Quantum Device and Method for Controlling Quantum Device

Abstract

This quantum device has: a WTe2 layer having a first surface and a second surface opposite to the first surface; a first insulating layer provided on the first surface; a second insulating layer provided on the second surface; a first normally conductive metal electrode, a second normally conductive metal electrode, and a third normally conductive metal electrode, which are provided on the first insulating layer; a first control unit for controlling the electric potentials of the first normally conductive metal electrode, the second normally conductive metal electrode, and the third normally conductive metal electrode; a superconductive metal wiring which is provided on the second insulating layer and has a first terminal and a second terminal; and a second control unit for controlling the superconductor phase difference between the first terminal and the second terminal. In a plan view from a direction perpendicular to the first surface: the WTe2 layer has a first edge and a second edge which form a narrowed part; the narrowed part is provided between the first terminal and the second terminal; the first normally conductive metal electrode overlaps a portion of the first edge distanced from the narrowed part in one direction; the second normally conductive metal electrode overlaps a portion of the first edge distanced from the narrowed part in another direction; and the third normally conductive metal electrode overlaps a portion of the second edge distanced from the narrowed part in the one direction.

Description

Technical Field

[0001] The present disclosure relates to a quantum device and a method for controlling the quantum device.

Background Art

[0002] As a quantum computer with error tolerance, the realization of a quantum computer (topological quantum computer) including topological qubits using the position exchange (braiding) of Majorana particles is expected. Topological qubits require a function to exchange positions without colliding four Majorana particles. Non-Patent Document 1 proposes a quantum device that controls the positions of Majorana particles by changing the magnetic flux in a structure composed of a two-dimensional topological material and a superconducting metal.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, it is not easy to stably manufacture the quantum device described in Non-Patent Document 1.

[0006] An object of the present disclosure is to provide a quantum device that can be stably manufactured and a method for controlling the quantum device. **Means for Solving the Problems**

[0007] According to one aspect of the present disclosure, there is provided a quantum device including a WTe2 layer having a first surface and a second surface opposite to the first surface, a first insulating layer provided on the first surface, a second insulating layer provided on the second surface, a first normal-conducting metal electrode, a second normal-conducting metal electrode, and a third normal-conducting metal electrode provided on the first insulating layer, a first control unit configured to control potentials of the first normal-conducting metal electrode, the second normal-conducting metal electrode, and the third normal-conducting metal electrode, a superconducting metal wiring provided on the second insulating layer and having a first end and a second end, and a second control unit configured to control a superconducting phase difference between the first end and the second end. In a plan view from a direction perpendicular to the first surface, the WTe2 layer has a first edge and a second edge that form a constriction portion, the constriction portion is provided between the first end and the second end, the first normal-conducting metal electrode overlaps a portion of the first edge that is separated from the constriction portion in one direction, the second normal-conducting metal electrode overlaps a portion of the first edge that is separated from the constriction portion in the other direction, and the third normal-conducting metal electrode overlaps a portion of the second edge that is separated from the constriction portion in one direction. **Advantages of the Invention**

[0008] According to the present disclosure, it can be stably manufactured. **Brief Description of the Drawings**

[0009]

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DETAILED DESCRIPTION OF THE INVENTION

[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 descriptions may be omitted. In the present disclosure, the X1-X2 direction, the Y1-Y2 direction, and the Z1-Z2 direction are taken as directions orthogonal to each other. A plane including the X1-X2 direction and the Y1-Y2 direction is referred to as an XY plane, a plane including the Y1-Y2 direction and the Z1-Z2 direction is referred to as a YZ plane, and a plane including the Z1-Z2 direction and the X1-X2 direction is referred to as a ZX plane. For convenience, the Z1-Z2 direction is taken as the vertical direction, the Z1 side is the upper side, and the Z2 side is the lower side. Further, a plan view means viewing an object from the Z1 or Z2 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. FIG. 1 is a schematic diagram showing the quantum device according to the first embodiment. FIG. 2 is a top view showing a part of the quantum device according to the first embodiment. FIG. 3 is a cross-sectional view showing the quantum device according to the first embodiment. In FIGS. 1 and 2, for convenience, the insulating layer is omitted. FIG. 3 corresponds to a cross-sectional view taken along line II-II in FIG. 2.

[0012] As shown in FIGS. 1 to 3, the quantum device 1 according to the first embodiment includes a substrate 91, an insulating layer 92, first normal-conducting metal electrodes 11 to 14, second normal-conducting metal electrodes 21 to 23, third normal-conducting metal electrodes 31 to 32, an insulating layer 61, a WTe2 layer 50, an insulating layer 62, and a superconducting metal loop 40. The quantum device 1 further includes a first control unit and a second control unit.

[0013] The insulating layer 92 is provided on the substrate 91. For example, the substrate 91 is a Si substrate, and the insulating layer 92 is a SiO2 layer. A laminate of the substrate 91 and the insulating layer 92 may be a substrate with an oxide layer.

[0014] The first normal-conducting metal electrodes 11 to 14, the second normal-conducting metal electrodes 21 to 23, and the third normal-conducting metal electrodes 31 to 32 are provided on the insulating layer 92. The first normal-conducting metal electrodes 11 to 14, the second normal-conducting metal electrodes 21 to 23, and the third normal-conducting metal electrodes 31 to 32 are, for example, Au electrodes or Pd electrodes. The thickness of the first normal-conducting metal electrodes 11 to 14, the second normal-conducting metal electrodes 21 to 23, and the third normal-conducting metal electrodes 31 to 32 is, for example, 10 nm or more and 30 nm or less. A Ti film with a thickness of several nm may be provided between the insulating layer 92 and the first normal-conducting metal electrodes 11 to 14, the second normal-conducting metal electrodes 21 to 23, and the third normal-conducting metal electrodes 31 to 32. The arrangement of the first normal-conducting metal electrodes 11 to 14, the second normal-conducting metal electrodes 21 to 23, and the third normal-conducting metal electrodes 31 to 32 will be described later.

[0015] The insulating layer 61 is provided on the insulating layer 92 so as to cover the first normal-conducting metal electrodes 11 to 14, the second normal-conducting metal electrodes 21 to 23, and the third normal-conducting metal electrodes 31 to 32. The insulating layer 61 is, for example, a hexagonal BN (h-BN) layer. The thickness of the insulating layer 61 is, for example, 30 nm. The insulating layer 61 is an example of the first insulating layer.

[0016] The WTe2 layer 50 is provided on the insulating layer 61. WTe2 is a layered material. The WTe2 layer 50 includes one or a plurality of WTe2s stacked on each other. When the WTe2 layer 50 is composed of one layer of WTe2, the WTe2 layer 50 has helical edge channels. When the WTe2 layer 50 is composed of a plurality of layers of WTe2, the WTe2 layer 50 has hinge channels.

[0017] The WTe2 layer 50 has a lower surface 50A and an upper surface 50B opposite to the lower surface 50A. The insulating layer 61 covers the lower surface 50A of the WTe2 layer 50. Also, the first normal-conducting metal electrodes 11 to 14, the second normal-conducting metal electrodes 21 to 23, and the third normal-conducting metal electrodes 31 to 32 are provided so as to cover the insulating layer 61 between them and the WTe2 layer 50. The lower surface 50A is an example of the first surface.

[0018] The WTe2 layer 50 has, for example, an octagonal planar shape in which two rectangles partially overlap. In plan view, the WTe2 layer 50 has sides 111 to 118 and vertices 121 to 128. The sides 111, 113, 115, and 117 are parallel to the X1-X2 direction, and the sides 112, 114, 116, and 118 are parallel to the Y1-Y2 direction.

[0019] Vertex 121 is the intersection of side 111 and side 112. Side 111 extends from vertex 121 towards the X2 side, and side 112 extends from vertex 121 towards the Y2 side. Vertex 122 is the intersection of side 112 and side 113. Side 112 extends from vertex 122 towards the Y1 side, and side 113 extends from vertex 122 towards the X1 side. Vertex 123 is the intersection of side 113 and side 114. Side 113 extends from vertex 123 towards the X2 side, and side 114 extends from vertex 123 towards the Y2 side. Vertex 124 is the intersection of side 114 and side 115. Side 114 extends from vertex 124 towards the Y1 side, and side 115 extends from vertex 124 towards the X2 side. Vertex 125 is the intersection of side 115 and side 116. Side 115 extends from vertex 125 towards the X1 side, and side 116 extends from vertex 125 towards the Y1 side. Vertex 126 is the intersection of side 116 and side 117. Side 116 extends from vertex 126 towards the Y2 side, and side 117 extends from vertex 126 towards the X2 side. Vertex 127 is the intersection of side 117 and side 118. Side 117 extends from vertex 127 towards the X1 side, and side 118 extends from vertex 127 towards the Y1 side. Vertex 128 is the intersection of side 118 and side 111. Side 118 extends from vertex 128 towards the Y2 side, and side 111 extends from vertex 128 towards the X1 side.

[0020] The distance between vertex 122 and vertex 126 is, for example, 50 nm or more and 500 nm or less, and the WTe2 layer 50 has a constricted planar shape in the vicinity of vertices 122 and 126. The WTe2 layer 50 has a first edge 51 including sides 111 to 113 and a second edge 52 including sides 115 to 116. The first edge 51 and the second edge 52 constitute a constricted portion 53 in the vicinity of vertices 122 and 126. The distance between vertex 122 and vertex 126 is preferably 100 nm or more and 450 nm or less, and more preferably 150 nm or more and 400 nm or less.

[0021] The first normal-conducting metal electrodes 11 to 14 overlap, in plan view, with the portions (sides 111 to 112) of the first edge 51 that are away from the constricted portion 53 in one direction. For example, the first normal-conducting metal electrode 11 overlaps with side 112, and the first normal-conducting metal electrodes 12 to 14 overlap with side 111. The first normal-conducting metal electrodes 12 to 14 are arranged in this order from vertex 121 toward vertex 128. The length of the first normal-conducting metal electrodes 11 to 14 in the direction along the first edge 51 is, for example, 100 nm or more and 500 nm or less, preferably 150 nm or more and 450 nm or less, and more preferably 200 nm or more and 400 nm or less. Also, the interval between the first normal-conducting metal electrodes 11 to 14 in the direction along the first edge 51 is, for example, 30 nm or more and 100 nm or less, preferably 40 nm or more and 90 nm or less, and more preferably 50 nm or more and 80 nm or less.

[0022] The second normal-conducting metal electrodes 21 to 23 overlap, in plan view, with the portion (side 113) of the first edge 51 that is away from the constricted portion 53 in the other direction. For example, the second normal-conducting metal electrodes 21 to 23 overlap with side 113. The second normal-conducting metal electrodes 21 to 23 are arranged in this order from vertex 122 toward vertex 123. The length of the second normal-conducting metal electrodes 21 to 23 in the direction along the first edge 51 is, for example, 100 nm or more and 500 nm or less, preferably 150 nm or more and 450 nm or less, and more preferably 200 nm or more and 400 nm or less. Also, the interval between the second normal-conducting metal electrodes 21 to 23 in the direction along the first edge 51 is, for example, 30 nm or more and 100 nm or less, preferably 40 nm or more and 90 nm or less, and more preferably 50 nm or more and 80 nm or less.

[0023] The third normal-conducting metal electrodes 31 to 32 overlap, in plan view, with portions (sides 115 to 116) of the second edge 52 that are separated from the constriction portion 53 in one direction. For example, the third normal-conducting metal electrode 31 overlaps with side 116, and the third normal-conducting metal electrode 32 overlaps with side 115. The length of the third normal-conducting metal electrodes 31 to 32 in the direction along the second edge 52 is, for example, 100 nm or more and 500 nm or less, preferably 150 nm or more and 450 nm or less, and more preferably 200 nm or more and 400 nm or less. Also, the interval between the third normal-conducting metal electrodes 31 to 32 in the direction along the second edge 52 is, for example, 30 nm or more and 100 nm or less, preferably 40 nm or more and 90 nm or less, and more preferably 50 nm or more and 80 nm or less.

[0024] The insulating layer 62 is provided on the insulating layer 92 so as to cover the WTe2 layer 50. The insulating layer 62 is, for example, an h-BN layer. The thickness of the insulating layer 62 is preferably 10 nm or less, more preferably 5 nm or less, and even more preferably 3 nm or less. The lower limit of the thickness of the insulating layer 62 is, for example, 1 nm. The insulating layer 62 covers the upper surface 50B of the WTe2 layer 50. The upper surface 50B is an example of the second surface. The insulating layer 62 is an example of the second insulating layer.

[0025] The superconducting metal loop 40 is provided on the insulating layer 62. The material of the superconducting metal loop 40 is, for example, Al or Nb. A slit 40S is formed in the superconducting metal loop 40, and the superconducting metal loop 40 includes a first end 40A and a second end 40B sandwiching the slit 40S therebetween. The slit 40S overlaps with the constriction portion 53 in plan view. Also, the superconducting metal loop 40 is provided so as to cover the insulating layer 62 between it and the WTe2 layer 50.

[0026] The first control unit includes a DC power source 71 individually connected to each of the first normal-conducting metal electrodes 11 to 14, the second normal-conducting metal electrodes 21 to 23, and the third normal-conducting metal electrodes 31 to 32, and a first control circuit 72 that controls the DC power source 71.

[0027] The second control unit includes an AC circuit 81 and a second control circuit 82 that controls the AC circuit 81. The AC circuit 81 includes an AC power supply 83 and an inductor 84 through which current flows from the AC power supply 83. The inductor 84 is disposed near the superconducting metal loop 40. The magnetic flux in the superconducting metal loop 40 changes due to the magnetic field formed by the inductor 84. That is, the second control unit controls the superconducting phase difference between the first end 40A and the second end 40B by changing the magnetic flux in the superconducting metal loop 40.

[0028] In the quantum device 1, a phase change between a topological insulator and a superconductor occurs in the WTe2 layer 50 according to the carrier concentration at an extremely low temperature of 4K or lower, for example, 1K or lower. For example, when a voltage equal to or higher than the threshold value is applied to the first normal-conducting metal electrode 11, carriers are induced in the vicinity of the first normal-conducting metal electrode 11 and the WTe2 layer 50 becomes a superconductor. On the other hand, when the application of a voltage equal to or higher than the threshold value stops, the WTe2 layer 50 becomes a topological insulator in the vicinity of the first normal-conducting metal electrode 11. Hereinafter, a state in which a voltage equal to or higher than the threshold value is applied to the normal-conducting metal electrode may be referred to as an on state, and a state in which a voltage equal to or higher than the threshold value is not applied may be referred to as an off state.

[0029] Furthermore, when there are a superconducting portion and a topological insulator portion in the WTe2 layer 50, Majorana particles are generated on the topological insulator side of the boundary between the superconducting portion and the topological insulator portion at the edge of the WTe2 layer 50. Therefore, the position of the Majorana particles can be adjusted by selecting a normal-conducting metal electrode that is turned on by the first control unit and moving the boundary between the superconducting portion and the topological insulator portion.

[0030] Furthermore, by controlling the superconducting phase difference between the first end 40A and the second end 40B by the second control unit, the positions can be exchanged between the Majorana particles on the first edge 51 and the Majorana particles on the second edge 52 in the vicinity of the constriction portion 53.

[0031] Next, an example of the control method of the quantum device 1 according to the first embodiment will be described. FIG. 4 is a timing chart showing an example of the control method of the quantum device 1 according to the first embodiment. FIGS. 5 to 12 are schematic diagrams showing changes in the states of Majorana particles. In this example, it is assumed that the first normal-conducting metal electrodes 13 to 14, the second normal-conducting metal electrodes 22 to 23, and the third normal-conducting metal electrode 31 are always in the on state under the control of the first control unit. FIG. 4 shows the voltage changes of the first normal-conducting metal electrodes 11 to 12, the second normal-conducting metal electrode 21, and the third normal-conducting metal electrode 32, and the change in the superconducting phase difference between the first terminal 40A and the second terminal 40B. The voltage V0 in FIG. 4 is less than the threshold value, and the voltage V1 is greater than or equal to the threshold value. In FIGS. 5 to 12, the electrodes in the on state are shown by thick lines. The ellipse enclosing the two Majorana particles in FIGS. 5 to 12 indicates that these two Majorana particles are coupled, and the dashed ellipse indicates that the coupling is weaker than that of the solid-line ellipse. Also, the dashed arrows in FIGS. 5 to 12 indicate the tunneling of Majorana particles, and the two-dot chain arrows indicate the movement of Majorana particles.

[0032] As described above, Majorana particles are generated at the edges of the WTe2 layer. Hereinafter, the position of Majorana particles may be described with reference to the normal-conducting metal electrodes. That is, the position of Majorana particles may be described based on a plan view.

[0033] In this example, as shown in FIG. 4, in the initial state at time t0, it is assumed that the first superconducting metal electrodes 11 to 12, the second superconducting metal electrode 21, and the third superconducting metal electrode 32 are in the off state under the control of the first control unit. In this case, the WTe2 layer 50 becomes a superconductor in the vicinity of the first superconducting metal electrodes 13 to 14, and Majorana particles are generated on the X2 side of the first superconducting metal electrode 14, and Majorana particles are also generated between the first superconducting metal electrode 13 and the first superconducting metal electrode 12. Further, the WTe2 layer 50 becomes a superconductor in the vicinity of the second superconducting metal electrodes 22 to 23, and Majorana particles are generated on the X1 side of the second superconducting metal electrode 23, and Majorana particles are also generated between the second superconducting metal electrode 21 and the second superconducting metal electrode 22. Furthermore, the WTe2 layer 50 becomes a superconductor in the vicinity of the third superconducting metal electrode 31, and Majorana particles are generated on the Y1 side of the third superconducting metal electrode 31, and Majorana particles are also generated between the third superconducting metal electrode 31 and the third superconducting metal electrode 32.

[0034] Hereinafter, as shown in FIG. 5, the Majorana particles generated between the first superconducting metal electrode 13 and the first superconducting metal electrode 12 are denoted as γ1, the Majorana particles generated between the second superconducting metal electrode 21 and the second superconducting metal electrode 22 are denoted as γ2, the Majorana particles generated on the Y1 side of the third superconducting metal electrode 31 are denoted as γ3, and the Majorana particles generated between the third superconducting metal electrode 31 and the third superconducting metal electrode 32 are denoted as γ4. Also, the Majorana particles generated on the X2 side of the first superconducting metal electrode 14 are denoted as γ5, and the Majorana particles generated on the X1 side of the second superconducting metal electrode 23 are denoted as γ6.

[0035] Also, as shown in FIG. 4, in the initial state, it is assumed that the superconducting phase difference between the first terminal 40A and the second terminal 40B is π rad by the second control unit.

[0036] In the above initial state, the Majorana particle γ3 and the Majorana particle γ4 are coupled. Hereinafter, in an example of this control method, the Majorana particle γ1 and the Majorana particle γ2 are moved clockwise so as not to cross each other, and their positions are exchanged.

[0037] As shown in FIG. 4, at time t0, the voltage applied to the second superconducting metal electrode 21 starts to increase, and at time t1, the second superconducting metal electrode 21 is turned on. As a result, the superconducting range of the WTe2 layer spreads on side 113, and as shown in FIG. 6, the Majorana particle γ2 moves to the X2 side of the second superconducting metal electrode 21. Also, at time t1, the voltage applied to the third superconducting metal electrode 32 starts to increase. As a result, the superconducting range of the WTe2 layer gradually spreads on side 115, and as shown in FIG. 6, the Majorana particle γ4 starts to move to the X1 side along the second edge 52, and the coupling between the Majorana particle γ3 and the Majorana particle γ4 gradually weakens. Further, at time t1, the superconducting phase difference starts to decrease. As a result, as shown in FIG. 6, the coupling between the Majorana particle γ2 and the Majorana particle γ3 gradually strengthens.

[0038] Thereafter, as shown in FIG. 4, at time t2, the third superconducting metal electrode 32 is turned on and the superconducting phase difference is set to 0 rad. As a result, as shown in FIG. 7, the Majorana particle γ2 moves to the X1 side of the third superconducting metal electrode 32 by tunneling. Also, the Majorana particle γ3 moves between the first superconducting metal electrode 11 and the second superconducting metal electrode 21 of the first edge 51 through the constriction portion 53, and the Majorana particle γ4 moves to the Y1 side of the third superconducting metal electrode 31.

[0039] Thereafter, as shown in FIG. 4, at time t3, the voltage applied to the first superconducting metal electrode 12 starts to increase. As a result, the superconducting range of the WTe2 layer gradually spreads on side 111, and the Majorana particle γ1 starts to move to the X1 side along the first edge 51.

[0040] Thereafter, as shown in FIG. 4, at time t4, the first superconducting metal electrode 12 is turned on. As a result, as shown in FIG. 8, the Majorana particle γ1 moves between the first superconducting metal electrode 11 and the first superconducting metal electrode 12. Also, at time t4, the voltage applied to the first superconducting metal electrode 11 starts to increase, and the voltage applied to the second superconducting metal electrode 21 starts to decrease. As a result, the superconducting range of the WTe2 layer gradually expands at the side 112, and the Majorana particle γ1 starts to move along the first edge 51 toward the Y2 side, while the superconducting range of the WTe2 layer gradually narrows at the side 113, and the Majorana particle γ3 starts to move along the first edge 51 toward the X1 side.

[0041] Thereafter, as shown in FIG. 4, at time t5, the first superconducting metal electrode 11 is turned on and the second superconducting metal electrode 21 is turned off. Since the Majorana particle γ3 is coupled to the Majorana particle γ4, as shown in FIG. 9, the Majorana particle γ1 moves between the second superconducting metal electrode 21 and the second superconducting metal electrode 22 by tunneling.

[0042] Thereafter, as shown in FIG. 4, at time t6, the voltage applied to the first superconducting metal electrode 11 and the voltage applied to the third superconducting metal electrode 32 start to decrease. As a result, the superconducting range of the WTe2 layer gradually narrows at the sides 112 and 115, and as shown in FIG. 10, the Majorana particle γ3 starts to move along the first edge 51 toward the Y1 side, and the Majorana particle γ2 starts to move along the second edge 52 toward the X2 side and the Y1 side. Also, at time t6, the superconducting phase difference starts to increase. As a result, as shown in FIG. 10, the coupling between the Majorana particle γ3 and the Majorana particle γ4 gradually weakens.

[0043] Thereafter, as shown in FIG. 4, at time t7, the first superconducting metal electrode 11 and the third superconducting metal electrode 32 are turned off, and the superconducting phase difference is set to π rad. As a result, as shown in FIG. 11, the Majorana particle γ2 moves between the first superconducting metal electrode 11 and the first superconducting metal electrode 12 by tunneling. Also, the Majorana particle γ4 moves to the Y2 side of the third superconducting metal electrode 31, and the Majorana particle γ3 moves to the Y1 side of the third superconducting metal electrode 31 of the second edge 52 through the constriction portion 53.

[0044] Also, at time t7, the voltage applied to the first superconducting metal electrode 12 starts to decrease, and at time t8, the first superconducting metal electrode 12 is turned on. As a result, the superconducting range of the WTe2 layer expands in the side 111, and as shown in FIG. 12, the Majorana particle γ2 moves between the first superconducting metal electrode 12 and the first superconducting metal electrode 13.

[0045] In this way, the Majorana particle γ1 and the Majorana particle γ2 can be moved clockwise so as not to cross each other, and their positions can be exchanged.

[0046] Thus, according to the quantum device 1 according to the first embodiment, the positions of the Majorana particles within the first edge 51 and within the second edge 52 can be controlled by the first control unit, and the tunneling of the Majorana particles between the first edge 51 and the second edge 52 can be controlled by the second control unit. That is, the control of the positions of the Majorana particles within the first edge 51 and within the second edge 52 and the control of the tunneling of the Majorana particles between the first edge 51 and the second edge 52 can be performed independently. Therefore, excellent controllability can be obtained.

[0047] In addition, the superconducting phase difference between the first end 40A and the second end 40B of the superconducting metal loop 40 can cause an interaction between the Majorana particles on the first edge 51 and the Majorana particles on the second edge 52. Therefore, the distance between the first edge 51 and the second edge 52 in the constriction portion 53 does not need to be reduced to such an extent that coupling due to the quantum tunneling effect occurs. The distance between the vertex 122 and the vertex 126 may be, for example, 50 nm or more. Accordingly, it is easy to form the WTe2 layer provided with the constriction portion 53, and the quantum device 1 can be stably manufactured.

[0048] Next, a method for manufacturing the quantum device 1 according to the first embodiment will be described. FIGS. 13 to 18 are top views showing the method for manufacturing the quantum device 1 according to the first embodiment. FIGS. 19 to 24 are cross-sectional views showing the method for manufacturing the quantum device 1 according to the first embodiment.

[0049] First, as shown in FIGS. 13 and 19, a substrate 91 having an insulating layer 92 formed on its upper surface is prepared. For example, the substrate 91 is a Si substrate, and the insulating layer 92 is a SiO2 layer. A laminate of the substrate 91 and the insulating layer 92 may be a substrate with an oxide layer. FIG. 19 corresponds to a cross-sectional view taken along line XIX-XIX in FIG. 13.

[0050] Next, as shown in FIGS. 14 and 20, first normal-conducting metal electrodes 11 to 14, second normal-conducting metal electrodes 21 to 23, and third normal-conducting metal electrodes 31 to 32 are formed on the insulating layer 92. The first normal-conducting metal electrodes 11 to 14, the second normal-conducting metal electrodes 21 to 23, and the third normal-conducting metal electrodes 31 to 32 are, for example, Au electrodes or Pd electrodes. The first normal-conducting metal electrodes 11 to 14, the second normal-conducting metal electrodes 21 to 23, and the third normal-conducting metal electrodes 31 to 32 can be formed, for example, by vapor deposition and lift-off methods. In order to improve the adhesion, a Ti film having a thickness of several nm may be formed between the insulating layer 92 and the first normal-conducting metal electrodes 11 to 14, the second normal-conducting metal electrodes 21 to 23, and the third normal-conducting metal electrodes 31 to 32. FIG. 20 corresponds to a cross-sectional view taken along line XX-XX in FIG. 14.

[0051] Thereafter, as shown in FIGS. 15 and 21, an insulating layer 61 is provided so as to cover the first normal-conducting metal electrodes 11 to 14, the second normal-conducting metal electrodes 21 to 23, and the third normal-conducting metal electrodes 31 to 32 on the insulating layer 92. The insulating layer 61 is, for example, an h-BN layer. FIG. 21 corresponds to a cross-sectional view taken along line XXI-XXI in FIG. 15.

[0052] Subsequently, a WTe2 layer is provided on the insulating layer 61. Then, by processing the WTe2 layer by lithography, a WTe2 layer having a first edge 51, a second edge 52, and a constriction portion 53 is formed as shown in FIGS. 16 and 22. FIG. 22 corresponds to a cross-sectional view taken along line XXII-XXII in FIG. 16.

[0053] Thereafter, as shown in FIGS. 17 and 23, an insulating layer 62 is provided so as to cover the WTe2 layer 50 on the insulating layer 92. The insulating layer 62 is, for example, an h-BN layer. FIG. 23 corresponds to a cross-sectional view taken along line XXIII-XXIII in FIG. 17.

[0054] After providing the insulating layer 62, a superconducting metal loop 40 is formed on the insulating layer 92 as shown in FIGS. 18 and 24. The material of the superconducting metal loop 40 is, for example, Al or Nb. The superconducting metal loop 40 can be formed, for example, by a vapor deposition method and a lift-off method.

[0055] Thereafter, although not shown, a first control unit and a second control unit are provided.

[0056] In this way, the quantum device 1 according to the first embodiment can be manufactured.

[0057] Note that the insulating layer 92 may be a laminate of a first h-BN layer and a second h-BN layer. In this case, after providing the WTe2 layer, the first h-BN layer is laminated without processing the WTe2 layer, and then the first h-BN layer and the WTe2 layer are processed to form the WTe2 layer 50, and then the second h-BN layer may be laminated so as to cover the WTe2 layer 50 and the first h-BN layer. In this case, it is easy to suppress the oxidation of the WTe2 layer 50.

[0058] In addition, in order to control the superconducting phase difference in the constriction portion 53 using the superconducting metal loop 40, it is preferable that the distance between the superconducting metal loop 40 and the WTe2 layer 50 is small. For this reason, before forming the superconducting metal loop 40, it is preferable to thin-film the portion of the insulating layer 62 where the superconducting metal loop 40 is to be formed by dry etching or the like until it has a thickness of about 1 nm to 3 nm, for example.

[0059] (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 second control unit. FIG. 25 is a schematic diagram showing a quantum device according to the second embodiment. FIG. 26 is a cross-sectional view showing a part of the quantum device according to the second embodiment. FIG. 26 corresponds to a cross-sectional view taken along line XXVI-XXVI in FIG. 25. In FIG. 25, the insulating layer is omitted for convenience.

[0060] As shown in FIGS. 25 and 26, in the quantum device 2 according to the second embodiment, the superconducting metal loop 40 includes a first loop portion 41 including a first end 40A, a second loop portion 42 including a second end 40B, and an aluminum oxide film 43 sandwiched between the first loop portion 41 and the second loop portion 42. The first loop portion 41 and the second loop portion 42 are Josephson-junctioned to each other via the aluminum oxide film 43. The second control unit further includes a DC power supply 85 connected between the first loop portion 41 and the second loop portion 42. The second control circuit 82 controls the DC power supply 85.

[0061] Other configurations are the same as those in the first embodiment.

[0062] In the quantum device 2, the second control unit can control the superconducting phase difference between the first end 40A and the second end 40B of the superconducting metal loop 40 by changing the potential difference between the first loop portion 41 and the second loop portion 42.

[0063] (Third Embodiment) Next, the third embodiment will be described. The third embodiment is mainly different from the second embodiment in terms of the arrangement of the superconducting metal loop 40. FIG. 27 is a schematic diagram showing a quantum device according to the third embodiment. In FIG. 27, for the sake of convenience, the insulating layer is omitted.

[0064] As shown in FIG. 27, in the quantum device 3 according to the third embodiment, in a plan view, the superconducting metal loop 40 is arranged so as not to overlap with any of the first normal-conducting metal electrodes 11 to 14, the second normal-conducting metal electrodes 21 to 23, and the third normal-conducting metal electrodes 31 to 32.

[0065] Other configurations are the same as those in the second embodiment.

[0066] According to the third embodiment, it is possible to make it difficult for an unintentional interaction to occur between the superconducting metal loop 40 and the first normal-conducting metal electrodes 11 to 14, the second normal-conducting metal electrodes 21 to 23, and the third normal-conducting metal electrodes 31 to 32.

[0067] Also, in the third embodiment, it is easy to make the insulating layer 62 thinner as a whole. For this reason, even without performing the process of thinning the insulating layer 62 as described above, it is possible to easily control the superconducting phase difference in the constriction portion 53 using the superconducting metal loop 40.

[0068] Note that the arrangement of the superconducting metal loop 40 in the third embodiment may be applied to the first embodiment.

[0069] The number of the first normal-conducting metal electrodes, the second normal-conducting metal electrodes, and the third normal-conducting metal electrodes is not limited, but it is preferably 2 or more for each. More first normal-conducting metal electrodes, second normal-conducting metal electrodes, and third normal-conducting metal electrodes may be provided. Also, the planar shape of the WTe2 layer is not limited to a shape in which two rectangles partially overlap. Further, the superconducting metal loop may be located on the substrate side with respect to the WTe2 layer, and the first normal-conducting metal electrodes, the second normal-conducting metal electrodes, and the third normal-conducting metal electrodes may be located on the side away from the WTe2 layer.

[0070] 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

[0071] 1, 2, 3: Quantum device 11, 12, 13, 14: First normal-conducting metal electrode 21, 22, 23: Second normal-conducting metal electrode 31, 32: Third normal-conducting metal electrode 40: Superconducting metal loop 40A: First end 40B: Second end 40S: Slit 41: First loop portion 42: Second loop portion 43: Aluminum oxide film 50: WTe2 layer 51: First edge 52: Second edge 53: Constriction portion 61, 62: Insulating layer 71: DC power supply 72: First control circuit 81: AC circuit 82: Second control circuit 85: DC power supply γ1, γ2, γ3, γ4, γ5, γ6: Majorana particles

Claims

1. A WTe layer having a first surface and a second surface opposite to the first surface ２ and, a first insulating layer provided on the first surface; a second insulating layer provided on the second surface; a first normal-conducting metal electrode, a second normal-conducting metal electrode, and a third normal-conducting metal electrode provided on the first insulating layer; a first control unit for controlling the potentials of the first normal-conducting metal electrode, the second normal-conducting metal electrode, and the third normal-conducting metal electrode; a superconducting metal wiring provided on the second insulating layer and having a first end and a second end; a second control unit for controlling the superconducting phase difference between the first end and the second end; characterized by comprising: in a plan view from a direction perpendicular to the first surface, The WT e ２ layer has a first edge and a second edge that form a constricted portion, the constriction portion is provided between the first end and the second end, the first normal-conducting metal electrode overlaps a portion of the first edge that is separated from the constriction portion in one direction, the second normal-conducting metal electrode overlaps a portion of the first edge that is separated from the constriction portion in the other direction, the third normal-conducting metal electrode overlaps a portion of the second edge that is separated from the constriction portion in one direction, a quantum device.

2. The superconducting metal wiring has a loop having a slit between the first end and the second end, and the second control unit controls the superconducting phase difference by changing the magnetic flux in the loop. The quantum device according to claim 1.

3. The superconducting metal wiring includes: a first loop portion including the first end; a second loop portion including the second end and Josephson-junctioned to the first loop portion; characterized by comprising: the second control unit controls the superconducting phase difference by changing the potential difference between the first loop portion and the second loop portion. The quantum device according to claim 1.

4. The quantum device according to any one of claims 1 to 3, characterized in that a plurality of the first normal-conducting metal electrodes overlap a portion of the first edge that is separated from the constriction portion in one direction.

5. The quantum device according to claim 4, characterized in that the distance in the direction along the first edge between adjacent first normal-conducting metal electrodes is 30 nm or more and 100 nm or less.

6. The quantum device according to claim 4 or 5, characterized in that a plurality of the second normal-conducting metal electrodes overlap a portion of the first edge that is separated from the constriction portion in the other direction.

7. The quantum device according to claim 6, characterized in that the distance in the direction along the first edge between adjacent second normal-conducting metal electrodes is 30 nm or more and 100 nm or less.

8. The quantum device according to any one of claims 1 to 7, characterized in that a plurality of the third superconducting metal electrodes overlap a portion of the second edge that is separated from the constriction portion in one direction.

9. The quantum device according to claim 8, characterized in that the distance in the direction along the second edge between adjacent third superconducting metal electrodes is 30 nm or more and 100 nm or less.

10. The quantum device according to any one of claims 1 to 9, characterized in that the length of the first superconducting metal electrode in the direction along the first edge is 100 nm or more and 500 nm or less.

11. The quantum device according to any one of claims 1 to 10, characterized in that the length of the second superconducting metal electrode in the direction along the first edge is 100 nm or more and 500 nm or less.

12. The quantum device according to any one of claims 1 to 11, characterized in that the length of the third superconducting metal electrode in the direction along the first edge is 100 nm or more and 500 nm or less.

13. The quantum device according to any one of claims 1 to 12, characterized in that the distance between the first edge and the second edge in the constriction portion is 50 nm or more and 500 nm or less.

14. A WTe layer having a first surface and a second surface opposite to the first surface ２ and a first insulating layer provided on the first surface, a second insulating layer provided on the second surface, a first superconducting metal electrode, a second superconducting metal electrode, and a third superconducting metal electrode provided on the first insulating layer, a superconducting metal wiring provided on the second insulating layer and having a first end and a second end, having, in a plan view from a direction perpendicular to the first surface, The aforesaid WTe ２ layer has a first edge and a second edge that form a constricted portion, the constriction portion is provided between the first end and the second end, the first superconducting metal electrode overlaps a portion of the first edge that is separated from the constriction portion in one direction, the second superconducting metal electrode overlaps a portion of the first edge that is separated from the constriction portion in the other direction, A control method for a quantum device, characterized in that the third superconducting metal electrode overlaps a portion of the second edge that is separated from the constriction portion in one direction, a step of controlling the potentials of the first superconducting metal electrode, the second superconducting metal electrode, and the third superconducting metal electrode, a step of controlling the superconducting phase difference between the first end and the second end, A control method for a quantum device, characterized by comprising the above.

15. The superconducting metal wiring has a loop having a slit between the first end and the second end, and the superconducting phase difference is controlled by changing the magnetic flux in the loop. The method for controlling a quantum device according to claim 14, characterized in that.

16. The superconducting metal wiring is a first loop portion including the first end, a second loop portion including the second end and Josephson-junctioned to the first loop portion, and has The superconducting phase difference is controlled by changing the potential difference between the first loop portion and the second loop portion. The method for controlling a quantum device according to claim 14, characterized in that.

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