Quantum apparatus and method for manufacturing a quantum apparatus

Abstract

This invention provides a topological quantum device and a method for manufacturing the same, in which an oxide film that suppresses the penetration of Cooper pairs from an S-wave superconductor into a two-dimensional topological insulator is substantially absent. [Solution] The quantum device 2 comprises a two-dimensional topological insulator 6, which is a single layer of tungsten ditelluride having a 1T'-type crystal structure and is disposed on or above the support 4, and a coating 8 covering the two-dimensional topological insulator, which includes an S-wave superconductor 10 having W atoms, Te atoms, and metal atoms. The S-wave superconductor is positioned so that Cooper pairs can penetrate from the S-wave superconductor into the edges of the two-dimensional topological insulator.

Description

[Technical Field]

[0001] This invention relates to a quantum device and a method for manufacturing a quantum device. [Background technology]

[0002] Majorana particles are unique particles that are themselves antiparticles. Recently, it has been proposed that quasiparticles with Majorana particle characteristics (hereinafter referred to as Majorana quasiparticles) can appear in solids. Following this proposal, research aimed at realizing Majorana quasiparticles is being actively conducted. The realization of Majorana quasiparticles is important not only for physics but also for the realization of quantum computers that are robust against disturbances (see, for example, Non-Patent Document 1).

[0003] One device attracting attention for generating Majorana quasiparticles is a device having a two-dimensional topological insulator, also known as a quantum spin Hall insulator (hereinafter referred to as a topological quantum device) (see, for example, Non-Patent Document 2). Majorana quasiparticles appear by joining a superconductor to the edge of a two-dimensional topological insulator. Quantum operations based on Majorana quasiparticles (i.e., quantum gate operations) can be realized by a qubit having multiple topological devices (hereinafter referred to as a Majorana qubit) (see, for example, Non-Patent Document 2).

[0004] Incidentally, it has been reported that when a Td-WTe2 / Pd contact is heat-treated at 180°C, a superconducting region is formed at the Td-WTe2 / Pd interface (for example, Non-Patent Document 3). Furthermore, techniques have been reported for reducing contact resistance by joining transition metal dichalcogenides (e.g., TiS2, MoS2) with dissimilar materials (e.g., other transition metal dichalcogenides, palladium, and bismuth) (see, for example, Patent Documents 1-4). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-79313 [Patent Document 2] International Publication No. 2021 / 002070 [Patent Document 3] U.S. Patent Application Publication No. 2019 / 0378715 [Patent Document 4] U.S. Patent Application Publication No. 2021 / 0359099 Specification [Non-patent literature]

[0006] [Non-Patent Document 1] Osamu Machida, et al., "Observation of a Zero-Energy State Suggesting a Majorana Bound State," Journal of the Physical Society of Japan, 2020, Vol. 75, No. 9, pp. 570-572. [Non-Patent Document 2] B van Heck, et al., “Minimal circuit for a flux-controlled Majorana qubit in a quantum spin-Hall insulator”, Phys. Scr. T164 (2015) 014007 [Non-Patent Document 3] Manabu Ohtomo, et al., “Josephson junctions of Weyl semimetal WTe2 induced by spontaneous nucleation of PdTe superconductor”, Applied Physics Express 15, The Japan Society pf Applied Physics, 2022, 075003 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Majorana quasiparticles appear at the edge of the range where a special type of superconductivity called topological superconductivity is realized (see, for example, Non-Patent Document 1).

[0008] Incidentally, it has been reported that one-dimensional chiral p-wave superconductivity is a form of topological superconductivity. One-dimensional chiral p-wave superconductivity is achieved when Cooper pairs from an S-wave superconductor penetrate a narrow region (i.e., the edge) along the outer periphery of a two-dimensional topological insulator.

[0009] A topological quantum device comprises a two-dimensional topological insulator, an S-wave superconductor in contact with a portion of the edge of the two-dimensional topological insulator, and ferromagnets positioned on either side of the S-wave superconductor. When the topological quantum device is cooled, Cooper pairs penetrate from the S-wave superconductor to the edge of the two-dimensional topological insulator. This penetration of Cooper pairs (i.e., proximity effect) then realizes one-dimensional chiral p-wave superconductivity (i.e., a type of topological superconductivity) at the edge of the two-dimensional topological insulator. This one-dimensional chiral p-wave superconductivity is terminated by the ferromagnets positioned on either side of the S-wave superconductor, resulting in the appearance of Majorana quasiparticle pairs.

[0010] Cooper pairs penetrating the edge of a two-dimensional topological insulator penetrate through the interface between the two-dimensional topological insulator and the S-wave superconductor (hereinafter referred to as the heterointerface). However, conventional topological quantum devices have a problem in that an oxide film that suppresses the proximity effect is formed between the two-dimensional topological insulator and the S-wave superconductor during the manufacturing process.

[0011] This is because, due to the structure of conventional topological quantum devices, at least one of the two-dimensional topological insulator and the S-wave superconductor is exposed to the atmosphere before a heterointerface can be formed. Therefore, the present invention aims to solve this problem. [Means for solving the problem]

[0012] In one embodiment, the quantum device includes a support, a two-dimensional topological insulator which is a monolayer of tungsten ditelluride having a 1T'-type crystal structure and is disposed on or above the support, and a film that covers the two-dimensional topological insulator and includes an S-wave superconductor having tungsten atoms, tellurium atoms, and metal atoms different from the tungsten atoms and the tellurium atoms. The S-wave superconductor is disposed so as to contact a part of an end portion of the two-dimensional topological insulator.

Advantages of the Invention

[0013] On one side, according to the present invention, a topological quantum device can be provided in which an oxide film that suppresses the intrusion of Cooper pairs (i.e., proximity effect) from an S-wave superconductor into a two-dimensional topological insulator is substantially absent.

Brief Description of the Drawings

[0014] [Figure 1] FIG. 1 is a plan view showing an example of a quantum device according to Embodiment 1. [Figure 2] FIG. 2 is a cross-sectional view of the quantum device 2 taken along line II-II shown in FIG. 1. [Figure 3] FIG. 3 is a plan view for explaining the physical properties of the two-dimensional topological insulator 6. [Figure 4] FIG. 4 is an energy band diagram of the two-dimensional topological insulator 6 at the end portion E. [Figure 5] FIG. 5 is a plan view showing an example of the positional relationship between the two-dimensional topological insulator 6 and the S-wave superconductor 10. [Figure 6] FIG. 6 is a process flow diagram showing an example of a method for manufacturing a quantum device according to Embodiment 1 (hereinafter referred to as the first manufacturing method). [Figure 7] FIG. 7 is a process flow diagram showing an example of the first step S1. [Figure 8] FIG. 8 is a cross-sectional view of the process of the first manufacturing method. [Figure 9] FIG. 9 is a cross-sectional view of the process of the first manufacturing method. [Figure 10]Figure 10 is a cross-sectional view of the first manufacturing method. [Figure 11] Figure 11 is a cross-sectional view of the first manufacturing method. [Figure 12] Figure 12 is a cross-sectional view of the first manufacturing method. [Figure 13] Figure 13 is a cross-sectional view of the first manufacturing method. [Figure 14] Figure 14 is a cross-sectional view of the first manufacturing method. [Figure 15] Figure 15 is a process flow diagram showing an example of the third step, S3. [Figure 16] Figure 16 is a plan view showing an example of the positional relationship between a single-layer 1T'-WTe2106 and a multi-layer WTe2109. [Figure 17] Figure 17 is a process flow diagram showing another example of a method for manufacturing a quantum device according to Embodiment 1 (hereinafter referred to as the second manufacturing method). [Figure 18] Figure 18 is a process flow diagram showing an example of the fifth step, S5. [Figure 19] Figure 19 is a cross-sectional view of the second manufacturing method. [Figure 20] Figure 20 is a cross-sectional view of the second manufacturing method. [Figure 21] Figure 21 is a cross-sectional view of the second manufacturing method. [Figure 22] Figure 22 is a cross-sectional view of the second manufacturing method. [Figure 23] Figure 23 is a cross-sectional view of the second manufacturing method. [Figure 24] Figure 24 is a plan view showing an example of the positional relationship between the single-layer 1T'-WTe2106 and the S-wave superconductor 210. [Figure 25] Figure 25 is a perspective view of a quantum device 302 having a support 4, a two-dimensional topological insulator 6 placed on the support 4, and an S-wave superconductor 310 covering a portion of the two-dimensional topological insulator 6. [Figure 26] Figure 26 is an example of a process cross-sectional view showing an example of a method for manufacturing a quantum device 302 by depositing an aluminum film. [Figure 27]Figure 27 is an example of a process cross-sectional view showing an example of a method for manufacturing a quantum device 302 by depositing an aluminum film. [Figure 28] Figure 28 is a perspective view of a quantum device 402 having a support 4, an S-wave superconductor 410 placed on the support 4, and a two-dimensional topological insulator 406 covering a portion of the S-wave superconductor 410. [Figure 29] Figure 29 is a plan view showing an example of a modified quantum apparatus 2 described with reference to Figures 1 and 2. [Figure 30] Figure 30 is a cross-sectional view along the line XXX-XXX in Figure 29. [Figure 31] Figure 31 is a plan view showing an example of another modified form of the quantum apparatus 2 described with reference to Figures 1 and 2. [Figure 32] Figure 32 is a cross-sectional view along the line XXXII-XXXII in Figure 31. [Figure 33] Figure 33 is a plan view showing an example of a quantum apparatus according to Embodiment 2. [Figure 34] Figure 34 is a cross-sectional view along the upper line XXXIV-XXXIV. [Figure 35] Figure 35 is a plan view showing an example of a quantum apparatus according to Embodiment 3. [Figure 36] Figure 36 is a cross-sectional view along the upper line XXXVI-XXXVI. [Figure 37] Figure 37 is an enlarged view of the area 660 enclosed by the dashed line in Figure 36. [Figure 38] Figure 38 is an enlarged view of the area 670 enclosed by the dashed line in Figure 37. [Figure 39] Figure 39 is an enlarged view of the area 672 enclosed by the dashed line in Figure 35. [Figure 40] Figure 40 is a process flow diagram showing an example of a manufacturing method for the quantum device 602 shown in Figure 35 (hereinafter referred to as the third manufacturing method). [Figure 41] Figure 41 is a cross-sectional view of the third manufacturing method. [Figure 42] Figure 42 is a cross-sectional view of the third manufacturing method. [Figure 43] Figure 43 is a cross-sectional view of the third manufacturing method. [Figure 44] Figure 44 is a cross-sectional view of the third manufacturing method. [Figure 45] Figure 45 is a cross-sectional view of the third manufacturing method. [Figure 46] Figure 46 is a cross-sectional view showing an example of a quantum device (hereinafter referred to as Modified Example 1) in which the first and second Josephson junctions have an insulator as an intermediate layer. [Figure 47] Figure 47 is an enlarged view of the area 860 enclosed by the dashed line in Figure 46. [Figure 48] Figure 48 is a process flow diagram showing an example of the manufacturing method for the modified example 1. [Figure 49] Figure 49 is a plan view of the vicinity of the first Josephson joint J1m in Modification Example 1. [Figure 50] Figure 50 is an enlarged view of the area 870 enclosed by the dashed line in Figure 49. [Figure 51] Figure 51 shows a cross-section of an example of a quantum device that does not have a normal conductor 668 and a metal film 834 (hereinafter referred to as Modified Example 2). [Figure 52] Figure 52 is a process flow diagram showing an example of the manufacturing method for the modified example 2. [Modes for carrying out the invention]

[0015] Embodiments of the present invention will be described below with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and their equivalents. Parts having the same structure are denoted by the same reference numerals even if the drawings are different, and their descriptions are omitted.

[0016] (Embodiment 1) (1) Structure Figure 1 is a plan view showing an example of a quantum device according to Embodiment 1 (hereinafter referred to as quantum device 2). Figure 2 is a cross-sectional view of quantum device 2 along the line II-II shown in Figure 1. Quantum device 2 includes a support 4, a two-dimensional topological insulator 6 placed on the support 4, and a coating 8 covering the two-dimensional topological insulator 6.

[0017] (1-1) Support 4 (see Figures 1 and 2) Support 4 is, for example, a silicon substrate.

[0018] The support 4 is not limited to a silicon substrate. The support 4 may be, for example, a sapphire substrate. Silicon substrates and sapphire substrates are highly reliable substrates used in the manufacture of semiconductor devices. However, the support 4 is not limited to substrates used in the manufacture of semiconductor devices. The support 4 may be, for example, a substrate having a silicon substrate and a silicon oxide film covering the silicon substrate.

[0019] (1-2) Two-dimensional topological insulator 6 (see Figures 1 and 2) The two-dimensional topological insulator 6 is a monolayer (hereinafter referred to as monolayer 1T'-WTe2) obtained from a single crystal of tungsten ditelluride (i.e., 1T'-WTe2) having a 1T'-type crystal structure. A monolayer is the thinnest layer that can be exfoliated from a single crystal of a layered material (e.g., 1T'-WTe2).

[0020] Layered materials are crystals composed of multiple stacked monolayers. Each monolayer within a layered material is bonded to another monolayer located perpendicular to it by weak bonding forces (e.g., van der Waals forces). A monolayer is a layer in a layered material in which atoms are periodically arranged only in the horizontal direction (i.e., the direction parallel to the monolayer) and the vertical direction (i.e., the direction perpendicular to the monolayer).

[0021] Figure 3 is a plan view illustrating the physical properties of the two-dimensional topological insulator 6. The two-dimensional topological insulator 6 has a bulk B (see Figure 3) with a forbidden band (i.e., a band gap) and an end E without a forbidden band. The end E is a part of the two-dimensional topological insulator 6 that includes the outer periphery of the two-dimensional topological insulator 6 and surrounds the center of the two-dimensional topological insulator 6 (i.e., bulk B).

[0022] Figure 4 is the energy band diagram of the two-dimensional topological insulator 6 at edge E. The horizontal axis represents the wave number, and the vertical axis represents the electron energy. Two energy bands (hereinafter referred to as edge bands) EB1 and EB2 are localized at edge E of the two-dimensional topological insulator 6. At edge E, as in bulk B, there is also a valence band VB and a conduction band CB. Since the two edge bands EB1 and EB2 each fill the space between the valence band VB and the conduction band CB, there is no band forbidden at edge E.

[0023] The spins of electrons belonging to edge bands EB1 and EB2 are oriented in specific directions. Specifically, the spins of electrons belonging to one edge band EB1 (referred to as the first energy band as appropriate) are oriented in one direction perpendicular to the two-dimensional topological insulator 6 (referred to as the first direction as appropriate). The spins of electrons belonging to the other edge band EB2 (referred to as the second energy band as appropriate) are oriented in the opposite direction to the above-mentioned direction (referred to as the second direction as appropriate). Therefore, if the spin of an electron belonging to edge band EB1 is up-spin, the spin of an electron belonging to edge band EB2 is down-spin.

[0024] The edge bands E1 and E2 are also one-dimensional bands localized at the edge E of the two-dimensional topological insulator 6. As is clear from the above explanation, the two-dimensional topological insulator 6 has spin-polarized one-dimensional bands. This is a special property of two-dimensional topological insulators.

[0025] (1-3) Film 8 The coating 8 (see Figures 1 and 2) comprises an S-wave superconductor 10 having tungsten atoms, tellurium atoms, and a metal atom (hereinafter referred to as the first metal atom), and a hexagonal boron nitride 12 in contact with the two-dimensional topological insulator 6 and the S-wave superconductor 10. The two-dimensional topological insulator 6 (see Figure 2) is placed between the coating 8 and the support 4. The first metal atom is a metal atom different from the tungsten atoms and tellurium atoms.

[0026] The S-wave superconductor 10 is a superconductor obtained, for example, by diffusing a first metal atom into tungsten ditelluride (i.e., WTe2). The first metal atom is preferably one of palladium, platinum, or niobium atoms. An S-wave superconductor is a superconductor in which Cooper pairs with a symmetry called S-waves appear when cooled below the critical temperature. Most superconductors, such as Al, are S-wave superconductors. Hexagonal boron nitride 12 is a layered material.

[0027] The thickness of the hexagonal boron nitride 12 is preferably 1 nm or more and 100 nm or less (see "(3-1-2) Second step S2"). More preferably, the thickness of the hexagonal boron nitride 12 is 10 nm or more and 20 nm or less.

[0028] Figure 5 is a plan view showing an example of the positional relationship between a two-dimensional topological insulator 6 (see Figure 1) and an S-wave superconductor 10. The two-dimensional topological insulator 6 is drawn with a solid line. The S-wave superconductor 10 is drawn with a dashed line.

[0029] The S-wave superconductor 10 is positioned at the end E (see Figure 3) of the two-dimensional topological insulator 6 so that Cooper pairs can penetrate from the S-wave superconductor 10. For example, the S-wave superconductor 10 is positioned so as to be in contact with a portion of the outer circumference 15 of the two-dimensional topological insulator 6 (see Figure 5).

[0030] More precisely, the S-wave superconductor 10 is in contact only with the first portion 14a of the outer circumference 15 and the second portion 14b of the outer circumference 15. The second portion 14b is a part of the outer circumference 15 that is in contact with both ends of the first portion 14a.

[0031] In this case, the S-wave superconductor 10 is in contact with a portion 16 of the two-dimensional topological insulator 6 (see Figure 2). On the other hand, the hexagonal boron nitride 12 is in contact with a portion 18 of the two-dimensional topological insulator 6 that is not covered by the S-wave superconductor 10.

[0032] As described later, the two-dimensional topological insulator 6 and the S-wave superconductor 10 (or its precursor) are materials that can be separated from a single crystal in a space where the atmosphere is removed (for example, inside a glove box filled with an inert gas) (see "(3) Manufacturing Method"). Furthermore, it is also possible to join the two-dimensional topological insulator 6 and the S-wave superconductor 10 (or its precursor) in the same space where the atmosphere is removed (see "(3) Manufacturing Method" again).

[0033] Therefore, according to Embodiment 1, a topological quantum device can be provided in which an oxide film that suppresses the penetration of Cooper pairs from the S-wave superconductor 10 into the two-dimensional topological insulator 6 is substantially absent.

[0034] (2) Operation When Cooper pairs enter a region containing a spin-polarized one-dimensional band, a superconducting gap opens in the spin-polarized one-dimensional band. This effectively realizes one-dimensional chiral p-wave superconductivity, a type of topological superconductivity.

[0035] The single-layer 1T'-WTe2 exhibits properties as a two-dimensional topological insulator below 100K. When the metal atom (i.e., the first metal atom) of the S-wave superconductor 10 is a palladium atom (i.e., a Pd atom), the critical temperature of the S-wave superconductor 10 is near 1.5K (see, for example, Non-Patent Document 3).

[0036] Therefore, when the quantum device 2 is cooled to, for example, below 1K, the single-layer 1T'-WTe2 exhibits the properties of a two-dimensional topological insulator. That is, a spin-polarized one-dimensional band appears at the edge E of the two-dimensional topological insulator 6. Furthermore, Cooper pairs are generated in the S-wave superconductor 10, and these Cooper pairs penetrate the edge E of the two-dimensional topological insulator 6.

[0037] Then, a superconducting gap opens in the spin-polarized one-dimensional band that appears at the edge E of the two-dimensional topological insulator 6. As a result, one-dimensional chiral p-wave superconductivity is effectively realized at the edge E of the two-dimensional topological insulator 6. In other words, by cooling the quantum device 2 to near absolute zero (for example, below 1K), one-dimensional chiral p-wave superconductivity, the stage on which Majorana quasiparticles appear, is realized.

[0038] Incidentally, the S-wave superconductor 10 is positioned, for example, so as to be in contact with a portion of the outer periphery 15 of the two-dimensional topological insulator 6 (see "(1-3) Coating 8"). This arrangement allows Cooper pairs to penetrate the edges E of the two-dimensional topological insulator 6.

[0039] However, under certain conditions, the S-wave superconductor 10 does not need to be in contact with the outer periphery of the two-dimensional topological insulator 6. For example, an extremely thin dissimilar material (e.g., an oxide film of 0.5 nm or less) may be interposed between the outer periphery of the two-dimensional topological insulator 6 and the S-wave superconductor 10. Alternatively, the S-wave superconductor 10 may be in contact with the vicinity of the outer periphery of the two-dimensional topological insulator 6, rather than the outer periphery of the two-dimensional topological insulator 6. Even in these cases, penetration into the end E of the Cooper pair is possible.

[0040] (3) Manufacturing method (3-1) First manufacturing method Figure 6 is a process flow diagram showing an example of a method for manufacturing a quantum device according to Embodiment 1 (hereinafter referred to as the first manufacturing method). Figures 8 to 14 are cross-sectional views of the first manufacturing method. As shown in Figure 6, the first manufacturing method comprises a first step S1, a second step S2, and a third step S3.

[0041] (3-1-1) First step S1 (See Figures 8-12) First, the upper surface s3 (referred to as the third surface) of a single layer 106 (referred to as single layer 1T'-WTe2 or first single layer) separated from a single crystal of tungsten ditelluride having a 1T'-type crystal structure (referred to as the first single crystal) is covered with a coating 108a (see Figure 12(c)). The coating 108a (hereinafter referred to as the first coating) has a layered material 109 (hereinafter referred to as multilayer WTe2) separated from a single crystal of tungsten ditelluride (referred to as the second single crystal) and hexagonal boron nitride 112 in contact with the layered material 109.

[0042] The separation of single-layer 1T'-WTe2106 is performed in an air-free space (e.g., inside a glove box filled with an inert gas). Similarly, the separation of multi-layer WTe2109 is performed in an air-free space.

[0043] Single-layer 1T'-WTe2106 is an example of a two-dimensional topological insulator 6, as described with reference to Figures 1 and 2. Hexagonal boron nitride 112 is an example of hexagonal boron nitride 12, as described with reference to Figures 1 and 2.

[0044] Figure 7 is a process flow diagram showing an example of the first process S1. The first process S1 shown in Figure 7 has steps S1a, S1b, and S1c.

[0045] (a) Step S1a (see Figure 8) First, a PDMS / PVC stamp 120 (see Figure 8) is formed.

[0046] Specifically, first, two chemical solutions (a resin called the main component and its curing agent) for forming polydimethylsiloxane (PDMS) are mixed to create a mixture. This mixture is then dropped onto the surface of a glass slide 124.

[0047] Next, rotate the glass slide 124 so that the side with the mixture is facing downwards. With the side with the mixture facing downwards, wait until the mixture on the glass slide 124 hardens. Then, a transparent, highly elastic, dome-shaped polydimethylsiloxane 122 (hereinafter referred to as the PDMS dome) is formed.

[0048] Finally, a polyvinyl chloride (PVC) film (not shown) is attached to the PDMS dome 122. This completes the PDMS / PVC stamp 120.

[0049] Instead of polyvinyl chloride film, a polycarbonate film may be attached to the PDMS dome 122. Furthermore, instead of the PDMS dome 122, a dome-shaped acrylic resin may be formed.

[0050] (b) Step S1b (see Figure 9) —Separation of hexagonal boron nitride 112— Next, hexagonal boron nitride 112 in flake form is separated (e.g., exfoliated) from the hexagonal boron nitride single crystal and attached to the first substrate 130a (see Figure 9(a)). Then, the first substrate 130a with the attached hexagonal boron nitride 112 is placed in a glove box filled with an inert gas (hereinafter referred to as the first glove box). The inert gas is, for example, argon (the same applies hereinafter). The separation of hexagonal boron nitride 112 and its subsequent attachment to the first substrate 130a may be carried out inside the first glove box filled with an inert gas.

[0051] The first substrate 130a is a substrate having a silicon substrate 126a and an SiO2 film 128a covering the surface of the silicon substrate 126a (the same applies to the second substrate 130b and the third substrate 130c, which will be described later). The separation of hexagonal boron nitride 112 and its subsequent attachment to the first substrate 130a are performed by the adhesive tape method.

[0052] The adhesive tape method is a method for obtaining thin slices of a layered material from a single crystal of that material using adhesive tape (see, for example, Non-Patent Document 3). First, separate adhesive tapes are attached to the front and back surfaces of the single crystal of the layered material. Next, the layered material is cleaved by pulling these adhesive tapes apart. Furthermore, the layered material, which has been thinned by cleavage, is cleaved again using adhesive tape. By repeating this re-cleaving, an extremely thin layered material (i.e., a thin slice) is obtained. At this stage, the thin slice of the layered material remains attached to the adhesive tape.

[0053] Next, the thin piece attached to the adhesive tape is pressed against the substrate (for example, the first substrate 130a). Finally, the adhesive tape with the piece attached is pulled away from the substrate. At this time, a final cleavage occurs, and an even thinner piece is left behind on the substrate.

[0054] During the repeated cleavage of the layered material, numerous thin pieces of varying thicknesses adhere to the adhesive tape. Therefore, the thickness of the thin pieces left on the substrate varies. From these pieces, a thin piece with an appropriate thickness is selected. This selected piece is the product of the adhesive tape method (e.g., hexagonal boron nitride 112). The appropriate thickness for hexagonal boron nitride 112 is described later in "(3-1-2) Second Step S2". The same applies to the appropriate thickness for the multilayer WTe2109, which will be described later.

[0055] The selection of thin sections is based, for example, on their transparency. Transparency increases as the thin section becomes thinner. Therefore, selecting a thin section of appropriate thickness is straightforward based on its transparency.

[0056] The transparency of a thin section can be easily determined by observing it under an optical microscope. The selection of the thin section may also be based on the film thickness measured using an atomic force microscope.

[0057] —Isolation of multilayer WTe2109— Furthermore, within the first glove box filled with inert gas, the multilayer WTe2109 is separated from the tungsten ditelluride single crystal (i.e., the second single crystal) and deposited onto the second substrate 130b (see Figure 9(b)). The separation of the multilayer WTe2109 and its subsequent deposition onto the second substrate 130b are performed by the adhesive tape method.

[0058] The second single crystal is, for example, tungsten ditelluride having a Td-type crystal structure. The second single crystal may also be a single crystal of tungsten ditelluride having a crystal structure other than Td-type (for example, 1T-type or 1T'-type).

[0059] Needless to say, the separation process of the multilayer WTe2109 is carried out inside the first glove box, but the operation of the equipment used in the process is performed by workers outside the first glove box (the same applies hereafter).

[0060] —Separation of single-layer 1T'-WTe2106— Furthermore, within the first glove box filled with inert gas, a single layer of 1T'-WTe2106 is separated from a single crystal of tungsten ditelluride having a 1T'-type crystal structure (i.e., the first single crystal) and attached to the third substrate 130c (see Figure 9(c)). The separation of the single layer of 1T'-WTe2106 and its subsequent attachment to the third substrate 130c are performed by the adhesive tape method.

[0061] Since the single-layer 1T'-WTe2106 has high transparency, it is only about 2% darker than the surface of the third substrate 130c. On the other hand, the thin films other than single-layer 1T'-WTe2106 are at least 4-6% darker than the third substrate 130c. Therefore, it is easy to select single-layer 1T'-WTe2106 from among the many thin films attached to the third substrate 130c. The selection of single-layer 1T'-WTe2106 may also be based on the measured thickness of the thin film. The thickness of single-layer 1T'-WTe2 is 0.7 nm.

[0062] (c) Step S1c (See Figures 10-12) Finally, using the PDMS / PVC stamp 120 (see Figure 10(a)), the multilayer WTe2109 (see Figure 9(b)) and the single-layer 1T'-WTe2106 (see Figure 9(c)) are attached to the hexagonal boron nitride 112 (see Figure 9(a)) in that order. Step S1c is performed inside the first glove box where the first to third substrates 130a, 130b, and 130c are stored.

[0063] Specifically, first, the first substrate 130a (see Figure 10(a)) to which hexagonal boron nitride 112 is attached is heated to 65-75°C, for example, on a hot plate (not shown), inside a first glove box filled with inert gas. As a result, the hexagonal boron nitride 112 is also heated to 65-75°C.

[0064] Next, the PDMS / PVC stamp 120 is pressed against the heated hexagonal boron nitride 112 (see Figure 10(b)). This pressing is continued for a while to allow the hexagonal boron nitride 112 to adhere to the PDMS / PVC stamp 120. As mentioned above, polyvinyl chloride (not shown) is attached to the PDMS dome 122 (see Figure 10(a)). The hexagonal boron nitride 112 adheres to this polyvinyl chloride.

[0065] When polyvinyl chloride is heated, it becomes more likely to adhere to other substances. When the PDMS / PVC stamp 120 is pressed against heated hexagonal boron nitride 112, the polyvinyl chloride attached to the PDMS dome 122 is also heated. As a result, the hexagonal boron nitride 112 adheres to the heated polyvinyl chloride. Consequently, the hexagonal boron nitride 112 adheres to the PDMS / PVC stamp 120.

[0066] Subsequently, the PDMS / PVC stamp 120 is pulled away from the first substrate 130a. The hexagonal boron nitride 112 remains attached to the PDMS / PVC stamp 120 and is peeled off from the first substrate 130a (see Figure 10(c)).

[0067] Next, the second substrate 130b (see Figure 11(a)) to which the multilayer WTe2109 is attached is heated to 65-75°C, for example, on a hot plate (not shown). This heating also heats the multilayer WTe2109 to 65-75°C.

[0068] Next, the PDMS / PVC stamp 120 is pressed against the heated multilayer WTe2109 so that the hexagonal boron nitride 112 is in contact with a portion of the multilayer WTe2109 (see Figure 11(b)). This pressing is continued for a while to allow the multilayer WTe2109 to adhere to the PDMS / PVC stamp 120.

[0069] Thin pieces separated from single crystals of layered materials have extremely flat surfaces. When such thin pieces are brought into contact with each other, they adhere to one another. Since hexagonal boron nitride 112 and multilayer WTe2109 are thin pieces separated from single crystals of layered materials, multilayer WTe2109 adheres not only to the PDMS / PVC stamp 120 but also to the hexagonal boron nitride 112 (and so on).

[0070] Subsequently, the PDMS / PVC stamp 120 is peeled away from the second substrate 130b. As a result, the multilayer WTe2109 is peeled off from the second substrate 130b while still adhering to the PDMS / PVC stamp 120 and the hexagonal boron nitride 112 (see Figure 11(c)). Through these steps, a first coating 108a is formed, having the multilayer WTe2109 and the hexagonal boron nitride 112 in contact with the multilayer WTe2109. At this point, the first coating 108a is adhering to the PDMS / PVC stamp 120.

[0071] Next, the third substrate 130c (see Figure 12(a)) to which the single-layer 1T'-WTe2106 is attached is heated to 65-75°C, for example, on a hot plate (not shown). This heating also heats the single-layer 1T'-WTe2106 to 65-75°C.

[0072] Next, the first coating 108a attached to the PDMS / PVC stamp 120 is pressed against the heated single layer 1T'-WTe2106 (see Figure 12(b)). This pressing is continued for a while to allow the single layer 1T'-WTe2106 to adhere to the first coating 108a. Then, the PDMS / PVC stamp 120 is pulled away from the third substrate 130c. As a result, the single layer 1T'-WTe2106 is peeled off from the third substrate 130c while still attached to the first coating 108a (see Figure 12(c)).

[0073] Through the steps described so far, the hexagonal boron nitride 112 is coated with the multilayer WTe2109 and the single layer 1T'-WTe2106 in that order. As a result, the upper surface s3 of the single layer 1T'-WTe2106 is covered with the first coating 108a so that the hexagonal boron nitride 112 is in contact with the upper surface s3 of the single layer 1T'-WTe2106 (see Figure 12(c)). This coating is carried out so that the multilayer WTe2109 is in contact with a portion of the outer periphery of the single layer 1T'-WTe2106.

[0074] Figure 16 is a plan view showing an example of the positional relationship between a single layer 1T'-WTe2106 and a multilayer WTe2109. The single layer 1T'-WTe2106 is drawn with a solid line. The multilayer WTe2109 is drawn with a dashed line.

[0075] As shown in Figure 16, in the first step S1, the upper surface s3 of the single layer 1T'-WTe2106 (see Figure 12(c)) is covered with the first coating 108a so that the multilayer WTe2109 is in contact with a portion 114c (hereinafter referred to as the third portion) of the outer circumference 115 of the single layer 1T'-WTe2106.

[0076] More precisely, the upper surface s3 is covered with the first coating 108a such that the multilayer WTe2109 is in contact only with the third portion 114c of the outer circumference 115 of the single layer 1T'-WTe2106, and only with the third portion 114c of the fourth portion 114d, which is a part of the outer circumference 115 and is in contact with both ends of the third portion 114c.

[0077] The third portion 114c of the outer perimeter 115 of the single-layer 1T'-WTe2106 is an example of the first portion 14a (see Figure 5) of the outer perimeter of the two-dimensional topological insulator 6. The fourth portion 114d of the outer perimeter 115 is an example of the second portion 14b of the outer perimeter of the two-dimensional topological insulator 6.

[0078] (3-1-2) Second process S2 (see Figure 13) After the first step S1 (see Figure 6), the single layer 1T'-WTe2106 and the first coating 108a are attached to the support 104 such that the lower surface s4 of the single layer 1T'-WTe2106 is positioned between the upper surface s3 of the single layer 1T'-WTe2106 and the support 104 (see Figure 13(c)). The lower surface s4 (referred to as the fourth surface as appropriate) is a surface of the single layer 1T'-WTe2106 that extends along the upper surface s3 of the single layer 1T'-WTe2106 (i.e., the third surface).

[0079] The second step S2 is also carried out in the first glove box, following step S1c of the first step S1. The support 104 is an example of the support 4 described with reference to Figures 1 and 2. The support 104 is, for example, a silicon substrate.

[0080] As described above, in the first step S1, the single-layer 1T'-WTe2106 is separated from the first single crystal (i.e., the single crystal of 1T'-WTe2) in a space where the atmosphere has been removed (see "(b) Step S1b"). The single-layer 1T'-WTe2106 is then placed in a space where the atmosphere has been removed (for example, inside a first glove box filled with inert gas) until the second step S2 is completed.

[0081] Similarly, in the first step S1, the multilayer WTe2109 is separated from the second single crystal (i.e., the single crystal of WTe2) in an air-free space (see "(b) step S1b"). The multilayer WTe2109 is then left in an air-free space until the second step S2 is completed.

[0082] Specifically, first, the support 104 is heated to 125-135°C in a first glove box filled with inert gas, for example, on a hot plate (not shown) (see Figure 13(a)). At this point, the first coating 108a is still attached to the polyvinyl chloride (not shown) on the DMS / PVC stamp 120 (see Figure 13(a)). Furthermore, the single layer 1T'-WTe2106 is attached to the first coating 108a.

[0083] Next, the first coating 108a attached to the PDMS / PVC stamp 120 and the single layer 1T'-WTe2106 are pressed against the heated support 104 (see Figure 13(b)). This pressing is continued for a while.

[0084] As a result, the polyvinyl chloride in the PDMS / PVC stamp 120 is heated to 125-135°C. Consequently, the adhesive strength of the polyvinyl chloride decreases. The adhesive strength of polyvinyl chloride increases at around 70°C and decreases around 130°C.

[0085] Subsequently, the PDMS / PVC stamp 120 is pulled away from the support 104. As a result, the single layer 1T'-WTe2106 and the first coating 108a are left behind on the support 104 (see Figure 13(c)). That is, the single layer 1T'-WTe2106 and the first coating 108a adhere to the support 104 such that the lower surface s4 of the single layer 1T'-WTe2106 is positioned between the upper surface s3 of the single layer 1T'-WTe2106 and the support 104.

[0086] The film thickness of hexagonal boron nitride 112 (see Figure 13(c)) is preferably 1 to 100 nm. More preferably, the film thickness of hexagonal boron nitride 112 is 10 to 20 nm. The number of single layers n in the multilayer WTe2109 is preferably 3 to 10 (film thickness 2 to 7 nm). More preferably, the number of single layers n in the multilayer WTe2109 is 4 to 9. Most preferably, the number of single layers n in the multilayer WTe2109 is 5 to 8.

[0087] If the film thickness of the hexagonal boron nitride 112 is 100 nm or less, and the number of single layers n in the multilayer WTe2109 is 10 or less, the hexagonal boron nitride 112 and the multilayer WTe2109 will bend sufficiently and adhere closely to the support 104. Furthermore, if the film thickness of the hexagonal boron nitride 112 is 1 nm or more, and the number of single layers n in the multilayer WTe2109 is 3 or more, the hexagonal boron nitride 112 and the multilayer WTe2109 will be able to reliably block the atmosphere.

[0088] Therefore, as long as the film thickness of hexagonal boron nitride 112 and the number of layers of the multilayer WTe2109 are within the range described above, the single-layer 1T'-WTe2106 is reliably sealed by the first coating 108a and the support 104. That is, the single-layer 1T'-WTe2106 is reliably isolated from the atmosphere surrounding it. The same is true even after the multilayer WTe2109 is transformed into an S-wave superconductor 110 (see Figure 14(c)) by the third step S3.

[0089] If the hexagonal boron nitride 112 is too thick, a gap will form between the hexagonal boron nitride 112 and the support 104, and the single-layer 1T'-WTe2106 will not be sealed. The same applies if the multilayer WTe2109 is too thick.

[0090] The single layer 1T'-WTe2106 separated from the first single crystal is a bare single layer. Therefore, when the single layer 1T'-WTe2106 is exposed to the atmosphere, the entire layer is oxidized by the oxygen and moisture in the atmosphere. However, through the processes up to this point, the single layer 1T'-WTe2106 is sealed by the first coating 108a and the support 104. For this reason, even if the support 104 to which the single layer 1T'-WTe2106 is attached is removed to the atmosphere after the second step S2, the single layer 1T'-WTe2106 is hardly oxidized.

[0091] (3-1-3) Third process S3 (see Figure 14) After the second step S2, metal atoms different from tungsten atoms and tellurium atoms (referred to as second metal atoms as appropriate) are diffused into the multilayer WTe2109 to form an S-wave superconductor 110 having tungsten atoms, tellurium atoms and second metal atoms (see Figure 14(c)).

[0092] The second metal atoms that diffuse into the multilayer WTe2109 are atoms of the same element as the first metal atoms present in the S-wave superconductor 10 (see Figures 1 and 2). In other words, the first metal atom is an atom of a specific metal element (e.g., palladium), and the second metal atom is also an atom of this specific metal element (e.g., palladium) (and so on).

[0093] Therefore, the second metal atom is preferably one of palladium, platinum, or niobium. The S-wave superconductor 110 is an example of the S-wave superconductor 10 described with reference to Figures 1 and 2.

[0094] Figure 15 is a process flow diagram showing an example of the third process S3 (see Figure 6). A specific example of the third process S3 will be described below based on Figures 14 and 15. The third process S3 includes a first sub-process SS1 and a second sub-process SS2 (see Figure 15).

[0095] (a) First sub-process SS1 (see Figures 14(a) and (b)) First, a metal 134 containing a second metal atom (see Figure 14(b)) is placed in the exposed portion 132 of the multilayer WTe2109 (see Figure 14(a)) (first sub-step SS1).

[0096] Specifically, first, the support 104 (see Figure 14(a)) to which the first coating 108a and the single layer 1T'-WTe2106 are attached is removed from the first glove box. Then, a photoresist film (not shown) having an opening is formed on the exposed portion 132 (hereinafter referred to as the exposed portion) of the multilayer WTe2109.

[0097] A metal film, for example, containing palladium atoms, is deposited on this photoresist film (hereinafter referred to as the first photoresist film) and the exposed portion 132 using a vacuum deposition apparatus. Next, the first photoresist film is removed using a remover or the like. As a result, the metal film deposited on the first photoresist film is removed together with the photoresist film, leaving behind a film-like metal 134 (hereinafter referred to as the metal film 134) deposited on the exposed portion 132 (see Figure 14(b)). In other words, the metal film 134 is placed on the exposed portion 132 by, for example, the lift-off of the metal film containing palladium atoms.

[0098] In the example shown in Figure 14(b), the metal film 134 covers only the top surface (i.e., the exposed portion 132) of the multilayer WTe2109, and does not cover the side surface 133 of the multilayer WTe2109 (see Figure 14(a)). However, the metal film 134 may cover not only the top surface of the multilayer WTe2109 but also the side surface 133 of the multilayer WTe2109. This side surface 133 is also one of the "exposed portions of the multilayer WTe2109".

[0099] (b) Second sub-process SS2 (see Figure 14(c)) Next, the metal film 134 and the multilayer WDe2109 are heated to diffuse the second metal atoms into the multilayer WDe2109. Specifically, for example, the support 104 to which the multilayer WDe2109 is attached is heated by a hot plate in a glove box filled with an inert gas.

[0100] As a result, an S-wave superconductor 110 having tungsten atoms, tellurium atoms, and a second metal atom (for example, a palladium atom) is formed (see Figure 14(c)). Thus, a quantum device 102a having a coating 108 containing the S-wave superconductor 110 and a single layer 1T'-WTe2106 is completed (see Figure 14(c)). Quantum device 102a is an example of quantum device 2 described with reference to Figures 1 and 2.

[0101] When the second metal atom diffuses into the multilayer WTe2109, the multilayer WTe2109 transforms into an S-wave superconductor 110 (see Figure 14(c)) having tungsten atoms, tellurium atoms, and the second metal atom. As a result, the first coating 108a (see Figure 14(a)) having the multilayer WTe2109 transforms into a coating 108 having the S-wave superconductor 110. Coating 108 (see Figure 14(c)) is an example of coating 8 described with reference to Figures 1 and 2. The S-wave superconductor 110 is an example of S-wave superconductor 10 described with reference to Figures 1 and 2.

[0102] The composition of the S-wave superconductor 110 obtained by the diffusion of the second metal atom may be spatially non-uniform. For example, if the metal film 134 is a palladium film, the area near the metal film 134 will be PdTe, and the area away from the metal film 134 will be a mixed crystal of palladium (i.e., Pd) and WTe2 (i.e., Pd x W 1-x This becomes Te2).

[0103] When the second metal atom is a palladium atom, the heating temperature of the metal film 134 and the multilayer WDe2109 is preferably 150°C to 300°C. More preferably, the heating temperature is 200°C to 250°C.

[0104] In the first sub-process SS1, the support 104 is first removed from the first glove box filled with inert gas. The multilayer WTe2109 is then exposed to the atmosphere, and the exposed portion 132 of the multilayer WTe2109 (more precisely, the exposed portion 132 and the exposed side surface 133) is oxidized. However, the thickness of the region oxidized by the atmosphere is at most 1-2 nm from the surface of the multilayer WTe2109 (i.e., the thickness of two single layers). The second metal atoms pass through the oxide film formed in this region, converting the multilayer WTe2109 into a superconductor.

[0105] The heating temperatures mentioned above (i.e., 150°C to 300°C) are sufficiently high for the second metal atoms to pass through the oxide film covering the multilayer WTe2109 and reach the multilayer WTe2109. On the other hand, within the heating temperature range mentioned above, it is virtually impossible for the second metal atoms to pass through the multilayer WTe2109 and reach the monolayer 1T'-WTe2106. In other words, the monolayer 1T'-WTe2106 will not be altered by the diffusion of the second metal atoms.

[0106] The thickness of the metal film 134 is preferably 1 nm to 4 nm (for example, 2 nm). If the thickness of the metal film 134 is within this range and the number of single layers in the multilayer WTe2109 is 3 to 10, the second metal atoms (for example, palladium atoms) will diffuse into the multilayer WTe2109 without excess or deficiency. The above range for the number of single layers in the multilayer WTe2109 (i.e., 3 to 10) is the preferred range for the number of single layers described in "(3-1-2) Second step S2".

[0107] In the first manufacturing method described with reference to Figures 6-14, the second metal atoms diffuse from the metal film 134 deposited on the upper surface of the multilayer WTe2109. However, the second metal atoms may also diffuse from a metal film (e.g., a normal conductor) in contact with the lower surface of the multilayer WTe2109 (see Embodiment 3).

[0108] (3-1-4) Advantages of the first manufacturing method —First Advantage— When the monolayer 1T'-WTe2106 separated from the first single crystal is exposed to the atmosphere, the entire monolayer is oxidized and becomes a simple insulator rather than a two-dimensional topological insulator.

[0109] According to the first manufacturing method, the single-layer 1T'-WTe2106 is separated from the first single crystal in a space where the atmosphere is removed, and covered by the first coating 108a in the same space (see Figure 13(c)). Therefore, according to the first manufacturing method, a quantum device 2 having substantially unoxidized single-layer 1T'-WTe2106 (i.e., a two-dimensional topological insulator 6) can be provided. In the following explanation, this advantage will be referred to as the first advantage.

[0110] Furthermore, hexagonal boron nitride is virtually impermeable to oxygen and water molecules. As shown in Figure 14(c), the two-dimensional topological insulator 106 is placed between the coating 108 having hexagonal boron nitride 112 and the support 104, so even if the quantum device 102a is taken out into the atmosphere, the two-dimensional topological insulator 106 is hardly oxidized.

[0111] —Second Advantage— According to the first manufacturing method, the single-layer 1T'-WTe2106 is not exposed to the atmosphere. However, if the lower surface BS1 of the multilayer WTe2109 (see Figure 13(a)) (i.e., the surface in contact with the single-layer 1T'-WTe2106) is oxidized, an oxide film will be interposed between the single-layer 1T'-WTe2106 and the multilayer WTe2109. Such an oxide film makes it difficult for Cooper pairs to penetrate from the S-wave superconductor 110 formed from the multilayer WTe2109 to the single-layer 1T'-WTe2106 (i.e., the two-dimensional topological insulator 6).

[0112] However, according to the first manufacturing method, the multilayer WTe2109 is separated from the second single crystal in a space where the atmosphere is removed, and is deposited on the single-layer 1T'-WTe2106 in the same space (see Figure 13(a)). Therefore, according to the first manufacturing method, the bottom surface BS1 of the multilayer WTe2109 is hardly oxidized. Consequently, according to the first manufacturing method, the interposition of an oxide film between the S-wave superconductor 110 and the single-layer 1T'-WTe2106 (i.e., the two-dimensional topological insulator 6) can be suppressed (hereinafter referred to as the second advantage).

[0113] The oxide film interposed between the S-wave superconductor 110 and the monolayer 1T'-WTe2106 suppresses the penetration of Cooper pairs from the S-wave superconductor 110 into the monolayer 1T'-WTe2106. Therefore, such an oxide film is undesirable because it makes it difficult to realize one-dimensional chiral p-wave superconductivity.

[0114] (3-2) Second manufacturing method Figure 17 is a process flow diagram showing another example of a method for manufacturing a quantum device according to Embodiment 1 (hereinafter referred to as the second manufacturing method). Figures 19 to 23 are cross-sectional views of the second manufacturing method. The second manufacturing method has a fifth step S5 and a sixth step S6, as shown in Figure 17. The second manufacturing method is similar to the first manufacturing method. Therefore, the same parts as the first manufacturing method will be omitted or simplified in the explanation.

[0115] (3-2-1) Step 5 S5 (See Figures 19-22) First, the upper surface s3 of the first single layer 106 (i.e., single layer 1T'-WTe2) separated from the first single crystal is covered with a coating 108b (see Figure 22(c)). The coating 108b (hereinafter referred to as the second coating) has an S-wave superconductor 210 and hexagonal boron nitride 112 in contact with the S-wave superconductor 210.

[0116] The separation of the single-layer 1T'-WTe2106 is performed in a space where the atmosphere is removed (for example, inside a glove box filled with an inert gas). The first single crystal is a single crystal of tungsten ditelluride having a 1T'-type crystal structure, as described above. The S-wave superconductor 210 is a superconductor having a metal atom different from the tungsten and tellurium atoms (hereinafter referred to as the third metal atom), as well as tungsten atoms and tellurium atoms. The S-wave superconductor 210 is an example of the S-wave superconductor 10 described with reference to Figures 1 and 2.

[0117] The third metal atom is preferably one of palladium, platinum, or niobium. The third metal atom is an atom of the same element as the first metal atom. The first metal atom is a metal atom (but different from tungsten and tellurium) found in the S-wave superconductor 10 shown in Figures 1 and 2.

[0118] Figure 18 is a process flow diagram showing an example of the fifth step S5 (see Figure 17). The fifth step S5 shown in Figure 18 has steps S1a, S5b, and S5c.

[0119] (a) Step S1a (see Figure 8) First, a PDMS / PVC stamp 120 (see Figure 8) is formed. Step S1a is the process described with reference to Figure 7. Therefore, a detailed explanation of step S1a will be omitted.

[0120] (b) Step S5b (see Figure 19) —Separation of hexagonal boron nitride 112— Next, flaky hexagonal boron nitride 112 is separated from the hexagonal boron nitride single crystal and deposited onto the fourth substrate 130d (see Figure 19(a)). Subsequently, the fourth substrate 130d with the deposited hexagonal boron nitride 112 is placed in a glove box filled with an inert gas (hereinafter referred to as the second glove box). The separation of the hexagonal boron nitride 112 and its subsequent deposition onto the fourth substrate 130d may be carried out inside the second glove box filled with an inert gas. This process is substantially the same as the process described with reference to Figure 9(a). Therefore, a detailed explanation of this process is omitted.

[0121] ―S-wave superconductor 210(M x W 1-x Separation of Te2 thin sections - Furthermore, in a second glove box filled with inert gas, the flake-shaped S-wave superconductor 210 is separated from the single crystal and attached to the fifth substrate 130e (see Figure 19(b)).

[0122] For example, in a second glove box filled with inert gas, a single crystal (hereinafter referred to as single crystal M) whose constituent elements are tungsten, tellurium, and a metal (more precisely, a metallic element different from tungsten and tellurium) x W 1-x Thin flakes are separated from the material (referred to as Te2) and attached to the fifth substrate 130e. These flakes are an example of the S-wave superconductor 210. The separation of the flakes and their subsequent attachment to the fifth substrate 130e are performed by the adhesive tape method.

[0123] Single crystal M x W 1-x Te2 is a mixed crystal whose composition is represented by the following chemical formula (1).

[0124] Mx W 1-x Te2 ····· (1) However, M is an element symbol representing a metal element (specifically, a metal element different from tungsten and tellurium). The metal element represented by M is preferably any one of palladium, platinum, and niobium. The third metal atom (i.e., the metal atom included in the S-wave superconductor 210) is an atom of the metal represented by the element symbol M. x is a number greater than 0 and less than 1. x is preferably a number greater than 0 and less than 0.3 (or a number greater than 0.7 and less than 1).

[0125] Single crystal M x W 1-x Te2 is an S-wave superconductor. Therefore, the single crystal M x W 1-x A thin film separated from Te2 is also an S-wave superconductor.

[0126] —Separation of monolayer 1T′-WTe2 106— Furthermore, in the second glove box filled with an inert gas, the monolayer 1T′-WTe2 106 is separated from the first single crystal and attached to the sixth substrate 130f (see FIG. 19(c)). This step is substantially the same as the step described with reference to FIG. 9(c). Therefore, a detailed description of this step is omitted.

[0127] (c) Step S5c (see FIGS. 20 to 22) Finally, using the PDMS / PVC stamp 120 (see FIG. 8), the S-wave superconductor 210 (see FIG. 19(b)) and the monolayer 1T′-WTe2 106 (see FIG. 19(c)) are attached to the hexagonal boron nitride 112 (see FIG. 19(a)) in this order. Step S5c is performed in the second glove box in which the fourth to sixth substrates 130d, 130e, and 130f are stored.

[0128] Specifically, first, the fourth substrate 130d (see Figure 20(a)) to which hexagonal boron nitride 112 is attached is heated to 65-75°C, for example, on a hot plate (not shown), inside a second glove box filled with inert gas. As a result, the hexagonal boron nitride 112 is also heated to 65-75°C.

[0129] Next, the PDMS / PVC stamp 120 is pressed against the heated hexagonal boron nitride 112 (see Figure 20(b)). This pressing is continued for a while to allow the hexagonal boron nitride 112 to adhere to the PDMS / PVC stamp 120.

[0130] Subsequently, the PDMS / PVC stamp 120 is pulled away from the fourth substrate 130d. As a result, the hexagonal boron nitride 112 remains attached to the PDMS / PVC stamp 120 and is peeled off from the fourth substrate 130d (see Figure 20(c)).

[0131] Next, the fifth substrate 130e (see Figure 21(a)) to which the S-wave superconductor 210 is attached is heated to 65-75°C, for example, on a hot plate (not shown). This heating also heats the S-wave superconductor 210 to 65-75°C.

[0132] Next, the PDMS / PVC stamp 120 is pressed against the heated S-wave superconductor 210 so that the hexagonal boron nitride 112 covers a portion of the S-wave superconductor 210 (see Figure 21(b)). This pressing is continued for a while to allow the S-wave superconductor 210 to adhere to the PDMS / PVC stamp 120 and the hexagonal boron nitride 112.

[0133] Subsequently, the PDMS / PVC stamp 120 is peeled away from the fifth substrate 130e. As a result, the S-wave superconductor 210 is peeled off from the fifth substrate 130e while still attached to the PDMS / PVC stamp 120 and the hexagonal boron nitride 112 (see Figure 21(c)). Through these steps, a second coating 108b is formed, having the S-wave superconductor 210 and the hexagonal boron nitride 112 in contact with the S-wave superconductor 210.

[0134] Next, the sixth substrate 130f (see Figure 22(a)) to which the single-layer 1T'-WTe2106 is attached is heated to 65-75°C, for example, on a hot plate (not shown). This heating also heats the single-layer 1T'-WTe2106 to 65-75°C.

[0135] Next, the second coating 108b attached to the PDMS / PVC stamp 120 is pressed against the heated single layer 1T'-WTe2106 (see Figure 22(b)). This pressing is continued for a while to allow the single layer 1T'-WTe2106 to adhere to the second coating 108b. Then, the PDMS / PVC stamp 120 is pulled away from the sixth substrate 130f. As a result, the single layer 1T'-WTe2106 is peeled off the sixth substrate 130f while still attached to the second coating 108b (see Figure 22(c)).

[0136] Through the processes described so far, the hexagonal boron nitride 112 is converted to an S-wave superconductor 210 (i.e., M x W 1-x The Te2 flakes and the single layer 1T'-WTe2106 adhere in this order. As a result, the upper surface s3 of the single layer 1T'-WTe2106 is covered by the second coating 108b (see Figure 22(c)).

[0137] More specifically, the upper surface s3 of the single layer 1T'-WTe2106 is covered with a second coating 108b such that hexagonal boron nitride 112 is in contact with the upper surface s3 of the single layer 1T'-WTe2106. This coating is further applied so that an S-wave superconductor 210 is in contact with a portion of the outer periphery of the single layer 1T'-WTe2106.

[0138] Figure 24 is a plan view showing an example of the positional relationship between the single-layer 1T'-WTe2106 and the S-wave superconductor 210. The single-layer 1T'-WTe2106 is drawn with a solid line. The S-wave superconductor 210 is drawn with a dashed line.

[0139] As shown in Figure 24, in the fifth step S5, the upper surface s3 of the single layer 1T'-WTe2106 (see Figure 22(c)) is covered with the second film 108b so that the S-wave superconductor 210 is in contact with a portion 114c (i.e., the third portion) of the outer circumference 115 of the single layer 1T'-WTe2106.

[0140] More precisely, the upper surface s3 is covered with a second coating 108b such that the S-wave superconductor 210 is in contact only with the third portion 114c of the outer perimeter 115 of the single layer 1T'-WTe2106, and only with the third portion 114c of the fourth portion 114d, which is a part of the outer perimeter 115 and is in contact with both ends of the third portion 114c.

[0141] (3-2-2) Sixth step S6 (see Figure 23) After the fifth step S5 (see Figure 17), the single layer 1T'-WTe2106 and the second coating 108b are attached to the support 4 such that the lower surface s4 (i.e., the fourth surface) of the single layer 1T'-WTe2106 is positioned between the upper surface s3 and the support 4 (see Figure 23(c)).

[0142] As described above, in the fifth step S5, the single layer 1T'-WTe2106 is separated from the first single crystal (i.e., the single crystal of 1T'-WTe2) in a space where the atmosphere has been removed (see "(b) Step S5b"). The single layer 1T'-WTe2106 is then left in a space where the atmosphere has been removed until the sixth step S6 is completed.

[0143] Similarly, in the fifth step S5, the S-wave superconductor 210 is subjected to single crystal M in a space where the atmosphere has been removed. x W 1-x It is separated from Te2 (see "(b) Step S5b"). The S-wave superconductor 210 is then placed in an airless space until the sixth step S6 is completed.

[0144] Specifically, first, the support 104 is heated to 125-135°C in a second glove box filled with inert gas, for example, using a hot plate (not shown) (see Figure 23(a)). At this point, the second coating 108b is still attached to the polyvinyl chloride (not shown) on the DMS / PVC stamp 120 (see Figure 23(a)). Furthermore, the single layer 1T'-WTe2106 is attached to the second coating 108b.

[0145] Next, the second coating 108b attached to the PDMS / PVC stamp 120 and the single layer 1T'-WTe2106 are pressed against the heated support 104 (see Figure 23(b)). This pressing is continued for a while. As a result, the polyvinyl chloride on the DMS / PVC stamp 120 is heated to 125-135°C. Consequently, the adhesive strength of the polyvinyl chloride decreases.

[0146] Subsequently, the PDMS / PVC stamp 120 is pulled away from the support 104. As a result, the single layer 1T'-WTe2106 and the second coating 108b are left behind on the support 104 (see Figure 23(c)). That is, the single layer 1T'-WTe2106 and the second coating 108b adhere to the support 4 such that the lower surface s4 of the single layer 1T'-WTe2106 is positioned between the upper surface s3 and the support 4.

[0147] Finally, the support 104, to which the single-layer 1T'-WTe2106 and the second coating 108b are attached, is removed from the second glove box filled with inert gas.

[0148] As a result, quantum device 102b is completed, having a second coating 108b containing the S-wave superconductor 210 and a single layer 1T'-WTe2106 (see Figure 23(c)). Quantum device 102b is an example of quantum device 2 as described with reference to Figures 1 and 2. The second coating 108b is an example of coating 8 as described with reference to Figures 1 and 2.

[0149] In the process illustrated in step S5b (see Figure 18), the S-wave superconductor 210 is a single crystal M x W 1-xIt is separated from Te2. However, the S-wave superconductor 210 may also be formed from a single crystal of tungsten ditelluride (hereinafter referred to as single-crystal WTe2). Two methods for forming the S-wave superconductor 210 from single-crystal WTe2 are shown below.

[0150] In the first example, small fragments of tungsten ditelluride (hereinafter referred to as WDe2 fragments) are first separated from a single crystal WDe2 using the adhesive tape method. The thickness of the WDe2 fragments to be separated is, for example, several nanometers.

[0151] Next, the separated WTe2 pieces are pressed against a silicon substrate to adhere to it. Then, a metal film (for example, a Pd film, a Pt film, or an Nb film) is deposited on top of the WTe2 pieces.

[0152] The thickness of the deposited metal film is, for example, 0.5 to 2 nm. Finally, the silicon substrate to which the WDe2 fragments are attached is heated inside a second glove box filled with inert gas. Then, metal atoms diffuse from the metal film deposited on the WDe2 fragments into the WDe2 fragments, forming an S-wave superconductor 210.

[0153] In the second example, first, a metal film (for example, a Pd film, a Pt film, or an Nb film) is deposited on a silicon substrate. The thickness of the deposited metal film is, for example, 0.5 to 2 nm. Next, small pieces of WDe2 separated from single crystal WDe2 using the adhesive tape method are attached to the deposited metal film.

[0154] Finally, the silicon substrate with the WDe2 fragments attached is heated inside a second glove box filled with inert gas. As a result, metal atoms diffuse from the metal film on the silicon substrate to the WDe2 fragments, forming an S-wave superconductor 210.

[0155] Incidentally, there is more than one crystal structure for single-crystal WTe2. The formation of S-wave superconductor 210 is possible regardless of the crystal structure of the single-crystal WTe2. The main crystal structures of single-crystal WTe2 are Td-type, 1T-type, and 1T'-type.

[0156] (3-2-3) Advantages of the second manufacturing method The second manufacturing method has the same advantages as the first manufacturing method (i.e., the first and second advantages).

[0157] According to the second manufacturing method, the single-layer 1T'-WTe2106 is separated from the second single crystal in an air-free space and covered with the second coating 108b (see Figure 23(c)). Thus, according to the second manufacturing method, a quantum device 2 having substantially unoxidized single-layer 1T'-WTe2106 (i.e., a two-dimensional topological insulator 6) can be provided (i.e., the first advantage).

[0158] According to the second manufacturing method, the S-wave superconductor 210 is separated from the single crystal in an air-free space and deposited onto the single-layer 1T'-WTe2106 (see Figure 23(a)). Therefore, according to the second manufacturing method, oxidation of the lower surface BS2 of the S-wave superconductor 210 is almost nonexistent. Consequently, according to the second manufacturing method, the interposition of an oxide film between the S-wave superconductor 210 and the single-layer 1T'-WTe2106 (i.e., the two-dimensional topological insulator 6) can be suppressed (i.e., the second advantage).

[0159] (4) Comparative Example (4-1) Comparative Example 1 Figure 25 is a perspective view of a quantum device 302 (hereinafter referred to as Comparative Example 1) having a support 4, a two-dimensional topological insulator 6 placed on the support 4, and an S-wave superconductor 310 covering a portion of the two-dimensional topological insulator 6. The S-wave superconductor 310 is arranged to cover a portion of the outer periphery of the two-dimensional topological insulator 6.

[0160] The two-dimensional topological insulator 6 is a single layer 1T'-WTe2. The S-wave superconductor 310 is an aluminum film. The S-wave superconductor 310 may also be a metal film other than an aluminum film (for example, a niobium film).

[0161] Quantum device 302 differs from quantum device 2, as described with reference to Figures 1 and 2, in that it does not have a coating covering the two-dimensional topological insulator 6. Furthermore, quantum device 302 differs from quantum device 2 in that it has a metal film such as an aluminum film (i.e., an S-wave superconductor 310) instead of the S-wave superconductor 10, as described with reference to Figures 1 and 2.

[0162] It might seem that a quantum device 302 could be realized by depositing a metal film on a portion of the two-dimensional topological insulator 6, for example, by vacuum deposition. However, since the two-dimensional topological insulator 6 is not covered by a film, the two-dimensional topological insulator 6 (i.e., single-layer 1T'-WTe2) is oxidized during the manufacturing of the quantum device 302. When single-layer 1T'-WTe2 is oxidized, it changes from a two-dimensional topological insulator to a simple insulator. Therefore, it is difficult to realize a quantum device 302 having a two-dimensional topological insulator 6 that is single-layer 1T'-WTe2 (i.e., Comparative Example 1).

[0163] Figures 26 and 27 are cross-sectional views illustrating an example of a method for manufacturing a quantum device 302 by aluminum film deposition. First, a single layer of 1T'-WTe2106 is separated from the first single crystal (i.e., a single crystal of 1T'-WTe2) by the adhesive tape method. Then, the separated single layer of 1T'-WTe2106 is attached to a support 4 (see Figure 26(a)). These steps are performed inside a glove box filled with inert gas.

[0164] Next, a photoresist film 336 is applied to the support 4 to which the single-layer 1T'-WTe2106 is attached (see Figure 26(b)). This process is also carried out inside a glove box filled with inert gas. Up to this point, the single-layer 1T'-WTe2106 is hardly oxidized.

[0165] Next, the support 4 coated with the photoresist film 336 is removed from the glove box and exposed to the atmosphere. Then, an opening 338 is formed in the photoresist film 336 to expose a portion 316 of the single layer 1T'-WTe2106 (hereinafter referred to as the joint) (see Figure 26(c)).

[0166] Specifically, a portion of the photoresist film 336 (specifically, the portion covering the joint 316 and its vicinity) is irradiated with light. Then, the support 4 coated with the photoresist film 336 is immersed in a developer solution. As a result, the portion of the photoresist film 336 that was irradiated with light is removed, and an opening 338 is formed. After that, the support 4 is washed with water to remove the developer solution. Finally, any moisture adhering to the photoresist film 336, etc., is removed.

[0167] Next, an aluminum film 340 is deposited on and inside the photoresist film 336 having an opening 338 (see Figure 27(a)). Finally, the photoresist film 336 is removed using a remover or the like. As a result, the aluminum on the photoresist film 336 is removed together with the photoresist film 336.

[0168] As a result, the aluminum film 342 (see Figure 27(b)) in contact with a portion of the outer periphery of the single-layer 1T'-WTe2106 is left on the support 4. That is, the lift-off of the aluminum film 340 forms the aluminum film 342 in contact with a portion of the outer periphery of the single-layer 1T'-WTe2106. The aluminum film 342 is an example of the S-wave superconductor 310 described with reference to Figure 25.

[0169] The single-layer 1T'-WTe2106 is not exposed to the atmosphere until an opening 338 (see Figure 26(c)) is formed in the photoresist film 336. However, once the opening 338 is formed, the junction 316 of the single-layer 1T'-WTe2106 is exposed to the atmosphere. As a result, the junction 316 is oxidized first (see Figure 26(c)).

[0170] To form the aperture 338, the partially irradiated photoresist film 336 is developed. Then, the photoresist film 336 with the formed aperture 338 and the junction 316 are washed with water. This washing also oxidizes the junction 316. This is because the single layer 1T'-WTe2106 is also oxidized by water.

[0171] As the process progresses and the photoresist film 336 (see Figure 27(a)) is removed along with the unwanted portion of the aluminum film 340, the portion 318 of the single layer 1T'-WTe2106 other than the junction 316 (hereinafter referred to as the non-junction portion) is also exposed to the atmosphere (see Figure 27(b)). As a result, in addition to the junction 316, the non-junction portion 318 is also oxidized.

[0172] The oxidized single layer 1T'-WTe2106 is not a two-dimensional topological insulator, but merely an insulator. Therefore, even if the manufacturing method shown in Figures 26 and 27 is performed, a quantum device 302 (see Figure 25) having a two-dimensional topological insulator 6 cannot be formed.

[0173] In the example described with reference to Figures 26 and 27, the S-wave superconductor 310 is formed by lift-off. The S-wave superconductor 310 may also be formed by other methods (e.g., photolithography and etching). However, even if the S-wave superconductor 310 is formed by other methods, oxidation of the monolayer 1T'-WTe2106 is unavoidable.

[0174] On the other hand, according to the first manufacturing method, the quantum device 2 is formed with almost no oxidation of the single-layer 1T'-WTe2106 (i.e., a two-dimensional topological insulator) (see "(3-1-4) Advantages of the First Manufacturing Method"). The same applies when the quantum device 2 is formed using the second manufacturing method.

[0175] (4-2) Comparative Example 2 Figure 28 is a perspective view of a quantum device 402 (hereinafter referred to as Comparative Example 2) having a support 4, an S-wave superconductor 410 placed on the support 4, and a two-dimensional topological insulator 406 covering a portion of the S-wave superconductor 410. The two-dimensional topological insulator 406 is positioned so that a portion of its outer periphery is in contact with the S-wave superconductor 410.

[0176] The two-dimensional topological insulator 406 is a single-layer 1T'-WTe2. The S-wave superconductor 410 is a metal film such as an aluminum film. The S-wave superconductor 410 may also be a metal film other than an aluminum film (for example, a niobium film).

[0177] In Comparative Example 1, the S-wave superconductor 310 covers a portion of the two-dimensional topological insulator 6 (see Figure 25). On the other hand, in Comparative Example 2, the two-dimensional topological insulator 406 covers a portion of the S-wave superconductor 410. Except for this point, the structure of Comparative Example 2 is substantially the same as that of Comparative Example 1. Even with this structure, a portion of the outer periphery of the two-dimensional topological insulator 6 is in contact with the S-wave superconductor 410, so one-dimensional chiral p-wave superconductivity can be realized.

[0178] Furthermore, the portion of the two-dimensional topological insulator 406 that covers the S-wave superconductor 410 is raised above its surroundings. However, this raised portion is not depicted in Figure 28.

[0179] It seems that quantum device 402 could be manufactured by covering a portion of a metal film (e.g., an aluminum film) formed by photolithography and etching with a single layer of 1T'-WTe2. However, since photolithography is performed in the atmosphere, the S-wave superconductor 410 (e.g., the formed aluminum film) would be covered with an oxide film.

[0180] When the S-wave superconductor 410 is covered with an oxide film, it becomes difficult for Cooper pairs to penetrate from the S-wave superconductor 410 into the two-dimensional topological insulator 406.

[0181] Therefore, quantum device 402 does not function properly. Even if a metal film (e.g., an aluminum film) is formed by a method other than photolithography and etching, an oxide film covering the S-wave superconductor 410 is formed. Therefore, the conclusion is the same.

[0182] On the other hand, according to the first manufacturing method, oxidation of the portion of the surface of the S-wave superconductor 110 (see Figure 14(c)) that is in contact with the S-wave superconductor 110 can be suppressed (second advantage). Therefore, the quantum device 2 according to Embodiment 1 operates normally. The same applies when the quantum device 2 is formed by the second manufacturing method.

[0183] Furthermore, since the two-dimensional topological insulator 406 in Comparative Example 2 (see Figure 28) is not covered with a coating, the two-dimensional topological insulator 406 is oxidized during the manufacturing of the quantum device 402. This oxidation can be avoided by covering the two-dimensional topological insulator 406 with a coating. However, the formation of an oxide film covering the S-wave superconductor 410 cannot be avoided.

[0184] (5) Variant (5-1) Variation 1 Figure 29 is a plan view showing an example of a modified version of quantum apparatus 2 (hereinafter referred to as quantum apparatus 2m1) described with reference to Figures 1 and 2. Figure 30 is a cross-sectional view along the line XXX-XXX in Figure 29.

[0185] Quantum device 2m1 has a coating 8m1 that is different from coating 8 described with reference to Figures 1 and 2. In coating 8 described with reference to Figures 1 and 2, hexagonal boron nitride 12 covers a portion of the S-wave superconductor 10 (see Figures 1 and 2). On the other hand, in coating 8m1 of quantum device 2m1, the S-wave superconductor 10m1 covers a portion of the hexagonal boron nitride 12m1 (see Figures 29 and 30).

[0186] Aside from this point, quantum device 2m1 has substantially the same structure as quantum device 2, which was described with reference to Figures 1 and 2. For example, the chemical composition and crystal structure of the S-wave superconductor 10m1 are the same as those of the S-wave superconductor 10 (the same applies to Comparative Example 2, which will be described later). Since a portion of the outer periphery of the two-dimensional topological insulator 6 is in contact with the S-wave superconductor 10m1, quantum device 2m1 can also realize one-dimensional chiral p-wave superconductivity.

[0187] The quantum device 2m1 can be manufactured by appropriately modifying step S1c (see Figure 7) of the first manufacturing method according to the structure of the coating 8m1. Specifically, hexagonal boron nitride 112 (see Figure 9(a)) and single layer 1T'-WTe2106 (see Figure 9(c)) are deposited onto a multilayer WTe2109 (see Figure 9(b)) in that order.

[0188] Alternatively, the quantum device 2m1 can be manufactured by appropriately modifying step S5c (see Figure 18) of the second manufacturing method according to the structure of the coating 8m1. Specifically, hexagonal boron nitride 112 (see Figure 19(a)) and single layer 1T'-WTe2106 (see Figure 19(c)) are deposited onto the S-wave superconductor 210 (see Figure 19(b)) in this order. According to Modification 1, the variations of the quantum device according to Embodiment 1 are increased.

[0189] (5-2) Modification 2 Figure 31 is a plan view showing an example of another modified form of quantum apparatus 2 (hereinafter referred to as quantum apparatus 2m2) described with reference to Figures 1 and 2. Figure 32 is a cross-sectional view along the line XXXII-XXXII in Figure 31.

[0190] Quantum device 2m2 has a coating 8m2 that is different from coating 8 described with reference to Figures 1 and 2. In coating 8 described with reference to Figures 1 and 2, hexagonal boron nitride 12 covers a portion of the S-wave superconductor 10 (see Figure 2). On the other hand, in coating 8m2 of quantum device 2m2, hexagonal boron nitride 12m2 covers the entire S-wave superconductor 10 (see Figures 31 and 32).

[0191] Aside from this point, quantum device 2m2 has substantially the same structure as quantum device 2, which was described with reference to Figures 1 and 2. Since a portion of the outer periphery of the two-dimensional topological insulator 6 is in contact with the S-wave superconductor 10m2, quantum device 2m2 can also realize one-dimensional chiral p-wave superconductivity.

[0192] The quantum device 2m2 can be manufactured by appropriately modifying step S1c (see Figure 7) of the first manufacturing method according to the structure of the coating 8m2. Specifically, the pressing of hexagonal boron nitride 112 onto the multilayer WTe2109 (see Figures 11(a) and 11(b)) is modified so that the hexagonal boron nitride 112 covers the entire multilayer WTe2109.

[0193] Alternatively, the second manufacturing method can be manufactured by appropriately modifying step S5c (see Figure 18) according to the structure of the coating 8m2. Specifically, the pressing of the hexagonal boron nitride 112 onto the S-wave superconductor 210 (see Figures 21(a) and 21(b)) is modified so that the hexagonal boron nitride 112 covers the entire S-wave superconductor 210. According to the second modification, the variations of the quantum device according to Embodiment 1 are increased.

[0194] In the example described with reference to Figures 1 and 2, the two-dimensional topological insulator 6 is in contact with the support 4. However, a new material (e.g., hexagonal boron nitride) may be interposed between the two-dimensional topological insulator 6 and the support 4. That is, the two-dimensional topological insulator 6 may be placed above the support 4.

[0195] This structure can be realized, for example, in step S1c of the first manufacturing method, by attaching the multilayer WTe2109 (see Figure 12(c)), the single layer 1T'-WTe2106, and the new component to the hexagonal boron nitride 112 in this order. In the second step S2 (see Figure 6), the single layer 1T'-WTe2106 (see Figure 13(c)), the first coating 108a, and the new component are attached to the support 104. The above structure can also be realized by similarly modifying the second manufacturing method.

[0196] The S-wave superconductor 10 according to Embodiment 1 (see Figures 1 and 2) has tungsten atoms, tellurium atoms, and a first metal atom (i.e., a metal atom different from the tungsten and tellurium atoms). The precursor of this S-wave superconductor 10 (i.e., multilayer WTe2) readily adheres to a two-dimensional topological insulator 6 (i.e., single-layer 1T'-WTe2) and can be obtained in an atmosphere-free space. Furthermore, the two-dimensional topological insulator 6 can also be obtained in an atmosphere-free space. Therefore, the precursor of the S-wave superconductor 10 and the two-dimensional topological insulator 6 can be obtained in an atmosphere-free space, and the precursor of the S-wave superconductor 10 can be attached to the two-dimensional topological insulator 6 (see "(3-1) First Manufacturing Method").

[0197] Therefore, it is possible to form a heterointerface between the S-wave superconductor 10 precursor and the two-dimensional topological insulator 6 in a space where the atmosphere is removed (i.e., the second advantage). Thus, according to Embodiment 1, it is possible to suppress the interposition of an oxide film between the S-wave superconductor 10 and the two-dimensional topological insulator 6. The conclusion is the same even when a quantum device is formed using a flaky S-wave superconductor 210 instead of the S-wave superconductor 10 precursor (see "(3-2) Second Manufacturing Method").

[0198] Furthermore, since the quantum device according to Embodiment 1 has a coating 8 covering the two-dimensional topological insulator 6, oxidation of the two-dimensional topological insulator 6 can also be suppressed according to Embodiment 1 (i.e., the first advantage).

[0199] In addition to single-layer 1T'-WTe2, other known two-dimensional topological insulators include HgTe / CdTe quantum wells. However, quantum devices capable of enabling Cooper pairs to penetrate such two-dimensional topological insulators have not yet been realized.

[0200] (Embodiment 2) Embodiment 2 has parts in common with Embodiment 1. Therefore, the parts in common with Embodiment 1 will be omitted or simplified in their explanation.

[0201] (1) Structure Figure 33 is a plan view showing an example of a quantum apparatus according to Embodiment 2. Two XXXIV-XXXIV lines are shown in Figure 33. Figure 34 is a cross-sectional view along the upper XXXIV-XXXIV line. The cross-sectional view along the upper XXXIV-XXXIV line and the cross-sectional view along the lower XXXIV-XXXIVI line are substantially the same.

[0202] The quantum apparatus 502 shown in Figure 33 (i.e., an example of a quantum apparatus according to Embodiment 2) is a device in which a ferromagnetic material 550 is added to the quantum apparatus 2 shown in Figure 1. The ferromagnetic material 550 is arranged such that Majorana quasiparticle pairs appear at specific positions within the two-dimensional topological insulator 6.

[0203] For example, the ferromagnetic material 550 includes a first ferromagnetic material 550a arranged on top of hexagonal boron nitride 12, and a second ferromagnetic material 550b also arranged on top of hexagonal boron nitride 12. The first ferromagnetic material 550a, the S-wave superconductor 10, and the second ferromagnetic material 550b are arranged in this order along the end E (see Figure 3) of the two-dimensional topological insulator 6.

[0204] In this arrangement, one of the Majorana quasiparticle pairs appears, for example, at a first position P1 between the first ferromagnet 550a and the S-wave superconductor 10, within the end E (see Figure 3) of the two-dimensional topological insulator 6 (see "(2) Operation"). The other of the Majorana quasiparticle pair appears, for example, at a second position P2 between the second ferromagnet 550b and the S-wave superconductor 10, within the end E of the two-dimensional topological insulator 6. In other words, the above arrangement of the first and second ferromagnets 550a and 550b causes the Majorana quasiparticle pair to appear at specific positions P1 and P2 within the two-dimensional topological insulator 6.

[0205] The first and second ferromagnetic materials 550a and 550b are, for example, cobalt or chromium. The distance from the S-wave superconductor 10 to the first ferromagnetic material 550a is preferably shorter than the leakage distance LD of the Cooper pair penetrating from the S-wave superconductor 10 to the two-dimensional topological insulator 6. Similarly, the distance from the S-wave superconductor 10 to the second ferromagnetic material 550b is preferably shorter than the above-mentioned leakage distance LD.

[0206] (2) Operation When the quantum device 502 is cooled to near absolute zero, one-dimensional chiral p-wave superconductivity, the stage for the emergence of Majorana quasiparticle pairs, is realized at the end E of the two-dimensional topological insulator 6 (see Figure 3) (see "(2) Operation" in Embodiment 1).

[0207] The first ferromagnet 550a terminates this one-dimensional chiral p-wave superconductivity at a first position P1 in the vicinity of the first ferromagnet 550a. Similarly, the second ferromagnet 550b terminates its one-dimensional chiral p-wave superconductivity at a second position P2 in the vicinity of the second ferromagnet 550b.

[0208] As a result, the edges of one-dimensional chiral p-wave superconductivity are formed at the first and second positions P1 and P2, respectively, in the vicinity of the first and second ferromagnets 550a and 550b. Then, Majorana quasiparticles (i.e., Majorana zero modes) appear at the first and second positions P1 and P2, respectively. In other words, pairs of Majorana quasiparticles appear.

[0209] (3) Manufacturing method First, a quantum apparatus 2 (see Figures 1 and 2) according to Embodiment 1 is formed. Then, for example, by lift-off, the first and second ferromagnetic materials 550a and 550b are formed on the hexagonal boron nitride 12.

[0210] The quantum device according to Embodiment 2 comprises a quantum device in which there is substantially no oxide film that suppresses the penetration of Cooper pairs from an S-wave superconductor to a two-dimensional topological insulator (i.e., a quantum device according to Embodiment 1), and a ferromagnet that terminates one-dimensional chiral p-wave superconductivity. Therefore, according to Embodiment 2, a quantum device in which Majorana quasiparticle pairs appear can be realized.

[0211] (Embodiment 3) Embodiment 3 has parts in common with Embodiments 1 and 2. Therefore, the parts in common with Embodiments 1 and 2 will be omitted or simplified in their explanation.

[0212] (1) Structure Figure 35 is a plan view showing an example of a quantum apparatus according to Embodiment 3. Two XXXVI-XXXVI lines are shown in Figure 35. Figure 36 is a cross-sectional view along the upper XXXVI-XXXVI line. The cross-sectional view along the upper XXXVI-XXXVI line and the cross-sectional view along the lower XXXVI-XXXVI line are substantially the same.

[0213] Figure 37 is an enlarged view of the area 660 enclosed by the dashed line in Figure 36. The quantum device 602 shown in Figure 35 is a device obtained by adding a superconducting circuit 662 and a microwave resonator 664 to the quantum device according to Embodiment 2. The quantum device 602 is an example of a quantum device according to Embodiment 3.

[0214] The coating 608 of the quantum device 602 has an S-wave superconductor 610 and hexagonal boron nitride 612 covering the entire S-wave superconductor 610. However, the hexagonal boron nitride 612 may cover only a part of the S-wave superconductor 610 (see "(4-2) Modification 2"). The chemical composition and crystal structure of the S-wave superconductor 610 are the same as those of the S-wave superconductor 10 according to Embodiment 1. The S-wave superconductor 610 is an example of the S-wave superconductor 10 according to Embodiment 1.

[0215] The superconductor circuit 662 includes a first superconductor 666a and a second superconductor 666b that is different from the S-wave superconductor 610 and the first superconductor 666a (see Figures 35 and 36). The first superconductor 666a has an upper surface s1 (referred to as the first surface as appropriate) that is in contact with the S-wave superconductor 610 and a lower surface s2 (referred to as the second surface as appropriate) that is located between the upper surface s1 and the support 4 (see Figure 36).

[0216] The superconducting circuit 662 further includes a normal conductor 668 in contact with the upper surface s1 of the first superconductor 666a and the second superconductor 666b (see Figure 36). The normal conductor 668 contains a metal atom of the same element as the metal atoms contained in the S-wave superconductor 610 (hereinafter referred to as the fourth metal atom). The fourth metal atom is a metal atom different from the tungsten atom and the tellurium atom (for example, a palladium atom or a platinum atom).

[0217] Furthermore, in the examples shown in Figures 35 and 36, the superconductor circuit 662 also has an insulating film 678 covering the side surface of the first superconductor 666a (see Figure 37). The insulating film 678 is, for example, an oxide film (i.e., a native oxide film) that forms when the first superconductor 666a is exposed to the atmosphere during the manufacturing process of the quantum device 602. The insulating film 678 prevents a short circuit between the first superconductor 666a and the second superconductor 666b.

[0218] Figure 38 is an enlarged view of the area 670 enclosed by the dashed line in Figure 37. The superconductor circuit 662 has a first Josephson junction J1 which includes a portion 666aP of the first superconductor 666a, a portion 668P of the normal conductor 668, and a portion 666bP of the second superconductor 666b.

[0219] The first Josephson junction J1 is the Josephson junction through which the upper XXXVI-XXXVI line shown in Figure 35 passes. The superconductor circuit 662 also has a second Josephson junction J2 through which the lower XXXVI-XXXVI line passes. The second Josephson junction J2 also has a portion of the first superconductor 666a, a portion of the normal conductor 668, and a portion of the second superconductor 666b. As shown in Figure 35, the second Josephson junction J2 is connected in parallel to the first Josephson junction J1 by the first superconductor 666a and the second superconductor 666b.

[0220] Figure 39 is an enlarged view of the area 672 enclosed by the dashed line in Figure 35. The superconductor circuit 662 has an opening 674 in which a portion 675 is located between the first Josephson junction J1 and the second Josephson junction J2 (see Figure 39). However, the opening 674 may be an opening that is entirely located between the first Josephson junction J1 and the second Josephson junction J2.

[0221] The microwave resonator 664 has a first transmission line 676a and a second transmission line 676b that is different from the first transmission line 676a (see Figure 35). Between the first transmission line 676a and the second transmission line 676b, a two-dimensional topological insulator 6, an S-wave superconductor 610, and a superconducting circuit 662 are arranged.

[0222] The first superconductor 666a and the second superconductor 666b are elemental metals such as aluminum, niobium, tantalum, palladium, titanium, indium, tin, and lead. The first superconductor 666a and the second superconductor 666b may also be materials containing multiple elements, such as molybdenum-rhenium and niobium compounds. The normal conductor 668 is, for example, palladium or platinum.

[0223] (2) How to use and operation The quantum device 602 is one of the minimal circuits for a flux-controlled Majorana qubit having a two-dimensional topological insulator (i.e., a quantum spin Hall insulator) (see, for example, Non-Patent Document 2). The quantum device 602 shown in Figure 35 has only one S-wave superconductor 610 in contact with the outer periphery of the two-dimensional topological insulator 6. However, the minimal circuit for a flux-controlled Majorana qubit may have multiple S-wave superconductors in contact with the outer periphery of the two-dimensional topological insulator 6. By appropriately combining these devices derived from quantum device 602 with quantum device 602, a Majorana qubit can be formed (see, for example, Non-Patent Document 2).

[0224] When a Majorana qubit formed in this manner (hereinafter referred to as "this qubit") is cooled to near absolute zero, multiple pairs of Majorana quasiparticles appear. This activates the this qubit.

[0225] The quantum state of this qubit can be rotated, for example, by changing the magnetic flux passing through the aperture 674 of the superconducting circuit 662 (see, for example, Non-Patent Document 2). The quantum state of this qubit can be observed, for example, based on the resonant frequency of the microwave resonator 664 (see, for example, Non-Patent Document 2).

[0226] (3) Manufacturing method Figure 40 is a process flow diagram showing an example of a manufacturing method for the quantum device 602 shown in Figure 35 (hereinafter referred to as the third manufacturing method). Figures 41 to 45 are cross-sectional views of the third manufacturing method. As shown in Figure 40, the third manufacturing method includes a fourth process S4 and steps S7 to S11.

[0227] (3-1) Fourth process S4 (see FIG. 41) First, a laminated film 680 including a normal conductor 768 and a first superconductor 666a positioned between the normal conductor 768 and the support 4 is formed on a part of the support 4 (see FIG. 41).

[0228] The normal conductor 768 has metal atoms (hereinafter, fifth metal atoms) of the same element (for example, palladium or platinum) as the fourth metal atoms included in the S-wave superconductor 610 (see FIGS. 35 and 36). The normal conductor 768 is, for example, a simple substance of palladium or platinum. The first superconductor 666a is, for example, a simple substance of aluminum.

[0229] The laminated film 680 is formed, for example, by lift-off. Specifically, first, a photoresist film (not shown) having an opening is formed on the support 4. Next, a superconducting film (for example, an aluminum film) and a normal conductor film (for example, a palladium film or a platinum film) are deposited in this order by vacuum evaporation on the photoresist film and inside the opening.

[0230] Finally, the deposited film on the photoresist film is removed together with the photoresist film. Then, the laminated film 680 remains on a part of the support 4. Since the removal of the photoresist film is performed in the atmosphere, the side surface of the first superconductor 666a is covered with a natural oxide film (for example, an aluminum oxide film). On the other hand, since palladium and platinum exemplified as the normal conductor 768 are metals that are difficult to be oxidized, the oxide film covering the normal conductor 768 can be ignored.

[0231] (3-2) Step S7 (see FIG. 42) Next, a second superconductor 666b (see FIGS. 35 and 36) and a microwave resonator 664 that are in contact with two locations of the normal conductor 768 (see FIG. 42) are formed. By forming the second superconductor 666b, the first and second Josephson junctions J1, J2 (see FIG. 35) are completed.

[0232] Specifically, the second superconductor 666b and the microwave resonator 664 are formed by lift-off of a superconducting film (for example, an aluminum film).

[0233] (3-3) Step S8 (see FIG. 43) Next, the upper surface s3 of the single-layer 1T'-WTe2 106 is covered with a first film 708a having a multilayer WTe2 109 and hexagonal boron nitride 612 (see FIG. 43). Step S8 is performed in a space from which air has been removed (for example, inside a glove box filled with an inert gas).

[0234] Step S8 is a modified example of the first step S1 described with reference to FIGS. 8 to 12. The first film 708a is a modified example of the first film 108a shown in FIG. 12(c). The first film 708a is different from the first film 108a shown in FIG. 12(c) in that it has a multilayer WTe2 109 and hexagonal boron nitride 612 that covers the entire upper surface of the multilayer WTe2 109.

[0235] (3-4) Step S9 (see FIG. 44) Next, the single-layer 1T'-WTe2 106 and the first film 708a are attached to the support 4 (see FIG. 44). This attachment is performed so that only the multilayer WTe2 109 among the single-layer 1T'-WTe2 106 and the multilayer WTe2 109 contacts the normal conductor 768.

[0236] Step S9 is performed in the above-described space from which air has been removed following step S8. Step S9 is a modified example of the second step S2 described with reference to FIG. 13.

[0237] (3-5) Step S10 (see FIGS. 44 and 45) Next, the normal conductor 768 and the multilayer WTe2109 are heated to diffuse the fifth metal atoms into the multilayer WTe2109 (see Figure 44). This diffusion transforms the multilayer WTe2109 into an S-wave superconductor 610 (see Figure 45). That is, the normal conductor 768 and the multilayer WTe2109 are heated so that the fifth metal atoms present in the normal conductor 768 diffuse into the multilayer WTe2109 to form an S-wave superconductor 610. Step S10 is a modified example of the third step S3 described with reference to Figure 14.

[0238] Specifically, the support 4, to which the single-layer 1T'-WTe2106 and the first coating 708a are attached, is heated by a hot plate in a glove box filled with inert gas (see "(3-1-3) Third Step S3" in Embodiment 1). This heating forms a coating 608 having an S-wave superconductor 610 and hexagonal boron nitride 612.

[0239] Due to the heating described above, a portion of the normal conductor 768 is lost, and the first superconductor 666a comes into contact with the S-wave superconductor 610 (see Figure 45). On the other hand, the normal conductor 768 becomes a normal conductor 668 that is in contact with the upper surface s1 of the first superconductor 666a and the second superconductor 666b.

[0240] The above heating process is preferably terminated when the portion of the multilayer WTe2109 in contact with the single-layer 1T'-WTe2106 reaches the superconducting region (i.e., the region where superconductivity occurs). Such heating suppresses the unintended diffusion of the fifth metal atom into the single-layer 1T'-WTe2106.

[0241] Such heating is achieved by heating for a relatively short time. For example, if the normal conductor 768 is a palladium film, the heating temperature is 150-250°C, and the heating time is 1.5-2.5 minutes, the superconducting region reaches the portion of the multilayer WTe2109 that is in contact with the single layer 1T'-WTe2106. However, the superconducting region does not reach the upper surface of the multilayer WTe2109 (assuming the multilayer WTe2109 has 10 single layers).

[0242] By the way, the term "superconductor" refers to an object in which superconductivity occurs. Therefore, an object in which superconductivity occurs only in a part is also a superconductor. In other words, multilayer WTe2109, in which only a part is a superconducting region, is also an S-wave superconductor 610.

[0243] (3-6) Step S11 (See Figure 35) Finally, the first ferromagnetic material 550a (see Figure 35) and the second ferromagnetic material 550b are formed on the hexagonal boron nitride 612, for example, by lift-off of the ferromagnetic film (see "(3) Manufacturing Method" in Embodiment 2).

[0244] By the way, in the example shown in Figure 40, the fourth step S4 and step S7 are performed before step S8 (a modified version of the first step S1). However, the fourth step S4 and step S7 may also be performed after step S8 (a modified version of the first step S1) and before step S9 (a modified version of the second step S2).

[0245] (4) Variations (4-1) Experimental variation 1 (4-1-1) Structure The first Josephson junction J1, as described with reference to Figure 38, includes a normal conductor (more precisely, a portion of the normal conductor 668, 668P) as an intermediate layer. The same applies to the second Josephson junction J2. However, the quantum device according to Embodiment 3 may have an insulator as an intermediate layer.

[0246] Figure 46 is a cross-sectional view showing an example of a quantum device (hereinafter referred to as Modification 1) in which the first and second Josephson junctions have an insulator as an intermediate layer. Figure 46 shows a cross-sectional view along a line crossing the first Josephson junction. Figure 47 is an enlarged view of the area 860 enclosed by the dashed line in Figure 46. Modification 1 is similar to quantum device 602 described with reference to Figures 35-39. Therefore, the explanation of parts common to quantum device 602 will be omitted or simplified.

[0247] Modification Example 1 has a superconductor circuit 862 including a first superconductor 866a, a second superconductor 866b, and an insulator 878 covering the second superconductor 866b (see FIG. 46). Further, Modification Example 1 has a metal film 834 covering the upper surface of the first superconductor 866a instead of the normal conductor 668.

[0248] The first superconductor 866a is a modification of the first superconductor 666a described with reference to FIGS. 35 to 39. The second superconductor 866b is a modification of the second superconductor 666b described with reference to FIGS. 35 to 39.

[0249] The first and second superconductors 866a and 866b are, for example, aluminum. The metal film 834 is, for example, any one of a palladium film, a platinum film, and a niobium film. The insulator 878 is, for example, an oxide film (e.g., aluminum oxide) of the second superconductor 866b.

[0250] The superconductor circuit 862 has a first Josephson junction J1m (see FIG. 47) including a portion 866aP of the first superconductor 866a, a portion 878P of the insulator 878, and a portion 866bP of the second superconductor 866b. The superconductor circuit 862 further has a second Josephson junction (not shown) having substantially the same structure as the first Josephson junction J1m. The first Josephson junction J1m included in the superconductor circuit 862 is a modification of the first Josephson junction J1 (see FIG. 38). The same applies to the second Josephson junction included in the superconductor circuit 862.

[0251] According to Modification Example 1, the variations of the quantum device according to Embodiment 3 increase.

[0252] (4-1-2) Manufacturing Method FIG. 48 is a process flow diagram showing an example of the manufacturing method of Modification Example 1 (hereinafter referred to as the fourth manufacturing method). As shown in FIG. 48, the fourth manufacturing method has steps S12 to S15, S8, S9m, S10m, and S11. Steps S8 and S11 are the steps described with reference to FIG. 40.

[0253] (a) Step S12 First, a microwave resonator 664 having first and second transmission lines 676a and 676b is formed on the support 4 by the lift-off of a superconductor (e.g., aluminum) (see Figure 46).

[0254] (b) Step S13 Next, a two-layer resist film (not shown) having a cross-linking structure is formed between the formed first and second transmission lines 676a and 676b. This two-layer resist film has a lower layer in contact with the support 4 and an upper layer supported by the lower layer. The upper layer has a portion that protrudes from the lower layer (a so-called overhang) and an opening surrounded by this portion (hereinafter referred to as a resist opening). The resist opening has a first opening having substantially the same planar shape as the first superconductor 866a and a second opening having substantially the same planar shape as the second superconductor 866b.

[0255] Next, the support 4 on which the two-layer resist film is formed is mounted in a vacuum deposition apparatus. Then, a superconductor (for example, aluminum) is deposited onto the support 4 through the resist openings in the two-layer resist film.

[0256] This deposition process forms the second superconductor 866b. The deposition of the second superconductor 866b is carried out by oblique deposition. Oblique deposition is a technique for forming a thin film by using material vapor incident at an oblique angle onto a substrate (for example, a support 4).

[0257] As described above, the resist opening has a first opening and a second opening. The second superconductor 866b is formed by material vapor incident on the support 4 through the second opening. On the other hand, a thin film having substantially the same planar shape as the first superconductor 866a is formed by material vapor incident on the support 4 through the first opening. This thin film (hereinafter referred to as the first dummy thin film) is not included in the superconductor circuit 862 of the modified example 1.

[0258] (c) Step S14 Next, oxygen is introduced into the vacuum deposition apparatus in which the second superconductor 866b is formed. This forms an insulator 878 (for example, aluminum oxide) that covers the surface of the second superconductor 866b. The pressure of the oxygen introduced into the vacuum deposition apparatus is, for example, 1 to 10 Torr.

[0259] (d) Step S15 Next, oxygen is evacuated from the vacuum deposition apparatus. Furthermore, the support 4 is rotated 180°. This rotation changes the angle of incidence of the material vapor. Subsequently, a superconductor (e.g., aluminum) and a normal conductor (e.g., palladium or platinum) are deposited onto the support 4 through the resist opening, in that order. This deposition forms the first superconductor 866a and a normal conductor film covering the upper surface of the first superconductor 866a.

[0260] As described above, the resist opening has a first opening and a second opening. Material vapor incident on the support 4 through the first opening forms the first superconductor 866a and a normal conductor film. On the other hand, material vapor incident on the support 4 through the second opening forms a thin film having substantially the same planar shape as the second superconductor 866b. This thin film (hereinafter referred to as the second dummy thin film) is not included in the superconductor circuit 862 of the modified example 1.

[0261] (e) Steps S8, S9m, S10m, S11 Steps S8 and S11 are processes described with reference to Figures 40 and 43. Therefore, the description of steps S8 and S11 will be omitted.

[0262] Steps S9m and S10m are variations of steps S9 and S10, which were explained with reference to Figure 40, etc. The explanation of step S9 (see "(3-4) Step S9") becomes the explanation of step S9m by replacing "normal conductor 768" with "metal film". The explanation of step S10 (see "(3-5) Step S10") becomes the explanation of step S10m by replacing "normal conductor 768" with "metal film" and further replacing "normal conductor 668" with "metal film 834". Therefore, the explanations of steps S9m and S10m are omitted.

[0263] Step S9m is a modified version of the second step S2, as described with reference to Figure 13. Step S10m is a modified version of the third step S3, as described with reference to Figure 14.

[0264] Steps S8, S9m, S10m, and S11 arrange the two-dimensional topological insulator 6 and the coating 608 on the support 4. This completes the modified example 1 (see Figure 46).

[0265] Step S12 may be performed after step S15. For example, step S12 may be performed between step S15 and step S8 or after step S11.

[0266] Figure 49 is a plan view of the vicinity of the first Josephson junction J1m in Modification Example 1. Figure 50 is an enlarged view of the area 870 enclosed by the dashed line in Figure 49. Figure 46, mentioned above, is a cross-sectional view along a line that crosses Modification Example 1 (hereinafter referred to as the cross line). The line XLVI-XLVI shown in Figure 50 is part of this cross line. In a plan view, the first Josephson junction J1m is formed at position X where the insulator 878 and the metal film 834 intersect (see Figure 50).

[0267] A second dummy thin film (not shown) is formed near the insulator 878 (i.e., near the second superconductor 866b) (see Figure 49). A first dummy thin film (not shown) is formed near the metal film 834 (i.e., near the first superconductor 866a) (see Figure 49). To avoid complicating the diagram, the first and second dummy thin films are not shown in Figure 49.

[0268] (4-2) Modification 2 (4-2-1) Structure The quantum device 602 shown in Figure 36 has a normal conductor 668 in contact with the upper surface of the first superconductor 666a. Similarly, the modified example 1 shown in Figure 46 has a metal film 834 in contact with the upper surface of the first superconductor 866a. However, the quantum device according to Embodiment 3 does not need to have either the normal conductor 668 or the metal film 834.

[0269] Figure 51 shows a cross-section of an example of a quantum device without a normal conductor 668 and a metal film 834 (hereinafter referred to as Modification 2). Modification 2 differs from Modification 1, which was described with reference to Figure 46, in that it does not have a metal film 834. Furthermore, Modification 2 differs from Modification 1, which was described with reference to Figure 46, in that the hexagonal boron nitride 12 of the coating 908 covers only a portion of the S-wave superconductor 610. Except for these points, Modification 2 has substantially the same structure as Modification 1.

[0270] (4-2-2) Manufacturing method Figure 52 is a process flow chart showing an example of the manufacturing method for Modification Example 2 (hereinafter referred to as the fifth manufacturing method). The fifth manufacturing method is similar to the fourth manufacturing method (i.e., the manufacturing method for Modification Example 1). Therefore, the explanation of the parts common to the fourth manufacturing method will be omitted or simplified.

[0271] (a) Steps S12-14 Steps S12-S14 are the process described with reference to Figure 48. Steps S12-S14 form a microwave resonator 664, a second superconductor 866b (e.g., aluminum), and an insulator 878 (e.g., aluminum oxide) covering the second superconductor 866b.

[0272] (b) Step S15m Next, a first superconductor 866a in contact with the insulator 878 is formed by oblique deposition of aluminum. Step S15m is a modified example of step S15 shown in Figure 48.

[0273] (c) First step S1 The first step S1 is the step described with reference to Figure 6. In the first step S1, the upper surface s3 of the single layer 1T'-WTe2106 (i.e., the two-dimensional topological insulator 6) is covered with a first coating 108a including the multilayer WTe2109 (see Figure 12(c)).

[0274] (d) Step S2m Next, the native oxide film (e.g., aluminum oxide) covering the surface of the first superconductor 866a is removed or reduced. The native oxide film is removed, for example, by HF vapor. Alternatively, the native oxide film is reduced, for example, by hydrogen plasma.

[0275] Subsequently, the first coating 108a (see Figure 12(c)) and the single layer 1T'-WTe2106 (i.e., the two-dimensional topological insulator 6) are attached to the support 4 (see Figure 51). This attachment is carried out so that the multilayer WTe2109 is in contact with the first superconductor 866a (see Figure 51).

[0276] Step S2m is a modified version of the second step S2, as described with reference to Figure 6.

[0277] (e) Step S3s Step S3s is substantially the same as the third step S3 described with reference to Figures 6 and 14. Step S3s causes the second metal atoms to diffuse from the metal film 134 into the multilayer WTe 2109. As a result, the S-wave superconductor 610 is formed.

[0278] (f) Step S11s Finally, step S11s forms the first and second ferromagnetic materials 550a, 550b (see Figure 35) on the coating 908. Step S11s is substantially the same as step S11 shown in Figure 48. Modification 2 increases the variations of the quantum apparatus according to Embodiment 3.

[0279] In the fifth manufacturing method shown in Figure 52, the S-wave superconductor 610 is formed by the first manufacturing method described with reference to Figure 6, for example. However, the S-wave superconductor 610 may also be formed by the second manufacturing method described with reference to Figure 17, for example.

[0280] In the modified example 2 shown in Figure 51, the S-wave superconductor 610 is in contact with the upper surface s1 of the first superconductor 866a. That is, the edge of the S-wave superconductor 610 is resting on top of the first superconductor 866a.

[0281] However, the S-wave superconductor 610 may be in contact with the lower surface s2 of the first superconductor 866a. That is, the edge of the first superconductor 866a may ride up onto the S-wave superconductor 610. In this case, steps S13-S14 and S15m are performed after step S3s.

[0282] The quantum apparatus of Embodiment 3 comprises an apparatus in which Majorana quasiparticle pairs appear (i.e., a quantum apparatus according to Embodiment 2) and a circuit for performing quantum operations based on Majorana quasiparticle pairs (i.e., a superconductor circuit 662 and a microwave resonator 664). Accordingly, Embodiment 3 provides a minimal circuit for Majorana qubits (see, for example, Non-Patent Document 3).

[0283] While embodiments of the present invention have been described above, embodiments 1 to 3 are illustrative and not limiting. For example, the coatings illustrated in embodiments 1 to 3 have hexagonal boron nitride. However, coatings according to embodiments 1 to 3 may have another substance (for example, amorphous boron nitride or graphene) instead of hexagonal boron nitride. The same applies to the first and second coatings.

[0284] Hexagonal boron nitride is a layered material having multiple monolayers. However, the coatings according to Embodiments 1 to 3 may have only one monolayer of hexagonal boron nitride instead of hexagonal boron nitride.

[0285] The quantum apparatus according to Embodiments 2-3 has first and second ferromagnetic materials. However, the quantum apparatus according to Embodiments 2-3 may have electrodes that apply an electric field to the end E of a two-dimensional topological insulator 6 instead of the first and second ferromagnetic materials. One-dimensional chiral p-wave superconductivity can also be terminated by applying an electric field.

[0286] The quantum apparatus according to Embodiments 2-3 has multiple ferromagnetic materials. However, the quantum apparatus according to Embodiments 2-3 may have only one ferromagnetic material. For example, the quantum apparatus according to Embodiments 2-3 may have a single ferromagnetic material with both ends located at the positions where the first and second ferromagnetic materials 550a and 550b (see Figure 33) are arranged.

[0287] The glove boxes used in the manufacturing methods according to Embodiments 1 to 3 are filled with argon. However, these glove boxes may be filled with an inert gas other than argon (for example, helium, neon, krypton, xenon, and nitrogen).

[0288] In the manufacturing method according to Embodiments 1 to 3, the single-layer 1T'-WTe2 and the multi-layer WTe2 are placed inside a glove box filled with inert gas until the second step S2 is completed. However, the single-layer 1T'-WTe2 and the multi-layer WTe2 may be placed in a space other than the inside of the glove box. The single-layer 1T'-WTe2 and the multi-layer WTe2 may be placed, for example, inside a vacuum device from which the atmosphere has been evacuated until the second step S2 is completed.

[0289] The following additional information is disclosed regarding the above embodiments 1 to 3.

[0290] (Note 1) Support and A monolayer of tungsten ditelluride having a 1T'-type crystal structure, comprising a two-dimensional topological insulator disposed on or above the support, The invention comprises an S-wave superconductor having tungsten atoms, tellurium atoms, and metal atoms different from the tungsten and tellurium atoms, and a coating covering the two-dimensional topological insulator, The S-wave superconductor is arranged so as to be in contact with a portion of the end of the two-dimensional topological insulator. Quantum device.

[0291] (Note 2) The two-dimensional topological insulator has a first energy band localized at the end and a second energy band localized at the end and different from the first energy band. The spin of the electrons belonging to the first energy band is oriented in the first direction. The spin of an electron belonging to the second energy band is oriented in a second direction opposite to the first direction. The quantum device described in Appendix 1 as a key feature.

[0292] (Note 3) The S-wave superconductor is in contact only with the first portion of the outer circumference and the second portion of the outer circumference that is in contact with both ends of the first portion. The two-dimensional topological insulator is disposed between the coating and the support. A quantum device characterized by the features described in Appendix 1 or 2.

[0293] (Note 4) The coating further comprises hexagonal boron nitride in contact with the two-dimensional topological insulator and the S-wave superconductor. A quantum device characterized by the features described in Appendix 1 or 2.

[0294] (Note 5) The aforementioned monolayer is a monolayer obtained from the tungsten ditelluride single crystal, The aforementioned metal atom is one of palladium, platinum, or niobium atoms. A quantum device characterized by the features described in Appendix 1 or 2.

[0295] (Note 6) Furthermore, the ferromagnetic material is arranged such that pairs of Majorana quasiparticles appear at specific locations within the two-dimensional topological insulator. A quantum device characterized by the features described in Appendix 1 or 2.

[0296] (Note 7) Furthermore, a superconducting circuit having a first superconductor in contact with the S-wave superconductor, a second superconductor different from the S-wave superconductor and the first superconductor, a first Josephson junction including a portion of the first superconductor and a portion of the second superconductor, a second Josephson junction including a portion of the first superconductor and a portion of the second superconductor and connected in parallel to the first Josephson junction, and an opening in which at least a portion is located between the first Josephson junction and the second Josephson junction, The microwave resonator has a first transmission line and a second transmission line different from the first transmission line. The two-dimensional topological insulator, the S-wave superconductor, and the superconducting circuit are arranged between the first transmission path and the second transmission path. The quantum device described in Appendix 6 as having distinctive features.

[0297] (Note 8) The first superconductor has a first surface in contact with the S-wave superconductor and a second surface located between the first surface and the support. The superconducting circuit further includes a normal conductor having the metal atoms, which is in contact with the first surface of the first superconductor and the second superconductor. The first Josephson junction and the second Josephson junction each further have a portion of the normal conductor. The quantum device described in Appendix 7 as a key feature.

[0298] (Note 9) A first step involves covering the third surface of a first monolayer separated from a first single crystal of tungsten ditelluride having a 1T'-type crystal structure with a first coating having a layered material separated from a second single crystal of tungsten ditelluride, A second step is to attach the first single layer and the first coating to the support such that, after the first step, the fourth surface of the first single layer that extends along the third surface is positioned between the third surface and the support, The process includes a third step, after the second step, of diffusing metal atoms different from tungsten atoms and tellurium atoms into the layered material to form an S-wave superconductor having tungsten atoms, tellurium atoms, and the metal atoms, The first step is to cover the third surface of the first single layer with the first coating such that the layered material is in contact only with the third portion of the third portion of the outer periphery of the first single layer and the fourth portion of the outer periphery that is in contact with both ends of the third portion. The first single layer is separated from the first single crystal in a space where the atmosphere is removed, and thereafter is placed in a space where the atmosphere is removed until the second step is completed. The layered material is separated from the second single crystal in a space where the atmosphere has been removed, and is then placed in the space where the atmosphere has been removed until the second step is completed. A method for manufacturing quantum devices.

[0299] (Note 10) The first coating further comprises hexagonal boron nitride in contact with the layered material, The first step is a step of covering the third surface with the first coating such that the hexagonal boron nitride is in contact with the third surface. A method for manufacturing the quantum device described in Appendix 9, which is a key feature.

[0300] (Note 11) The third step is a first sub-step in which a metal containing the metal atoms is placed in the exposed portion of the layered material, The invention includes a second sub-step of heating the metal and the layered material to diffuse the metal atoms into the layered material. A method for manufacturing a quantum apparatus as described in Appendix 9 or 10.

[0301] (Note 12) Furthermore, prior to the second step, there is a fourth step of forming a laminated film on a portion of the support, which includes a normal conductor having the metal atoms and a first superconductor located between the normal conductor and the support. The second step is to attach the first single layer and the first coating to the support such that only the layered material among the first single layer and the layered material is in contact with the normal conductor. The third step is a step of heating the normal conductor and the layered material so that the metal atoms diffuse into the layered material and the S-wave superconductor is formed. A method for manufacturing a quantum apparatus as described in Appendix 9 or 10.

[0302] (Note 13) The number of single layers in the aforementioned layered material is 3 or more and 10 or less. The aforementioned metal atom is one of palladium, platinum, or niobium atoms. A method for manufacturing a quantum apparatus as described in Appendix 9 or 10.

[0303] (Note 14) A fifth step involves covering the third surface of a first monolayer separated from a first single crystal of tungsten ditelluride having a 1T'-type crystal structure with a second film containing an S-wave superconductor having metal atoms different from tungsten atoms and tellurium atoms, as well as tungsten atoms and tellurium atoms. The process includes a sixth step of attaching the first single layer and the second coating to the support such that, after the fifth step, the fourth surface of the first single layer, which extends along the third surface, is positioned between the third surface and the support. The fifth step is to cover the third surface of the first single layer with the second coating such that the S-wave superconductor is in contact with only the third portion of the third portion of the outer periphery of the first single layer and the fourth portion of the outer periphery that is in contact with both ends of the third portion. The first single layer is separated from the first single crystal in a space where the atmosphere is removed, and thereafter is placed in a space where the atmosphere is removed until the sixth step is completed. The S-wave superconductor is formed or separated from a single crystal in a space devoid of air, and thereafter is placed in a space devoid of air until the sixth step is completed. A method for manufacturing quantum devices.

[0304] (Note 15) The second coating further comprises hexagonal boron nitride in contact with the S-wave superconductor. The aforementioned metal atom is one of palladium, platinum, or niobium atoms. The fifth step is a step of covering the third surface with the second coating so that the hexagonal boron nitride is in contact with the third surface. A method for manufacturing the quantum device described in Appendix 14, which is a key feature. [Explanation of symbols]

[0305] 2:Quantum device 4:Support 6: Two-dimensional topological insulator 8:Coating 10,110: S-wave superconductor 12,112: Hexagonal boron nitride 106: Single layer 109: Layered material 550: Ferromagnetic material 662: Superconductor Circuits 664: Microwave resonator 666a: First superconductor 666b: Second superconductor 668: Normal conductor 674 :Aperture 676a: First transmission line 676b: Second transmission line

Claims

1. Support and A monolayer of tungsten ditelluride having a 1T' type crystal structure, comprising a two-dimensional topological insulator disposed on or above the support, The invention comprises an S-wave superconductor having tungsten atoms, tellurium atoms, and metal atoms different from the tungsten and tellurium atoms, and a coating covering the two-dimensional topological insulator, The S-wave superconductor is arranged so as to be in contact with a portion of the end of the two-dimensional topological insulator. Quantum device.

2. The two-dimensional topological insulator has a first energy band localized at the end and a second energy band localized at the end and different from the first energy band. The spin of the electrons belonging to the first energy band is oriented in the first direction. The spin of an electron belonging to the second energy band is oriented in a second direction opposite to the first direction. The quantum apparatus as described in claim 1, characterized by its features.

3. The S-wave superconductor is in contact only with the first portion of the outer circumference and the second portion of the outer circumference that is in contact with both ends of the first portion. The two-dimensional topological insulator is disposed between the coating and the support. A quantum apparatus characterized by the features of claim 1 or 2.

4. The coating further comprises hexagonal boron nitride in contact with the two-dimensional topological insulator and the S-wave superconductor. A quantum apparatus characterized by the features of claim 1 or 2.

5. The aforementioned monolayer is a monolayer obtained from the tungsten ditelluride single crystal, The metal atom is one of palladium, platinum, or niobium. A quantum apparatus characterized by the features of claim 1 or 2.

6. Furthermore, the ferromagnetic material is arranged such that pairs of Majorana quasiparticles appear at specific locations within the two-dimensional topological insulator. A quantum apparatus characterized by the features of claim 1 or 2.

7. Furthermore, a superconducting circuit having a first superconductor in contact with the S-wave superconductor, a second superconductor different from the S-wave superconductor and the first superconductor, a first Josephson junction including a portion of the first superconductor and a portion of the second superconductor, a second Josephson junction including a portion of the first superconductor and a portion of the second superconductor and connected in parallel to the first Josephson junction, and an opening in which at least a portion is located between the first Josephson junction and the second Josephson junction, The microwave resonator has a first transmission line and a second transmission line different from the first transmission line. The two-dimensional topological insulator, the S-wave superconductor, and the superconducting circuit are arranged between the first transmission path and the second transmission path. The quantum apparatus as described in claim 6, characterized by its features.

8. The first superconductor has a first surface in contact with the S-wave superconductor and a second surface located between the first surface and the support. The superconducting circuit further includes a normal conductor having the metal atoms, which is in contact with the first surface of the first superconductor and the second superconductor. The first Josephson junction and the second Josephson junction each further have a portion of the normal conductor. The quantum apparatus as described in claim 7, characterized by its features.

9. A first step involves covering the third surface of a first monolayer separated from a first single crystal of tungsten ditelluride having a 1T'-type crystal structure with a first coating having a layered material separated from a second single crystal of tungsten ditelluride, A second step is to attach the first single layer and the first coating to the support such that, after the first step, the fourth surface of the first single layer that extends along the third surface is positioned between the third surface and the support, The third step involves diffusing metal atoms different from tungsten atoms and tellurium atoms into the layered material after the second step, thereby forming an S-wave superconductor having tungsten atoms, tellurium atoms, and the metal atoms. The first step is to cover the third surface of the first single layer with the first coating such that the layered material is in contact only with the third portion of the third portion of the outer periphery of the first single layer and the fourth portion of the outer periphery that is in contact with both ends of the third portion. The first single layer is separated from the first single crystal in a space where the atmosphere is removed, and thereafter is placed in a space where the atmosphere is removed until the second step is completed. The layered material is separated from the second single crystal in a space where the atmosphere is removed, and is then placed in the space where the atmosphere is removed until the second step is completed. A method for manufacturing quantum devices.

10. The first coating further comprises hexagonal boron nitride in contact with the layered material, The first step is a step of covering the third surface with the first coating such that the hexagonal boron nitride is in contact with the third surface. A method for manufacturing a quantum apparatus as described in claim 9.

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