguide 13 on the X2 side of the beam splitter 14. The second optical switch 16 has, for example, a MEMS variable directional coupler.

[0017] Two photodetectors 17 are arranged for each beam splitter 14 on the opposite side to the second optical waveguide 13. The photodetectors 17 detect the optical output of the beam splitter 14. The photodetectors 17 may be connected to the beam splitter 14 directly, or may be connected via an optical waveguide or an optical fiber. The photodetectors 17 are, for example, single photon detectors.

[0018] Next, a quantum computing method using the quantum device 1 according to the first embodiment will be described.

[0019] First, an example of entangling between the central quantum bit 11 (11B) and the quantum bit 11 (11A) on the X2 side of the central quantum bit 11 (11B) among the three quantum bits 11 will be described. In this case, the first optical switch 15 arranged on the X1 side of the first optical waveguide 12 (12A) to which the quantum bit 11A is connected, and the first optical switch 15 arranged on the X2 side of the first optical waveguide 12 (12B) to which the quantum bit 11B is connected are turned on. In addition, the two second optical switches 16 between the first optical waveguide 12A and the first optical waveguide 12B are turned on.

[0020] In this state, when quantum bits 11A and 11B are simultaneously irradiated with light, the photon emitted from quantum bit 11A passes through first optical waveguide 12A and second optical waveguide 13 and enters beam splitter 14, and the photon emitted from quantum bit 11B passes through first optical waveguide 12B and second optical waveguide 13 and enters beam splitter 14. The photons that have passed through beam splitter 14 then enter two photodetectors 17 in a quantum entangled state.

[0021] Next, an example of entangling between the quantum bit 11A on the X2 side of the quantum bit 11B and the quantum bit 11 (11C) on the X1 side among the three quantum bits 11 will be described. In this case, the first optical switch 15 arranged on the X1 side of the first optical waveguide 12A and the first optical switch 15 arranged on the X2 side of the first optical waveguide 12 (12C) to which the quantum bit 11C is connected are turned on. In addition, two second optical switches 16 provided for either one of the two beam splitters 14 between the first optical waveguide 12A and the first optical waveguide 12C are turned on.

[0022] In this state, when quantum bits 11A and 11C are simultaneously irradiated with light, the photon emitted from quantum bit 11A passes through first optical waveguide 12A and second optical waveguide 13 and enters beam splitter 14, and the photon emitted from quantum bit 11C passes through first optical waveguide 12C and second optical waveguide 13 and enters beam splitter 14. The photons that have passed through beam splitter 14 then enter two photodetectors 17 in a quantum entangled state.

[0023] In the first embodiment, quantum operations are performed in this manner. That is, when any combination of three quantum bits 11 is connected to one another, relaying of quantum information via another quantum bit 11 (swap operation) is not required. In this manner, according to the first embodiment, quantum bits 11 can be connected without a swap operation. The same applies to the case where four or more first optical waveguides 12 to which quantum bits 11 are connected are connected to the second optical waveguide 13.

[0024] Furthermore, when diamond color centers are used as quantum bits in a conventional two-dimensional quantum device, four-way switches in the same number as the quantum bits and beam splitters in twice the number of the quantum bits are required. In this case, the unit cell becomes large, making it difficult to achieve high integration of the quantum device. In contrast, in this embodiment, the first optical switch 15 and the second optical switch 16 only switch between optical connection and non-connection, so that elements significantly smaller than the four-way switch can be used as the first optical switch 15 and the second optical switch 16. Furthermore, the number of beam splitters 14 may be smaller than the number of quantum bits 11. For this reason, the first embodiment is suitable for high integration.

[0025] Second embodiment Next, a second embodiment will be described. The second embodiment differs from the first embodiment mainly in the number of quantum bits connected to the first optical waveguide. Fig. 2 is a diagram showing a quantum device according to the second embodiment.

[0026] 2, in quantum device 2 according to the second embodiment, a plurality of pairs of quantum bits 11 and third optical switches 28 are provided for one first optical waveguide 12. The quantum bit 11 is indirectly connected to the first optical waveguide 12 via the third optical switch 28. The third optical switch 28 switches between optical connection and non-connection between the quantum bit 11 and the first optical waveguide 12. The third optical switch 28 is disposed on the Y1 side of the quantum bit 11. The third optical switch 28 has, for example, a MEMS variable directional coupler.

[0027] The other configuration is similar to that of the first embodiment.

[0028] Next, a quantum computing method using the quantum device 2 according to the second embodiment will be described.

[0029] First, an example of entangling between one of the multiple quantum bits 11A provided in the first optical waveguide 12A and one of the multiple quantum bits 11B provided in the first optical waveguide 12B will be described. In this case, the third optical switch 28 (28A) provided in the quantum bit 11A to be entangled and the third optical switch 28 (28B) provided in the quantum bit 11B to be entangled are turned on. In addition, the first optical switch 15 arranged on the X1 side of the first optical waveguide 12A and the first optical switch 15 arranged on the X2 side of the first optical waveguide 12B are turned on. Furthermore, the two second optical switches 16 between the first optical waveguide 12A and the first optical waveguide 12B are turned on.

[0030] In this state, when light is simultaneously irradiated onto quantum bits 11A and 11B to be entangled, similarly to the first embodiment, the photon emitted from quantum bit 11A passes through first optical waveguide 12A and second optical waveguide 13 and enters beam splitter 14, and the photon emitted from quantum bit 11B passes through first optical waveguide 12B and second optical waveguide 13 and enters beam splitter 14. The photons that have passed through beam splitter 14 then enter two photodetectors 17 in a quantum entangled state (entangled state).

[0031] Next, an example of entangling between one of the multiple quantum bits 11A provided in the first optical waveguide 12A and one of the multiple quantum bits 11C provided in the first optical waveguide 12C will be described. In this case, the third optical switch 28A provided in the quantum bit 11A to be entangled and the third optical switch 28 (28C) provided in the quantum bit 11C to be entangled are turned on. In addition, the first optical switch 15 arranged on the X1 side of the first optical waveguide 12A and the first optical switch 15 arranged on the X2 side of the first optical waveguide 12C are turned on. Furthermore, two second optical switches 16 provided for either one of the two beam splitters 14 between the first optical waveguide 12A and the first optical waveguide 12C are turned on.

[0032] In this state, when light is simultaneously irradiated onto quantum bits 11A and 11C to be entangled, similarly to the first embodiment, the photon emitted from quantum bit 11A passes through first optical waveguide 12A and second optical waveguide 13 and enters beam splitter 14, and the photon emitted from quantum bit 11C passes through first optical waveguide 12C and second optical waveguide 13 and enters beam splitter 14. The photons that have passed through beam splitter 14 then enter two photodetectors 17 in a quantum entangled state.

[0033] The second embodiment also provides the same effects as the first embodiment. In addition, entanglement can be performed between a larger number of quantum bits 11. Furthermore, even if the number of quantum bits 11 is increased from the first embodiment, the number of beam splitters 14 and photodetectors 17 is the same as in the first embodiment. For this reason, the second embodiment is more suitable for high integration.

[0034] Third embodiment Next, a third embodiment will be described. The third embodiment differs from the second embodiment mainly in the number of quantum bits connected to the first optical waveguide. Fig. 3 is a diagram showing a quantum device according to the third embodiment.

[0035] 3, in the quantum device 3 according to the third embodiment, three first optical waveguides 12 (12A, 12B, and 12C) are arranged not only on the Y2 side of the second optical waveguide 13 but also on the Y1 side of the second optical waveguide 13. Similarly to the three first optical waveguides 12 on the Y2 side, a plurality of pairs of quantum bits 11 and third optical switches 28 are provided for the three first optical waveguides 12 on the Y1 side of the second optical waveguide 13. However, on the Y1 side of the second optical waveguide 13, the third optical switch 28 is arranged on the Y2 side of the quantum bit 11.

[0036] Furthermore, for the three first optical waveguides 12 on the Y1 side of the second optical waveguide 13, two first optical switches 15 are arranged for each first optical waveguide 12 near the end of the first optical waveguide 12 on the Y2 side.

[0037] The other configuration is similar to that of the second embodiment.

[0038] The third embodiment also provides the same effects as the second embodiment. Moreover, entanglement can be performed between a larger number of quantum bits 11. Furthermore, even if the number of quantum bits 11 is further increased from the second embodiment, the number of beam splitters 14 and photodetectors 17 is the same as in the second embodiment. Therefore, the third embodiment is more suitable for high integration.

[0039] (Fourth embodiment) Next, a fourth embodiment will be described. The fourth embodiment differs from the first embodiment mainly in the arrangement of the first optical waveguide and the second optical waveguide. Fig. 4 is a diagram showing a quantum device according to the fourth embodiment.

[0040] As shown in FIG. 4, the quantum device 4 according to the fourth embodiment has 120 quantum bits 11, 10 first optical waveguides 12, four second optical waveguides 13, 24 beam splitters 14, 40 first optical switches 15, 48 second optical switches 16, and 48 photodetectors 17.

[0041] Five of the ten first optical waveguides 12 extend in the Y1-Y2 direction and are arranged side by side in the X1-X2 direction. The remaining five extend in the X1-X2 direction and are arranged side by side in the Y1-Y2 direction. The five first optical waveguides 12 extending in the Y1-Y2 direction and the five first optical waveguides 12 extending in the X1-X2 direction are perpendicular to each other. Twelve pairs of quantum bits 11 and third optical switches 28 are provided for one first optical waveguide 12.

[0042] For the first optical waveguide 12 extending in the Y1-Y2 direction, two sets of quantum bits 11 and third optical switches 28 are arranged in a region between the intersections with the first optical waveguide 12 extending in the X1-X2 direction, a region on the Y1 side of the intersection closest to the Y1 side, and a region on the Y2 side of the intersection closest to the Y2 side. In each of these regions, one set of quantum bits 11 and third optical switches 28 is arranged on the X1 side and one set of quantum bits 11 and third optical switches 28 is arranged on the X2 side of the first optical waveguide 12. In the set arranged on the X1 side of the first optical waveguide 12, the third optical switch 28 is arranged on the Y2 side of the quantum bit 11. In the set arranged on the X2 side of the first optical waveguide 12, the third optical switch 28 is arranged on the Y1 side of the quantum bit 11.

[0043] For the first optical waveguide 12 extending in the X1-X2 direction, two sets of quantum bits 11 and third optical switches 28 are arranged in a region between the intersections with the first optical waveguide 12 extending in the Y1-Y2 direction, a region on the X1 side of the intersection closest to the X1 side, and a region on the X2 side of the intersection closest to the X2 side. In each of these regions, one set of quantum bits 11 and third optical switches 28 is arranged on the Y1 side and one on the Y2 side of the first optical waveguide 12. In the set arranged on the Y1 side of the first optical waveguide 12, the third optical switch 28 is arranged on the X1 side of the quantum bit 11. In the set arranged on the Y2 side of the first optical waveguide 12, the third optical switch 28 is arranged on the X2 side of the quantum bit 11.

[0044] One second optical waveguide 13 extends in the X1-X2 direction and is disposed near the Y1-side ends of the five first optical waveguides 12 extending in the Y1-Y2 direction, away from the five first optical waveguides 12. The other second optical waveguide 13 extends in the X1-X2 direction and is disposed near the Y2-side ends of the five first optical waveguides 12 extending in the Y1-Y2 direction, away from the five first optical waveguides 12. The other second optical waveguide 13 extends in the Y1-Y2 direction and is disposed near the X1-side ends of the five first optical waveguides 12 extending in the X1-X2 direction, away from the five first optical waveguides 12. The remaining second optical waveguide 13 extends in the Y1-Y2 direction and is disposed near the X2 side ends of the five first optical waveguides 12 extending in the X1-X2 direction, away from the five first optical waveguides 12. These four second optical waveguides 13 are connected to each other via quarter-circular arc-shaped optical waveguides 13X connected to the ends of each second optical waveguide 13.

[0045] Two first optical switches 15 are disposed near each end of the first optical waveguide 12. The first optical switches 15 switch between optical connection and non-connection between the first optical waveguide 12 and the second optical waveguide 13.

[0046] The eight beam splitters 14 are disposed one by one in a region between the junctions of the two second optical waveguides 13 extending in the X1-X2 direction and the first optical waveguide 12. The other two beam splitters 14 are disposed on the X1 side of the junctions of the two second optical waveguides 13 extending in the X1-X2 direction and the first optical waveguide 12 located closest to the X1 side. The other two beam splitters 14 are disposed on the X2 side of the junctions of the two second optical waveguides 13 extending in the X1-X2 direction and the first optical waveguide 12 located closest to the X2 side. The other eight beam splitters 14 are disposed one by one in a region between the junctions of the two second optical waveguides 13 extending in the Y1-Y2 direction and the first optical waveguide 12. The other two beam splitters 14 are disposed on the Y1 side of the junction between the two second optical waveguides 13 extending in the Y1-Y2 direction and the first optical waveguide 12 located closest to the Y1 side. The remaining two beam splitters 14 are disposed on the Y2 side of the junction between the two second optical waveguides 13 extending in the Y1-Y2 direction and the first optical waveguide 12 located closest to the Y2 side.

[0047] Two second optical switches 16 are disposed for each beam splitter 14 near the second optical waveguide 13. In addition, two photodetectors 17 are disposed for each beam splitter 14 on the opposite side to the second optical waveguide 13.

[0048] According to the fourth embodiment, two quantum bits 11 provided in different first optical waveguides 12 can be connected without performing a swap operation. Therefore, more sets of quantum bits 11 can be connected. For example, the quantum bits 11 can be connected without performing a swap operation for a set of a quantum bit 11 provided in a first optical waveguide 12 extending in the X1-X2 direction and a quantum bit 11 provided in a first optical waveguide 12 extending in the Y1-Y2 direction. Furthermore, the number of beam splitters 14 is only 24 for 120 quantum bits 11. Therefore, it is extremely suitable for high integration.

[0049] Fifth embodiment Next, a fifth embodiment will be described. The fifth embodiment relates to a quantum computer. Fig. 5 is a diagram showing a quantum computer according to the fifth embodiment.

[0050] The quantum computer 5 according to the fifth embodiment includes a general-purpose computer 501, a control unit 502, and a quantum device 503. The control unit 502 controls the quantum device 503 based on a control signal from the general-purpose computer 501. As the quantum device 503, a quantum device according to any of the first to fourth embodiments is used. The control unit 502 and the quantum device 503 are housed in a cryostat 504.

[0051] The quantum computer 5 makes it possible to perform stable quantum operations without performing swap operations.

[0052] In the present disclosure, the quantum bit may include a diamond color center that extracts photons using a solid immersion lens. The quantum bit may be an ion trap quantum bit using an ion, a superconducting quantum bit using an element that converts quantum information into photons, or a silicon quantum bit.

[0053] The optical waveguide may be made of a material that allows photons to pass therethrough, such as sapphire, silicon carbide, silicon nitride, etc. An optical fiber may be used as a part of the optical waveguide.

[0054] The material of the photonic crystal used in the beam splitter may be a material that allows photons to pass through, such as sapphire, silicon carbide, silicon nitride, etc. Also, a half mirror may be used in the beam splitter.

[0055] Although the preferred embodiments have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims. [Explanation of symbols]

[0056] 1, 2, 3, 4, 503: Quantum Devices 5: Quantum computers 11, 11A, 11B, 11C: qubits 12, 12A, 12B, 12C: 1st optical waveguide 13:Second optical waveguide 14: Beam splitter 15: First optical switch 16: Second optical switch 17: Photodetector 28, 28A, 28B, 28C: Third optical switch

Claims

1. three first optical waveguides to which quantum bits are connected; A second optical waveguide; A beam splitter; a first optical switch provided in each of the three first optical waveguides, the first optical switch switching between optical connection and non-connection between the first optical waveguide and the second optical waveguide; a second optical switch that switches between optical connection and non-connection between the second optical waveguide and the beam splitter; The quantum device according to the present invention comprises:

2. 10. The quantum device of claim 1, wherein the first optical switch comprises a first Microelectromechanical Systems variable directional coupler and the second optical switch comprises a second Microelectromechanical Systems variable directional coupler.

3. 3. The quantum device according to claim 1, further comprising a third optical switch that switches between optical connection and non-connection between the quantum bit and each of the three first optical waveguides.

4. 4. The quantum device of claim 3, wherein the third optical switch comprises a third micro-electro-mechanical systems variable directional coupler.

5. 5. The quantum device according to claim 3, wherein each of the first optical waveguides includes a plurality of pairs of the quantum bit and the third optical switch.

6. A plurality of the beam splitters are provided, 4. The quantum device according to claim 1, wherein the beam splitter is provided between each of contact points between the first optical waveguide and the second optical waveguide.

7. The quantum device according to claim 1 , wherein the beam splitter comprises a photonic crystal.

8. 8. The quantum device according to claim 1, further comprising a photodetector for detecting an optical output of the beam splitter.

9. 9. The quantum device of claim 1, wherein the quantum bit comprises a diamond color center.

10. A quantum processing apparatus comprising the quantum device according to claim 1 .

11. A quantum computing method using a quantum device, comprising: The quantum device comprises: Three first optical waveguides to which quantum bits including diamond color centers are connected; A second optical waveguide; A beam splitter; a first optical switch provided in each of the three first optical waveguides, the first optical switch switching between optical connection and non-connection between the first optical waveguide and the second optical waveguide; a second optical switch that switches between optical connection and non-connection between the second optical waveguide and the beam splitter; having controlling the first optical switch to optically connect the two first optical waveguides and the second optical waveguide; controlling the second optical switch to optically connect a portion of the second optical waveguide between the two first optical waveguides and the beam splitter; simultaneously irradiating two of the quantum bits connected to the two first optical waveguides with light; The quantum computing method according to the present invention comprises the steps of:

12. the quantum device includes a third optical switch that switches between optical connection and non-connection between the quantum bit and each of the three first optical waveguides; 12. The quantum computing method according to claim 11, further comprising the step of controlling the third optical switch to optically connect the two quantum bits and the first optical waveguide before the step of simultaneously irradiating the two quantum bits with light.

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