Resonance frequency tuning of fixed-frequency qubits

Abstract

A method includes forming a capacitor pad (304A, 304B) for a nonlinear resonator. The method includes comparing a resonant frequency of the nonlinear resonator with a target frequency to determine whether the resonant frequency falls within a range of the target frequency. A device includes a first capacitor pad, the first capacitor pad including a superconducting material, the first capacitor pad being configured to be coupled to a first end of a logic circuit element. The device includes a second capacitor pad, the second capacitor pad including a second superconducting material, the capacitor pad being configured to be coupled to a second end of the logic circuit element. The second capacitor pad includes a first portion (306A, 306B); a second portion (308A, 308B); and a bridge (310A, 310B) configured to electrically connect the first portion (306A, 306B) and the second portion (308A, 308B).

Description

Technical Field

[0001] The present invention generally relates to a superconductor device, a method of manufacturing and a system for manufacturing a superconducting qubit resonator. More specifically, the present invention relates to an apparatus, method and system for resonant frequency adjustment of a fixed frequency qubit. Background Art

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

[0003] Molecules and subatomic particles obey the laws of quantum mechanics, the branch of physics that explores how the physical world works at the most fundamental level. At this level, particles behave in strange ways, assume more than one state at the same time, and interact with other particles that are very far away. Quantum computing exploits these quantum phenomena to process information.

[0004] The computers we use today are called classical computers (also referred to herein as "conventional" computers or conventional nodes, or "CNs"). Conventional computers use conventional processors, semiconductor memories, and magnetic or solid-state storage devices manufactured using semiconductor materials and techniques, in the so-called von Neumann architecture. Specifically, the processors in conventional computers are binary processors, i.e., they operate on binary data represented in 1s and 0s.

[0005] Quantum processors (q-processors) use the odd properties of entangled quantum bit devices (referred to herein as "qubits" or "qubits") to perform computational tasks. In the specific domain where quantum mechanics operates, particles of matter can exist in multiple states, such as an "on" state, an "off" state, and both "on" and "off" at the same time. Where binary computing using semiconductor processors is limited to using only on and off states (equivalent to 1 and 0 in binary code), quantum processors use these quantum states of matter to output signals that are useful in data computation.

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

[0007] Using these two principles, qubits operate as more complex information processors, enabling quantum computers to operate in a way that solves problems that are difficult to solve using traditional computers. IBM has successfully built and demonstrated the operability of a quantum processor (IBM is a registered trademark of 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 with a non-superconducting material. When the metal in the superconducting layer is made superconducting, for example by lowering the temperature of the metal to a specific cryogenic temperature, electron pairs can tunnel from one superconducting layer through the non-superconducting layer to the other superconducting layer. In a superconducting qubit, this Josephson junction (which has an inductance) is electrically coupled in parallel with one or more capacitive devices that form a nonlinear resonator.

[0009] In the superconducting state, the material firstly offers no resistance to the passage of electric current. When the resistance drops to zero, the current can circulate inside the material without dissipating any energy. Secondly, the material exhibits the Meissner effect, i.e., external magnetic fields do not penetrate the superconductor, but remain on its surface, as long as they are weak enough. When the material no longer exhibits one or both of these properties, it is said to no longer be superconducting.

[0010] The critical temperature of a superconducting material is the temperature at which the material begins to exhibit superconducting properties. Superconducting materials present very low or zero resistivity to the flow of electric current. The critical field is the highest magnetic field for a given temperature at which the material remains superconducting.

[0011] Superconductors are generally classified into one of two types. Type I superconductors exhibit a single transition at a critical field. When the critical field is reached, a Type I superconductor changes from a non-superconducting state to a superconducting state. Type II superconductors include two critical fields and two transition regions. At or below the lower critical field, Type II superconductors exhibit a superconducting state. Above the upper critical field, Type II superconductors do not exhibit superconducting properties. Between the upper and lower critical fields, Type II superconductors exhibit a mixed state. In the mixed state, Type II superconductors exhibit an incomplete Meissner effect, where an external magnetic field in quantized packets at specific locations penetrates the superconducting material.

[0012] The Meissner effect is caused by the generation of a persistent current at the surface of a superconductor material. A persistent current is a permanent current that does not require an external power source. The persistent current generates an opposite magnetic field to cancel the external magnetic field throughout the body of the superconductor material. In the superconducting state, the persistent current does not decay over time due to the zero resistance characteristic.

[0013] The information processed by the qubits is emitted in the form of microwave energy in the microwave frequency range. The microwave emissions are captured, processed, and analyzed to decrypt the quantum information encoded therein. In order for quantum computations with qubits to be reliable, quantum circuits (e.g., the qubits themselves, readout circuits associated with these qubits, and other types of superconducting quantum logic circuits) must not alter the energy state of these particles or microwave emissions in any significant way. This operational constraint on any circuit that operates with quantum information requires special considerations in the manufacture of semiconductor and / or superconductor structures used in such circuits.

[0014] The readout circuitry typically uses a resonator to couple to the qubit through electromagnetic resonance (usually microwave or radio frequency resonance). The resonator in the readout circuitry includes inductive and capacitive elements. Some qubits are fixed frequency qubits, i.e., their resonant frequency is immutable. Other qubits are frequency tunable qubits. A Q-processor can employ fixed frequency qubits, frequency tunable qubits, or a combination thereof.

[0015] The present invention recognizes that fixed-frequency qubits are designed to be fixed in frequency to improve immunity to noise. The present invention recognizes that when the resonant frequencies of two adjacent qubits on a chip are the same or within a frequency threshold band, or their higher transition frequencies are at or near resonance, negative effects may occur, such as crosstalk, quantum decoherence, energy decay, generation of mixed states, unintended information transfer, quantum state leakage, etc. The present invention further recognizes that such qubits may also negatively affect the performance or utility of certain quantum gates, such as cross-resonance gates that have strict requirements on the spectrum of resonant frequencies of the qubits on which the gate operates. The present invention further recognizes that one of the challenges in quantum processors based on fixed-frequency qubits is frequency crowding or frequency conflict 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 when the microwave signal turns on the interaction (on interaction strength) and the interaction between neighboring qubits (off interaction strength). The illustrative embodiments further recognize that yet another challenge in quantum processors based on fixed frequency qubits is to enable a gate of interest without creating unwanted interactions at other gates. The present invention further recognizes that imperfections in fabrication and materials used in currently available fabrication methods for fixed frequency qubits result in deviations from the expected resonant frequency.

[0017] FIG1 depicts a zoomed image of a qubit with capacitive coupling to an external circuit. Image 100 shows a portion of a qubit chip. Coupling capacitor 102 is coupled to a transmission line (not visible) that carries an electromagnetic signal out of a Josephson junction 104. Capacitor pad 106 is a capacitive device that drives the Josephson junction 104 and forms a nonlinear resonator. A ground plane (not visible) typically surrounds all or part of this structure.

[0018] The present invention recognizes that the resonant frequency of a qubit is inherently fixed when the qubit is manufactured (i.e., when the Josephson junction and capacitive elements of the qubit oscillator are manufactured on a 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 manufactured with at least 2, but often 8, 16, or more qubits on a single q-processor chip. Summary of the invention

[0019] The present invention provides a superconducting device, and a method and system for manufacturing the same. The method of the present invention includes forming a capacitor pad for a nonlinear resonator. In an embodiment of the present invention, the method includes comparing the resonant frequency of the nonlinear resonator with a target frequency to determine whether the resonant frequency falls within the range of the target frequency.

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

[0021] The portion may include a bridge. The segment 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 failing to fall within an acceptable 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, the first capacitor pad includes a superconducting material, the first capacitor pad is configured to be coupled to a first end of a logic circuit element. The device may include a second capacitor pad, the second capacitor pad includes a second superconducting material, the capacitor pad is configured to be coupled 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 manufacturing system includes a lithography component that, when operating to manufacture a superconducting device, performs operations including: forming a capacitor pad of a nonlinear resonator; comparing a resonant frequency of the nonlinear resonator with a target frequency to determine whether the resonant frequency falls within a range of the target frequency; and removing a portion of the capacitor pad in response to the resonant frequency not falling within the range.

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

[0028] Embodiments of the present invention include a manufacturing system for manufacturing a superconducting device. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The novel features of the invention are set forth in the appended claims. However, the invention itself, as well as the preferred mode of use, further objects and advantages thereof, will be best understood by reference to the following detailed description of illustrative embodiments of the invention when read in conjunction with the accompanying drawings, in which:

[0030] FIG1 depicts a scaled image of a qubit with capacitive coupling to an external circuit;

[0031] Figure 2 depicts steps in a manufacturing process of a fixed frequency resonator according to an embodiment of the present invention;

[0032] Figure 3depicts steps in a second manufacturing process for manufacturing a fixed frequency resonator according to an embodiment of the present invention;

[0033] Figure 4 depicting the steps in the second manufacturing process;

[0034] Figure 5 depicting steps in a second manufacturing process;

[0035] Figure 6 depicts a configuration of a fixed frequency resonator according to an embodiment of the present invention;

[0036] Figure 7 depicts results of a simulation for determining a resonant frequency of a fixed frequency resonator;

[0037] Figure 8 depicts a flow chart of a manufacturing process for manufacturing a fixed frequency resonator according to an embodiment of the present invention; and

[0038] Fig. 9 Depicted is a flow chart of a second example manufacturing process for manufacturing a fixed frequency resonator in accordance with an embodiment of the present invention. DETAILED DESCRIPTION

[0039] Embodiments of the invention used to describe the present invention generally address and solve the above-mentioned problems in superconducting qubit resonators for fixed frequency qubits. Embodiments of the present invention provide a fabrication method for resonant frequency tuning of fixed frequency qubits.

[0040] Embodiments of the present invention may be implemented as a superconducting qubit resonator. A method for manufacturing a superconducting qubit resonator may be implemented as a software application. The application may be configured to operate in conjunction with an existing semiconductor / superconductor manufacturing system (such as a lithography system).

[0041] For clarity of description, and without implying any limitation thereto, simplified diagrams of example superconducting qubit resonators are used in the accompanying drawings to describe embodiments of the present invention. In the actual fabrication of the superconducting qubit resonator, there may be additional structures not shown or described herein, or structures different from those shown and described herein, without departing from the scope of the present invention. Similarly, within the scope of the present invention, the structures shown or described in the example superconducting qubit resonator may be fabricated differently to produce similar operations or results as described herein.

[0042] As described herein, the different shaded portions in the two-dimensional diagrams of example structures, layers and configurations are intended to represent different structures, layers, materials and configurations in example manufacturing. Different structures, layers, materials and configurations can be manufactured using suitable materials known to those of ordinary skill in the art.

[0043] The specific shapes, positions, orientations, or sizes of the shapes depicted herein are not intended to limit the invention unless such features are expressly described as features of the invention. The shapes, positions, orientations, sizes, or some combination thereof are selected solely for clarity of the drawings and descriptions, and may have been exaggerated, minimized, or otherwise changed from the actual shapes, positions, orientations, or sizes that might be used in actual lithography to achieve the objectives. And may have been exaggerated, minimized, or otherwise changed from the actual shapes, positions, orientations, or sizes that might be used in actual lithography to achieve the objectives.

[0044] Embodiments of the present invention, when implemented in an application, cause a manufacturing process to perform certain steps as described herein. The steps of the manufacturing process are shown in several figures. In a specific manufacturing process, not all steps are necessary. Some manufacturing processes may implement steps in different orders, combine certain steps, remove or replace certain steps, or perform certain combinations of these steps and other step operations without departing from the scope of the present invention.

[0045] Merely by way of example, embodiments of the present invention are described with respect to certain types of materials, electrical properties, structures, configurations, layer orientations, directions, steps, operations, planes, dimensions, quantities, data processing systems, environments, components, and applications. Any particular representation of these and other similar products is not intended to limit the present invention. Any suitable representation of these and other similar workpieces may be selected within the scope of the present invention.

[0046] The embodiments of the present invention are described using specific designs, architectures, layouts, schematics and tools only as examples, and do not limit the present invention. The embodiments of the present invention can be used in combination with other designs, architectures, layouts, schematics and tools of equivalent or similar purposes.

[0047] The embodiments in this disclosure are only for clarity of description, and do not limit the present invention. Any advantages listed here are only examples and are not intended to limit the present invention. Additional or different advantages can be achieved through specific embodiments of the present invention. In addition, specific embodiments of the present invention may have some, all or not have the advantages listed above.

[0048] The qubits are used merely as example superconducting quantum logic circuits in which embodiments of the present invention may be used. Based on this disclosure, one of ordinary skill in the art will be able to conceive of many other superconducting quantum logic circuits and conventional logic circuits in which the resonant frequency adjustment of the present invention would be useful, and they are considered within the scope of the present invention.

[0049] Figure 2 Depicted are the steps of a manufacturing process for making a fixed frequency resonator. Figure 2-5The various steps of a second fabrication process for fabricating a fixed frequency resonator are depicted. The fixed frequency resonators formed by these two example processes are structurally different, as described below, but are functionally equivalent to be used interchangeably in place of capacitor pad 106 in FIG. 1 .

[0050] See also Figure 2 , capacitor pads 204A, 204B represent capacitive devices fabricated in the manner described herein, and may be used, for example, in place of capacitor pad 106 in FIG. 1 .

[0051] Capacitor pads 204A, 204B drive Josephson junction 202 and form a nonlinear resonator. 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, including both ends of the range). The superconducting material of capacitor pads 204A, 204B may be niobium. The manufacturing system may sputter the superconducting material onto the substrate to form capacitor pads 204A, 204B. Capacitor pads 204A, 204B may have a length L.

[0052] Each of the capacitor pads 204A, 204B may have a corresponding capacitance value. The capacitance value is 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 formula Proportional to the resonant frequency f of the fixed frequency resonator.

[0053] In step 200, embodiments of the present invention enable a manufacturing system to remove a portion of capacitor pads 204A, 204B, thereby forming first portions 206A, 206B and second portions 208A, 208B. For example, embodiments of the present invention can enable a manufacturing system to remove capacitor pad material using laser ablation or ion beam milling. First portions 206A, 206B maintain electrical connection with Josephson junction 202 and form a modified nonlinear resonator. Embodiments of the present invention enable a manufacturing system to remove second portions 208A, 208B from a capacitive device, thereby reducing the total capacitance and increasing the resonant frequency of a fixed frequency resonator.

[0054] Removing capacitor pad material from both capacitor pads may not be necessary. A reduction in the area of ​​only one of the two pads (e.g., from pad 204A but not from 204B) is effective in changing the total capacitance C and, therefore, the resonant frequency f. Removal from both pads is depicted and described for clarity of description only and not as a limitation of the present invention. Asymmetric removal from the capacitor pads (including no removal from one of the pads) is contemplated within the scope of the present invention to produce the effects described herein.

[0055] continue Figure 2 , the first portions 206A and 206B are symmetrical. For example, the sizes of the first portions 206A and 206B can be approximately equal, between 0% and 5%, inclusive. In another embodiment of the present invention, the first portions 206A and 206B are asymmetrical. For example, the sizes of the first portions 206A and 206B can be different, greater than 5% up to as much as 40%.

[0056] Second portions 208A and 208B are symmetrical. For example, second portions 208A and 208B may be approximately equal in size, between 0-5%, inclusive. In another embodiment of the present invention, second portions 208A and 208B are asymmetrical. For example, second portions 208A and 206B may differ in size, greater than 5% up to approximately 200%. In another step, an embodiment of the present invention enables a manufacturing system to remove only a portion of capacitor pad 204A, thereby forming first portion 206A and second portion 208A.

[0057] In an embodiment of the present invention, the manufacturing system removes a length ΔL of the capacitor pad material from the length L of the capacitor pads 204A, 204B. In another embodiment of the present invention, ΔL includes the length of a cut. For example, the manufacturing system may remove a length of the capacitor pad material between 1-5 microns, including both ends of the range. In one embodiment, ΔL includes the length of the cut and the length of the corresponding second portion.

[0058] In another embodiment of the present 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 opposite end of the fixed frequency resonator. In another embodiment of the present invention, the manufacturing system removes a portion of the capacitor pad 204A at an oblique angle to the length L of the capacitor pad 204A. Step 300 may be repeated to remove additional capacitor pad material and reach a desired resonant frequency of the fixed frequency resonator.

[0059] See also Figure 3, capacitor pads 304A, 304B represent capacitive devices fabricated in the manner described herein, which may be used, for example, in place of capacitor pad 106 in FIG. 1 .

[0060] Capacitor pads 304A, 304B drive Josephson junction 302 and form a nonlinear resonator. 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.

[0061] In step 300, embodiments of the present invention enable a manufacturing system to remove segments of capacitor pads 304A, 304B to form first portions 306A, 306B; second portions 308A, 308B; and bridges 310A, 310B. For example, embodiments may enable a manufacturing system to mask and etch capacitor pads to remove segments of corresponding capacitor pads. In step 300, embodiments of the present invention enable a manufacturing system to form corresponding gaps between first portions 306A, 306B and second portions 308A, 308B.

[0062] The bridges 310A, 310B electrically connect the second portions 308A, 308B to the first portions 306A, 306B. For example, the second portions 308A, 308B and the bridges 310A, 310B contribute to the capacitance value 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 and form a modified nonlinear resonator.

[0063] In an embodiment of the present invention, first portions 306A and 306B are symmetrical. For example, first portions 306A and 306B may be approximately equal in size, between 0-5%, including both ends of the range. In another embodiment of the present invention, first portions 306A and 306B are asymmetrical. For example, first portions 306A and 306B may differ in size, greater than 5% up to 40%.

[0064] In an embodiment of the present invention, second portions 308A and 308B are symmetrical. For example, second portions 308A and 308B may be approximately equal in size, between 0-5%, including both ends of the range. In another embodiment of the present invention, second portions 308A and 308B are asymmetrical. For example, second portions 308A and 308B may differ in size, greater than 5% up to about 200%. In another step, an embodiment of the present invention enables a manufacturing system to remove only a portion of capacitor pad 304A, thereby forming first portion 306A and second portion 308A.

[0065] In an embodiment of the present invention, the manufacturing system removes a length of capacitor pad material from capacitor pads 304A, 304B. In another embodiment of the present invention, the removed material includes the length of the cut. For example, the manufacturing system may remove a length of capacitor pad material between 1-5 microns, including both ends of the range. In an embodiment, the removed material includes the length of the cut and the length of the corresponding second portion.

[0066] In another embodiment of the present invention, the manufacturing system removes a portion of capacitor pad 304A at a first end of the fixed frequency resonator and a portion of capacitor pad 304B at an opposite end of the fixed frequency resonator. In another embodiment, the manufacturing system removes a portion of capacitor pad 304A at an oblique angle to the length of capacitor pad 304A.

[0067] See also Figure 4 , which depicts steps in a second manufacturing process. Capacitor pads 404A, 404B represent capacitive devices manufactured in the manner described herein (eg, which may be used in place of capacitor pad 106 in FIG. 1 ).

[0068] Capacitor pads 404A, 404B drive Josephson junction 402 and form a nonlinear resonator. In an embodiment, capacitor pads 404A, 404B include a material that exhibits superconductivity in a portion of the cryogenic temperature range. For example, the superconducting material of capacitor pads 404A, 404B may be niobium.

[0069] In step 400, embodiments of the present invention enable a manufacturing system to remove multiple segments of capacitor pads 404A, 404B to form first portions 406A, 406B; second portions 410, third portions 414, fourth portions 418, fifth portions 422, sixth portions 426, and bridges 408, 412, 416, 420, 424. For example, embodiments of the present invention can enable a manufacturing system to mask and etch capacitor pads to remove multiple segments of corresponding capacitor pads. In step 400, embodiments of the present invention enable a manufacturing system to form corresponding gaps between first portion 406A and portions 410, 414, 418, and to form corresponding gaps between first portion 406B and portions 422, 426.

[0070] The bridges 408, 412, 416 electrically connect the portions 410, 414, 418 to the first portion 406A. For example, the portions 410, 414, 418 and the bridges 408, 412, 416 contribute to the capacitance value of the corresponding capacitor pads. The bridges 420, 424 electrically connect the portions 422, 426 to the first portion 406B. For example, the portions 422, 426 and the bridges 420, 424 contribute to the capacitance value 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 to the Josephson junction 402 and form a modified nonlinear resonator.

[0071] In an embodiment of the present invention, first portions 406A and 406B are symmetrical. For example, first portions 406A and 406B may be approximately equal in size, between 0-5%, including both ends of the range. In another embodiment of the present invention, first portions 406A and 406B are asymmetrical. For example, first portions 406A and 406B may be different in size, greater than 5% up to 40%.

[0072] In an embodiment of the present invention, at least two of the portions 410, 414, 418, 422, 426 are symmetrical. For example, at least two of the portions 410, 414, 418, 422 may be approximately equal in size, between 0-5%, including both ends of the range. In another embodiment, at least two of the portions 410, 414, 418, 422, 426 are asymmetrical. For example, at least two of the portions 410, 414, 418, 422, 426 may differ in size by more than 5% up to about 200%.

[0073] These examples of capacitor pad materials, deposition methods, and material removal methods are not intended to be limiting. Based on this disclosure, one of ordinary skill in the art will be able to conceive of many other materials and methods suitable for forming and removing portions of capacitor pads, and these materials and methods are considered within the scope of the present invention.

[0074] See also Figure 5 , which depicts the steps in a second example manufacturing process. Figure 3 Fabrication continued on the modified fixed-frequency resonator.

[0075] In step 500, embodiments of the present invention cause a manufacturing system to remove bridge members 506A, 506B, thereby separating first portions 504A, 504B and second portions 508A, 508B. For example, embodiments may cause a manufacturing system to remove capacitor pad material using laser ablation or ion beam milling. First portions 504A, 504B maintain electrical connection to Josephson junction 502 and form a further modified nonlinear resonator. Embodiments of the present invention cause a manufacturing system to remove second portions 508A, 508B and bridge members 506A, 506B from the capacitive device, thereby reducing the overall capacitance and increasing the resonant frequency of the fixed frequency resonator. Step 500 may be repeated to remove additional capacitor pad material and achieve a desired resonant frequency of the fixed frequency resonator. For example, a manufacturing system may remove capacitor pad material as in Figure 4 Additional bridge in the modified nonlinear resonator.

[0076] See also Figure 6 , configuration 600 is similar to Figure 3 An example of a modified nonlinear resonator in a fixed frequency resonator.

[0077] Configuration 600 includes a Josephson junction 602, first portions 606A, 606B; second portions 608A, 608B; and a bridge 610. Bridges 612, 614, 616 are Figure 3 An example bridge formed in step 300 of FIG.

[0078] See also Figure 7 , which depicts the results of a simulation used to determine the resonant frequency of an example fixed frequency resonator. Figure 6 is based on Figure 4 A modified nonlinear resonator with multiple bridges as depicted in FIG. Specifically, in a non-limiting example implementation, the original capacitor pad size is 500 microns long and 120 microns wide, the length of the first two segments is 35 microns, the length of the second two segments is 40 microns, the length of the gap between each segment and the central portion of the capacitor pad is 5 microns, and the length of the bridges connecting each segment to the central portion of the capacitor pad across the gap is each 5 microns and the width is 5 microns. The removal process of each bridge separates the respective segment from the central portion of the capacitor pad.

[0079] 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.

[0080] See also Figure 8 , which depicts a flow chart of a manufacturing process for manufacturing a fixed frequency resonator. The process 800 can be configured to operate in conjunction with existing semiconductor / superconductor manufacturing systems (eg, photolithography systems).

[0081] In an embodiment of the present invention, a manufacturing system forms a capacitor pad (block 802). In an embodiment of the present invention, a frequency resonator includes a capacitor pad. In one embodiment of the present invention, a manufacturing system compares a resonant frequency of a frequency resonator (qubit) to a target frequency (block 804). In an embodiment of the present invention, a manufacturing system determines that the resonant frequency is within an acceptable range of the target frequency (block 806). For example, a manufacturing system may determine that the resonant frequency is within one-half of one percent of the target frequency. In an embodiment of the present invention, a manufacturing system determines that the resonant frequency falls outside an acceptable range of the target frequency. For example, a manufacturing system may determine that the resonant frequency differs from the target frequency by more than one-half of one percent. If the manufacturing system determines that the resonant frequency falls outside an acceptable range (the "no" path of block 806), the manufacturing system removes a portion of the capacitor pad (block 808). Process 800 then returns to block 804 to continue. If the manufacturing system determines that the resonant frequency is within an acceptable range (the "yes" path of block 806), process 800 ends.

[0082] See also Fig. 9 , which depicts a flow chart of a second example manufacturing process for manufacturing a fixed frequency resonator. Process 900 may be configured to operate in conjunction with existing semiconductor / superconductor manufacturing systems, such as photolithography systems.

[0083] In an embodiment of the present invention, a manufacturing system forms a capacitor pad (block 902). In an embodiment of the present invention, a frequency resonator includes a capacitor pad. In an embodiment of the present invention, a manufacturing system removes a segment of the capacitor pad to form a bridge (block 904). For example, a manufacturing system may remove a segment of the capacitor pad to form a first portion and a second portion with a gap therebetween. In an embodiment, the bridge electrically connects the first portion and the second portion. In an embodiment of the present invention, a manufacturing system compares a resonant frequency of the frequency resonator (qubit) to a target frequency (block 906). In an embodiment, the manufacturing system determines that the resonant frequency is within an acceptable range of the target frequency (block 908). For example, the manufacturing system may determine that the resonant frequency is within one-half of one percent of the target frequency. In an embodiment of the present invention, the manufacturing system determines that the resonant frequency falls outside an acceptable range of the target frequency. For example, the manufacturing system may determine that the resonant frequency differs from the target frequency by more than one-half of one percent. If the manufacturing system determines that the resonant frequency falls outside the acceptable range (no path of block 908), the manufacturing system removes the bridge of the capacitor pad (block 910). Process 900 then returns to block 906 to continue. If the manufacturing system determines that the resonant frequency is within an acceptable range (“yes” path of block 908 ), process 900 ends.

[0084] Various embodiments of the present invention are described herein with reference to the relevant drawings. Without departing from the scope of the present invention, alternative embodiments may be designed. Although different connections and positional relationships (e.g., above, below, adjacent, etc.) are described between elements in the following description and the drawings, it will be appreciated by those skilled in the art that many positional relationships described herein are orientation-independent when the function is maintained even if the orientation changes. Unless otherwise indicated, these connections and / or positional relationships may be direct or indirect, and the present invention is not intended to be limited in this regard. Thus, the coupling of entities may refer to direct or indirect coupling, and the positional relationship between entities may be direct or indirect positional relationship. As an example of an indirect positional relationship, the reference to forming layer "A" on layer "B" in this specification includes the case where one or more intermediate layers (e.g., layer "C") are between layer "A" and layer "B", as long as the relevant features and functions of layer "A" and layer "B" are not substantially changed by this or these intermediate layers.

[0085] The following definitions and abbreviations are used to interpret the claims and specification. As used herein, the terms "comprises," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, mixture, process, method, article, or apparatus that includes a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus.

[0086] Additionally, the term "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms "at least one" and "one or more" should be understood to include any integer greater than or equal to one, i.e., one, two, three, four, etc. The term "plurality" should be understood to include any integer greater than or equal to 2, i.e., two, three, four, five, etc. The term "connected" may include both indirect "connected" and direct "connected."

[0087] References in the specification to "one embodiment," "an embodiment," "an example embodiment," etc. indicate that the described embodiment may include a particular feature, structure, or characteristic, but each embodiment may or may not include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Further, when a particular feature, structure, or characteristic is described in conjunction with an embodiment, it is considered to be within the knowledge of those skilled in the art to affect such feature, structure, or characteristic in conjunction with other embodiments, whether or not explicitly described.

[0088] The terms "about", "substantially", "approximately" and variations thereof are intended to include the degree of error associated with the measurement of a particular quantity based on the equipment available at the time of filing this application. For example, "about" may include a range of ±8% or 5%, or 2% of a given value.

[0089] The description of different embodiments of the present invention has been presented for illustrative purposes, but is not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope of the present invention. The terms used herein are selected to best explain the principles of the present invention, practical applications, or technical improvements in technology found in the marketplace, or to enable those of ordinary skill in the art to understand the embodiments of the present invention described herein.

Claims

1. A method comprising: forming a capacitor pad for a nonlinear resonator, the capacitor pad comprising a first portion electrically connected to a Josephson junction, a second portion arranged with a gap from the first portion, and a bridge arranged adjacent to the gap and electrically connecting the first portion and the second portion; comparing a resonant frequency of the nonlinear resonator with a target frequency to determine whether the resonant frequency falls within a range of the target frequency; as well as In response to the resonant frequency not falling within the range, the bridge in the capacitor pad is removed, and the first portion and the second portion are separated by the gap and the removed portion of the bridge to form a modified nonlinear resonator, wherein the modified nonlinear resonator includes the Josephson junction and a portion of the capacitor pad that maintains an electrical connection with the Josephson junction.

2. The method of claim 1, wherein the bridge is formed by masking and etching the capacitor pad. 3 . The method of claim 1 , further comprising forming a plurality of bridges on the capacitor pad.

4. The method of claim 3, wherein the plurality of bridges are formed by masking and etching the capacitor pads.

5. The method of claim 1, further comprising: In response to the resonant frequency not falling within the range, the second portion of the capacitor pad is removed. The method of claim 1 , wherein the bridge is removed by laser ablation. The method of claim 1 , wherein the bridge is removed by ion beam milling.

8. A nonlinear resonator, comprising: a first capacitor pad comprising a superconducting material, the first capacitor pad being configured to be coupled to a first end of a logic circuit element being a Josephson junction; a second capacitor pad including a second superconducting material, the second capacitor pad being configured to be coupled to a second terminal of the logic circuit element, the second capacitor pad comprising: a first portion electrically connected to the second end; a second portion disposed at a distance from the first portion; and a bridge disposed adjacent to the gap, configured to electrically connect the first portion and the second portion, the bridge being removable and configured such that when the bridge is removed, the first portion and the second portion are separated due to the gap and the removed portion of the bridge, The nonlinear resonator includes the Josephson junction, the first capacitor pad maintaining electrical connection with the Josephson junction, and a portion of the second capacitor pad.

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

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

11. The nonlinear resonator of claim 8, wherein the bridge is configured to be removable by ion beam milling.

12. The nonlinear resonator of claim 9, wherein the first capacitor pad further comprises: Part I; Part II; as well as A bridge is configured to electrically connect the first portion and the second portion.

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

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

15. The nonlinear resonator of claim 8, wherein the first capacitor pad further comprises: Multiple parts; as well as A plurality of bridges are configured to electrically connect adjacent portions of the plurality of portions.

16. The nonlinear resonator of claim 15, wherein the plurality of sections are asymmetric.

17. A superconductor manufacturing system comprising a lithographic component, the superconductor manufacturing system performing the steps of the method of any one of claims 1 to 7 when operating to manufacture a superconducting device.

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