Quantum device, quantum computing device, and quantum computing method

Abstract

This quantum device comprises: a first qubit that has a first electron spin and a first nuclear spin; a second qubit that has a second electron spin; a first entanglement part that irradiates the first qubit with a first high-frequency radio wave pulse and, by dynamical decoupling, generates a quantum entanglement state in the first electron spin and the first nuclear spin; a first photon generation part that irradiates the first qubit with light and generates a first photon which reflects the spin state of the first electron spin; a second photon generation part that irradiates the second qubit with light and generates a second photon which reflects the spin state of the second electron spin; and a second entanglement part that generates a quantum entanglement state in the first photon and the second photon.

Description

Technical Field

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

Background Art

[0002] Research and development of quantum computers are being carried out as one of the next-generation computing technologies. For example, a method has been proposed in which color centers in diamond are used as quantum bits and quantum computing is performed between two quantum bits. On the other hand, a method has also been proposed to extend the coherence time by dynamical decoupling between nuclear spins and electron spins in diamond.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the conventional technology, it is impossible to obtain a good fidelity in the quantum entanglement state while extending the coherence time.

[0006] An object of the present disclosure is to provide a quantum device, a quantum computing apparatus, and a quantum computing method capable of obtaining a good fidelity in the quantum entanglement state while extending the coherence time.

Means for Solving the Problems

[0007] According to one aspect of the present disclosure, there is provided a quantum device including: a first qubit including a first electron spin and a first nuclear spin; a second qubit including a second electron spin; a first entanglement unit that irradiates the first qubit with a first high-frequency electromagnetic wave pulse and generates a quantum entanglement state in the first electron spin and the first nuclear spin by dynamical decoupling; a first photon generation unit that irradiates the first qubit with light and generates a first photon reflecting the spin state of the first electron spin; a second photon generation unit that irradiates the second qubit with light and generates a second photon reflecting the spin state of the second electron spin; and a second entanglement unit that generates a quantum entanglement state in the first photon and the second photon.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to obtain a good fidelity in the quantum entanglement state while extending the coherence time.

Brief Description of the Drawings

[0009]

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[0010] Hereinafter, embodiments of the present disclosure will be specifically described with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration may be denoted by the same reference numerals, and redundant description may be omitted. In the present disclosure, the X1-X2 direction and the Y1-Y2 direction are orthogonal to each other.

[0011] (First Embodiment) First, the 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 computing device such as a quantum computer. FIG. 1 is a top view showing the quantum device according to the first embodiment. FIG. 2 is a cross-sectional view showing the quantum device according to the first embodiment. FIG. 2 corresponds to a cross-sectional view taken along line II-II in FIG. 1.

[0012] As shown in FIGS. 1 and 2, the quantum device 1 according to the first embodiment includes a substrate 100, an optical waveguide 111, an optical waveguide 112, a signal line 121, a ground line 125, and a signal line 122. The quantum device 1 further includes a beam splitter 130, a photodetector 131, a photodetector 132, an optical fiber 141, an optical fiber 142, a light irradiation unit 151, and a light irradiation unit 152.

[0013] The optical waveguides 111, 112, signal lines 121, ground line 125, and signal line 122 are provided on the substrate 100 and extend parallel to each other. The ground line 125 is provided between the signal line 121 and the signal line 122. The optical waveguide 111 is provided between the signal line 121 and the ground line 125. The optical waveguide 112 is provided between the signal line 122 and the ground line 125.

[0014] The signal line 121, ground line 125, and signal line 122 are, for example, metal lines. The materials of the signal line 121, ground line 125, and signal line 122 are, for example, Al, Cu, or Au, etc.

[0015] The optical waveguide 111 has a diamond waveguide and includes a color center 161 of diamond. The optical waveguide 112 has a diamond waveguide and includes a color center 162 of diamond. The color centers 161 and 162 are, for example, nitrogen-vacancy centers (NV centers) composed of nitrogen and vacancies. The color centers 161 and 162 may be silicon-vacancy centers (SiV centers) composed of silicon and vacancies, germanium-vacancy centers (GeV centers) composed of germanium and vacancies, tin-vacancy centers (SnV centers) composed of tin and vacancies, lead-vacancy centers (PbV centers) composed of lead and vacancies, or boron-vacancy centers (BV centers) composed of boron and vacancies. Color centers other than diamond may also be used. For example, silicon carbide (SiC) or boron nitride (BN), etc. may be used.

[0016] The optical waveguides 111 and 112 may have a diamond waveguide and a waveguide made of a material through which visible light optically connected to this diamond waveguide transmits, for example, silicon oxide or aluminum oxide, etc.

[0017] For example, the optical waveguide 111 is optically connected to the beam splitter 130 via the optical fiber 141, and the optical waveguide 112 is optically connected to the beam splitter 130 via the optical fiber 142. The beam splitter 130 includes, for example, a diamond photonic crystal. Instead of the optical fibers 141 and 142, waveguides such as silicon oxide or aluminum oxide may be used.

[0018] A photodetector 131 and a photodetector 132 are optically connected to the beam splitter 130. The photodetectors 131 and 132 may be directly connected to the beam splitter 130, or may be connected via an optical waveguide or an optical fiber. The photodetectors 131 and 132 are, for example, single-photon detectors.

[0019] The light irradiation unit 151 irradiates light on the color center 161, and the light irradiation unit 152 irradiates light on the color center 162. The light irradiation unit 151 irradiates laser light via a confocal microscope, irradiates laser light from the fiber end face via an optical fiber, or irradiates laser light via an optical fiber and an optical waveguide.

[0020] In the quantum device 1 configured as described above, the color center 161 functions as the first qubit, and the color center 162 functions as the second qubit.

[0021] Next, the configuration of the quantum circuit corresponding to the quantum device 1 according to the first embodiment will be described. FIG. 3 is a diagram showing the configuration of the quantum circuit corresponding to the quantum device according to the first embodiment.

[0022] As shown in FIG. 3, the color center 161 includes an electron spin 11 and a nuclear spin 12, and the color center 162 includes an electron spin 21 and a nuclear spin 22. The electron spin 11 is an example of the first electron spin, and the nuclear spin 12 is an example of the first nuclear spin. The electron spin 21 is an example of the second electron spin, and the nuclear spin 22 is an example of the second nuclear spin.

[0023] By irradiating the color center 161 with an RF (radio frequency) signal pulse 171 via the signal line 121, a quantum entanglement state can be generated in the first electron spin 11 and the first nuclear spin 12 by dynamical decoupling. Also, by irradiating the color center 162 with an RF signal pulse 172 via the signal line 122, a quantum entanglement state can be generated in the second electron spin 21 and the second nuclear spin 22 by dynamical decoupling. The signal line 121 is an example of a first entanglement part, and the signal line 122 is an example of a fourth entanglement part. The RF signal pulse 171 is an example of a first high-frequency electromagnetic wave pulse, and the RF signal pulse 172 is an example of a second high-frequency electromagnetic wave pulse. Note that "R" in FIG. 3 n " indicates a control gate for rotation around the n-axis (n is any of x, y, z).

[0024] Also, when the color center 161 is irradiated with light by the light irradiation unit 151, a photon 13 is generated by a luminescence transition. When the color center 162 is irradiated with light by the light irradiation unit 152, a photon 23 is generated by a luminescence transition. When the photons 13 and 23 are generated simultaneously, the beam splitter 130 generates a quantum entanglement state in the photons 13 and 23. The light irradiation unit 151 is an example of a first photon generation unit, and the light irradiation unit 152 is an example of a second photon generation unit. The beam splitter 130 is an example of a second entanglement part.

[0025] When performing a quantum operation using the quantum device 1, the color center 161 is irradiated with the RF signal pulse 171, and a quantum entanglement state is generated in the first electron spin 11 and the first nuclear spin 12 by dynamical decoupling.

[0026] Next, irradiate the color centers 161 with green light or red light or both from the light irradiation unit 151, irradiate the color center 162 with green light from the light irradiation unit 152, and perform initialization. Next, irradiate the color centers 161 and 162 with red light from the light irradiation unit 151 and the light irradiation unit 152, respectively, and detect photons 13 and 23 by the photodetectors 131 and 132 via the beam splitter 130. This operation is performed until an entangled state (superposed state) is generated. Note that the green light and the red light are lights suitable for the NV center, and when other color centers are used, lights of other colors may be used.

[0027] Also, at a timing not affected by dynamical decoupling, irradiate the color center 161 with red light from the light irradiation unit 151 and irradiate the color center 162 with red light from the light irradiation unit 152. The timing not affected by dynamical decoupling is, for example, the N-th timing when the phase is changed by 2π / N for dynamical decoupling.

[0028] In this way, while extending the coherence time by dynamical decoupling, a good fidelity can be obtained in the quantum entanglement state between the color center 161, which is an example of the first qubit, and the color center 162, which is an example of the second qubit.

[0029] Further, since the ground line 125 is provided between the signal line 121 and the optical waveguide 112, the color center 162 is shielded from the signal line 121 by the ground line 125. Therefore, even when the distance between the color center 161 and the color center 162 is small, the color center 162 is less likely to be affected by the RF signal pulse 171. Similarly, the color center 161 is less likely to be affected by the RF signal pulse 172 irradiated from the signal line 122 to the color center 162. The ground line 125 is an example of a shielding member.

[0030] (Second Embodiment) Next, the second embodiment will be described. FIG. 4 is a diagram showing the configuration of a quantum circuit corresponding to the quantum device according to the second embodiment.

[0031] The quantum device 2 according to the second embodiment has two combinations of an optical waveguide 111, an optical waveguide 112, a signal line 121, a ground line 125, a signal line 122, a beam splitter 130, a photodetector 131, a photodetector 132, an optical fiber 141, an optical fiber 142, a light irradiation unit 151, and a light irradiation unit 152. Therefore, as shown in FIG. 4, the quantum device 2 has two combinations of color centers 161 and 162. The quantum device 2 further has a beam splitter 230 that generates an entangled state between two color centers 162. The beam splitter 230 is an example of a third entanglement unit.

[0032] Other configurations are the same as those in the first embodiment.

[0033] In the quantum device 2 configured as described above, for example, a quantum operation is performed using two electron spins 21 via the beam splitter 230, and one electron spin 21 is measured at a timing not affected by dynamical decoupling. By performing such processing, the quantum information of the one electron spin 21 is quantum teleported to the electron spin 11 included in the same combination as the one electron spin 21.

[0034] Also in the second embodiment, it is possible to obtain a good fidelity in the entangled state while extending the coherence time by dynamical decoupling. In addition, a plurality of qubits can be integrated and arranged.

[0035] (Third Embodiment) Next, the third embodiment will be described. FIG. 5 is a diagram showing the configuration of a quantum circuit corresponding to the quantum device according to the third embodiment.

[0036] In the quantum device 3 according to the third embodiment, as shown in FIG. 5, the optical waveguide 111 includes two color centers 161. Although not shown, the light irradiation unit 151 is provided for each color center 161.

[0037] Other configurations are the same as those in the first embodiment.

[0038] Also according to the third embodiment, it is possible to obtain a good fidelity in the entangled state of quanta while extending the coherence time by dynamical decoupling. In addition, a plurality of qubits can be integrated and arranged.

[0039] (Fourth Embodiment) Next, the fourth embodiment will be described. The fourth embodiment relates to a quantum computer. FIG. 6 is a diagram showing a quantum computer according to the fourth embodiment.

[0040] The quantum computer 4 according to the fourth embodiment includes a general-purpose computer 401, a control unit 402, and a quantum device 403. The control unit 402 controls the quantum device 403 based on a control signal from the general-purpose computer 401. As the quantum device 403, a quantum device according to any one of the first to third embodiments is used. The control unit 402 and the quantum device 403 are housed in a cryostat 404.

[0041] The quantum computer 4 can perform stable quantum operations.

[0042] Although the preferred embodiments and the like have been described in detail above, the present invention is not limited to the above-described embodiments and the like, and various modifications and substitutions can be made to the above-described embodiments and the like without departing from the scope described in the claims.

Explanation of Reference Numerals

[0043] 1, 2, 3, 403: Quantum device 4: Quantum computer 11, 21: Electron spin 12, 22: Nuclear spin 13, 23: Photons 111, 112: Optical waveguides 121, 122: Signal lines 125: Ground line 130, 230: Beam splitters 131, 132: Photodetectors 151, 152: Light irradiation units 161, 162: Color centers 171, 172: RF signal pulses

Claims

1. A first quantum bit having a first electron spin and a first nuclear spin, a second quantum bit having a second electron spin, a first entanglement unit that irradiates the first quantum bit with a first high-frequency electromagnetic wave pulse and generates an entangled state in the first electron spin and the first nuclear spin by dynamical decoupling, a first photon generation unit that irradiates the first quantum bit with light and generates a first photon reflecting the spin state of the first electron spin, a second photon generation unit that irradiates the second quantum bit with light and generates a second photon reflecting the spin state of the second electron spin, a second entanglement unit that generates an entangled state in the first photon and the second photon, A quantum device, characterized by comprising the above.

2. The quantum device according to claim 1, characterized by having a plurality of combinations of the first quantum bit, the second quantum bit, the first entanglement unit, the first photon generation unit, the second photon generation unit, and the second entanglement unit, and having a third entanglement unit that generates an entangled state in two of the second photons in which an entangled state has been generated by the second entanglement unit.

3. The quantum device according to claim 1 or 2, characterized by having a plurality of the first quantum bits, wherein the first photon generation unit selectively irradiates one of the plurality of first quantum bits with light.

4. The quantum device according to any one of claims 1 to 3, characterized in that the second entanglement unit has a beam splitter.

5. The quantum device according to any one of claims 1 to 4, characterized by having a shielding member that shields the second quantum bit from the first high-frequency electromagnetic wave pulse.

6. The second quantum bit includes a second nuclear spin, The quantum device according to any one of claims 1 to 5, characterized by having a fourth entanglement unit that irradiates the second quantum bit with a second high-frequency electromagnetic wave pulse and generates an entangled state in the second electron spin and the second nuclear spin by dynamical decoupling.

7. A quantum computing device, characterized by including the quantum device according to any one of claims 1 to 6.

8. A quantum computing method using a quantum device, wherein the quantum device has a first quantum bit having a first electron spin and a first nuclear spin, and a second quantum bit having a second electron spin, and includes the above. Irradiating the first qubit with a first high-frequency electromagnetic wave pulse to generate an entangled state in the first electron spin and the first nuclear spin by dynamical decoupling; Irradiating the first qubit with light to generate a first photon reflecting the spin state of the first electron spin, and irradiating the second qubit with light to generate a second photon reflecting the spin state of the second electron spin; Generating an entangled state in the first photon and the second photon; A quantum computing method characterized by comprising the above steps.

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