Method for manufacturing junctions to form qubits

Abstract

A method for fabricating a Josephson junction for superconducting qubits includes: providing a substructure (500) having a surface in which a first trench and a second trench (306 and 308) perpendicular to each other are defined. The method further includes: evaporating a first superconducting material (700) to deposit the first superconducting material in the first trench, and evaporating a second superconducting material (701) to deposit the second superconducting material in the first trench to form a first lead (710); and forming an oxide layer (800) on the first and second superconducting materials. The method includes: evaporating a third superconducting material (900) at an angle substantially perpendicular to the surface (502) of the substructure to deposit the third superconducting material in the second trench without rotating the substructure to form a second lead (910). A vertical Josephson junction electrically connected by the first and second leads is formed at the intersection of the first and second trenches.

Description

Technical Field

[0001] The presently claimed embodiments of the present invention relate to superconducting qubits, and more specifically, to methods for manufacturing superconducting qubits and qubits manufactured using such methods. Background Technology

[0002] Quantum computing is based on reliable control of quantum bits (referred to as qubits throughout this document). The fundamental operations required to implement quantum algorithms are a set of single-qubit and two-qubit operations that establish correlation between two individual qubits. To meet the error threshold of quantum computing and to achieve reliable quantum simulation, high-fidelity implementation of two-qubit operations is desirable.

[0003] A superconducting quantum processor (having one or more superconducting qubits) comprises a superconducting metal (e.g., Al, Nb, etc.) on an insulating substrate (e.g., Si or high-resistivity Si, Al₂O₃, etc.). Superconducting quantum processors are typically planar two-dimensional lattice structures of individual qubits linked by couplers with various lattice symmetries (e.g., square, hexagonal, etc.), and readout structures located on a flip chip. The couplers can be made of capacitors, resonators, coils, or any microwave component that provides coupling between qubits.

[0004] The conventional method for fabricating superconducting qubits is based on the standard Josephson junction, which uses the Dolan or Manhattan method to form the bridge. These methods require numerous steps, including rotating the substrate supporting the qubit during the deposition of the superconducting material. Summary of the Invention

[0005] One aspect of the present invention provides a method for fabricating a Josephson junction for superconducting qubits. The method includes: providing a substructure having a surface defining a first trench and a second trench, the first trench being substantially perpendicular to and intersecting the second trench, the substructure having a bridge structure extending above the first trench adjacent to the intersection of the first and second trenches. The method further includes: depositing a first superconducting material at a grazing angle along a first direction to deposit the first superconducting material in the first trench so as to extend below the bridge structure from the first direction. The method further includes: depositing a second superconducting material substantially opposite to the first direction at the grazing angle to deposit the second superconducting material in the first trench so as to extend below the bridge structure from the grazing angle substantially opposite to the first direction, and providing a first superconducting lead. The method further includes: oxidizing the first superconducting material and the second superconducting material to form an oxide layer on the first superconducting material and the second superconducting material at least within the first trench; and evaporating a third superconducting material at an angle substantially perpendicular to the surface of the substructure to deposit the third superconducting material in the second trench within the substructure without rotating the substructure to form a second superconducting lead. The method further includes: stripping the deposited regions of the first superconducting material, the second superconducting material, and the third superconducting material and the oxide layer to leave a vertical Josephson junction at the intersection of the first trench and the second trench, the vertical Josephson junction being electrically connected at a first end via the first superconducting lead and at a second end via the second superconducting lead.

[0006] Another aspect of the present invention provides a superconducting qubit. The superconducting qubit is fabricated by the following steps: 1) providing a substructure having a surface defining a first trench and a second trench, the first trench being substantially perpendicular to and intersecting the second trench, the substructure having a bridge structure extending above the first trench; 2) depositing a first superconducting material at a grazing angle along a first direction to deposit the first superconducting material in the first trench so as to extend from the first direction below the bridge structure; 3) depositing a second superconducting material substantially opposite to the first direction at the grazing angle to deposit the second superconducting material in the first trench so as to extend from the grazing angle substantially opposite to the first direction below the bridge structure, and providing a first superconducting lead; 4) oxidizing the first superconducting qubit... 5) Deposit a third superconducting material at an angle substantially perpendicular to the surface of the substructure to deposit the third superconducting material in the second trench within the substructure without rotating the substructure, thereby forming a second superconducting lead; and 6) Strip the deposited regions of the first, second, and third superconducting materials and the oxide layer to leave a vertical Josephson junction at the intersection of the first and second trenches, the vertical Josephson junction being electrically connected at its first end via the first superconducting lead and at its second end via the second superconducting lead. Attached Figure Description

[0007] The functionality of the relevant elements of this disclosure, as well as the economy of combination and manufacture of the components, will become more apparent when the following description and appended claims are considered in conjunction with the accompanying drawings, all of which form part of this specification, wherein the same reference numerals denote corresponding components in the various drawings. However, it should be clearly understood that the drawings are for illustrative and descriptive purposes only and are not intended to limit the invention.

[0008] Figure 1A This is a schematic side view of a substrate according to an embodiment of the present invention, wherein a superconducting material is deposited on the substrate;

[0009] Figure 1B This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material is deposited on the substrate;

[0010] Figure 2A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate;

[0011] Figure 2B It is according to an embodiment of the present invention. Figure 2A The schematic cross-sectional view of the substrate shown by the dashed line 2B-2B, on which a superconducting material and a sacrificial resist layer are deposited;

[0012] Figure 3A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, and trenches are formed in the resist layer;

[0013] Figure 3B It is according to an embodiment of the present invention. Figure 3A The schematic cross-sectional view of the substrate shown by the dashed line 3B-3B shows a superconducting material and a sacrificial resist layer deposited on the substrate, with trenches formed in the resist layer.

[0014] Figure 4A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, and trenches are formed in the resist layer;

[0015] Figure 4B It is according to an embodiment of the present invention. Figure 4A The schematic cross-sectional view of the substrate shown by the dashed lines 4B-4B shows a superconducting material and a sacrificial resist layer deposited on the substrate, with trenches formed in the resist layer.

[0016] Figure 5A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, and trenches and bridges are formed in the resist layer;

[0017] Figure 5B It is according to an embodiment of the present invention. Figure 5A The schematic cross-sectional view of the substrate shown by the dashed lines 5B-5B shows a superconducting material and a sacrificial resist layer deposited on the substrate, with trenches and bridges formed in the resist layer.

[0018] Figure 6A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, and trenches and bridges are formed in the resist layer;

[0019] Figure 6B It is according to an embodiment of the present invention. Figure 6A The schematic cross-sectional view of the substrate shown by the dashed lines 6B-6B shows a superconducting material and a sacrificial resist layer deposited on the substrate, with trenches and bridges formed in the resist layer.

[0020] Figure 7AThis is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, and trenches and bridges are formed in the resist layer;

[0021] Figure 7B It is according to an embodiment of the present invention. Figure 7A The schematic cross-sectional view of the substrate shown by the dashed lines 7B-7B shows a superconducting material and a sacrificial resist layer deposited on the substrate, with trenches and bridges formed in the resist layer, and the superconducting material being vapor-deposited along the first trench.

[0022] Figure 8A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, trenches and bridges are formed in the resist layer, and a superconducting material is deposited on the resist layer;

[0023] Figure 8B It is according to an embodiment of the present invention. Figure 8A The schematic cross-sectional view of the substrate shown by the dashed lines 8B-8B shows a superconducting material and a sacrificial resist layer deposited on the substrate, with trenches and bridges formed in the resist layer, and the superconducting material being vapor-deposited along the first trench.

[0024] Figure 9A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, trenches and bridges are formed in the resist layer, and the superconducting material is deposited on the resist layer by means of a first vapor deposition and a second vapor deposition.

[0025] Figure 9B It is according to an embodiment of the present invention. Figure 9A The schematic cross-sectional view of the substrate shown by the dashed lines 9B-9B shows a superconducting material and a sacrificial resist layer deposited on the substrate, with trenches and bridges formed in the resist layer, and the superconducting material being vapor-deposited along the second trench.

[0026] Figure 10A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, and the superconducting material is deposited in a first trench and a second trench;

[0027] Figure 10B It is according to an embodiment of the present invention. Figure 10A The schematic cross-sectional view of the substrate shown by the dashed lines 10B-10B shows a superconducting material and a sacrificial resist layer deposited on the substrate, with trenches and bridges formed in the resist layer, and the superconducting material being vapor-deposited along the second trench.

[0028] Figure 11AThis is a schematic top view of a qubit device formed according to the above method according to an embodiment of the present invention;

[0029] Figure 11B It is according to an embodiment of the present invention. Figure 11A A schematic cross-sectional view of the qubit device formed by the dashed lines 11B-11B shown in the figure;

[0030] Figure 11C It is according to an embodiment of the present invention. Figure 11A A schematic cross-sectional view of the qubit device formed by the dashed lines 11C-11C shown in the figure;

[0031] Figure 12A These are magnified scanning electron microscope (SEM) images showing a qubit device formed using the method described above according to an embodiment of the present invention; and

[0032] Figure 12B The image shown is a reduced-size scanning electron microscope (SEM) image illustrating a qubit device formed using the method described above according to an embodiment of the present invention. Detailed Implementation

[0033] In one embodiment, this document provides a method for fabricating a Josephson junction for superconducting qubits. In one embodiment, the method includes: providing a substructure comprising a substrate and a superconducting material. Figure 1A This is a schematic side view of a substrate on which a superconducting material is deposited, according to an embodiment of the present invention. In one embodiment, providing a substructure includes providing a substrate 100 and depositing a superconducting material 102 on a surface (e.g., top surface) 100A of the substrate 100.

[0034] In one embodiment, the substrate 100 can be any non-conductive material, including but not limited to silicon (Si), germanium (Ge), and sapphire. In one embodiment, the superconducting material 102 can be any superconducting material, including but not limited to niobium (Nb), aluminum (Al), etc.

[0035] Figure 1B This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material is deposited on the substrate. In one embodiment, providing the substructure includes: removing a portion 102A of the superconducting material 102 from a surface 100A of the substrate 100 to expose a portion 100B of the surface 100A of the substrate. Figure 1BA portion 102A of the superconducting material 102 that has been removed is shown. In one embodiment, removing a portion 102A of the superconducting material 102 from the surface 100A of the substrate 100 to expose a portion 100B of the surface 100A of the substrate 100 includes: a plurality of sectors 104 (e.g., four) forming the superconducting material 102 and associated buses 106. The plurality of sectors (e.g., four) 104 are spaced apart by the exposed portion 100B of the surface 100A of the substrate 100. The plurality of sectors 104 define coupling pads for coupling to a Josephson junction, as will be described in detail in the following paragraphs. Buses or resonators 106 are configured to couple to the plurality of sectors 104 for transmitting microwave energy to and from the Josephson junction. A gap 105 formed between each of the plurality of sectors 104 and its corresponding bus or resonator 106 defines a coupling capacitor. Although the multiple sectors 104 are shown herein as having a “sector” shape, it must be understood that the sector or pad 104 is not limited to a “sector” shape, but can be any other shape, such as any polygonal (triangle, square, rectangle, pentagon, hexagon, etc.) shape or circular (semicircle, disk, etc.) shape.

[0036] Figure 2A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate. Figure 2B It is according to an embodiment of the present invention. Figure 2A The diagram shows a schematic cross-sectional view of the substrate along the dashed lines 2B-2B, on which a superconducting material and a sacrificial resist layer are deposited. In one embodiment, after removing a portion 102A of the superconducting material 102 from surface 100A of substrate 100 to expose a portion 100B of surface 100A of substrate 100, the substructure is provided by depositing a first resist layer 202 on the superconducting material 102 and on the exposed portion 100B of surface 100A of substrate 100. In another embodiment, the substructure is provided by depositing a second resist layer 204 on the first resist layer 202 to form a superimposed first and second resist layer.

[0037] In one embodiment, the first resist layer 202 may be, for example, a methyl methacrylate (MMA) layer, while the second resist layer 204 may be, for example, a polymethyl methacrylate (PMMA) layer. In one embodiment, the set of sacrificial resist layers 202 and 204 is selected such that the first resist layer 202 (e.g., MMA) is etched faster than the second resist layer 204 (e.g., PMMA), as will be described in further detail in the following paragraphs.

[0038] Figure 3AThis is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, and trenches are formed in the resist layer. Figure 3B It is according to an embodiment of the present invention. Figure 3A The schematic cross-sectional view of the substrate shown by the dashed lines 3B-3B shows a superconducting material and a sacrificial resist layer deposited on the substrate, with trenches formed in the resist layer. Figure 4A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, and trenches are formed in the resist layer. Figure 4B It is according to an embodiment of the present invention. Figure 4A The schematic cross-sectional view of the substrate shown by the dashed lines 4B-4B shows a superconducting material and a sacrificial resist layer deposited on the substrate, with trenches formed in the resist layer.

[0039] In one embodiment, after depositing the sacrificial resist layers 202 and 204, providing the substructure further includes: applying electron beam or beam lithography to expose a first portion 302 of the stacked first and second resist layers 202 and 204, and to expose a second portion 304 of the stacked first and second resist layers 202 and 204, such as... Figure 3A and 4A As shown.

[0040] In one embodiment, providing the substructure after applying electron beam or beam lithography further includes: removing the exposed first portion 302 of the superimposed first and second resist layers 202 and 204 to form a first trench 306 (e.g., Figure 3B (as shown), and removing the exposed second portion 304 of the superimposed first and second resist layers 202 and 204 to form the second trench 308 (as shown). Figure 4B As shown). Figure 3B As shown, the first resist layer 202 is removed from the exposed first portion 302 to define the first trench 306. Figure 4B As shown, the first resist layer 204 is also removed from the exposed second portion 304 to define the second trench 308. In one embodiment, the first trench 306 and the second trench 308 are substantially perpendicular to each other. The first trench 306 is substantially perpendicular to and intersects with the second trench 308.

[0041] In addition, such as Figure 4B As shown, the second resist layer 204 is also removed from the exposed second portion 304 to define the second trench 308. However, as Figure 3BAs shown, the second resist layer 204 is also removed from the exposed first portion 302 to form a first trench 306 except near the intersection of the first and second trenches 306 and 308, thereby forming a bridge structure 402 extending over the first trench 306 with the remaining portion of the second resist layer 204. In one embodiment, the bridge structure 402 is substantially parallel to the second trench 308.

[0042] Bridge 402 includes two strips 402A and 402B of the second resist layer 204, both of which traverse the first trench 306 and are substantially parallel to either side of the second trench 308, starting from that side, such as... Figure 3A , 3B As shown in 4A and 4B. In one embodiment, the two bands 402A and 402B that form the bridge 402 are formed because the first resist layer 202 (e.g., MMA) below the two bands 402A is etched faster than the second resist layer 204 (e.g., PMMA).

[0043] Figure 5A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, and trenches and bridges are formed in the resist layer. Figure 5B It is according to an embodiment of the present invention. Figure 5A The diagram shows a schematic cross-sectional view of the substrate represented by dashed lines 5B-5B, on which a superconducting material and a sacrificial resist layer are deposited, and trenches and bridges are formed within the resist layer. Figure 5B As shown, for example, the band 402B in the bridge structure 402 formed in the second resist layer 204 extends over the first trench 306.

[0044] Figure 6A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, and trenches and bridges are formed in the resist layer. Figure 6B It is according to an embodiment of the present invention. Figure 6A The diagram shows a schematic cross-sectional view of the substrate, indicated by dashed lines 6B-6B, on which a superconducting material and a sacrificial resist layer are deposited, and trenches and bridges are formed within the resist layer. Figure 6B As shown, in the cross-section along line 6B-6B, in this region of the substructure or substrate 100, neither the first resist layer 202 nor the second resist layer 204 is etched or removed. Therefore, the bridge structure 402 (including strips 402A and 402B) is formed only near and parallel to the second trench 308, and the bridge structure traverses the first trench 306.

[0045] As a result, Figure 3A , 4AThe images shown from the top in 5A and 6A, as well as those in Figure 3B , 4B The provided substructure 500, shown in various cross-sections in 5B and 6B, includes: a substrate 100, a superconducting material 102, resist layers 202 and 204, trenches 306 and 308, and a bridge structure 402. For example, Figure 6A As shown, substructure 500 has a surface 502 in which first and second grooves 306 and 308 are defined. The first groove 306 is substantially perpendicular to and intersects the second groove 308. Substructure 500 has a bridge structure 402 adjacent to the intersection of the first and second grooves 306 and 308 and extending above the first groove 306.

[0046] Figure 7A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, and trenches and bridges are formed in the resist layer. Figure 7B It is according to an embodiment of the present invention. Figure 7A The schematic cross-sectional view of the substrate shown by the dashed lines 7B-7B shows a superconducting material and a sacrificial resist layer deposited on the substrate, with trenches and bridges formed in the resist layer, and the superconducting material being vapor-deposited along the first trench.

[0047] like Figure 7A and 7B The method for fabricating a Josephson junction for superconducting qubits, as described herein, further includes: depositing (first deposition) superconducting material 700 along a first direction 702 at a grazing angle to deposit superconducting material 700 in a first trench 306, so as to extend from the first direction 702 below the bridge structure 402 (below bands 402A and 402B of the bridge structure 402). Figure 7A and 7B The method of fabricating a Josephson junction for superconducting qubits, as described herein, further includes: depositing (second deposition) superconducting material 701 in a direction 704 substantially opposite to the first direction 702 at a substantially grazing angle to deposit superconducting material 701 in a first trench 306 so as to extend from an angle substantially opposite to the first direction 702 below the bridge structure 402 (below the bands 402A and 402B of the bridge structure 402) to provide a first superconducting lead 710.

[0048] In one embodiment, depositing superconducting material 700 at a grazing angle along a first direction 702 to deposit superconducting material 700 in a first trench 306 includes depositing superconducting material 700 below bridge structure 402. In one embodiment, depositing superconducting material 701 at a substantially grazing angle in a direction 704 substantially opposite to the first direction 702 to deposit superconducting material 701 in a first trench 306 includes depositing superconducting material 701 in regions (not shown) that are shielded by bridge structure 402 and are not filled or partially filled by superconducting material 700 during the deposition of superconducting material 700.

[0049] In one embodiment, the grazing angle can be any angle between approximately 5 degrees and 85 degrees relative to the surface 502 of the substructure 500. In one embodiment, the grazing angle is between 55 degrees and 65 degrees. In another embodiment, the grazing angle is approximately 45 degrees. In one embodiment, the grazing angle is selected based on the material type of the resist layers 202 and 204 used, based on the dimensions of the bridge 402 (i.e., the dimensions of band 402A and band 402B), the dimensions (e.g., width) of the first trench 306, and / or the thickness or depth of the resist layers 202 and 204.

[0050] Figure 8A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, trenches and bridges are formed in the resist layer, and the superconducting material is deposited on the resist layer. Figure 8B It is according to an embodiment of the present invention. Figure 8A The schematic cross-sectional view of the substrate shown by the dashed lines 8B-8B shows a superconducting material and a sacrificial resist layer deposited on the substrate, with trenches and bridges formed in the resist layer, and the superconducting material being vapor-deposited along the first trench. Cross-sections along lines 8B-8B and along the second trench 308 are also shown. Figure 8B As shown, superconducting materials 700 and 701 are deposited on a stack of superconducting material 102 and resist layers 202 and 204. However, as Figure 8B As shown, virtually no superconducting materials 700 and 701 are deposited in the second trench 308. In fact, superconducting materials 700 and 701 are as follows: Figure 7A The superconducting materials 700 and 701 are deposited in two opposite directions at a grazing angle, and the bridge structure 402 (including two strips 402A and 402B) prevents the superconducting materials 700 and 701 from depositing in the second trench 308. However, a cross-section along the second trench 308 is shown. Figure 8BAlso shown is a portion 309 of the superconducting materials 700 and 701 deposited during the first and second vapor deposition processes. The portion 309 of the superconducting materials 700 and 701 is deposited because the spacing between the bands 402A and 402B of the bridge 402 corresponds to the width of the second trench 308. Due to the bands 402A and 402B of the bridge 402, a gap 311 exists on each side of the portion 309.

[0051] As described above and as Figure 9A As further shown, after depositing superconducting materials 700, 701 by performing a first evaporation and a second evaporation at a grazing angle, the method includes: oxidizing the superconducting materials 700, 701 to form an oxide or oxide layer 800 on the superconducting materials 700, 701 at least within a first trench 306, such as... Figure 9B As shown in the image.

[0052] Figure 9A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, trenches and bridges are formed in the resist layer, and the superconducting material is deposited on the resist layer by means of a first vapor deposition and a second vapor deposition. Figure 9B It is according to an embodiment of the present invention. Figure 9A The schematic cross-sectional view of the substrate shown by the dashed lines 9B-9B shows a superconducting material and a sacrificial resist layer deposited on the substrate, with trenches and bridges formed in the resist layer, and the superconducting material being vapor-deposited along the second trench.

[0053] like Figure 9B As shown, during the formation of oxide layers 800 on superconducting materials 700 and 701, at least within the first trench 306, an oxide layer 800 of the superconducting material is formed on the superconducting materials 700 and 701, such as... Figure 9B As shown. Figure 9B As shown, an oxide layer 800 is formed anywhere superconducting materials 700, 701 are present, including the first trench 306. The oxide layer 800 is also formed on top of a portion 309 of superconducting materials 700, 701 located in the middle of the second trench 308.

[0054] like Figure 9B As further shown, after forming the oxide layer 800, the method includes: depositing a superconducting material 900 at an angle substantially perpendicular to the surface 502 of the substructure 500 to deposit the superconducting material 900 in a second trench 308 within the substructure 500 (third deposition). The deposition of the superconducting material 900 is performed without rotating the substructure 500. Figure 9BAs shown, a superconducting material layer 900 is also deposited in the first trench 306, thereby sandwiching the oxide layer 800 between the superconducting materials 700, 701 and the superconducting layer 900. Thus, a stack of superconducting material layers 700, 701, oxide layer 800 and superconducting material layer 900 is provided at the center of the first trench 306.

[0055] like Figure 9B As shown, the thickness of the first resist layer 202 is selected such that a gap “G” is provided between the superconducting material 900 (deposited during the third evaporation) and the second resist layer forming the bridge structure 402.

[0056] Figure 10A This is a schematic top view of a substrate according to an embodiment of the present invention, wherein a superconducting material and a sacrificial resist layer are deposited on the substrate, and the superconducting material is deposited in a first trench and a second trench. Figure 10B It is according to an embodiment of the present invention. Figure 10A The schematic cross-sectional view of the substrate shown by the dashed lines 10B-10B shows a superconducting material and a sacrificial resist layer deposited on the substrate, with trenches and bridges formed in the resist layer, and the superconducting material being vapor-deposited along the second trench.

[0057] like Figure 10B As shown, superconducting material 900 is deposited in the second trench 308 within the substructure 500 at an angle substantially perpendicular to the surface 502 of the substructure 500 (third deposition). The deposition of the superconducting material 900 forms a second superconducting lead 910, as shown. Figure 10B As shown. During the third evaporation, superconducting material was also deposited on portions 309 of the superconducting materials 700 and 701, which have oxide layers thereon. Additionally, as... Figure 10B As shown, the superconducting material 900 is also filled during the first and second evaporation processes ( Figure 8B (As shown) gaps 311 are created on each side of portion 309. Therefore, at the center of the second trench 308, a stack of superconductor layers 700, 701, oxide layer 800 and superconductor material layer 900 is provided.

[0058] The method of fabricating a Josephson junction for superconducting qubits further includes stripping regions of deposited superconducting materials 700, 701, and 900 and oxide layer 800 to leave a vertical Josephson junction at the intersection of first and second trenches 306 and 308, the vertical Josephson junction being electrically connected at its first end by a first superconducting lead 710 and at its second end by a second superconducting lead 910.

[0059] In one embodiment, superconducting materials 102, 700, 701, and 900 can be the same superconducting material or different superconducting materials. For example, superconducting material 102 can be niobium, and superconducting materials 700, 701, and 900 can be aluminum or other superconducting materials. Alternatively, superconducting materials 700, 701, and 900 can also be different superconducting materials. Furthermore, superconducting material 102 can be the same superconducting material as superconducting material 700, superconducting material 701, or superconducting material 900.

[0060] Figure 11A This is a schematic top view of a qubit device formed according to the method described above, based on an embodiment of the present invention. The qubit device includes: a plurality of sectors 104 formed of superconducting material 102, and a first trench 306 therein filled with superconducting materials 700, 101, and 900 (other than other materials) forming a first lead 710, and a second trench 308 therein filled with superconducting materials 700, 101, and 900 (other than other materials) forming a second lead 910.

[0061] Figure 11B It is according to an embodiment of the present invention. Figure 11A A schematic cross-sectional view of the qubit device formed by the dashed lines 11B-11B shown. Figure 11C It is according to an embodiment of the present invention. Figure 11A A schematic cross-sectional view of the qubit device formed by the dashed lines 11C-11C shown. Figure 11B and 11C As shown, the Josephson junction "JJ" is vertically formed by stacking superconducting material layers 700, 701, oxide layer 800, and superconducting material layer 900. The Josephson junction JJ is connected to the superconducting material 102 of two sectors 104 via a first lead 710 along the first trench 306, and to the superconducting material 102 of two other sectors 104 via a second lead 910.

[0062] Figure 12A This is a magnified scanning electron microscope (SEM) image showing a qubit device formed using the method described above according to an embodiment of the present invention. The first and second evaporations for depositing superconducting materials 700 and 701, and the third evaporation for depositing superconducting material 900, are indicated by arrows in the SEM image. The central feature in the image, referenced by the characters "JJ," corresponds to a Josephson junction. The Josephson junction comprises a stack of superconducting material layers 700 and 701, an oxide layer 800, and a superconducting material layer 900.

[0063] Figure 12B This is a reduced-size scanning electron microscope (SEM) image showing a qubit device formed using the method described above according to an embodiment of the present invention. Figure 12BAs shown, the Josephson junction (JJ) is connected to a first lead 710, which connects the JJ to a first pair of sectors, quadrants, or pads 104. The Josephson junction is also connected to a second lead 910, which connects the JJ to a second pair of sectors, quadrants, or pads 104.

[0064] In the preceding paragraphs, some embodiments of the invention described the fabrication of sectors, quadrants, or pads 104 individually by depositing superconducting material 102 on substrate 100. However, according to another embodiment of the invention, sectors, quadrants, or pads 104 and associated buses 106 can be fabricated simultaneously with the deposition of superconducting materials 700 and 701, i.e., during the first and second evaporation processes. In this case, the method includes: evaporating superconducting material 700 at a grazing angle along a first direction to deposit superconducting material 700 on surface 100A of substrate 100; and evaporating superconducting material 701 at a substantially grazing angle substantially opposite to the first direction to deposit superconducting material 701 on surface 100A of substrate 100, thereby forming four sectors 104 and associated buses 106. The four sectors or pads 104 are separated by exposed portions 102B of surface 102A of substrate 100.

[0065] As can be understood from the above paragraphs, a superconducting qubit device is also provided, which is fabricated by the method described above. The method described above for forming the Josephson junction (JJ) of the superconducting qubit device allows for a reduction in the number of steps in fabricating the qubit device, for example, by eliminating the rotation of the substrate or substructure and instead performing a third evaporation deposition vertically relative to the surface of the substrate or substructure to deposit the superconducting layer 900. Furthermore, during the fabrication of the Josephson junction, the leads are also fabricated simultaneously with the Josephson junction, which allows for better contact resulting in lower inductance lines. Moreover, the method according to some embodiments of the invention allows for the substantial elimination of unwanted shading for better interconnection, thereby improving the transfer of microwave energy to and from the Josephson junction.

[0066] Various embodiments of the invention have been described for illustrative purposes, but are not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles of the embodiments, their practical application, or technical improvements to technologies found in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for fabricating a Josephson junction for superconducting qubits, comprising: Provided a substructure having a surface in which a first groove and a second groove are defined, the first groove being substantially perpendicular to and intersecting the second groove, the substructure having a bridge structure extending above the first groove adjacent to the intersection of the first groove and the second groove; A first superconducting material is vapor-deposited along a first direction at a grazing angle to deposit the first superconducting material in the first trench so as to extend from the first direction under the bridge structure; A second superconducting material is deposited substantially at the grazing angle, substantially opposite to the first direction, to deposit the second superconducting material in the first trench so as to extend from the grazing angle below the bridge structure substantially opposite to the first direction and to provide a first superconducting lead; Oxidize the first superconducting material and the second superconducting material to form an oxide layer on the first superconducting material and the second superconducting material at least within the first trench; A third superconducting material is vapor-deposited at an angle substantially perpendicular to the surface of the substructure to deposit the third superconducting material in the second trench within the substructure without rotating the substructure to form a second superconducting lead; as well as The deposited first superconducting material, second superconducting material, and third superconducting material, along with the oxide layer, are stripped from the region to leave a vertical Josephson junction at the intersection of the first trench and the second trench. The vertical Josephson junction is electrically connected at its first end via the first superconducting lead and at its second end via the second superconducting lead.

2. The method according to claim 1, wherein, The first superconducting material, the second superconducting material, and the third superconducting material are the same superconducting material.

3. The method according to claim 1 or 2, wherein, The substructure provided includes: Provide substrate; A fourth superconducting material is deposited on the surface of the substrate; A portion of the fourth superconducting material is removed from the surface of the substrate to expose a portion of the surface of the substrate; A first resist layer is deposited on the fourth superconducting material and on the exposed portion of the surface of the substrate; and A second resist layer is deposited on the first resist layer to form a superimposed first resist layer and second resist layer.

4. The method according to claim 3, wherein, The fourth superconducting material is the same as the first superconducting material, the second superconducting material, or the third superconducting material.

5. The method according to claim 3, wherein, Providing the substructure also includes: Electron beam or beam lithography is applied to expose a first portion of the superimposed first and second resist layers and a second portion of the superimposed first and second resist layers.

6. The method according to claim 3, wherein, Providing the substructure also includes: Remove the exposed first portion of the superimposed first and second resist layers to form the first trench; and The exposed second portion of the superimposed first and second resist layers is removed to form a second trench, and a bridge structure with the remaining portion of the second resist layer is formed extending over the first trench, the bridge structure being substantially parallel to the second trench.

7. The method according to claim 6, wherein, Depositing the first superconducting material along the first direction at the grazing angle to deposit the first superconducting material in the first trench includes: depositing the first superconducting material under the bridge structure.

8. The method according to claim 7, wherein, Depositing the second superconducting material in the first trench at the grazing angle substantially opposite to the first direction includes depositing the second superconducting material in areas shielded by the bridge structure and not filled by the first superconducting material during the deposition of the first superconducting material.

9. The method according to claim 3, wherein, The substrate is selected from the group consisting of silicon, germanium and sapphire.

10. The method according to claim 3, wherein, The first superconducting material, the second superconducting material, the third superconducting material, and the fourth superconducting material are selected from the group consisting of niobium and aluminum.

11. The method according to claim 3, wherein, Removing a portion of the superconducting material from the surface of the substrate to expose the surface of the substrate includes: forming four sectors and associated busbars of the fourth superconducting material, the four sectors being separated by the exposed portion of the surface of the substrate.

12. The method according to claim 3, wherein, Depositing the first photoresist layer on the superconducting material and on the exposed portion of the surface of the substrate comprises: depositing a methyl methacrylate layer, and The deposition of the second resist layer on the first resist layer includes: depositing a polymethyl methacrylate layer.

13. The method according to any one of claims 1-2 and 4-12, wherein, The grazing angle is between 5 degrees and 85 degrees relative to the surface of the substructure.

14. The method according to any one of claims 1-2 and 4-12, further comprising: Provide substrate; The first superconducting material is vapor-deposited along the first direction at the grazing angle to deposit the first superconducting material on the surface of the substrate; The second superconducting material is deposited substantially at the grazing angle, substantially opposite to the first direction, to deposit the second superconducting material on the surface of the substrate to form four sectors of the first and second superconducting materials and associated buses, the four sectors being separated by exposed portions of the surface of the substrate.

15. A superconducting quantum bit, said superconducting quantum bit being fabricated by the following steps: Provided a substructure having a surface in which a first groove and a second groove are defined, the first groove being substantially perpendicular to and intersecting the second groove, the substructure having a bridge structure extending above the first groove; A first superconducting material is vapor-deposited along a first direction at a grazing angle to deposit the first superconducting material in the first trench so as to extend from the first direction under the bridge structure; A second superconducting material is deposited substantially at the grazing angle, substantially opposite to the first direction, to deposit the second superconducting material in the first trench so as to extend from the grazing angle below the bridge structure substantially opposite to the first direction and to provide a first superconducting lead; Oxidize the first superconducting material and the second superconducting material to form an oxide layer on the first superconducting material and the second superconducting material at least within the first trench; A third superconducting material is vapor-deposited at an angle substantially perpendicular to the surface of the substructure to deposit the third superconducting material in the second trench within the substructure without rotating the substructure to form a second superconducting lead; as well as The deposited first superconducting material, second superconducting material, and third superconducting material, along with the oxide layer, are stripped from the region to leave a vertical Josephson junction at the intersection of the first trench and the second trench. The vertical Josephson junction is electrically connected at its first end via the first superconducting lead and at its second end via the second superconducting lead.

16. The superconducting quantum bit according to claim 15, wherein, The first superconducting material, the second superconducting material, and the third superconducting material are the same superconducting material.

17. The superconducting quantum bit according to claim 15 or 16, wherein, The substructure provided includes: Provide substrate; A fourth superconducting material is deposited on the surface of the substrate; A portion of the fourth superconducting material is removed from the surface of the substrate to expose a portion of the surface of the substrate; A first resist layer is deposited on the fourth superconducting material and on the exposed portion of the surface of the substrate; and A second resist layer is deposited on the first resist layer to form a superimposed first resist layer and second resist layer.

18. The superconducting quantum bit according to claim 17, wherein, The fourth superconducting material is the same as the first superconducting material, the second superconducting material, or the third superconducting material.

19. The superconducting quantum bit according to claim 17, wherein, Providing the substructure also includes: Particle beam or beam lithography is applied to expose a first portion of the superimposed first and second resist layers and a second portion of the superimposed first and second resist layers.

20. The superconducting quantum bit according to claim 17, wherein, Providing the substructure also includes: Remove the exposed first portion of the superimposed first and second resist layers to form the first trench; and The exposed second portion of the superimposed first and second resist layers is removed to form a second trench, and a bridge structure with the remaining portion of the second resist layer is formed extending over the first trench, the bridge structure being substantially parallel to the second trench.

21. The superconducting quantum bit according to claim 20, wherein, Depositing the first superconducting material along the first direction at the grazing angle to deposit the first superconducting material in the first trench includes: depositing the first superconducting material under the bridge structure.

22. The superconducting quantum bit according to claim 21, wherein, Depositing the second superconducting material in the first trench at the grazing angle substantially opposite to the first direction includes depositing the second superconducting material in areas shielded by the bridge structure and not filled by the first superconducting material during the deposition of the first superconducting material.

23. The superconducting quantum bit according to claim 17, wherein, The substrate is selected from the group consisting of silicon, germanium and sapphire.

24. The superconducting quantum bit according to claim 17, wherein, The first superconducting material, the second superconducting material, the third superconducting material, and the fourth superconducting material are selected from the group consisting of niobium and aluminum.

25. The superconducting quantum bit according to claim 17, wherein, Removing a portion of the superconducting material from the surface of the substrate to expose the surface of the substrate includes: forming four sectors and associated busbars of the fourth superconducting material, the four sectors being separated by the exposed portion of the surface of the substrate.

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