Tuning the resonant frequency of fixed-frequency qubits

Abstract

In one embodiment, a method includes forming a capacitor pad for a nonlinear resonator. In one embodiment, the method includes comparing a resonant frequency of the nonlinear resonator to a target frequency to determine whether the resonant frequency is within a range of the target frequency. In one embodiment, a device includes a first capacitor pad including a superconducting material and configured to couple to a first end of a logic circuit element. In one embodiment, the device includes a second capacitor pad including a second superconducting material and configured to couple to a second end of the logic circuit element. In one embodiment, the second capacitor pad includes a first portion, a second portion, and a bridge configured to electrically connect the first portion and the second portion.

Description

[Technical field]

[0001] The present invention relates generally to superconducting devices, methods and systems for manufacturing superconducting qubit resonators, and more particularly to devices, methods and systems for resonant frequency tuning of fixed frequency qubits. [Background technology]

[0002] Hereinafter, the prefix "Q" or "q" on a word or phrase indicates a reference to that word or phrase in the context of quantum computing, unless clearly distinguished otherwise when used.

[0003] Molecular and subatomic particles are subject to the laws of quantum mechanics, a branch of physics that explores how the physical world works at the most fundamental level. At this level, particles exhibit strange behavior, exist in multiple states simultaneously, and interact with other particles at great distances. Quantum computing exploits these quantum phenomena to process information.

[0004] The computers we use today are known as classical computers (also referred to herein as "conventional" computers or conventional nodes, i.e. "CN"). Conventional computers use conventional processors manufactured using semiconductor materials and technology, semiconductor memory, and magnetic or solid-state storage devices, known as the von Neumann architecture. In particular, the processors in conventional computers are binary processors, i.e., processors that perform operations on binary data represented by 1s and 0s.

[0005] Quantum processors (q-processors) use the exotic properties of entangled quantum bit devices (referred to herein for brevity as "qubits") to perform computational tasks. In the particular domain where quantum mechanics operates, particles of matter can exist in multiple states, such as "on" states, "off" states, and states that are both "on" and "off" simultaneously. Whereas binary computations using semiconductor processors are limited to using only on and off states (corresponding to 1s and 0s in binary code), quantum processors exploit these quantum states of matter to output signals that can be used in data computations.

[0006] Conventional computers encode information with bits. Each bit can take on a value of 1 or 0. These 1s and 0s act as on / off switches that ultimately drive computer functions. Quantum computers, on the other hand, are based on qubits that operate according to two key principles of quantum physics: superposition and entanglement. Superposition means that each qubit can represent both 1 and 0 simultaneously. Entanglement means that qubits in a superposition state can be related to each other in a non-classical way, meaning that one state (whether that state is 1 or 0 or both) can depend on another state, and more information can be uncovered about two qubits when they are entangled than when they are processed separately.

[0007] Using these two principles, quantum bits act as more advanced information processors, enabling quantum computers to function in ways that solve problems that are difficult to solve using classical computers. IBM® has successfully built a quantum processor and demonstrated the operability of a quantum processor. (IBM® is a registered trademark of the International Business Machines Corporation in the United States and other countries.)

[0008] A superconducting qubit may include a Josephson junction. A Josephson junction is formed by separating two thin-film superconducting metal layers by a non-superconducting material. When the metal in the superconducting layer is made superconducting, for example by lowering its temperature to a specified cryogenic temperature, electron pairs can tunnel from one superconducting layer through the non-superconducting layer to the other superconducting layer. In a superconducting qubit, a Josephson junction with an inductance is electrically coupled in parallel with one or more capacitive devices to form a nonlinear resonator.

[0009] In the superconducting state, firstly, the material offers no resistance to the passage of electric current. When the resistance is zero, electric current can circulate in the material without consuming any energy. Secondly, the material exhibits the Meissner effect, i.e. if an external magnetic field is weak enough, it does not penetrate the superconductor but remains on its surface. When one or both of these properties are no longer exhibited in a material, the material is considered to be no longer superconducting.

[0010] The critical temperature of a superconducting material is the temperature at which the material begins to exhibit superconducting properties. A superconducting material has very low or zero resistance to the flow of electric current. The critical magnetic field is the maximum magnetic field for a given temperature below which the material remains superconducting.

[0011] Superconductors are generally classified into one of two types. Type 1 superconductors have a single transition at the critical magnetic field. Type 1 superconductors transition from a non-superconducting state to a superconducting state when the critical magnetic field is reached. Type 2 superconductors have two critical magnetic fields and two transitions. Type 2 superconductors are superconducting below the lower critical magnetic field. Type 2 superconductors do not exhibit superconducting properties above the upper critical magnetic field. Type 2 superconductors have a mixed state between the upper and lower critical magnetic fields. In the mixed state, type 2 superconductors have an incomplete Meissner effect, i.e., external magnetic fields penetrate through the superconductor material in quantized packets at specific locations.

[0012] The Meissner effect results from the creation of persistent electric currents on the surface of a superconductor material. Persistent currents are permanent electric currents that do not require an external power source. They generate opposing magnetic fields throughout the bulk of the superconducting material to cancel external magnetic fields. In the superconducting state, the persistent currents do not decay over time due to the zero-resistance nature of the material. Summary of the Invention [Problem to be solved by the invention]

[0013] The information processed by the qubits is radiated in the form of microwave energy in the microwave frequency range. The microwave radiation is captured, processed, and analyzed to decode the quantum information encoded therein. For quantum computation of qubits to be reliable, the quantum circuits, e.g., the qubits themselves, readout circuits associated with the qubits, and other types of superconducting quantum logic circuits, must not significantly alter the energy state of the particles or microwave radiation in any way. This operational constraint on any circuit that operates using quantum information requires special consideration in the fabrication of semiconductor and / or superconductor structures used in such circuits.

[0014] The readout circuit is typically coupled to the qubits by electromagnetic resonance (usually microwave or radio frequency resonance) using a resonator. The resonator in the readout circuit comprises an inductive element and a capacitive element. Some qubits are fixed frequency qubits, i.e. their resonant frequency cannot be changed. Other qubits are frequency tunable qubits. The q-processor can use fixed frequency qubits, frequency tunable qubits, or a combination thereof. [Means for solving the problem]

[0015] The present invention recognizes that designing fixed frequency qubits to be frequency-locked improves their immunity to noise. The present invention recognizes that when the resonant frequencies of two adjacent qubits on a chip are the same or within the threshold of a frequency band, or when their higher transition frequencies are on or close to resonance, adverse effects such as crosstalk, quantum decoherence, energy decay, generation of mixed states, unintended information transfer, quantum state leakage, etc. may occur. The present invention further recognizes that such qubits may also adversely affect the performance or usefulness of certain quantum gates, such as cross-resonant gates, which have stringent requirements on the spectrum of the resonant frequencies of the qubits on which the gates are operating. The present invention further recognizes that one of the challenges in quantum processors based on fixed frequency qubits is frequency crowding or frequency collisions between adjacent qubits.

[0016] The present invention recognizes that another challenge in quantum processors based on fixed frequency qubits is the low on / off ratio between the interactions between adjacent qubits when microwave signals turn on the interactions (when the interaction strength is on) and the interactions between adjacent qubits when these signals are disabled (when the interaction strength is off). Exemplary embodiments further recognize that another challenge in quantum processors based on fixed frequency qubits is enabling the gates of interest without generating undesired interactions with other gates. The present invention further recognizes that imperfections in the fabrication of fixed frequency qubits and in the materials used in currently available fabrication methods for fixed frequency qubits lead to deviations from the intended resonant frequency.

[0017] FIG. 1 shows a scaled image of a qubit with capacitive coupling to an external circuit. Image 100 shows a portion of a qubit chip. Coupling capacitor 102 couples to a transmission line (not shown) that carries the electromagnetic signal away from Josephson junction 104. Capacitor pad 106 is a capacitive device that drives Josephson junction 104 and forms a nonlinear resonator. A ground plane (not shown) typically surrounds all or part of the structure.

[0018] The present invention recognizes that the resonant frequency of a qubit is essentially fixed when the qubit is fabricated, i.e., when the Josephson junctions and the capacitive elements of the qubit oscillator are fabricated on the q-processor chip. The present invention further recognizes that in the simplest implementation of a q-processor, at least two qubits are required to implement a quantum logic gate. Thus, q-processor chips are typically fabricated with at least two, but often eight, sixteen, or more qubits on a single q-processor chip.

[0019] The present invention provides a superconducting device, and a method and system for its manufacture. The method includes forming a capacitor pad for a nonlinear resonator. In one embodiment of the present invention, the method includes comparing a resonant frequency of the nonlinear resonator to a target frequency to determine whether the resonant frequency is within a range of the target frequency.

[0020] In one embodiment of the invention, the method includes removing a portion of the capacitor pad in response to the resonant frequency not being within the range. In one embodiment of the invention, the method includes removing a segment of a second capacitor pad to form a bridge, the bridge electrically coupling a first portion of the second capacitor pad and a second portion of the second capacitor pad.

[0021] The portion may include a bridge. The segments may be removed by masking and etching the second capacitor pad. The method may include removing a plurality of segments of the second capacitor pad to form a plurality of bridges.

[0022] The portion may include a plurality of bridges. The plurality of segments may be removed by masking and etching the second capacitor pad. The method may include removing a second portion of the second capacitor pad in response to the resonant frequency not being within the tolerance range. The portion may be removed by laser ablation or by ion beam milling.

[0023] The device of the present invention includes a first capacitor pad including a superconducting material and configured to couple to a first end of a logic circuit element. The device may include a second capacitor pad including a second superconducting material and configured to couple to a second end of the logic circuit element. The second capacitor pad may include a first portion, a second portion, and a bridge configured to electrically connect the first portion and the second portion.

[0024] The bridge may be configured to be removable by masking and etching. The bridge may be configured to be removable by laser ablation or by ion beam milling.

[0025] The first capacitor pad may further include a first portion, a second portion, and a bridge configured to electrically connect the first portion and the second portion. The first capacitor pad and the second capacitor pad may be symmetrical or asymmetrical. The first capacitor pad may further include a plurality of portions, and a plurality of bridges configured to electrically connect adjacent portions of the plurality of portions. The plurality of portions may be asymmetrical.

[0026] In one embodiment of the present invention, a superconductor fabrication system includes a lithography component that, when operated to fabricate a superconducting device, performs operations including forming a capacitor pad for a nonlinear resonator, comparing a resonant frequency of the nonlinear resonator to a target frequency to determine whether the resonant frequency is within a range of the target frequency, and removing a portion of the capacitor pad in response to the resonant frequency not being within the range.

[0027] One embodiment of the present invention includes a manufacturing method for producing a superconducting device.

[0028] One embodiment of the present invention includes a manufacturing system for manufacturing a superconducting device.

[0029] The novel features of the invention are set forth in the appended claims, however the invention itself, together with the preferred modes of its use, together with its objects and advantages, will be best understood from the following detailed description of illustrative embodiments thereof, read in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0030] [Figure 1] 1 is a scaled image of a qubit with capacitive coupling to an external circuit. [Diagram 2] 3A-3D illustrate steps in a manufacturing process for a fixed frequency resonator, according to one embodiment of the present invention. [Diagram 3] 5A-5C illustrate steps of a second manufacturing process for producing a fixed frequency resonator according to an embodiment of the present invention. [Figure 4] 1A-1C illustrate steps of a second manufacturing process. [Diagram 5] 1A-1C illustrate steps of a second manufacturing process. [Figure 6] FIG. 2 illustrates a fixed frequency resonator configuration according to one embodiment of the present invention. [Figure 7]FIG. 13 illustrates the results of a simulation to determine the resonant frequency of a fixed frequency resonator. [Figure 8] 4 is a flow diagram of a manufacturing process for producing a fixed frequency resonator, in accordance with one embodiment of the present invention. [Figure 9] 4 is a flow diagram of a second exemplary manufacturing process for producing a fixed frequency resonator, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] The embodiments of the present invention used to illustrate the invention generally address and solve the above problems in superconducting qubit resonators for fixed frequency qubits. The embodiments of the present invention provide a fabrication method for tuning the resonant frequency of a fixed frequency qubit.

[0032] An embodiment of the present invention may be implemented as a superconducting qubit resonator. A method for fabricating a superconducting qubit resonator may be implemented as a software application. The application may be configured to operate in conjunction with existing semiconductor / superconductor fabrication systems, such as lithography systems.

[0033] For clarity of explanation, embodiments of the present invention are described using simplified diagrams of exemplary superconducting qubit resonators in the figures, and no limitation thereto is implied. In the actual fabrication of a superconducting qubit resonator, additional structures not shown or described herein, or structures different from those shown and described herein, may be present without departing from the scope of the present invention. Similarly, the structures shown or described in the exemplary superconducting qubit resonators may be fabricated in different ways to produce similar operation or results as described herein, within the scope of the present invention.

[0034] As described herein, different shaded portions in two-dimensional drawings of example structures, layers, and configurations are intended to represent different structures, layers, materials, and configurations in the example fabrication. The different structures, layers, materials, and configurations may be fabricated using suitable materials known to those of skill in the art.

[0035] The particular shapes, locations, positions, or dimensions of features shown herein are not intended to limit the invention unless such characteristics are expressly described as features of the invention. The shapes, locations, positions, dimensions, or some combination thereof, have been selected merely for clarity of the drawings and description, and may be exaggerated, optimized, or otherwise modified as compared to the actual shapes, locations, positions, or dimensions that may be used in actual photolithography to achieve the purpose.

[0036] An embodiment of the present invention, when implemented in an application, causes a manufacturing process to perform certain steps as described herein. The steps of the manufacturing process are illustrated in some figures. Not all steps may be required in a particular manufacturing process. Some manufacturing processes may perform steps in a different order, combine certain steps, remove or substitute certain steps, or perform some combination of these steps and other operations of steps without departing from the scope of the invention.

[0037] The embodiments of the present invention are described by way of example only with respect to specific types of materials, electrical properties, structures, configurations, layer orientations, directions, steps, operations, planes, dimensions, numbers, data processing systems, environments, components, and applications. Any specific manifestations of these and other similar artifacts are not intended to limit the present invention. Any suitable manifestations of these and other similar artifacts may be selected within the scope of the present invention.

[0038] The embodiments of the present invention are described using particular designs, architectures, layouts, diagrams, and tools as examples only and are not intended to be limiting of the present invention, and may be used in combination with other designs, architectures, layouts, diagrams, and tools of equivalent or similar purpose.

[0039] The examples in this disclosure are used only for clarity of explanation and are not intended to limit the present invention. Any advantages listed herein are merely examples and are not intended to limit the present invention. Additional or different advantages may be realized depending on the particular embodiment of the present invention. Moreover, a particular embodiment of the present invention may have some, all, or none of the advantages listed above.

[0040] The qubits are used only as exemplary superconducting quantum logic circuits in which an embodiment of the present invention may be employed. Those skilled in the art will be able to envision from this disclosure many other superconducting quantum logic circuits and conventional logic circuits in which the resonant frequency tuning of the present invention may be used, and are also considered to be within the scope of the present invention.

[0041] FIG 2 illustrates steps in a manufacturing process for producing a fixed frequency resonator. FIG 2-5 illustrate various steps in a second manufacturing process for producing a fixed frequency resonator. The fixed frequency resonators formed by the two exemplary processes are structurally different as described below, but are functionally equivalent so that they can be used interchangeably in place of the capacitor pad 106 of FIG 1.

[0042] Referring to FIG. 2, capacitor pads 204A, 204B represent capacitive devices fabricated according to methods described herein that can be used, for example, in place of capacitor pad 106 of FIG.

[0043] The capacitor pads 204A, 204B drive the Josephson junction 202 to form a nonlinear resonator. The capacitor pads 204A, 204B may include a material that exhibits superconductivity in a portion of the cryogenic temperature range between 70 and 0.01 K, inclusive. The superconducting material of the capacitor pads 204A, 204B may be niobium. The fabrication system may sputter the superconducting material onto a substrate to form the capacitor pads 204A, 204B. The capacitor pads 204A, 204B may have a length L.

[0044] Each of the capacitor pads 204A, 204B may have a corresponding capacitance value. The capacitance value is directly proportional to the area of ​​the corresponding capacitor pad. The fixed frequency resonator may be modeled as a lumped element LC circuit with a total capacitance C. Each capacitance value of the capacitor pads 204A, 204B contributes to the total capacitance C. The resonant frequency of the fixed frequency resonator is given by the equation

number

[0045] In step 200, an embodiment of the present invention has the fabrication system remove a portion of the capacitor pad 204A, 204B, thereby forming the first portion 206A, 206B and the second portion 208A, 208B. For example, an embodiment of the present invention can have the fabrication system remove the capacitor pad material using laser ablation or ion beam milling. The first portion 206A, 206B maintains electrical connection with the Josephson junction 202 and forms a modified nonlinear resonator. An embodiment of the present invention can have the fabrication system remove the second portion 208A, 208B from the capacitive device, thereby decreasing the total capacitance and increasing the resonant frequency of the fixed frequency resonator.

[0046] It may not be necessary to remove capacitor pad material from both capacitor pads. Reducing the area of ​​only one of the two pads, e.g., from pad 204A but not from pad 204B, is effective to change the total capacitance C and therefore the resonant frequency f. Removal from both pads is depicted and described merely for clarity of depiction and not as a limitation of the present invention. Asymmetric removal from the capacitor pads, including not removing from one of the pads, to produce the effects described herein is also contemplated within the scope of the present invention.

[0047] 2, first portions 206A and 206B are symmetric. For example, the sizes of first portions 206A and 206B may be approximately equal between 0 and 5 percent inclusive. In another embodiment of the invention, first portions 206A and 206B are asymmetric. For example, the sizes of first portions 206A and 206B may differ by more than 5 percent up to as much as 40 percent.

[0048] The second portions 208A and 208B are symmetric. For example, the sizes of the second portions 208A and 208B can be approximately equal between 0 and 5 percent, inclusive. In another embodiment of the invention, the second portions 208A and 208B are asymmetric. For example, the sizes of the second portions 208A and 208B can differ by more than 5 percent up to as much as about 200 percent. In another step, an embodiment of the invention has the manufacturing system remove only a portion of the capacitor pad 204A, thereby forming the first portion 206A and the second portion 208A.

[0049] In one embodiment of the invention, the fabrication system removes a length ΔL of capacitor pad material from capacitor pad 204A, 204B of length L. In another embodiment of the invention, ΔL includes the length of the cut. For example, the fabrication system may remove a length of capacitor pad material between 1 and 5 micrometers inclusive. In one embodiment, ΔL includes the length of the cut and the length of the corresponding second portion.

[0050] In another embodiment of the invention, the manufacturing system removes a portion of the capacitor pad 204A at a first end of the fixed frequency resonator and a portion of the capacitor pad 204B at an opposing end of the fixed frequency resonator. In another embodiment of the invention, the manufacturing system removes a portion of the capacitor pad 204A at an oblique angle relative to the length L of the capacitor pad 204A. Step 300 can be repeated to remove more capacitor pad material to arrive at a desired resonant frequency for the fixed frequency resonator.

[0051] Referring to FIG. 3, capacitor pads 304A, 304B represent capacitive devices fabricated according to methods described herein that can be used, for example, in place of capacitor pad 106 of FIG.

[0052] The capacitor pads 304A, 304B drive the Josephson junction 302 to form a nonlinear resonator. The capacitor pads 304A, 304B may include a material that exhibits superconductivity in a portion of the cryogenic temperature range. For example, the superconducting material may be niobium.

[0053] In step 300, an embodiment of the present invention has the manufacturing system remove segments of the capacitor pads 304A, 304B, thereby forming the first portions 306A, 306B, the second portions 308A, 308B, and the bridges 310A, 310B. For example, an embodiment may have the manufacturing system mask and etch the capacitor pads to remove corresponding segments of the capacitor pads. In step 300, an embodiment of the present invention has the manufacturing system form corresponding air gaps between the first portions 306A, 306B and the second portions 308A, 308B.

[0054] The bridges 310A, 310B electrically connect the second portions 308A, 308B with the first portions 306A, 306B. For example, the second portions 308A, 308B and the bridges 310A, 310B contribute to the capacitance of the corresponding capacitor pads. The first portions 306A, 306B, the second portions 308A, 308B, and the bridges 310A, 310B maintain electrical connection with the Josephson junction 302 to form a modified nonlinear resonator.

[0055] In one embodiment of the invention, first portions 306A and 306B are symmetric. For example, the sizes of first portions 306A and 306B may be approximately equal between 0 and 5 percent inclusive. In another embodiment of the invention, first portions 306A and 306B are asymmetric. For example, the sizes of first portions 306A and 306B may differ by more than 5 percent up to as much as 40 percent.

[0056] In one embodiment of the invention, second portions 308A and 308B are symmetric. For example, the sizes of second portions 308A and 308B can be approximately equal between 0 and 5 percent, inclusive. In another embodiment of the invention, second portions 308A and 308B are asymmetric. For example, the sizes of second portions 308A and 308B can differ by more than 5 percent up to as much as about 200 percent. In another step, one embodiment of the invention has the manufacturing system remove only a portion of capacitor pad 304A, thereby forming first portion 306A and second portion 308A.

[0057] In one embodiment of the invention, the fabrication system removes a length of capacitor pad material from capacitor pads 304A, 304B. In another embodiment of the invention, the removed material includes a length of a cut portion. For example, the fabrication system may remove a length of capacitor pad material between 1 and 5 micrometers inclusive. In one embodiment, the removed material includes a length of a cut portion and a corresponding second portion of a length.

[0058] In another embodiment of the invention, the fabrication system removes a portion of the capacitor pad 304A at a first end of the fixed frequency resonator and a portion of the capacitor pad 304B at an opposing end of the fixed frequency resonator. In another embodiment, the fabrication system removes a portion of the capacitor pad 304A at an oblique angle relative to the length of the capacitor pad 304A.

[0059] 4, which illustrates a step in a second manufacturing process, where capacitor pads 404A, 404B represent capacitive devices fabricated by methods described herein and that can be used, for example, in place of capacitor pad 106 of FIG.

[0060] The capacitor pads 404A, 404B drive the Josephson junction 402 to form a nonlinear resonator. In one embodiment, the capacitor pads 404A, 404B include a material that exhibits superconductivity in a portion of the cryogenic temperature range. For example, the superconducting material of the capacitor pads 404A, 404B can be niobium.

[0061] In step 400, an embodiment of the present invention has the manufacturing system remove multiple segments of the capacitor pad 404A, 404B, thereby forming the first portion 406A, 406B, the second portion 410, the third portion 414, the fourth portion 418, the fifth portion 422, the sixth portion 426, and the bridges 408, 412, 416, 420, 424. For example, an embodiment of the present invention can have the manufacturing system mask and etch the capacitor pad to remove multiple segments of the corresponding capacitor pad. In step 400, an embodiment of the present invention has the manufacturing system form corresponding voids between the first portion 406A and the portions 410, 414, 418, and form corresponding voids between the first portion 406B and the portions 422, 426.

[0062] The bridges 408, 412, 416 electrically connect the portions 410, 414, 418 with the first portion 406A. For example, the portions 410, 414, 418 and the bridges 408, 412, 416 contribute to the capacitance of the corresponding capacitor pads. The bridges 420, 424 electrically connect the portions 422, 426 with the first portion 406B. For example, the portions 422, 426 and the bridges 420, 424 contribute to the capacitance of the corresponding capacitor pads. The portions 406A, 406B, 410, 414, 418, 422, 426 and the bridges 408, 412, 416, 420, 424 maintain electrical connection with the Josephson junction 402 to form a modified nonlinear resonator.

[0063] In one embodiment of the invention, first portions 406A and 406B are symmetric. For example, the sizes of first portions 406A and 406B may be approximately equal between 0 and 5 percent inclusive. In another embodiment of the invention, first portions 406A and 406B are asymmetric. For example, the sizes of first portions 406A and 406B may differ by more than 5 percent up to 40 percent.

[0064] In one embodiment of the invention, at least two of the portions 410, 414, 418, 422, 426 are symmetrical. For example, the size of at least two of the portions 410, 414, 418, 422 may be approximately equal between 0 and 5 percent, inclusive. In another embodiment, at least two of the portions 410, 414, 418, 422, 426 are asymmetrical. For example, the size of at least two of the portions 410, 414, 418, 422, 426 may differ by more than 5 percent up to as much as about 200 percent.

[0065] These examples of capacitor pad materials, deposition methods, and material removal methods are not intended to be limiting, and one of ordinary skill in the art will be able to devise from this disclosure many other suitable materials and methods for forming and removing portions of the capacitor pad that are also contemplated as being within the scope of the present invention.

[0066] 5, which shows steps of a second exemplary manufacturing process: Manufacturing continues on the modified fixed frequency resonator of FIG.

[0067] In step 500, an embodiment of the invention has the fabrication system remove the bridges 506A, 506B, thereby separating the first portions 504A, 504B and the second portions 508A, 508B. For example, an embodiment can have the fabrication system remove the capacitor pad material using laser ablation or ion beam milling. The first portions 504A, 504B maintain electrical connection with the Josephson junction 502, further forming a modified nonlinear resonator. An embodiment of the invention has the fabrication system remove the second portions 508A, 508B and the bridges 506A, 506B from the capacitive device, thereby decreasing the total capacitance and increasing the resonant frequency of the fixed frequency resonator. Step 500 can be repeated to remove more capacitor pad material and reach a desired resonant frequency for the fixed frequency resonator. For example, the fabrication system can further remove the bridges, as in the modified nonlinear resonator of FIG. 4.

[0068] Referring to FIG. 6, configuration 600 is an example of a fixed frequency resonator similar to the modified nonlinear resonator of FIG.

[0069] Configuration 600 includes a Josephson junction 602, first portions 606A, 606B, second portions 608A, 608B, and a bridge 610. Bridges 612, 614, 616 are examples of bridges formed in step 300 of FIG.

[0070] Referring to FIG. 7, this figure shows the results of a simulation to determine the resonant frequency of an example fixed frequency resonator. The fixed frequency resonator is based on the modified nonlinear resonator with multiple bridges shown in FIG. 4, and the resonant frequency results of this fixed frequency resonator are shown in FIG. 6. Specifically, in a non-limiting exemplary implementation, the original capacitor pad size was 500 micrometers long and 120 micrometers wide, the two first segments were 35 micrometers long, the two second segments were 40 micrometers long, the gap between each segment and the central portion of the capacitor pad was 5 micrometers long, and the bridges connecting each segment to the central portion of the capacitor pad across the gap were each 5 micrometers long and 5 micrometers wide. A process of removing each bridge separated each segment from the central portion of the capacitor pad.

[0071] Data point 704 corresponds to the resonant frequency of the modified nonlinear resonator with no bridges removed. Data point 706 corresponds to the resonant frequency of the modified nonlinear resonator with one bridge removed. Data point 708 corresponds to the resonant frequency of the modified nonlinear resonator with two bridges removed. Data point 710 corresponds to the resonant frequency of the modified nonlinear resonator with three bridges removed. Data point 712 corresponds to the resonant frequency of the modified nonlinear resonator with four bridges removed. As can be seen, the resonant frequency of the modified nonlinear resonator increases with the removal of each bridge.

[0072] 8, this figure shows a flow diagram of a manufacturing process for fabricating a fixed frequency resonator. Process 800 can be configured to work in conjunction with existing semiconductor / superconductor manufacturing systems, such as lithography systems.

[0073] In one embodiment of the invention, the manufacturing system forms a capacitor pad (block 802). In one embodiment of the invention, the frequency resonator comprises a capacitor pad. In one embodiment of the invention, the manufacturing system compares the resonant frequency of the frequency resonator (qubit) to the target frequency (block 804). In one embodiment of the invention, the manufacturing system determines that the resonant frequency is within a tolerance range of the target frequency (block 806). For example, the manufacturing system may determine that the resonant frequency is within half of one percent of the target frequency. In one embodiment of the invention, the manufacturing system determines that the resonant frequency is outside of a tolerance range of the target frequency. For example, the manufacturing system may determine that the resonant frequency differs from the target frequency by more than half of one percent. If the manufacturing system determines that the resonant frequency is outside of the tolerance range (the "No" path of block 806), the manufacturing system removes a portion of the capacitor pad (block 808). The process 800 then continues back to block 804. If the manufacturing system determines that the resonant frequency is within the acceptable range (the "Yes" path from block 806), the process 800 ends.

[0074] 9, a flow diagram of a second exemplary manufacturing process for fabricating a fixed frequency resonator is shown. Process 900 can be configured to operate in conjunction with existing semiconductor / superconductor manufacturing systems, such as lithography systems.

[0075] In one embodiment of the invention, the manufacturing system forms a capacitor pad (block 902). In one embodiment of the invention, the frequency resonator comprises a capacitor pad. In one embodiment of the invention, the manufacturing system removes a segment of the capacitor pad to form a bridge (block 904). For example, the manufacturing system may remove a segment of the capacitor pad to form a first portion and a second portion with a gap therebetween. In one embodiment, the bridge electrically connects the first portion and the second portion. In one embodiment of the invention, the manufacturing system compares a resonant frequency of the frequency resonator (qubit) to a target frequency (block 906). In one embodiment, the manufacturing system determines that the resonant frequency is within a tolerance range of the target frequency (block 908). For example, the manufacturing system may determine that the resonant frequency is within 0.5 percent error of the target frequency. In one embodiment of the invention, the manufacturing system determines that the resonant frequency is outside a tolerance range of the target frequency. For example, the manufacturing system may determine that the resonant frequency differs from the target frequency by more than 0.5 percent. If the manufacturing system determines that the resonant frequency is outside the acceptable range (the "No" path out of block 908), the manufacturing system removes the bridge of the capacitor pad (block 910). The process 900 then continues back to block 906. If the manufacturing system determines that the resonant frequency is within the acceptable range (the "Yes" path out of block 908), the process 900 ends.

[0076] Various embodiments of the present invention are described herein with reference to the associated drawings. Alternative embodiments may be devised without departing from the scope of the present invention. In the following description and drawings, various connections and positional relationships between elements (e.g., above, below, adjacent, etc.) are described, but those skilled in the art will understand that many of the positional relationships described herein are independent of orientation, as the described functionality is maintained even when the orientation is changed. These connections and / or positional relationships may be direct or indirect, unless otherwise specified, and the present invention is not intended to be limited in this respect. Thus, the coupling of entities may refer to either direct or indirect coupling, and the positional relationship between entities may be a direct or indirect positional relationship. As an example of an indirect positional relationship, when referring to forming a layer "A" on a layer "B" in this specification, it includes the situation where there are one or more intermediate layers (e.g., layer "C") between layers "A" and "B", as long as the associated properties and functions of layers "A" and "B" are not substantially altered by the intermediate layers.

[0077] The following definitions and abbreviations shall be used for the interpretation of the claims and the specification. As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," "contains," or "containing," or any other variation thereof, are intended to include a non-exclusive inclusion. For example, a composition, mixture, process, method, article, or device that comprises recited elements is not necessarily limited to only those elements, but can include other elements not expressly recited or inherent to such composition, mixture, process, method, article, or device.

[0078] Moreover, the term "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or design described herein as "exemplary" should not necessarily be construed as preferred or advantageous over other embodiments or designs. The terms "at least one" and "one or more" are understood to include any integer number greater than or equal to one, i.e., 1, 2, 3, 4, etc. The term "multiple" is understood to include any integer number greater than or equal to two, i.e., 2, 3, 4, 5, etc. The term "connected" can include indirect and direct "connected."

[0079] References herein to "one embodiment," "an embodiment," "an exemplary embodiment," and the like indicate that the embodiment being described may include a particular feature, structure, or characteristic, but each embodiment may or may not include the particular feature, structure, or characteristic. Also, such phrases do not necessarily refer to the same embodiment. Moreover, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is believed to be within the knowledge of one of ordinary skill in the art to affect such feature, structure, or characteristic in connection with other embodiments, whether or not explicitly described.

[0080] The terms "about," "substantially," "approximately," and variations thereof are intended to include the degree of error associated with measurement of a particular quantity based on the equipment available at the time of this application. For example, "about" can include a range of ±8% or 5%, or 2% of a given value.

[0081] Although the description of various embodiments of the present invention has been presented for illustrative purposes, they 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 of the present invention. The terms used in this specification are selected to best explain the principles of the present invention, practical applications, or technical improvements over the art found in the market, or to enable those skilled in the art to understand the embodiments of the present invention described herein.

Claims

1. 1. A method comprising: forming a plurality of capacitor pads for a nonlinear resonator, each of the plurality of capacitor pads including a first portion electrically coupled to a Josephson junction, a second portion disposed across a gap from the first portion, and a bridge disposed adjacent to the gap and electrically coupling the first portion and the second portion; comparing a resonant frequency of the nonlinear resonator to a target frequency to determine whether the resonant frequency is within a range of the target frequency; in response to the resonant frequency not being within the range, removing the bridge of at least one of the plurality of capacitor pads to separate the first portion and the second portion by the gap and the removed portion of the bridge to form a modified nonlinear resonator including the Josephson junction and a portion of the plurality of capacitor pads that remains electrically coupled to the Josephson junction; A method comprising:

2. the bridge being formed by masking and etching each of the plurality of capacitor pads; The method of claim 1.

3. forming a plurality of bridges on each of the plurality of capacitor pads; The method according to claim 1 or 2.

4. the plurality of bridges being formed by masking and etching each of the plurality of capacitor pads; The method according to claim 3.

5. and further comprising the step of removing a second portion of at least one of the plurality of capacitor pads in response to the resonant frequency not being within the range.

5. The method according to claim 1 ,

6. the bridge is removed by laser ablation; A method according to any one of claims 1 to 5.

7. the bridge is removed by ion beam milling; A method according to any one of claims 1 to 5.

8. 1. A nonlinear resonator device comprising: a first capacitor pad including a first superconducting material and configured to couple to a first end of a logic circuit element, the logic circuit element being a Josephson junction; a second superconducting material and configured to couple to a second end of the logic circuit element; a first portion electrically coupled to the second end; a second portion disposed across a gap from the first portion; and a removable bridge disposed adjacent the gap and configured to electrically connect the first portion and the second portion, the bridge configured, when removed, to separate the first portion and the second portion by a removed portion of the bridge in conjunction with the gap; a second capacitor pad including: a Josephson junction and portions of the first capacitor pad and the second capacitor pad that remain electrically coupled to the Josephson junction.

9. the bridge is configured to be removable by masking and etching; The nonlinear resonator device of claim 8 .

10. the bridge is configured to be removable by laser ablation; The nonlinear resonator device of claim 8 .

11. the bridge being configured to be removable by ion beam milling; The nonlinear resonator device of claim 8 .

12. The first capacitor pad comprises: A first part, A second portion, and a bridge configured to electrically connect the first portion and the second portion Further comprising: The nonlinear resonator device of claim 9.

13. the first capacitor pad and the second capacitor pad are symmetrical; The nonlinear resonator device of claim 12.

14. the first capacitor pad and the second capacitor pad are asymmetric; The nonlinear resonator device of claim 12.

15. The first capacitor pad comprises: Multiple parts, and a plurality of bridges configured to electrically connect adjacent ones of the plurality of portions; Further comprising:

15. A nonlinear resonator device according to any one of claims 8 to 14.

16. the plurality of portions are asymmetric; 16. The nonlinear resonator device of claim 15.

17. A superconductor manufacturing system comprising a lithography component, which, when operated to manufacture a superconducting device, performs the steps of the method of any of claims 1 to 7. Superconductor manufacturing system.

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