EP-4022693-B1 - JUNCTION FABRICATION METHOD FOR FORMING QUBITS

EP4022693B1EP 4022693 B1EP4022693 B1EP 4022693B1EP-4022693-B1

Inventors

ADIGA, VIVEKANANDA
WYMORE, BENJAMIN
FOGEL, KEITH
SANDBERG, MARTIN

Dates

Publication Date: 20260513
Application Date: 20201110

Claims (14)

A method of making a Josephson junction for a superconducting qubit, comprising: providing a substructure having a surface with first and second trenches (306, 308) defined therein, said first trench (306) being substantially perpendicular to and intersecting said second trench (308), said substructure having a bridge structure (402) extending over said first trench (306) adjacent said intersection of said first and second trenches; evaporating a first superconducting material (700) at a glancing angle along a first direction (702) to deposit said first superconducting material (700) in said first trench (306) so as to extend under said bridge structure (402) from said first direction (702); evaporating a second superconducting material substantially at the glancing angle substantially opposite to the first direction (702) to deposit the second superconducting material in the first trench (306) so as to extend under said bridge structure (402) from said glancing angle substantially opposite to said first direction (702) and to provide a first superconducting lead (710); oxidizing the first and second superconducting materials to form an oxidized layer on the first and second superconducting materials at least within said first trench (306); evaporating a third superconducting material at an angle substantially perpendicular to said surface of the substructure to deposit the third superconducting material in said second trench (308) within the substructure without rotating the substructure to form a second superconducting lead (910); and lifting off regions of said deposited first, second and third superconducting materials and said oxide layer to leave a vertical Josephson Junction at said intersection of said first and second trenches (306, 308) electrically connected at a first end thereof through said first superconducting lead (710) and at a second end thereof through said second superconducting lead (910).
The method according to claim 1, wherein the first, second and third superconducting materials are a same superconducting material.
The method according to any of the preceding claims, wherein providing the substructure comprises: providing a substrate; depositing a fourth superconducting material on a surface of the substrate; removing a portion of the fourth superconducting material from the surface of the substrate to uncover a portion of the surface of the substrate; depositing a first resist layer on the fourth superconducting material and on the uncovered portion of the surface of the substrate; and depositing a second resist layer on the first resist layer to form superposed first and second resist layers.
The method according to the preceding claim, wherein the fourth superconducting material is a same superconducting material as the first, second or third superconducting material.
The method according to any of the preceding claims and with features of claim 3, wherein providing the substructure further comprises: applying electron beam or optical beam lithography to expose a first portion of the superposed first and second resist layers and to expose a second portion of the superposed first and second resist layers.
The method according to claim 5, wherein providing the substructure further comprises: removing the exposed first portion of the superposed first and second resist layers to form the first trench; and removing the exposed second portion of the superposed first and second resist layers to form the second trench (308) and form the bridge structure (402) extending over said first trench (306) with a remaining portion of the second resist layer, the bridge structure (402) being substantially parallel to the second trench (308).
The method according to the preceding claim, wherein evaporating the second superconducting material substantially at the glancing angle substantially opposite to the first direction to deposit the second superconducting material in the first trench (306) comprises depositing the second superconducting material in zones shadowed by the bridge structure (402) and not filled by the first superconducting material during the evaporating of the first superconducting material.
The method according to any of the preceding claims and with features of claim 3, wherein the substrate is selected from the group consisting of Silicon, Si, Germanium, Ge, and Sapphire.
The method according to any of the preceding claims and with features of claim 3, wherein the first, second, third and fourth superconducting materials are selected from the group consisting of Niobium, Nb, and Aluminum, Al.
The method according to any of the preceding claims and with features of claim 3, wherein removing the portion of the superconducting material from the surface of the substrate to uncover the portion of the surface of the substrate comprises forming four sectors of the fourth superconducting material and associated buses, the four sectors being separated apart by the uncovered portion of the surface of the substrate.
The method according to any of the preceding claims and with features of claim 3, wherein depositing the first resist layer on the superconducting material and on the uncovered portion of the surface of the substrate comprises depositing a layer of monomethyl methacrylate, MMA, and wherein depositing the second resist layer on the first resist layer comprises depositing a layer of polymethyl methacrylate, PMMA.
The method according to any of the preceding claims, wherein the glancing angle is between about 5 degrees and 85 degrees relative to the surface of the substructure.
The method according to any of the preceding claims, further comprising: providing a substrate; evaporating the first superconducting material at the glancing angle along the first direction to deposit said first superconducting material on a surface of the substrate; evaporating the second superconducting material substantially at the glancing 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 apart by the uncovered portion of the surface of the substrate.
A superconducting qubit, the superconducting qubit being made by: providing a substructure having a surface with first and second trenches defined therein, said first trench (306) being substantially perpendicular to and intersecting said second trench (308), said substructure having a bridge structure (402) extending over said first trench; evaporating a first superconducting material at a glancing angle along a first direction to deposit said first superconducting material in said first trench (306) so as to extend under said bridge structure (402) from said first direction; evaporating a second superconducting material substantially at the glancing angle substantially opposite to the first direction to deposit the second superconducting material in the first trench (306) so as to extend under said bridge structure (402) from said glancing angle substantially opposite to said first direction and to provide a first superconducting lead; oxidizing the first and second superconducting materials to form an oxidized layer on the first and second superconducting materials at least within said first trench; evaporating a third superconducting material at an angle substantially perpendicular to said surface of the substructure to deposit the third superconducting material in said second trench (308) within the substructure without rotating the substructure to form a second superconducting lead; and lifting off regions of said deposited first, second and third superconducting materials and said oxide layer to leave a vertical Josephson Junction at said intersection of said first and second trenches (308) electrically connected at a first end thereof through said first superconducting lead and at a second end thereof through said second superconducting lead.

Description

BACKGROUND The currently claimed embodiments of the present invention relate to superconducting qubits, and more specifically, to methods of making superconducting qubits and qubits made using the methods. Quantum computation is based on the reliable control of quantum bits (referred to herein throughout as qubits). The fundamental operations required to realize quantum algorithms are a set of single-qubit operations and two-qubit operations which establish correlations between two separate quantum bits. The realization of high fidelity two-qubit operations may be desirable both for reaching the error threshold for quantum computation and for reaching reliable quantum simulations. The superconducting quantum processor (having one or more superconducting qubits) includes superconducting metals (e.g., Al, Nb, etc.) on an insulating substrate (e.g., Si or high resistivity Si, Al2O3, etc.). The superconducting quantum processor is typically a planar two-dimensional lattice structure of individual qubits linked by a coupler in various lattice symmetry (for example, square, hexagonal, etc.), and a readout structure located on a flip-chip. The couplers can be made of a capacitor, a resonator, a coil or any microwave component that provides a coupling between qubits. Conventional methods of fabricating superconducting qubits are based on the standard Josephson junction fabrication using the Dolan or Manhattan methods to form bridges. The above methods require many steps including rotating a substrate supporting the qubit during a deposition of the superconducting material. US020180358537A1 relates to a technique to form a sidewall tunnel junction for superconducting devices. US020190042967A1 relates to superconducting qubit devices with Josephson Junctions utilizing resistive switching materials. WO002019180267A1 relates to a method for manufacturing of specially designed substrates for growth of nanostructures. SUMMARY An aspect of the present invention is to provide a method of making a Josephson junction for a superconducting qubit. The method includes providing a substructure having a surface with first and second trenches defined therein, the first trench being substantially perpendicular to and intersecting the second trench, the substructure having a bridge structure extending over the first trench adjacent the intersection of the first and second trenches. The method further includes evaporating a first superconducting material at a glancing angle along a first direction to deposit the first superconducting material in the first trench so as to extend under the bridge structure from the first direction. The method also includes evaporating a second superconducting material substantially at the glancing angle substantially opposite to the first direction to deposit the second superconducting material in the first trench so as to extend under the bridge structure from the glancing angle substantially opposite to the first direction and to provide a first superconducting lead. The method further includes oxidizing the first and second superconducting materials to form an oxidized layer on the first and second superconducting materials 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 also includes lifting off regions of the deposited 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 electrically connected at a first end thereof through the first superconducting lead and at a second end thereof through the second superconducting lead. Another aspect of the present invention is to provide a superconducting qubit. The superconducting qubit is made by: 1) providing a substructure having a surface with first and second trenches defined therein, the first trench being substantially perpendicular to and intersecting the second trench, the substructure having a bridge structure extending over the first trench; 2) evaporating a first superconducting material at a glancing angle along a first direction to deposit the first superconducting material in the first trench so as to extend under the bridge structure from the first direction; 3) evaporating a second superconducting material substantially at the glancing angle substantially opposite to the first direction to deposit the second superconducting material in the first trench so as to extend under the bridge structure from the glancing angle substantially opposite to the first direction and to provide a first superconducting lead; 4) oxidizing the first and second superconducting materials to form an oxidized layer on the first and second superconducting materials at least within