Quantum Device and Quantum Computing Device

Abstract

This quantum device comprises: a first optical waveguide comprising diamond; and a second optical waveguide optically coupled to the first optical waveguide and comprising a material having a lower refractive index than diamond. The first optical waveguide has a first region including a color center, a second region through which light propagating through the first region is propagated to the second optical waveguide, and a third region connected to the opposite side of the second region from the first region, and joined to the second optical waveguide.

Description

Technical Field

[0001] The present disclosure relates to quantum devices and quantum computing apparatuses.

Background Art

[0002] Research and development of quantum computers is being carried out as one of the next-generation computing technologies. There is a method of performing quantum computing using the spins and photons of diamond color centers, which are quantum elements, as quantum bits. This quantum computing is performed by entangling photons emitted from diamond at an extremely low temperature of about -270°C. Entanglement of photons is performed through an optical waveguide such as sapphire optically coupled to a diamond optical waveguide containing color centers.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] There is a large difference in the coefficient of thermal expansion between a diamond optical waveguide and an optical waveguide connected to the diamond optical waveguide. Therefore, even if they are joined with high precision at room temperature, when cooled to an extremely low temperature of about -270°C, the amounts of thermal deformation are greatly different, so that the optical propagation loss may increase due to strain. In addition, peeling may occur between these two optical waveguides, and the optical propagation loss may increase due to the peeling.

[0006] An object of the present disclosure is to provide a quantum device and a quantum computing device capable of suppressing an increase in optical propagation loss due to thermal deformation.

Means for Solving the Problems

[0007] According to one aspect of the present disclosure, there is provided a quantum device including a first optical waveguide made of diamond, and a second optical waveguide optically coupled to the first optical waveguide and made of a material having a refractive index lower than that of diamond, wherein the first optical waveguide has a first region including a color center, bonded to the second optical waveguide, a second region that propagates light propagating in the first region to the second optical waveguide, and a third region that is connected to the side of the second region opposite to the first region and is joined to the second optical waveguide. and the width of the second region decreases from the boundary with the first region toward the boundary with the third region, and the third region has a fourth region with a constant width

Effects of the Invention

[0008] According to the present disclosure, an increase in optical propagation loss due to thermal deformation can be suppressed.

Brief Description of the Drawings

[0009]

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Best Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be specifically described with reference to the accompanying drawings. In this specification and the drawings, for components having substantially the same functional configuration, the same reference numerals may be used to omit redundant descriptions. In the present disclosure, the X1-X2 direction, the Y1-Y2 direction, and the Z1-Z2 direction are orthogonal to each other. The plane including the X1-X2 direction and the Y1-Y2 direction is referred to as the XY plane, the plane including the Y1-Y2 direction and the Z1-Z2 direction is referred to as the YZ plane, and the plane including the Z1-Z2 direction and the X1-X2 direction is referred to as the ZX plane. For convenience, the Z1-Z2 direction is the vertical direction, the Z1 side is the upper side, and the Z2 side is the lower side. In addition, a plan view means viewing an object from the Z1 side, and a planar shape means the shape of an object viewed from the Z1 side.

[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 first optical waveguide 10 and a second optical waveguide 20. The first optical waveguide 10 is made of diamond, and the second optical waveguide 20 is made of a material having a refractive index lower than that of diamond. The material of the second optical waveguide 20 is, for example, sapphire, silicon, silicon carbide, silicon nitride, silicon oxide, or any combination thereof. The first optical waveguide 10 is laminated on the second optical waveguide 20. The second optical waveguide 20 is optically coupled to the first optical waveguide 10.

[0013] The first optical waveguide 10 has a first region 111, a second region 112, and a third region 113. The first region 111 contains color centers. The second region 112 propagates the light 30 propagating in the first region 111 to the second optical waveguide 20. The third region 113 is connected to the side of the second region 112 opposite to the first region 111. The third region 113 is joined to the second optical waveguide 20.

[0014] The height H1 and width W1 of the first region 111 satisfy the single-mode waveguide condition with respect to the light 30 propagating in the first region 111. For example, the height H1 is 0.25 times to 0.50 times the wavelength λ of the light 30, and the width W1 is 0.25 times to 0.60 times the wavelength λ. When the wavelength λ is 600 nm to 800 nm, the height H1 may be 150 nm to 300 nm, and the width W1 may be 150 nm to 300 nm. As a specific example, when the wavelength λ is 637 nm, the height H1 is 245 nm, and the width W1 is 284 nm. Note that the height H1 is the dimension of the first region 111 in the stacking direction (Z1-Z2 direction), and the width W1 is the dimension of the first region 111 in the direction (Y1-Y2 direction) perpendicular to the propagation direction (X1-X2 direction) and the Z1-Z2 direction of the light 30 in the first region 111.

[0015] The height H2 of the second region 112 is equal to the height H1 of the first region 111, and the width W2 of the second region 112 decreases from the boundary 112A with the first region 111 toward the boundary 112B with the third region 113. The cross-sectional area of the cross-section perpendicular to the X1-X2 direction of the second region 112 decreases from the boundary 112A toward the boundary 112B. For example, the width W2 and the cross-sectional area decrease linearly. The second region 112 has a trapezoidal planar shape. The width W2 of the second region 112 is a width at which a single mode cannot propagate at the boundary 112B. For example, at the boundary 112B, the height H2 is 0.25 times to 0.50 times the wavelength λ of the light 30, and the width W2 is 0.20 times to 0.60 times the wavelength λ. When the wavelength λ is 600 nm to 800 nm, at the boundary 112B, the height H2 may be 150 nm to 300 nm, and the width W2 may be 50 nm to 150 nm. Note that the height H2 is the dimension of the second region 112 in the Z1-Z2 direction, and the width W2 is the dimension of the second region 112 in the Y1-Y2 direction. When the light 30 that has propagated through the first region 111 leaks to the outside in the second region 112, the light 30 leaks to the region having the refractive index closest to that of diamond, which is the material of the second region 112, among the surrounding regions, so the light 30 is propagated to the second optical waveguide 20 such as sapphire.

[0016] The height H3 and the width W3 of the third region 113 are equal to the height H2 and the width W2 of the second region 112 at the boundary 112B, respectively. The third region 113 has a rectangular planar shape. The light 30 hardly propagates through the third region 113. The length L3 of the third region 113 is, for example, 100 nm or more, preferably 500 nm or more. Note that the height H3 is the dimension of the third region 113 in the Z1-Z2 direction, the width W3 is the dimension of the third region 113 in the Y1-Y2 direction, and the length L3 is the dimension of the third region 113 in the X1-X2 direction.

[0017] In the quantum device 1 configured as described above, the light 30 emitted from the color center propagates in the first region 111 and is propagated to the second optical waveguide 20 by the second region 112. The light 30 propagated to the second optical waveguide 20 is used for quantum computing.

[0018] Also, when the quantum device 1 is cooled to an extremely low temperature of about -270°C during quantum operation, the first optical waveguide 10 and the second optical waveguide 20 thermally contract depending on the thermal expansion coefficients of their respective materials. At this time, since the thermal expansion coefficients are different between the first optical waveguide 10 and the second optical waveguide 20, stress acts on the interface between the first optical waveguide 10 and the second optical waveguide 20. This stress concentrates at the tip on the X1 side of the first optical waveguide 10 and decreases in the X1 - X2 direction as it moves away from this tip. Therefore, the stress acting on the second region 112 and its vicinity is reduced compared to the case where the third region 113 is not provided. For this reason, an increase in optical propagation loss due to thermal deformation can be suppressed.

[0019] (Second Embodiment) Next, the second embodiment will be described. The second embodiment is mainly different from the first embodiment in terms of the configuration of the first optical waveguide. FIG. 3 is a top view showing the quantum device according to the second embodiment.

[0020] As shown in FIG. 3, in the quantum device 2 according to the second embodiment, a third region 213 is provided instead of the third region 113. The side surface of the end portion of the third region 213 on the side opposite to the second region 112, that is, the side surface of the end portion on the X1 side, is a curved surface. Other configurations of the third region 213 are the same as those of the third region 113.

[0021] Other configurations are the same as those of the first embodiment.

[0022] Also in the second embodiment, the same effects as those of the first embodiment can be obtained. Further, in the second embodiment, since the side surface of the end portion on the X1 side of the third region 213 is a curved surface, the stress acting on the end portion on the X1 side of the third region 213 is likely to be dispersed. Therefore, peeling and distortion of the third region 213 are suppressed, and the propagation of the peeling and distortion generated in the third region 213 to the second region 112 can be suppressed, and an increase in optical propagation loss can be further suppressed.

[0023] (Third Embodiment) Next, the third embodiment will be described. The third embodiment is mainly different from the second embodiment in terms of the configuration of the first optical waveguide. FIG. 4 is a cross-sectional view showing a quantum device according to the third embodiment.

[0024] As shown in FIG. 4, in the quantum device 3 according to the third embodiment, a third region 313 is provided instead of the third region 113. The height H3 of the third region 313 is smaller than the height H2 of the second region 112. Other configurations of the third region 313 are the same as those of the third region 113.

[0025] Other configurations are the same as those of the first embodiment.

[0026] Also in the third embodiment, the same effects as those of the second embodiment can be obtained. Further, in the third embodiment, since the height H3 of the third region 313 is smaller than the height H2 of the second region 112, the optical propagation of the light that has propagated to the second region 112 to the third region 313 can be suppressed.

[0027] Note that the planar shape of the third region 313 may be rectangular, similar to the third region 113. That is, the end face of the third region 313 may be planar.

[0028] (Fourth Embodiment) Next, the fourth embodiment will be described. The fourth embodiment is mainly different from the third embodiment in terms of the configuration of the first optical waveguide. FIG. 5 is a cross-sectional view showing a quantum device according to the fourth embodiment.

[0029] As shown in FIG. 5, in the quantum device 4 according to the fourth embodiment, a second region 412 is provided instead of the second region 112. The height H2 of the second region 412 decreases from the boundary 412A with the first region 111 toward the boundary 412B with the third region 313. Therefore, the cross-sectional area of the cross-section perpendicular to the X1-X2 direction of the second region 412 decreases from the boundary 412A toward the boundary 412B. For example, the height H2, the width W2, and the cross-sectional area decrease linearly. The height H2 of the second region 412 is a height at which a single mode cannot propagate at the boundary 412B. For example, at the boundary 412B, the height H2 is 0.20 times to 0.50 times the wavelength λ of the light 30, and the width W2 is 0.20 times to 0.60 times the wavelength λ. When the wavelength λ of the light 30 is 600 nm to 800 nm, at the boundary 412B, the height H2 of the second region 412 is equal to the height H3 of the third region 313. For example, the height H3 may be 50 nm to 150 nm. Other configurations of the second region 412 are the same as those of the second region 112.

[0030] Other configurations are the same as those of the third embodiment.

[0031] Also in the fourth embodiment, the same effects as those of the third embodiment can be obtained. Further, in the fourth embodiment, since the height H2 of the second region 412 decreases from the boundary 412A toward the boundary 412B, it is easier to propagate the light 30 to the second optical waveguide 20 by the second region 112.

[0032] (Fifth Embodiment) Next, the fifth embodiment will be described. The fifth embodiment is mainly different from the fourth embodiment in terms of the configuration below the second optical waveguide. FIG. 6 is a top view showing a quantum device according to the fifth embodiment. FIGS. 7 and 8 are cross-sectional views showing the quantum device according to the fifth embodiment. FIG. 7 corresponds to a cross-sectional view taken along line VII-VII in FIG. 6. FIG. 8 corresponds to a cross-sectional view taken along line VIII-VIII in FIG. 6.

[0033] As shown in FIGS. 6 to 8, the quantum device 5 according to the fifth embodiment has a substrate 51 and a cladding layer 52 in addition to the structure of the fourth embodiment. The cladding layer 52 is provided on the substrate 51. The second optical waveguide 20 is provided on the cladding layer 52. For example, the material of the substrate 51 is a sapphire substrate, and the material of the cladding layer 52 is silicon oxide (SiO2).

[0034] A hollow portion 53 is formed in the cladding layer 52. The hollow portion 53 is formed on the Z2 side (lower side) of the second region 412. The hollow portion 53 may be formed across the portion of the cladding layer 52 on the Z2 side of the second region 412 to the portion of the third region 313 on the Z2 side.

[0035] An optical waveguide layer 20B is provided on the cladding layer 52, and a groove 20A is formed between the optical waveguide layer 20B and the second optical waveguide 20. The material of the optical waveguide layer 20B is the same as the material of the second optical waveguide 20.

[0036] Also in the fifth embodiment, the same effects as those of the fourth embodiment can be obtained. Further, in the fifth embodiment, the second optical waveguide 20 is provided on the substrate 51 via the cladding layer 52, and the hollow portion 53 is formed in the cladding layer 52. Therefore, the stress acting on the second region 412 and its vicinity due to thermal deformation is relaxed. Accordingly, an increase in optical propagation loss due to thermal deformation can be further suppressed.

[0037] Next, a method for manufacturing the quantum device according to the fifth embodiment will be described. FIGS. 9 to 15 are cross-sectional views showing a method for manufacturing the quantum device according to the fifth embodiment. FIGS. 9 to 13 show changes in the cross-section along line VIII-VIII in FIG. 6. FIGS. 14 to 15 show changes in the cross-section along line VII-VII in FIG. 6.

[0038] First, as shown in FIG. 9, a substrate including a substrate 51, a clad layer 52X, and an optical waveguide layer 20X is prepared. The material of the clad layer 52X is the same as that of the clad layer 52, for example, silicon oxide. The material of the optical waveguide layer 20X is the same as that of the second optical waveguide 20, for example, sapphire. Next, a diamond layer 10X is provided on the optical waveguide layer 20X. For example, a diamond layer thicker than the height H3 of the first region 111 to be formed is formed, and the diamond layer is thinned until the thickness of the diamond layer becomes equal to the height H3.

[0039] Thereafter, as shown in FIG. 10, the diamond layer 10X is processed into the planar shape of the first optical waveguide 10. In the processing of the diamond layer 10X, for example, the formation of an electron beam (EB) resist, exposure using an EB exposure machine, development of the EB resist, and plasma etching using oxygen gas are performed in this order. A photoresist may be used instead of the EB resist. Also, wet etching may be performed as the etching. The diamond layer 10X may be processed using a focused ion beam (FIB).

[0040] Subsequently, as shown in FIGS. 11 and 14, the diamond layer 10X is processed three-dimensionally to form a first optical waveguide 10 having a first region 111, a second region 412, and a third region 313. The diamond layer 10X is processed using, for example, FIB. The diamond layer 10X may be processed through multiple photolithographies, or the diamond layer 10X may be processed through multiple EB exposures.

[0041] Next, as shown in FIG. 12, the optical waveguide layer 20X is processed to form the second optical waveguide 20. In processing the optical waveguide layer 20X, for example, a groove 20A is formed around the second optical waveguide 20, and the optical waveguide layer 20B is left around it. In processing the optical waveguide layer 20X, for example, formation of an EB resist, exposure using an EB exposure machine, development of the EB resist, and plasma etching using a chlorine-based gas are performed in this order. A photoresist may be used instead of the EB resist. Also, wet etching may be performed as the etching.

[0042] Thereafter, as shown in FIGS. 13 and 15, by processing the cladding layer 52X, a cladding layer 52 with a hollow portion 53 formed therein is obtained. In processing the cladding layer 52X, for example, vaporized hydrofluoric acid is used, and etching is performed through the groove 20A.

[0043] In this way, the quantum device 5 according to the fifth embodiment can be manufactured.

[0044] Note that in the first to fifth embodiments, the cross-sectional area of the cross-section perpendicular to the X1 - X2 direction of the third region does not necessarily have to be equal to the cross-sectional area S0 at the boundary between the third region and the second region, and may be less than the cross-sectional area S0. Also, the height H3 of the third region does not necessarily have to be equal to the height H2 at the boundary between the third region and the second region, and may be less than the height H2, and the width W3 of the third region does not necessarily have to be equal to the width W2 at the boundary between the third region and the second region, and may be less than the width W2.

[0045] (Sixth Embodiment) Next, the sixth embodiment will be described. The sixth embodiment relates to a quantum computer. FIG. 16 is a diagram showing the quantum computer according to the sixth embodiment.

[0046] The quantum computer 6 according to the sixth embodiment includes a general-purpose computer 601, a control unit 602, and a quantum device 603. The control unit 602 controls the quantum device 603 based on a control signal from the general-purpose computer 601. As the quantum device 603, a quantum device according to any one of the first to fifth embodiments is used. The control unit 602 and the quantum device 603 are housed in a cryostat 604.

[0047] The quantum computer 6 can perform stable quantum operations.

[0048] (Simulation) Next, the results of the simulation performed by the inventor of the present application will be described. In this simulation, for seven types of structures S1 to S7, when stress-free at 300K, the internal stress distribution when cooled to 4K was calculated. FIGS. 17 to 23 are diagrams showing the results of the simulation.

[0049] As shown in FIG. 17, in structure S1, a silicon oxide cladding layer 92 is provided on a sapphire substrate 91, a second optical waveguide 93 made of sapphire is provided on the cladding layer 92, and a first optical waveguide 94 made of diamond is provided on the second optical waveguide 93. The first optical waveguide 94 has a first region 94A and a second region 94B. The heights of the first region 94A and the second region 94B are 200 nm. The width of the first region 94A is 200 nm. The width of the second region 94B linearly decreases from the boundary with the first region 94A to the tip. The length of the second region 94B is 1500 nm.

[0050] FIG. 18 is an enlarged view of the region surrounded by the two-dot chain line XVIII in FIG. 17. In the simulation result for structure S1, the internal stress at the tip of the second region 94B was maximum at 55.5 GPa.

[0051] As shown in FIG. 19, in structure S2, the height of the second region 94B linearly decreases from the boundary with the first region 94A to the tip. Other conditions are the same as those of structure S1.

[0052] Figure 20 is an enlarged view of the area surrounded by the two-dot chain line XX in Figure 19. In the result of the simulation for the structure S2, the internal stress at the tip of the second region 94B was at most 25.0 GPa.

[0053] As shown in Figure 21, in the structure S3, the first optical waveguide 94 has a third region 94C in addition to the first region 94A and the second region 94B. The height of the third region 94C is 200 nm, and the width of the third region 94C is 100 nm. The width of the second region 94B linearly decreases from 200 nm to 100 nm from the boundary with the first region 94A to the boundary with the third region 94C. The length of the second region 94B is 500 nm, and the length of the third region is 1000 nm. Other conditions are the same as those of the structure S1. The structure S3 follows the structure of the first embodiment.

[0054] Figure 22 is an enlarged view of the area surrounded by the two-dot chain line XXII in Figure 21. Figure 23 is an enlarged view of the area surrounded by the two-dot chain line XXIII in Figure 21. In the result of the simulation for the structure S3, the internal stress at the tip of the third region 94C was at most 8.0 GPa, and the internal stress in the second region 94B was at most 5.0 GPa.

[0055] As shown in Figure 24, in the structure S4, the height of the third region 94C is 100 nm. Also, the height of the second region 94B linearly decreases from 200 nm to 100 nm from the boundary with the first region 94A to the boundary with the third region 94C. Other conditions are the same as those of the structure S3. The structure S4 follows the structure in which the tip of the third region 313 in the fourth embodiment is a plane.

[0056] Figure 25 is an enlarged view of the area surrounded by the two-dot chain line XXV in Figure 24. Figure 26 is an enlarged view of the area surrounded by the two-dot chain line XXVI in Figure 24. In the result of the simulation for the structure S4, the internal stress at the tip of the third region 94C was at most 6.2 GPa, and the internal stress in the second region 94B was at most 5.0 GPa.

[0057] As shown in FIG. 27, in structure S5, the height of the third region 94C is 100 nm. Other conditions are the same as those of structure S3. Structure S5 follows the structure with the tip of the third region 313 as a plane in the third embodiment.

[0058] FIG. 28 is an enlarged view of the region surrounded by the two-dot chain line XXVIII in FIG. 27. FIG. 29 is an enlarged view of the region surrounded by the two-dot chain line XXIX in FIG. 27. In the simulation results for structure S5, the maximum internal stress at the tip of the third region 94C was 6.0 GPa, and the maximum internal stress in the second region 94B was 8.6 GPa.

[0059] As shown in FIG. 30, in structure S6, the tip of the third region 313 is a curved surface. Other conditions are the same as those of structure S4. Structure S6 follows the structure of the fourth embodiment.

[0060] FIG. 31 is an enlarged view of the region surrounded by the two-dot chain line XXXI in FIG. 30. FIG. 32 is an enlarged view of the region surrounded by the two-dot chain line XXXII in FIG. 30. In the simulation results for structure S6, the maximum internal stress at the tip of the third region 94C was 9.0 GPa, and the maximum internal stress in the second region 94B was 4.0 GPa.

[0061] As shown in FIG. 33, in structure S7, a hollow portion 95 is formed in the cladding layer 92. Other conditions are the same as those of structure S6. Structure S7 follows the structure of the fifth embodiment.

[0062] FIG. 34 is an enlarged view of the region surrounded by the two-dot chain line XXXIV in FIG. 33. FIG. 35 is an enlarged view of the region surrounded by the two-dot chain line XXXV in FIG. 33. In the simulation results for structure S7, the maximum internal stress at the tip of the third region 94C was 6.0 GPa, and the maximum internal stress in the second region 94B was 3.0 GPa.

[0063] Thus, in the simulation, in structures S3 to S7, as compared with structures S1 and S2, the result that the internal stress in the second region 94B is significantly lower was obtained.

[0064] As described above in detail for the preferred embodiments and the like, 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

[0065] 1, 2, 3, 4, 5, 603: Quantum device 6: Quantum computer 10: First optical waveguide 20: Second optical waveguide 51: Substrate 52: Clad layer 53: Hollow portion 111: First region 112, 412: Second region 112A, 112B, 412A, 412B: Boundary 113, 213, 313: Third region

Claims

1. A first optical waveguide made of diamond, and a second optical waveguide optically coupled to the first optical waveguide and made of a material having a refractive index lower than that of diamond, and having the first optical waveguide comprising a first region containing color centers, a second region joined to the second optical waveguide and configured to propagate light propagating in the first region to the second optical waveguide, a third region connected to the side of the first region opposite to the second region and joined to the second optical waveguide, and having the width of the second region decreasing from the boundary with the first region toward the boundary with the third region, the third region having a fourth region with a constant width, a quantum device characterized thereby.

2. The fourth region is continuous with the second region, the quantum device according to Claim 1, characterized in that the width of the fourth region is equal to the width at the boundary of the fourth region with the second region.

3. The quantum device according to Claim 1 or 2, characterized in that the height of the second region decreases from the boundary with the first region toward the boundary with the third region.

4. The quantum device according to any one of Claims 1 to 3, characterized in that the side surface of the end portion of the third region opposite to the second region is a curved surface.

5. a substrate, and a cladding layer provided on the substrate, and having the second optical waveguide being provided on the cladding layer, the quantum device according to any one of Claims 1 to 4, characterized in that a hollow portion is formed in a portion of the cladding layer below the second region.

6. The quantum device according to Claim 5, characterized in that the hollow portion is formed from a portion of the cladding layer below the second region to a portion of the cladding layer below the third region.

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

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