Microfabricated air bridges for quantum circuits

Abstract

A method for fabricating a bridge structure in a quantum mechanical device, comprising: providing a substructure comprising a substrate having a layer of a first superconducting material deposited thereon, the layer of the first superconducting material being divided into a first portion, a second portion, and a third portion that are electrically insulated from one another; depositing a sacrificial layer on the substructure; electrically connecting the first portion and the second portion with a strip of a second superconducting material, the second superconducting material being different from the first superconducting material; and removing a portion of the sacrificial layer to form a bridging structure over the third portion between the first portion and the second portion, the bridging structure electrically connecting the first portion to the second portion without electrically connecting the third portion to the first portion and without electrically connecting the third portion to the second portion.

Description

Background Technology

[0001] The presently claimed embodiments of the present invention relate to quantum circuits, and more specifically, to a method of fabricating a bridge structure in a quantum mechanical device and a quantum mechanical device having the bridge structure.

[0002] Quantum computing is based on the reliable control of qubits (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 the correlation between two individual qubits. To meet the error threshold of quantum computing and to achieve reliable quantum simulation, the implementation of high-fidelity two-qubit operations is likely 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.). A superconducting quantum processor is typically a planar two-dimensional lattice structure or circuit consisting of multiple individual qubits linked by couplers in various lattice symmetries (e.g., square, hexagonal, etc.), and a readout structure located on a flip chip. The couplers can be made of capacitors, resonators, coils, or any microwave component that provides coupling between qubits.

[0004] Superconducting microwave circuits based on coplanar waveguides (CPWs) are susceptible to parasitic slot-line modes. These modes can couple to circuit elements, such as qubits, and thus cause signal loss and decoherence. To eliminate these spurious modes, cross-connections are typically made between the ground planes interrupted by the CPW. This is usually achieved using self-supporting bridging known as air bridges. However, problems remain in fabricating these air bridges, resulting in less-than-ideal quantum mechanical devices or circuits. Summary of the Invention

[0005] One aspect of the present invention is to provide a method for fabricating a bridge structure in a quantum mechanical device. The method includes providing a substructure comprising a substrate on which a first superconducting material layer is deposited, the first superconducting material layer being divided into a first portion, a second portion, and a third portion electrically insulated from each other. The method further includes depositing a sacrificial layer on the substructure and electrically connecting the first portion of the first superconducting material to the second portion using strips of a second superconducting material, the second superconducting material being different from the first superconducting material. The method further includes removing a portion of the sacrificial layer deposited on the substructure to form a bridge structure over the third portion between the first and second portions using strips of the second superconducting material, the bridge structure electrically connecting the first portion to the second portion without electrically connecting the third portion to the first portion and without electrically connecting the third portion to the second portion.

[0006] In one embodiment, providing the substructure includes providing a substrate having a surface, and depositing a first superconducting material layer on the surface of the substrate. In another embodiment, providing the substructure further includes etching the first superconducting material layer to form a first trench and a second trench to define a first portion, a second portion, and a third portion of the first superconducting material layer, such that the first portion, the second portion, and the third portion of the first superconducting material layer are spaced apart from each other by the etched first trench and the etched second trench.

[0007] In one embodiment, the substrate comprises silicon or sapphire. In one embodiment, the first superconducting material comprises niobium or aluminum. In one embodiment, the sacrificial layer comprises titanium (Ti), titanium nitride (TiN), or tantalum (Ta), or any combination thereof.

[0008] In one embodiment, depositing a sacrificial layer on a substructure includes sputtering a superconducting sacrificial material on the substructure. In one embodiment, electrically connecting a first portion of a first superconducting material to a second portion using a strip of a second superconducting material includes sputtering a compressive stress superconducting material to form a strip of the second superconducting material. In one embodiment, electrically connecting a first portion of a first superconducting material to a second portion using a strip of the second superconducting material includes attaching a first base pad of the strip to the first portion and attaching a second base pad of the strip to the second portion. In one embodiment, electrically connecting a first portion of a first superconducting material to a second portion using a strip of the second superconducting material includes using a porous strip of the second superconducting material to electrically connect the first portion of the first superconducting material to the second portion.

[0009] In one embodiment, removing the portion of the sacrificial layer deposited on the substrate includes etching the portion of the sacrificial layer below the strip to form a gap between the strip and the third portion of the first superconducting material, thereby defining a bridge structure over the third portion of the first superconducting material. In one embodiment, etching the portion of the sacrificial layer below the strip includes etching the portion of the sacrificial layer using acid etching. In one embodiment, etching the portion of the sacrificial layer below the strip includes etching the sacrificial layer deposited on the third portion below the strip, and etching the sacrificial layer deposited in the first trench and the second trench separating the first, second, and third portions, without etching the sacrificial layer at both ends of the strip.

[0010] In one embodiment, providing a substructure includes providing a substrate having a surface; depositing a sacrificial material layer on the surface of the substrate; selectively etching the sacrificial material layer to form spaced-apart first and second portions of the sacrificial material; selectively etching the substrate except for the first and second portions of the sacrificial material; depositing a first superconducting material layer on the etched substrate and on the first and second portions of the sacrificial material; and removing the deposited layer of the first superconducting material and the first and second portions of the sacrificial material to obtain a first superconducting material layer divided into first, second, and third portions electrically insulated from each other by the substrate material.

[0011] In one embodiment, depositing a sacrificial layer on top of the substructure includes sputtering a superconducting sacrificial material onto a first superconducting material layer. In another embodiment, removing a portion of the sacrificial layer deposited on the substrate includes etching the portion of the sacrificial layer below the strip and etching the substrate material separating the first, second, and third portions of the superconducting material to form a gap between the strip and the third portion of the first superconducting material to define a bridge structure over the third portion of the first superconducting material.

[0012] Another aspect of the present invention provides a quantum mechanical device comprising: a substrate; and a first superconducting material layer deposited on the substrate, the first superconducting material layer being divided into a first portion, a second portion, and a third portion electrically insulated from each other. The quantum mechanical device further includes a bridge structure connecting the first and second portions over the third portion located between the first and second portions, the bridge structure having strips of a second superconducting material configured to electrically connect the first and second portions of the first superconducting material. The second superconducting material of the strips is different from the first superconducting material.

[0013] In one embodiment, the second superconducting material strip is porous at least in the portion traversing the third portion of the first superconducting material layer. In one embodiment, the first and second portions of the first superconducting material are connected to the same ground potential. In one embodiment, the third portion of the first superconducting material is a signal line configured to carry electromagnetic signals to and from qubits. In one embodiment, the bridge structure is configured to substantially eliminate parasitic modes of planar microwave circuits. In one embodiment, the first and second portions of the first superconducting material layer are first and second signal lines configured to carry first electromagnetic signals to and from first qubits, and the third portion is a third signal line configured to carry second electromagnetic signals to and from second qubits.

[0014] In one embodiment, the quantum mechanical device further includes a plurality of regularly spaced bridge structures to electrically connect a first portion and a second portion of the first superconducting material layer at multiple locations within the first superconducting material layer. In one embodiment, the plurality of bridge structures are configured to connect the first portion and the second portion of the first superconducting material layer to the same ground potential.

[0015] For example, this bridge structure can be used to eliminate parasitic modes in planar microwave circuits by connecting ground planes or crossing signal lines. This allows access to the address space (fenced) in qubits, thus allowing for breaking the plane for superconducting two-dimensional (2D) quantum circuits. The bridge structure can include superconducting materials and be fabricated using a different process than the first-layer fabrication process used to fabricate the qubits and the rest of the circuit. This provides flexibility in using different materials. Furthermore, this method and quantum mechanical device achieve better yields due to prestress and the bending nature of the bridge structure. Additionally, there is no need to connect signal lines with different fabrication runs, thus reducing or minimizing signal loss. Attached Figure Description

[0016] 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 after considering the following description and appended claims with reference to 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 define limitations on the invention.

[0017] Figure 1A This is a schematic side view of a substructure including a substrate on which a first superconducting material is deposited, according to an embodiment of the present invention;

[0018] Figure 1B This is a schematic top view of a substructure including a substrate on which a first superconducting material is deposited, according to an embodiment of the present invention;

[0019] Figure 2 This is a schematic top view of a substrate on which superconducting material is deposited, according to another embodiment of the present invention;

[0020] Figure 3 This is a schematic side view of a substrate having a first superconducting material and a sacrificial resist layer deposited thereon, according to an embodiment of the present invention.

[0021] Figure 4A This is a schematic top view of a substructure according to an embodiment of the present invention, the substructure having strips of a second superconducting material formed thereon on a third portion of a first superconducting material;

[0022] Figure 4B This is a schematic top view of a substructure according to an embodiment of the present invention, the substructure having a strip of second superconducting material formed thereon on a third portion, the strip being electrically connected to a fourth and a fifth portion of a first superconducting material;

[0023] Figure 5 This is a schematic side view of a substructure having a bridge structure with strips of a second superconducting material formed thereon, according to an embodiment of the present invention.

[0024] Figure 6 This is a scanning electron microscope (SEM) image illustrating a bridge structure comprising a strip and base pads at both ends of the strip according to an embodiment of the present invention;

[0025] Figure 7 The image is a scanning electron microscope (SEM) image according to an embodiment of the present invention, showing a plurality of bridge structures arranged along the length of an electromagnetic transmission line;

[0026] Figure 8A This is a schematic side view of a substrate having a sacrificial layer deposited thereon, according to another embodiment of the present invention;

[0027] Figure 8B This is a schematic top view of a substrate having an etched sacrificial layer deposited thereon, according to another embodiment of the present invention;

[0028] Figure 8C According to another embodiment of the present invention, along Figure 8B The schematic cross-sectional view of the substrate with an etched sacrificial layer deposited thereon, taken from line 8C-8C, is shown.

[0029] Figure 8D This is a schematic cross-sectional view of a substrate having an etched sacrificial material layer and a selectively etched substrate according to another embodiment of the present invention;

[0030] Figure 9A This is a schematic top view of a substrate according to another embodiment of the present invention, on which a first superconducting material layer is also deposited;

[0031] Figure 9B According to the embodiments of the present invention, along Figure 9A The schematic cross-sectional view of the substrate taken at line 9B-9B shown shows that a first superconducting material layer is also deposited on the substrate.

[0032] Figure 10A This is a schematic top view of a substrate according to an embodiment of the present invention, the substrate having a first superconducting material layer deposited thereon, the first superconducting material layer being divided into a first portion, a second portion and a third portion;

[0033] Figure 10B This is a schematic cross-sectional view of a substrate according to an embodiment of the present invention, on which a first superconducting material layer is deposited. The first superconducting material layer is divided into a first portion, a second portion, and a third portion, which are electrically insulated from each other by protrusions in the substrate. The cross-sectional view is along... Figure 10A The lines shown are cut from 10A-10B; and

[0034] Figure 11 This is a schematic cross-sectional view of a bridge structure formed on a substructure according to another embodiment of the present invention. Detailed Implementation

[0035] In one embodiment of the invention, a method for fabricating a bridge structure in a quantum mechanical device is provided. The method includes providing a substructure 100 having a substrate 102 having a first superconducting material layer 104 deposited thereon. Figure 1A This is a schematic side view of a substructure 100 including a substrate 102 on which a first superconducting material 104 is deposited, according to an embodiment of the present invention. Figure 1B This is a schematic top view of a substructure 100 including a substrate 102 on which a first superconducting material 104 is deposited, according to an embodiment of the present invention. In one embodiment, the substrate 102 may be, for example, silicon or sapphire. In one embodiment, the first superconducting material 104 may include niobium (Nb), aluminum (Al), etc.

[0036] like Figure 1B As shown, the first superconducting material layer 104 is divided into a first portion 104A, a second portion 104B, and a third portion 104C that are electrically insulated from each other. The first portion 104A, the second portion 104B, and the third portion 104C are electrically insulated from each other by a first trench 106A between the first portion 104A and the third portion 104C, and a second trench 106B between the second portion 104B and the third portion 104C. The substrate 102 is visible through the first and second trenches, as shown. Figure 1B As shown.

[0037] In one embodiment, the substrate 102 has a surface 102A on which a first superconducting material layer 104 is deposited, such as Figure 1A As shown. In one embodiment, providing the substructure 100 includes etching a first superconducting material layer 104 to form a first trench 106A and a second trench 106B to define a first portion 104A, a second portion 104B, and a third portion 104C of the first superconducting material layer 104, such that the first portion 104A, the second portion 104B, and the third portion 104C of the first superconducting material layer 104 are spaced apart from each other by the etched first trench 106A and the etched second trench 106B. In one embodiment, the third portion 104C is located between the first portion 104A and the second portion 104B, as shown. Figure 1B As shown.

[0038] In one embodiment, a first portion 104A and a second portion 104B of the first superconducting material 104 are connected to the same ground potential. In another embodiment, a third portion 104C of the first superconducting material 104 is a signal line configured to carry electromagnetic signals to and from qubits (not shown).

[0039] Figure 2 This is a schematic top view of a substrate on which a superconducting material is deposited, according to another embodiment of the present invention. In one embodiment, the method may further include providing a substructure 200 having a substrate 202 on which a first superconducting material layer 204 is deposited, such as... Figure 2 As shown, in this embodiment, the first superconducting material layer 204 has a first portion 204A, a second portion 204B, and a third portion 204C. In one embodiment, the first portion 204A and the second portion 204B of the first superconducting material layer 204 are connected to the same ground potential. In one embodiment, the third portion 204C of the first superconducting material 204 is a signal line configured to carry electromagnetic signals to or from a qubit (not shown). The first portion 204A, the second portion 204B, and the third portion 204C are electrically insulated from each other by a first trench 206A between the first portion 204A and the third portion 204C and a second trench 206B between the second portion 204B and the third portion 204C, as shown. Figure 2 As shown, substrate 202 is visible through the first and second trenches.

[0040] Similar to the previous embodiments, the substructure 200 includes etching a layer of the first superconducting material layer 204 to form a first trench 206A and a second trench 206B to define a first portion 204A, a second portion 204B, and a third portion 204C of the first superconducting material layer 204, such that the first portion 204A, the second portion 204B, and the third portion 204C of the first superconducting material layer 204 are spaced apart from each other by the etched first trench 206A and the etched second trench 206B.

[0041] In addition to the first portion 204A, the second portion 204B, and the third portion 204C, the first superconducting material layer 204 also includes a fourth portion 204D and a fifth portion 204E. The fourth portion 204D is electrically insulated from the first portions 204A, 204B, and 204C. Similarly, the fifth portion 204E is also electrically insulated from the first portions 204A, 204B, 204C, and 204D. The fourth portion 204D is electrically insulated from the first portion 204A by the presence of a trench 206C etched in the first superconducting material layer 204. The trench 206C is U-shaped to insulate the fourth portion 204D from the first portion 204A. The fifth portion 204E is electrically insulated from the second portion 204B by the presence of the trench 206D etched in the first superconducting material layer 204. The trench 206D is U-shaped to insulate the fifth portion 204E from the second portion 204B.

[0042] In one embodiment, both the first portion 204A and the second portion 204B are electrically connected to ground. In one embodiment, the third portion 204C is a first signal line configured to carry a first electromagnetic signal to or from a first qubit. In one embodiment, the fourth portion 204D and the fifth portion 204E, when connected to each other using a bridge structure, form a second signal line configured to carry a second electromagnetic signal to or from a second qubit.

[0043] Figure 3 This is a schematic side view of substrates 102, 202 on which a first superconducting material 104, 204 and a sacrificial resist layer 402 are deposited, according to an embodiment of the present invention. In one embodiment, the method further includes depositing a sacrificial layer 402 on substructures 100, 200. In one embodiment, the sacrificial layer comprises titanium (Ti), titanium nitride (TiN), or tantalum (Ta), or any combination thereof. In one embodiment, depositing the sacrificial layer 402 includes sputtering a superconducting sacrificial material on substructures 100, 200. In one embodiment, the sacrificial layer 402 is deposited on the first superconducting material layers 104, 204 and on substrates 102, 202 within trenches 106A, 106B, 206A, 206B, 206C, 206D.

[0044] In one embodiment, the method includes electrically connecting a first portion 104A, 204A of a first superconducting material 104, 204 to a second portion 104B, 204B using a strip 502 of a second superconducting material 404, wherein the second superconducting material 404 is different from the first superconducting materials 104, 204. Figure 4A This is a schematic top view of substructures 100, 200 according to an embodiment of the present invention, the substructure having strips 502 of a second superconducting material 404 formed thereon above the third portions 104C, 204C.

[0045] In one embodiment, a second superconducting material 404 is deposited on a sacrificial layer 402, such as Figure 3 As shown. The second superconducting material 404 differs from the first superconducting materials 104 and 204. In one embodiment, depositing the second superconducting material 404 on the substructures 100 and 200 includes sputtering compressive stress superconducting material 404 to form strips 502 of the second superconducting material 404, such as... Figure 4A As shown. In one embodiment, strip 502 traverses or crosses the third portions 104C, 204C, as... Figure 4A As shown. Although strip 502 is shown intersecting the third portions 104C, 204C at approximately right angles, it will be understood that strip 502 can be made to intersect the third portions 104C, 204C at any other angle. In one embodiment, electrically connecting the first portions 104A, 204A and the second portions 104B, 204B of the first superconducting materials 104, 204 using strip 502 of the second superconducting material 404 includes attaching a first base pad 502A at the end of strip 502 to the first portions 104A and 204A, and connecting a second base pad 502B at the end of strip 502 to the second portions 104B and 204B.

[0046] Figure 4BThis is a schematic top view of substructures 100 and 200 according to an embodiment of the present invention, the substructure having a strip 502 of a second superconducting material 404 formed thereon on a third portion 204C, the strip electrically connecting a fourth portion 204D and a fifth portion 204E. In one embodiment, the method may further include electrically connecting the fourth portion 204D and the fifth portion 204E of a first superconducting material 204 using a strip 503 of the second superconducting material 404, the second superconducting material 404 being different from the first superconducting material 204. In one embodiment, electrically connecting the fourth portion 204D and the fifth portion 204E of the first superconducting material 204 using a strip 503 of the second superconducting material 404 includes attaching a first base pad 503A at an end of the strip 503 to the fourth portion 204D and attaching a second base pad 503B at an end of the strip 503 to the fifth portion 204E to form a line, for example, for transmitting electromagnetic signals to or from a qubit. In this case, such as Figure 4B As shown, the strip 503 traverses the first portion 204A, the second portion 204B, and the third portion 204C. In one embodiment, the strip 503 of the second superconducting material 404 comprises a porous strip of the second superconducting material 404.

[0047] In one embodiment, the method includes removing a portion of the sacrificial layer 402 deposited on the substructures 100, 200 to form a bridge structure 602, wherein strips 502, 503 of the second superconducting material 404 are located above a third portion 104C, 204C between the first portions 104A, 204A and the second portions 104B, 204B. Figure 5 This is a schematic side view of substructures 100 and 200 having a bridge structure 602 with strips 502 and 503 formed thereon, according to an embodiment of the present invention. In one embodiment, a portion of the sacrificial layer 402 is removed near and below the strips 502 and 503 of the bridge structure 602 to form a void or gap “G” between the bridge structure 602 and the third portions 104C and 204C of the first superconducting materials 104 and 204. In one embodiment, the gap “G” may be, for example, between about 2 μm and 4 μm. In one embodiment, the bridge structure 602 passes over the third portions 104C and 204C of the first superconducting materials 104 and 204. Bridge structure 602 electrically connects the first parts 104A and 204A to the second parts 104B and 204B, but does not electrically connect the third parts 104C and 204C to the first parts 104A and 204A, and does not electrically connect the third parts 104C and 204C to the second parts 104B and 204B.

[0048] In one embodiment, removing the portion of the sacrificial layer 402 deposited on the substructures 100, 200 includes etching the portion of the sacrificial layer 402 located below the strip 502 to form a gap “G” between the strip 502 and the third portions 104C, 204C of the first superconducting materials 104, 204, thereby defining a bridge structure 602 over the third portions 104C, 204C of the first superconducting materials 104, 204. In one embodiment, etching the portion of sacrificial layer 402 below strip 502 includes etching the sacrificial layer 402 deposited on third portions 104C, 204C below strips 502, 503, and etching the sacrificial layer deposited in the first trenches 106A, 206A and the second trenches 106B, 206B separating the first portions 104A, 204A, the second portions 104B, 204B and the third portions 104C, 204C, but not etching the sacrificial layer 402 at both ends of strips 502, 503 that include the underlying base pads 502A, 503A and 502B, 503B. In one embodiment, etching the portion of sacrificial layer 402 below strips 502, 503 includes etching the portion of sacrificial layer 402 using acid etching.

[0049] Figure 6 These are scanning electron microscope (SEM) images according to an embodiment of the present invention, showing a bridge structure 602 comprising strips 502 and substrates 502A and 502B. The strips 502 of the bridge structure 602 are made of a porous superconducting material 404. The porosity of the strips 502 allows for the chemical etching of the sacrificial layer 402 beneath the strips 502 to form the bridge structure 602 by allowing a fluid chemical etchant to reach the sacrificial layer 402.

[0050] Figure 7 These are scanning electron microscope (SEM) images according to an embodiment of the present invention, showing a plurality of bridge structures 602 arranged along the length of an electromagnetic transmission line. Each bridge structure 602 electrically connects a first portion 104A, 204A of the first superconducting material 104, 204 to a second portion 104B, 204B (e.g., they are connected to ground potential), while crossing a third portion 104C, 204C of the first superconducting material 104, 204. The third portions 104C, 204C form part of a transmission line, for example, for carrying electromagnetic signals to or from qubits. In one embodiment, the plurality of bridge structures 602 may be regularly spaced to reduce or substantially eliminate parasitic modes that might otherwise occur.

[0051] Figure 8A This is a schematic side view of a substrate 802 on which a sacrificial layer 804 is deposited, according to another embodiment of the present invention. Figure 8B This is a schematic top view of a substrate 802 on which an etched sacrificial layer 804 is deposited, according to another embodiment of the present invention. Figure 8CAccording to another embodiment of the present invention, along Figure 8B The diagram shows a schematic cross-sectional view of a substrate 802 on which an etched sacrificial layer 804 is deposited, taken along line 8C-8C.

[0052] Similar to the method for manufacturing the bridge structure described above, the following method also includes providing a substrate 802 on which a sacrificial material layer 804 is deposited, such as Figure 8A As shown. In an embodiment, for example, the substrate 802 may be silicon or sapphire. In an embodiment, the sacrificial material layer 804 may be, for example, an oxide. However, other materials may also be used. The substrate 802 has a surface 802A. The method includes depositing a sacrificial material layer 804 on the surface 802A of the substrate 802, such as... Figure 9A As shown. In one embodiment, depositing a sacrificial material layer 804 on top of a substrate 802 includes sputtering a superconducting sacrificial material 804 on a surface 802A of the substrate 802. The method includes selectively etching the sacrificial material layer 804 to form spaced-apart first and second portions 804A and 804B of the sacrificial material 804, as shown. Figure 8B Top view and Figure 8C The cross-sectional view is shown.

[0053] The method also includes selectively etching the substrate 802 except for the first portion 804A and the second portion 804B of the sacrificial material 804. Figure 8D This is a schematic cross-sectional view of a substrate 802 having an etched sacrificial material layer 804 and a selectively etched substrate 802 according to another embodiment of the present invention. Figure 8D As shown, after etching the substrate 802, the first portion 804A and the second portion 804B are located on two corresponding protrusions 812A and 812B of the substrate 802.

[0054] The method also includes depositing a first superconducting material layer 806 on the etched substrate 802 and on a first portion 804A and a second portion 804B of the sacrificial material 804, such as Figure 9A and Figure 9B As shown. In one embodiment, the first superconducting material may be, for example, niobium (Nb). However, other superconducting materials may also be used. Figure 9A This is a schematic top view of a substrate 802 according to another embodiment of the present invention, on which a first superconducting material layer 806 is further deposited. Figure 9B It is along Figure 9A The diagram shows a schematic cross-sectional view of a substrate 802 on which a first superconducting material layer 806 is further deposited, obtained by lines 9B-9B. Figure 9BAs shown, in one embodiment, two protrusions 806A and 806B in the first superconducting material layer 806 are formed on top of corresponding protrusions 812A and 812B of the substrate 802, and first and second portions 804A and 804B of sacrificial material 804 are deposited on top of the corresponding protrusions.

[0055] The method further includes removing the deposited first superconducting material layer 806 and the first portion 804A and the second portion 804B of the sacrificial material 804 to obtain a first superconducting material layer 806 divided by the substrate material 802 into a first portion 1002A, a second portion 1002B, and a third portion 1002C that are electrically insulated from each other, such as... Figure 10A and 10B As shown. Figure 10A This is a schematic top view of a substrate 802 according to an embodiment of the present invention, on which a first superconducting material layer 806 divided into a first portion 1002A, a second portion 1002B, and a third portion 1002C is deposited. Figure 10A As shown, the deposited first superconducting material layer 806 and the first portion 804A and the second portion 804B of the sacrificial material 804 are removed until... Figure 9B Lines 10B-10B are shown to obtain a first superconducting material layer 806 divided into a first portion 1002A, a second portion 1002B, and a third portion 1002C. In one embodiment, the deposited first superconducting material layer 806 is removed by, for example, chemical or mechanical polishing (also known as a damascene process), wherein the superconducting material 806 is planarized. Then, the first portion 804A and the second portion 804B of the sacrificial material 804 are removed using, for example, a wet or dry etching process.

[0056] The first part 1002A, the second part 1002B, and the third part 1002C are electrically insulated from each other through protrusions 812A and 812B on the substrate 802, such as Figure 10B As shown. Figure 10B This is a schematic cross-sectional view of a substrate 802 according to an embodiment of the present invention, on which a first superconducting material layer 806 is deposited, which is divided into a first portion 1002A, a second portion 1002B, and a third portion 1002C. These portions are electrically insulated from each other by protrusions 812A and 812B of the substrate 802. The cross-section is along... Figure 10A The line shown is cut from line 10A-10B. (As shown...) Figure 10B As shown, the obtained substructure 1000 includes a substrate 802 on which a first superconducting material layer 806 is deposited, which is divided into a first part 1002A, a second part 1002B and a third part 1002C.

[0057] Following the steps described above, execute the procedure as referenced above. Figure 1A-5The steps described are similar to those used to obtain the bridge structure. Figure 11 This is a schematic cross-sectional view of a bridge structure 1100 formed on a substructure 1000 according to another embodiment of the present invention. To obtain the bridge structure 1100, the method further includes depositing a superconducting sacrificial layer 1102 on the substructure 1000. In one embodiment, the sacrificial superconducting layer may be made of, for example, titanium (Ti), titanium nitride (TiN), or tantalum (Ta), or any combination thereof. In one embodiment, depositing the sacrificial layer 1102 includes sputtering a superconducting sacrificial material on the substructure 1000. In one embodiment, the superconducting sacrificial layer 1102 is deposited on a first superconducting material layer 806 and on protrusions 812A and 812B of the substrate 802.

[0058] In one embodiment, the method includes electrically connecting a first portion 1002A of a first superconducting material 806 to a second portion 1002B using a strip 1104 of a second superconducting material 1106, wherein the second superconducting material 1106 is different from the first superconducting material 806.

[0059] In one embodiment, a second superconducting material 1106 is deposited on a superconducting sacrificial layer 1102. In one embodiment, depositing the second superconducting material 1106 on the substructure 1000 includes sputtering compressive stress superconducting material to form strips 1104 of the second superconducting material 1106, such as... Figure 11 As shown, in one embodiment, strip 1104 traverses the third portion 1002C, as... Figure 11 As shown. In one embodiment, electrically connecting the first portion 1002A and the second portion 1002B of the first superconducting material 806 using a strip 1104 of the second superconducting material 1106 includes attaching a first base pad 1104A of the strip 1104 to the first portion 1002A and attaching a second base pad 1104B of the strip 1104 to the second portion 1002B.

[0060] In one embodiment, the method includes removing a portion of the superconducting sacrificial layer 1102 deposited on the substructure 1000 to form a bridge structure 1100, wherein strips 1104 of the second superconducting material 1106 are located on a third portion 1002C between the first portion 1002A and the second portion 1002B. In one embodiment, a portion of the superconducting sacrificial layer 1102 is removed near and below the strips 1104 of the bridge structure 1100 to form a void or gap “G” between the bridge structure 1104 and the third portion 1002C of the first superconducting material 806. In one embodiment, the gap “G” may be, for example, between about 2 μm and 4 μm. In one embodiment, the bridge structure 1100 passes over the third portion 1002C of the first superconducting material 806. Bridge structure 1100 electrically connects the first part 1002A to the second part 1102B, but does not electrically connect the third part 1002C to the first part 1002A, nor does it electrically connect the third part 1002C to the second part 1002B.

[0061] In one embodiment, removing a portion of the superconducting sacrificial layer 1102 deposited on the substructure 1000 includes etching a portion of the superconducting sacrificial layer 1102 located beneath the strip 1104 to form a gap “G” between the strip 1104 and the third portion 1002C of the first superconducting material 806, thereby defining a bridge structure 1100 on the third portion 1002C of the first superconducting material 806, as shown. Figure 11 As shown. In one embodiment, etching the portion of the superconducting sacrificial layer 1102 located below the strip 1004 includes etching the sacrificial layer 1102 located below the strip 1104 deposited on the third portion 1002C, but not etching the sacrificial layer 1102 located at both ends of the strip 1104 including the underlying substrates 1104A and 1104B. In one embodiment, etching the portion of the superconducting sacrificial layer 1102 below the strip 1104 includes etching the portion of the sacrificial layer 1102 using, for example, acid etching.

[0062] As can be understood from the above paragraphs, a quantum mechanical device is provided. Figure 5 and 11 as well as Figure 6 and 7The SEM images schematically illustrate the components of the quantum mechanical device. In one embodiment, the quantum mechanical device includes substrates 102, 202, and 802. The quantum mechanical device also includes first superconducting material layers 104, 204, and 806 deposited on the substrates 102, 202, and 802. The first superconducting material layers 104, 204, and 806 are divided into first portions 104A, 204A, and 1002A, second portions 104B, 204B, and 1002B, and third portions 104C, 204C, and 1002C, which are electrically insulated from each other. The quantum mechanical device also includes bridge structures 602 and 1100, which are connected to the first portions 104A, 204A, 1002A and the second portions 104B, 204B, 1002B at a third portion 104C, 204C, 1002C located between the first portions 104A, 204A, 1002A and the second portions 104B, 204B, 1002B. Bridge structures 602 and 1100 include strips 502 and 1104 of a second superconducting material 404 and 1106, configured to electrically connect the first portions 104A, 204A, 1002A and the second portions 104B, 204B, 1002B of the first superconducting materials 104, 204, 806. The second superconducting material 404 and 1106 of the strips 502 and 1104 are different from the first superconducting materials 104, 204, 806.

[0063] In one embodiment, the second superconducting materials 404 and 1106 of strips 502 and 1104 are porous, at least in the portions 104C, 204C, and 1002C that traverse the first superconducting material layers 104, 204, and 806. In one embodiment, bridge structures 602 and 1100 are configured to substantially eliminate parasitic modes of planar microwave circuits.

[0064] In one embodiment, for example, as Figure 7 As shown, the quantum mechanical device includes a plurality of regularly spaced bridge structures 602, 1100 to electrically connect first portions 104A, 204A, 1002A and second portions 104B, 204B, 1002B of the first superconducting material layers 104, 204, 806 at multiple locations on the first superconducting material layers 104, 204, 806. In one embodiment, the plurality of bridge structures 602, 1100 are configured to connect the first portions 104A, 204A, 1002A and the second portions 104B, 204B, 1002B of the first superconducting material layers 104, 204, 806 to the same ground potential.

[0065] 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 existing technologies on the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for fabricating a bridge structure in a quantum mechanical device, comprising: A substructure including a substrate on which a first superconducting material layer is deposited, the first superconducting material layer being divided into a first portion, a second portion, and a third portion that are electrically insulated from each other; A layered sacrificial layer is deposited on the substructure; A strip of a second superconducting material is used to electrically connect the first part and the second part of the first superconducting material, wherein the second superconducting material is different from the first superconducting material. as well as A portion of the sacrificial layer deposited on the substructure is removed so that a bridge structure is formed over the third portion between the first and second portions using strips of the second superconducting material, the bridge structure electrically connecting the first portion to the second portion without electrically connecting the third portion to the first portion or the second portion; The method of electrically connecting the first portion and the second portion of the first superconducting material using the strip of the second superconducting material includes attaching a first base pad of the strip to the first portion and attaching a second base pad of the strip to the second portion, wherein a portion of the sacrificial layer is located below the first base pad and the second base pad; The removal of the portion of the sacrificial layer deposited on the substrate includes etching the portion of the sacrificial layer below the strip to form a gap between the strip and the third portion of the first superconducting material, thereby defining the bridge structure above the third portion of the first superconducting material; The etching of the portion of the sacrificial layer below the strip includes etching the sacrificial layer deposited on the third portion below the strip, and etching the sacrificial layer deposited in the first and second trenches separating the first, second, and third portions, without etching the portions of the sacrificial layer located below the first and second base pads at both ends of the strip.

2. The method according to claim 1, wherein, Providing the substructure includes providing the substrate having a surface, and depositing the first superconducting material layer on the surface of the substrate.

3. The method according to claim 2, wherein, Providing the substructure further includes etching the first superconducting material layer to form a first trench and a second trench, so as to define a first portion, a second portion and a third portion of the first superconducting material layer, such that the first portion, the second portion and the third portion of the first superconducting material layer are spaced apart from each other by the etched first trench and the etched second trench.

4. The method according to any one of claims 1 to 3, wherein the substrate comprises silicon or sapphire.

5. The method according to any one of claims 1 to 3, wherein, The first superconducting material includes niobium or aluminum.

6. The method according to any one of claims 1 to 3, wherein the sacrificial layer comprises titanium (Ti), titanium nitride (TiN), or tantalum (Ta), or any combination thereof.

7. The method according to any one of claims 1 to 3, wherein, Depositing the sacrificial layer on the substructure includes sputtering a superconducting sacrificial material onto the substructure.

8. The method according to any one of claims 1 to 3, wherein, Electrically connecting the first portion and the second portion of the first superconducting material using the strip of the second superconducting material includes sputtering compressive stress superconducting material to form the strip of the second superconducting material.

9. The method according to any one of claims 1 to 3, wherein, Electrically connecting the first portion and the second portion of the first superconducting material using the strip of the second superconducting material includes using a strip of porous second superconducting material to electrically connect the first portion and the second portion of the first superconducting material.

10. The method of claim 1, wherein etching the portion of the sacrificial layer below the strip comprises etching the portion of the sacrificial layer using acid etching.

11. The method according to any one of claims 1 to 3, wherein, The substructure provided includes: Provide a substrate with a surface; A sacrificial material layer is deposited on the surface of the substrate; The sacrificial material layer is selectively etched to form a spaced-apart first and second portion of the sacrificial material; Selectively etch the substrate except for the first and second portions of the sacrificial material; Deposit the first superconducting material layer on the etched substrate and on the first and second portions of the sacrificial material; and The deposited layer of the first superconducting material and the first and second portions of the sacrificial material are removed to obtain the first superconducting material layer, which is divided into a first portion, a second portion, and a third portion that are electrically insulated from each other by the substrate material.

12. The method according to claim 11, wherein, Depositing the sacrificial layer on top of the substructure includes sputtering superconducting sacrificial material onto the first superconducting material layer.

13. The method according to claim 12, wherein, Removing the portion of the sacrificial layer deposited on the substrate includes etching the portion of the sacrificial layer below the strip, and etching the substrate material separating the first, second, and third portions of the superconducting material to form a gap between the strip and the third portion of the first superconducting material, thereby defining the bridge structure above the third portion of the first superconducting material.

14. A quantum mechanical device, comprising: Substrate; A first superconducting material layer is deposited on the substrate, the layer being divided into a first portion, a second portion, and a third portion that are electrically insulated from each other; as well as A bridge structure manufactured by the method according to any one of claims 1 to 13, the bridge structure being connected to the first and second portions over the third portion located between the first and second portions, the bridge structure comprising strips of a second superconducting material configured to electrically connect the first and second portions of the first superconducting material. The second superconducting material of the strip is different from the first superconducting material.

15. The quantum mechanical device of claim 14, wherein the second superconducting material of the strip is porous at least in the portion that crosses the third portion of the first superconducting material layer.

16. The quantum mechanical device according to claim 14 or 15, wherein the first portion and the second portion of the first superconducting material are connected to the same ground potential.

17. The quantum mechanical device of claim 14 or 15, wherein the third portion of the first superconducting material is a signal line configured to carry electromagnetic signals to and from qubits.

18. The quantum mechanical device of claim 14 or 15, wherein the bridge structure is configured to substantially eliminate parasitic modes of planar microwave circuits.

19. The quantum mechanical device according to claim 14 or 15, wherein, The first portion and the second portion of the first superconducting material layer are configured as first signal lines and second signal lines to carry first electromagnetic signals to and from a first qubit, and the third portion is configured as a third signal line to carry second electromagnetic signals to and from a second qubit.

20. The quantum mechanical device of claim 14 or 15, further comprising a plurality of regularly spaced bridge structures for electrically connecting the first portion and the second portion of the first superconducting material layer at a plurality of locations in the first superconducting material layer.

21. The quantum mechanical device according to claim 20, wherein, The plurality of bridge structures are configured to connect the first portion and the second portion of the first superconducting material layer to the same ground potential.

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