Superconducting flexible circuit board having a metal structure for improved interfacing characteristics

Abstract

The flex circuit board may be used in transmitting signals in a quantum computing system. The flex circuit board may include at least one dielectric layer and at least one superconducting layer disposed on a surface of the at least one dielectric layer. The at least one superconducting layer may include a superconducting material. The superconducting material may become superconducting at a temperature less than about 3 Kelvin. The flex circuit board may have at least one metal structure electroplated on the at least one superconducting layer.

Description

Technical Field

[0001] Claim of Priority This application claims the benefit of priority of U.S. Provisional Application No. 63 / 079,263, filed on September 16, 2020, entitled "Superconducting Flex Circuit Boards having Metal Structures for Improved Interfacing Characteristics", which is incorporated herein by reference.

[0002] The present disclosure generally relates to quantum computing systems, and more specifically, to superconducting flex circuit boards having metal structures for improved interfacing characteristics for quantum computing applications.

Background Art

[0003] Quantum computing is a computational method that utilizes quantum effects such as superposition and entanglement of ground states to execute specific calculations more efficiently than classical digital computers. In contrast to digital computers that store and manipulate information in the form of bits such as "1" or "0", quantum computing systems can manipulate information using quantum bits ("qubits"). A qubit can refer to a quantum device that enables superposition of multiple states, for example, data in both the "0" and "1" states, and / or superposition of the data itself in multiple states. According to conventional terminology, the superposition of the "0" and "1" states in a quantum system can be represented as, for example, a|0〉 + b|1〉. The "0" and "1" states of a digital computer are similar to the respective |0〉 and |1〉 ground states of a qubit.

Summary of the Invention

Means for Solving the Problems

[0004] Aspects and advantages of embodiments of the present disclosure will be described in part in the following description, or can be learned from the description, or can be learned through the practice of the embodiments.

[0005] One exemplary aspect of the present disclosure is directed to a flexible circuit board used when transmitting signals in a quantum computing system. The flexible circuit board may include at least one dielectric layer and at least one superconducting layer disposed on a surface of the at least one dielectric layer. The at least one superconducting layer may include a superconducting material. The superconducting material may become superconducting at a temperature below about 3 Kelvin. The flexible circuit board may have at least one metal structure electroplated on the at least one superconducting layer.

[0006] Another exemplary aspect of the present disclosure is directed to a method of fabricating a flexible circuit board used when transmitting signals in a quantum computing system. The method may include depositing a first superconducting layer on a first side surface of a first dielectric layer. The method may include depositing a first metal film on the first superconducting layer. The method may include etching the first metal film to remove a first removed portion of the first metal film and leave a first remaining portion of the first metal film. The method may include electroplating a metal structure on the first remaining portion of the first metal film disposed on the first superconducting layer.

[0007] Another exemplary aspect of the present disclosure is directed to a method of operating a quantum computing system including a flexible circuit board. The method may include transmitting control pulses to one or more superconducting signal lines by one or more classical processors. The one or more superconducting signal lines may be disposed on one or more flexible circuit boards. The one or more flexible circuit boards may include at least one metal structure electroplated on the one or more superconducting signal lines. The method may include transmitting control pulses to one or more quantum computing devices via the one or more flexible circuit boards by the one or more signal lines. The method may include applying the control pulses by the one or more quantum computing devices to perform at least one quantum operation based at least in part on the control pulses.

[0008] Other aspects of the present disclosure are directed to various systems, devices, non-transitory computer-readable media, user interconnections, and electronic devices.

[0009] These and other features, aspects, and advantages of the various embodiments of the present disclosure will be better understood with reference to the following description and the appended claims. The accompanying drawings, which are incorporated herein and constitute a part of this specification, illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the relevant principles.

[0010] A detailed discussion of embodiments directed to those of ordinary skill in the art is set forth in the specification with reference to the accompanying drawings.

Brief Description of the Drawings

[0011]

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DETAILED DESCRIPTION OF THE INVENTION

[0012] Exemplary aspects of the present disclosure are directed to superconducting flexible circuit boards, such as superconducting flexible circuit boards useful in quantum computing systems having improved signal transmission. One of the challenges in quantum computing is related to communication between a supercooled quantum system (e.g., qubits) including quantum hardware and a classical computing system (e.g., a binary computing system). A quantum computing system can be at least partially controlled by a classical computing system. The classical computing system can be separated from the quantum hardware. For example, the quantum hardware can be disposed within a vacuum chamber (e.g., within a vacuum formed by a vacuum chamber), and / or the classical computing system can be disposed outside the vacuum chamber (e.g., outside the vacuum formed by a vacuum chamber). The vacuum chamber can provide a temperature gradient between a classical computing system that can operate at approximately room temperature and quantum hardware that can operate at approximately absolute zero (e.g., less than about 10 millikelvin).

[0013] In a quantum computing system, in order to accurately and reliably implement quantum gate operations and / or quantum state measurements, high-speed and robust communication between a classical computing system and a quantum system (e.g., qubits) may be required. To address this requirement, many systems use physical signal lines such as wires between the classical computing system and the quantum system.

[0014] As the complexity of quantum hardware increases (e.g., the number of qubits increases), there may be challenges in managing the physical signal lines between the classical computing system and the quantum hardware. For example, in some cases, each qubit may require one or more signal lines to transmit signals between qubits. For example, the number of signal lines required may increase at least approximately linearly, even if not exceeding linearly, in proportion to the number of qubits in the quantum system. For example, in some cases, even if some or all of the signal lines are multiplexed, four signal lines may be required for each qubit. Therefore, the increase in the density of quantum hardware can contribute to an increase in the density of signal lines and / or interconnections required between the signal lines and the components of the quantum computing system, such as the quantum hardware, the ends (e.g., inlets) of the vacuum chamber, the feedthroughs of various cooling stages, and / or other components. Furthermore, as the complexity of quantum hardware increases, it may be more susceptible to effects such as crosstalk, noise, and interference. Therefore, the signal lines need to provide sufficient performance with respect to other considerations such as thermal conductivity, noise, and / or crosstalk robustness.

[0015] As an example, many quantum computing applications employ superconducting qubits that achieve superconductivity or zero electrical resistance at temperatures near absolute zero, such as below about 3 Kelvin or near about 0 Kelvin. Thus, one of the challenges associated with quantum computing involves cooling quantum hardware with superconducting qubits to the temperature at which the superconducting qubits achieve superconductivity. For example, in some cases, the superconducting qubits need to be cooled to below about 0.1 Kelvin (K), such as below about 0.02 Kelvin or less than 20 millikelvin (mK). Typically, classical computing systems can be maintained at higher temperatures than quantum hardware, such as near room temperature. Physical signal lines may be connected to the quantum hardware and thus form a thermal conductor between the classical computing system and the quantum hardware. The physical signal lines can potentially reduce the efficiency of a cooling system (such as a cryogenic cooling system) configured to cool the quantum hardware and / or other components of the quantum computing system. Thus, even a single signal line can potentially increase the cooling requirements, and this problem can become more severe as the complexity of the quantum hardware continues to increase. Thus, the signal lines coupling the quantum hardware to the classical computing system desirably can be physically small (e.g., arranged in high density), provide a low thermal load, provide low electrical dissipation, and / or provide other desirable thermal characteristics.

[0016] As another example, it may be desirable to accurately drive qubits with signals from signal lines. For example, signal reflections from components of a quantum computing system can potentially have an adverse effect on the performance of quantum hardware. Thus, the signal lines can desirably have a low reflectivity (e.g., less than about 40 dB). Additionally and / or alternatively, the signal lines can desirably provide low distortion (e.g., pulse distortion) such that control signals are accurately transmitted through the signal lines. Low-distortion signal lines can provide improved accurate implementation of control signals and / or execution of quantum algorithms in quantum hardware and / or accurate readout from quantum hardware. Additionally and / or alternatively, the signal lines desirably provide low crosstalk (e.g., less than about 80 dB) between separate signal lines and / or other components. Signal lines that provide low crosstalk can provide improved isolated qubit communication such that signals on a signal line targeted at one qubit are separated from other qubits and / or contribute to noise reduction for each additional signal line.

[0017] As another example, noise and / or other external factors can potentially affect the performance of a quantum computing system. Signal lines that couple quantum hardware to a classical computing system desirably have little interference in the environment of the quantum hardware. For example, it is desirable for the signal lines to emit little or no thermal photons and / or contribute to other factors that can potentially interfere with the operation of the quantum hardware. In addition and / or alternatively, the quantum computing system can desirably block (e.g., by providing filtering) external thermal photons, signal noise, and / or other external factors from interfering with the operation of the quantum hardware.

[0018] Accordingly, some quantum computing systems can include one or more flexible circuit boards that include one or more signal lines. The flexible circuit board can be configured to transmit signals by one or more signal lines (e.g., via a vacuum chamber) to couple one or more classical processors to the quantum hardware. The flexible circuit board can include a plurality of signal lines and can provide significantly improved signal line density in addition to providing improved separation, reduced thermal conductivity, and / or improved scalability. For example, including a flexible circuit board for coupling a classical processor to the quantum hardware can provide an infrastructure that can reliably scale to an increasing number of qubits achieved in current quantum computing systems and / or expected in future quantum computing systems.

[0019] Including a flexible circuit board in a quantum computing system can provide improved signal communication within the quantum computing system. Further, the flexible circuit board may include a superconducting material such as a material that experiences superconductivity at a temperature below about 3 Kelvin to further improve signal communication, particularly in the colder regions of the quantum computing system. However, interfacing between flexible circuit boards can be complicated by including some superconducting materials. For example, difficulties may be encountered in forming high-quality electrical contacts between components that include superconducting materials such as separate flexible circuit boards. As an example, many superconducting materials may not be suitable in terms of malleability and / or other aspects to easily form precise interconnects between signal lines, for instance.

[0020] Systems and methods according to exemplary aspects of the present disclosure can provide solutions to these and / or other problems. According to an exemplary aspect of the present disclosure, a flexible circuit board used when transmitting signals in a quantum computing system can include at least one dielectric layer and at least one superconducting layer disposed on a surface of the at least one dielectric layer. The at least one superconducting layer may include a superconducting material. For example, the superconducting material may be superconducting at a temperature of less than about 3 Kelvin, such as about 20 millikelvin, such as about 1 Kelvin. As an example, the superconducting material may be niobium. In some embodiments, the dielectric layer may include polyimide.

[0021] The flexible circuit board may have at least one metal structure electroplated on the at least one superconducting layer. For example, the metal structure may be an interconnect pad. The interconnect pad may enable external connection to the superconducting layer by another flexible circuit board, a wire, or the like. The interconnect pad may improve interfacing with the superconducting layer, such as a signal line in the superconducting layer. For example, the interconnect pad can be configured to couple to at least one signal line of the superconducting layer. In some embodiments, the at least one superconducting layer has a first end and a second end on the opposite side. A first interconnect pad can be disposed at the first end of the at least one superconducting layer, and a second interconnect pad can be disposed at the second end of the at least one superconducting layer. Additionally and / or alternatively, in some embodiments, the metal structure may be a via plate. The via plate can cover or provide a covering for a via extending through at least a portion of the flexible circuit board. For example, the via plate can cover a via extending through at least one dielectric layer and at least one superconducting layer. In some embodiments, the at least one metal structure may include copper.

[0022] In some embodiments, at least one adhesive layer can be disposed between at least one superconducting layer and at least one metal structure. For example, the adhesive layer may be part of the metal structure, such as part of the metal structure formed by depositing the adhesive layer before electroplating at least one metal structure. Additionally and / or alternatively, the adhesive layer may be an additional adhesive layer configured to adhere the metal structure to the superconducting layer. In some embodiments, at least one adhesive layer is formed by etching a deposited metal film. The adhesive layer can be formed of any suitable material, such as copper, titanium, etc.

[0023] In some embodiments, the superconducting layer may include a first ground layer, a second ground layer, and a signal line layer disposed between the first ground layer and the second ground layer. The signal line layer may include one or more signal lines. Additionally and / or alternatively, the dielectric layer may include a first dielectric layer disposed between the first ground layer and the signal line layer and a second dielectric layer disposed between the second ground layer and the signal line layer. In some embodiments, the metal structure may include a plurality of interconnect pads disposed at each end of the first ground layer, the second ground layer, and / or the signal line layer. In some embodiments, at least one metal structure may include a via plate. The via plate can cover a via extending through the first ground layer, the first dielectric layer, the signal line layer, the second dielectric layer, and the second ground layer.

[0024] Another exemplary aspect of the present disclosure is directed to a method of fabricating a flexible circuit board for use in transmitting signals in a quantum computing system. The method may include depositing a superconducting layer (e.g., a first superconducting layer) on a first side of a dielectric layer (e.g., a first dielectric layer). For example, in some embodiments, the superconducting layer may be a superconducting signal line layer that includes a ground layer and / or one or more signal lines. The superconducting layer may be a superconducting material, or include a superconducting material, such as a material that superconducts at a temperature of less than about 3 Kelvin, about 1 Kelvin, such as about 20 millikelvin. As an example, the superconducting material may be niobium or may include niobium. The dielectric layer may be any suitable dielectric material, such as a flexible dielectric material such as polyimide.

[0025] The method may include depositing a metal film (e.g., a first metal film) on the superconducting layer. For example, the metal film may be deposited over an area that is wider than the final metal structure, such as over the entire surface of the superconducting layer. The metal film may include at least one layer. As an example, the metal film may be the same material as the final metal structure. As an example, the metal film may be copper or may include copper. For example, the metal film may be a first portion of the final metal structure formed by deposition. The metal film can serve to prevent the formation of contaminants (e.g., oxides) and / or to adhere the metal structure to the superconducting layer. Additionally and / or alternatively, the metal film may include an additional adhesion layer having a material different from the final metal structure, such as titanium. The additional adhesion layer may improve the adhesion of the metal structure and / or the metal film to the superconducting layer.

[0026] The method may include a step of etching a metal film to remove a removed portion of the metal film (e.g., a first removed portion) and leave the remaining portion of the metal film (e.g., a first remaining portion). For example, the remaining portion of the metal film can be masked so that only the removed portion of the metal film is etched. The removed portion of the metal film may be etched such that the remaining portion of the metal film has substantially the same size, shape, and / or area as the metal structure. For example, etching can remove unwanted regions of the metal film.

[0027] The method may include a step of electroplating a metal structure (e.g., a first metal structure) on the remaining portion of the metal film. For example, a part of the metal structure can be first formed as a metal film, and a second part of the metal structure can be formed by electroplating on the metal film. In this way, the metal structure can be attached to the superconducting material in the superconducting layer, thereby providing improved interfacing with the superconducting layer. The metal structure can be formed of any suitable material such as copper. The metal structure may be, for example, an interconnect pad, a via plate, and / or any other suitable metal structure.

[0028] This method may be repeated for any suitable number of layers of the flexible circuit board. As an example, the method may further include depositing a second superconducting layer on a second side of the first dielectric layer. For example, the first superconducting layer may be a ground layer, and the second superconducting layer may be a signal line layer. The second side of the first dielectric layer may be on the opposite side of the first side of the first dielectric layer. The method may further include depositing a second metal film on the second superconducting layer. The method may further include etching the second metal film to remove a second removed portion of the second metal film and leaving a second remaining portion of the second metal film. The method may further include electroplating a second metal structure on the second remaining portion of the second metal film disposed on the second superconducting layer. The method may further include depositing a second dielectric layer on the second superconducting layer. The method may further include depositing a third superconducting layer on the second dielectric layer. For example, the third superconducting layer may be a second ground layer. The method may further include depositing a third metal film on the third superconducting layer. The method may further include etching the third metal film to remove a third removed portion of the third metal film and leaving a third remaining portion of the third metal film. The method may further include electroplating a third metal structure on the third remaining portion of the third metal film disposed on the third superconducting layer. In this way, the method can provide a superconducting flexible circuit board including interconnect pads and / or via plates for each of the two ground layers and signal line layers.

[0029] In some embodiments, to provide a metal structure for vias, the method may include etching a via through each layer (e.g., dielectric layer, ground layer, and / or signal line) and depositing a metal film on the inner surface of the via. The metal structure (e.g., via plate) can then be electroplated on the metal film on the inner surface of the via. In this way, the metal film and / or metal structure can penetrate through each layer.

[0030] In some embodiments, the method can be performed without exposing the flexible circuit board to oxygen. For example, in some embodiments, depositing a first metal film on the superconducting layer is performed without exposing the superconducting layer to oxygen. As an example, a flexible circuit board including a superconducting layer and a dielectric layer may be placed in a vacuum before depositing the first metal film. The vacuum may be maintained until the risk of oxygen contamination is removed, for example, until the metal structure is successfully electroplated.

[0031] As used herein, "flexible circuit board" refers to at least one substantially planar substrate (e.g., a laminated substrate), or a substrate including one or more signal lines formed or otherwise disposed on another support having flexibility in at least one plane. As used herein, "flexibility" refers to the ability to deform without breaking (e.g., under mechanical stress, etc.). For example, a rectangular flexible circuit board may have flexibility along the largest surface of the rectangular flexible circuit board. The rectangular flexible circuit board may have flexibility and / or rigidity along at least a portion of its edge. Flexibility may be achieved as a property of the material from which the flexible circuit board and / or layers of the flexible circuit board are formed (e.g., metals such as copper, copper alloy, niobium, aluminum, dielectric materials, non-metals, polymers, rubber, etc.), or by hinges and / or segmentation of the flexible circuit board (e.g., hinges and / or segmentation of rigid portions), and / or by any other suitable method. The substrate may be exactly planar (e.g., having a substantially linear cross-section over its length and width), and / or may be substantially planar in the sense that, in at least one cross-section, the substrate is bent, wrinkled, or non-linear, but overall has a depth that is significantly smaller (e.g., less than about 10%) than its length and width.

[0032] In some embodiments, the flexible circuit board may include at least one ground layer. The ground layer may form the outer surface of the flexible circuit board, such as the outer surface along the maximum surface. In some embodiments, the flexible circuit board may include two ground layers, such as two parallel and spaced-apart ground layers. For example, the two ground layers may form the maximum outer surfaces of both sides of the flexible circuit board. The ground layer functions as an electrical insulation layer to separate the signal lines on one side of the ground layer from interfering signals on the other side of the ground layer (e.g., signal lines from other layers, other substrates, the environment, etc.). For example, the ground layer may be coupled to ground and / or other suitable grounds.

[0033] The ground layer may be or include any suitable conductive material. In some embodiments, the ground layer may be a superconducting ground layer including a superconducting material that achieves superconductivity at a temperature such as less than about 3 Kelvin, about 1 Kelvin, or about 20 millikelvin. By way of example, the ground layer may be or include niobium, tin, aluminum, molybdenum disulfide, BSCCO, and / or other suitable superconducting materials. Additionally and / or alternatively, the ground layer may be or include a material having high signal transmission performance characteristics such as low resistance, low reflectivity, low distortion, etc., so that the signal does not substantially change by passing through the signal line. By way of example, the ground layer may be or include copper, gold, and / or other suitable materials having high signal transmission performance characteristics. Additionally and / or alternatively, the ground layer may be or include a material having desirable thermal characteristics such as appropriately high and / or low heat transfer, such as copper, copper alloy, etc.

[0034] In some embodiments, the flexible circuit board may include at least one dielectric layer. The dielectric layer may be or include any suitable dielectric material such as a dielectric polymer. In some embodiments, the dielectric layer may be or include a flexible dielectric material. By way of example, the dielectric layer may be or include polyimide. At least a portion of the dielectric layer may be formed on or alternatively disposed adjacent to at least a portion of the inner surface of the ground layer. For example, in some embodiments, the inner surface of the ground layer can be combined with the outer surface of the dielectric layer. Further, in some embodiments, the inner surfaces of two dielectric layers can be combined with signal lines disposed therebetween.

[0035] The flexible circuit board may include one or more signal lines. The one or more signal lines may be disposed on the surface (e.g., inner surface) of at least one dielectric layer. By way of example, in some implementation forms, the one or more signal lines can be disposed between the opposing inner surfaces of two dielectric layers. The signal lines may be or include any suitable conductive material. In some embodiments, the signal lines may be or include superconducting signal lines including a superconducting material that achieves superconductivity at a temperature such as less than about 3 Kelvin, about 1 Kelvin, such as about 20 millikelvin. By way of example, the signal lines may be or include niobium, tin, aluminum, molybdenum disulfide, BSCCO, and / or other suitable superconducting materials. Additionally and / or alternatively, the signal lines may be or include a material having high signal transmission performance characteristics. By way of example, the signal lines may be or include copper, gold, and / or other suitable materials having high signal transmission performance characteristics. Additionally and / or alternatively, the signal lines may be or include a material having desirable thermal characteristics such as, for example, copper, copper alloy.

[0036] In some embodiments, the flexible circuit board may include one or more vias. For example, the vias may extend through a ground layer, a dielectric layer, and / or signal lines. The vias can help improve the separation of signal lines. In some embodiments, the vias can be plated with a via plate that extends along the vias. In some embodiments, the via plate may be a conductive material such as copper or may include a conductive material.

[0037] Systems and methods according to exemplary aspects of the present disclosure can provide many technical effects and advantages. For example, systems and methods according to exemplary aspects of the present disclosure can provide a metal structure formed on a superconducting material of a flexible circuit board to provide improved interfacing with the superconducting material. The metal structure can help with interfacing with the superconducting material. Thereby, for example, improved signal transmission characteristics of a quantum computing system can be provided.

[0038] As used herein, the terms "about" or "approximately" are used in conjunction with a recited numerical value and are intended to refer to within 10% of the recited numerical value.

[0039] Reference is now made to the drawings to discuss exemplary embodiments of the present disclosure in more detail.

[0040] FIG. 1 shows an exemplary quantum computing system 100. The exemplary system 100 is an example of a system implemented as a classical or quantum computer program on one or more classical computers or quantum computing devices in one or more locations and can implement the systems, components, and techniques described below. FIG. 1 shows an exemplary quantum computing system that can be used to implement aspects of the present disclosure. Those skilled in the art will understand that other quantum computing architectures or systems can be used without departing from the scope of the present disclosure using the disclosure provided herein.

[0041] System 100 includes quantum hardware 102 that communicates data with one or more classical processors 104. For example, the quantum hardware 102 can use qubits to represent and / or manipulate information. A qubit can be any suitable quantum device, or include such devices, that allows for a superposition of multiple states, such as data in both the "0" and "1" states. As an example, a qubit can be a unit of a superconducting material, or include a unit of a superconducting material, that achieves superconductivity at a temperature below about 3 Kelvin, such as about 20 mK or about 1 Kelvin.

[0042] The quantum hardware 102 may include components for performing quantum computing. For example, the quantum hardware 102 may include a quantum system 110, a control device 112, and a readout device 114 (e.g., a readout resonator). The quantum system 110 may include one or more multi-level quantum subsystems, such as a register of qubits. In some implementations, the multi-level quantum subsystem may include superconducting qubits, such as flux qubits, charge qubits, transmon qubits, gmon qubits.

[0043] The classical processor 104 may be a binary processor such as a processor that operates on data represented as a plurality of bits. As an example, a bit can be represented by a voltage difference between a low voltage (e.g., 0V) and a high voltage (e.g., 5V) at a reference point such as a memory cell, a circuit node, etc. The low voltage can be associated with the "0" state, and the high voltage can be associated with the "1" state. In addition to any other suitable functions of the classical processor 104, the classical processor 104 can be configured to control the quantum hardware 102. For example, the classical processor 104 can be coupled to the quantum hardware 102 (e.g., by a signal line), and / or can be configured to send control signals to use the quantum hardware 102 to perform quantum operations. As an example, the classical processor 104 can be configured to send control signals to perform quantum gate operations in the quantum hardware 102 (e.g., by a control device 112). Additionally and / or alternatively, the classical processor 104 can be configured to send control signals that cause the quantum hardware 102 to perform quantum state measurements and / or provide the quantum state measurement values to the classical processor 104 (e.g., by a readout device 114). For example, the classical processor 104 can receive measurement values of the quantum system 110 that are interpretable by the classical processor 104.

[0044] The type of multi-level quantum subsystem utilized by the system 100 can be various. For example, in some cases, it may be convenient to include one or more superconducting qubits, e.g., one or more readout devices 114 attached to transmons, fluxes, gmons, xmons, or other qubits.

[0045] A quantum circuit can be constructed and applied to a register of qubits included in a quantum system 110 via a plurality of signal lines (e.g., signal line 120 of FIG. 2) coupled to one or more control devices 112. Using an exemplary control device 112 operating on a register of qubits, a quantum logic gate or a circuit of quantum logic gates, such as a Hadamard gate, a controlled NOT (CNOT) gate, a controlled phase gate, a T gate, a multi-qubit quantum gate, a coupler quantum gate, etc., can be implemented. One or more control devices 112 can be configured to operate on the quantum system 110 through one or more respective control parameters (e.g., one or more physical control parameters). For example, in some implementations, the multi-level quantum subsystem may be a superconducting qubit, and the control device 112 may be configured to supply a control pulse to a control line (e.g., signal line 120 of FIG. 2) to generate a magnetic field and adjust the frequency of the qubit.

[0046] The quantum hardware 102 may further include a readout device 114 (e.g., a readout resonator). The measurement results 108 obtained via a measuring device can be provided to a classical processor 104 for processing and analysis. In some implementations, the quantum hardware 102 can include a quantum circuit, and the control device 112 and the readout device 114 can implement one or more quantum logic gates operating on the quantum system 110 via physical control parameters (e.g., microwave pulses) sent via the wires included in the quantum hardware 102. Further examples of control devices include arbitrary waveform generators where a DAC creates the signal.

[0047] The readout device 114 can be configured to perform quantum measurements on the quantum system 110 and send the measurement results 108 to the classical processor 104 (e.g., via the signal line 120 in FIG. 2). Further, the quantum hardware 102 can be configured to receive data specifying the physical control parameter values 106 from the classical processor 104 (e.g., via the signal line 120 in FIG. 2). The quantum hardware 102 can use the received physical control parameter values 106 to update the operations of the control device 112 and the readout device 114 on the quantum system 110. For example, the quantum hardware 102 can receive data specifying new values representing the voltage strengths of one or more DACs included in the control device 112, and accordingly update the operations of the DACs on the quantum system 110. The classical processor 104 can be configured to initialize the quantum system 110 to an initial quantum state, for example, by sending data specifying an initial set of the parameters 106 to the quantum hardware 102.

[0048] The readout device 114 can measure the state of an element of a quantum system, such as a qubit, by utilizing the impedance difference between the |0〉 and |1〉 states. For example, the resonance frequency of the readout resonator can take different values when the qubit is in the state |0〉 or the state |1〉 due to the non-linearity of the qubit. Thus, the microwave pulse reflected from the readout device 114 carries amplitude and phase shifts that depend on the qubit state. In some implementations, a parcel filter can be used together with the readout device 114 to prevent microwave propagation at the qubit frequency.

[0049] The system 100 includes a control device 112. The control device 112 can operate the quantum hardware 102. For example, the control device 112 can include a waveform generator configured to generate control pulses according to the exemplary aspects of the present disclosure.

[0050] In some implementations, the control device 112 may include a data processing device and associated memory. The memory can include a computer program having instructions that, when executed by the data processing device, cause the data processing device to perform one or more functions described herein, such as applying control signals to qubits and / or tunable couplers.

[0051] FIG. 2 shows an exemplary quantum computing system 100 according to an exemplary embodiment of the present disclosure. As shown in FIG. 2, the quantum hardware 102, such as, but not limited to, the quantum system 110, the control device 112, the readout device 114, and / or any other suitable components of the quantum hardware 102 discussed with respect to FIG. 1, can be disposed within the cryogenic cooling system 130. Additionally and / or alternatively, the classical processor 104 can be disposed outside of the cryogenic cooling system 130. The cryogenic cooling system 130 may be a vacuum chamber or may be disposed within a vacuum chamber. For example, the quantum hardware 102 and / or the signal line 120 (e.g., a flexible circuit board) can be supported by a chamber mount configured to be inserted into a vacuum canister to form a vacuum chamber. For example, the chamber mount can be configured to dispose the quantum hardware 102 in a vacuum (e.g., formed by a vacuum chamber). The cryogenic cooling system 130 is configured to provide a temperature gradient (e.g., multiple cooling stages) within the vacuum chamber. For example, a temperature gradient can be formed by multiple cryogenic cooling stages, such as stages of a dilution refrigerator. Exemplary stages of a dilution refrigerator can be, for example, a first intermediate clamp stage, a first stage pulse tube stage, a second intermediate clamp stage, a second stage pulse tube stage, a stationary stage, an intermediate heat exchange stage, a mixing chamber stage, a Joule-Thomson cooling stage, a helium liquefaction stage, and / or any other suitable stages of a dilution refrigerator, or can include the same.

[0052] The cryogenic cooling system 130 can be configured to cool the quantum hardware 102. Additionally and / or alternatively, the classical processor 104 is not cooled by the cryogenic cooling system 130. For example, the classical processor 104 can operate at a temperature near room temperature (e.g., about 300 Kelvin) and / or a temperature of about 100 Kelvin, while the quantum hardware 102 may need to be cooled by the cryogenic cooling system 130 to operate effectively because it can operate at a temperature near absolute zero (e.g., less than about 1 Kelvin).

[0053] The quantum computing system 100 may include signal lines 120. The signal lines 120 can couple the classical processor 104 to the quantum hardware 102. For example, the classical processor 104 and the quantum hardware 102 can perform signal communication such as transmitting the parameter 106 and / or the measurement result 108 of FIG. 1 in addition to any other suitable signals, so the classical processor 104 can be coupled to the quantum hardware 102 by the signal lines 120. For example, according to an exemplary aspect of the present disclosure, the signal lines 120 may be or may include one or more flexible circuit boards such as a superconducting flex circuit board configured to couple the quantum hardware 102 and the classical processor 104. Generally, the signal lines 120 include a physical connection and enable faster and / or more robust communication between the quantum hardware 102 and the classical processor 104. As shown in FIG. 2, the signal lines 120 can be at least partially disposed within the cryogenic cooling system 130 to provide a connection to the quantum hardware 102. An increase in the density of the signal lines 120 (e.g., associated with an increase in the complexity of the quantum hardware 102) can pose challenges in operating the quantum computing system 100, which can be mitigated by including a flexible circuit board according to an exemplary aspect of the present disclosure.

[0054] FIG. 3 shows an exemplary quantum computing system 300 according to an exemplary embodiment of the present disclosure. The quantum computing system 300 may include one or more classical processors 302 and quantum hardware 304 including one or more qubits. The quantum computing system 300 may include a chamber mount 308 configured to support the quantum hardware 304 and a vacuum chamber configured to receive the chamber mount 308 and dispose the quantum hardware 304 in a vacuum. The vacuum chamber may be able to form a cooling gradient from an end of the vacuum chamber (e.g., cap 307) to the quantum hardware 304. For example, the vacuum chamber may form a cooling gradient from a first temperature, such as room temperature (e.g., about 300 Kelvin), to a second temperature, such as absolute zero or near absolute zero (e.g., about 10 millikelvin), such that the qubits experience superconductivity in the quantum hardware 304. In some embodiments, the cooling gradient may be formed by a plurality of cooling stages where the temperature gradually rises and / or falls. As an example, the cooling stage may be a stage of a staged cryogenic cooling system, such as a dilution refrigerator.

[0055] The quantum computing system 300 can include one or more signal lines between the classical processor 302 and the quantum hardware 304. According to an exemplary aspect of the present disclosure, the quantum computing system 300 can include one or more flexible circuit boards 306 that include one or more signal lines. The flexible circuit board 306 can be configured to transmit signals via one or more signal lines through a vacuum chamber to couple one or more classical processors 302 to the quantum hardware 304. The flexible circuit board 306 can include a plurality of signal lines and can provide a significantly improved signal line density in addition to providing improved separation, reduced thermal conductivity, and / or improved scalability. For example, including a flexible circuit board 306 according to an exemplary aspect of the present disclosure to couple a classical processor 302 to the quantum hardware 304 can provide an infrastructure that can scale to an increasing number of qubits and / or future quantum computing systems that are achieved in current quantum computing systems and / or expected in future quantum computing systems. Exemplary flexible circuit boards that can be employed according to an exemplary aspect of the present disclosure are shown in FIGS. 4-6.

[0056] In some embodiments, some or all of the flexible circuit board 306 may include at least one ground layer. The ground layer can form the outer surface of the flexible circuit board 306, such as the outer surface along the maximum surface. In some embodiments, the flexible circuit board 306 may include two ground layers, such as two parallel and spaced-apart ground layers. For example, the two ground layers can form the maximum outer surfaces of both sides of the flexible circuit board 306. The ground layer functions as an electrical insulating layer to separate the signal lines on one side of the ground layer from interfering signals on the opposite side of the ground layer (e.g., signal lines from other layers, other substrates, the environment, etc.). For example, the ground layer can be coupled to ground and / or other suitable grounds.

[0057] The ground layer may be or may include any suitable conductive material. In some embodiments, the ground layer may be or may include a superconducting ground layer that includes a superconducting material that achieves superconductivity at a temperature of less than about 3 Kelvin, such as about 1 Kelvin, such as about 20 millikelvin. By way of example, the ground layer may be or may include niobium, tin, aluminum, molybdenum disulfide, BSCCO, and / or other suitable superconducting materials. Additionally and / or alternatively, the ground layer may be or may include a material having high signal transmission performance characteristics such as low resistance, low reflectivity, and low distortion so that the signal does not substantially change as it passes through the signal line. By way of example, the ground layer may be or may include copper, gold, and / or other suitable materials having high signal transmission performance characteristics. Additionally and / or alternatively, the ground layer may be or may include a material having desirable thermal characteristics such as appropriately high and / or low heat transfer, such as copper, a copper alloy, etc.

[0058] In some embodiments, the flexible circuit board 306 may include at least one dielectric layer. The dielectric layer may be or may include any suitable dielectric material, such as a dielectric polymer. In some embodiments, the dielectric layer may be or may include a flexible dielectric material. By way of example, the dielectric layer may be or may include polyimide. At least a portion of the dielectric layer may be formed on or otherwise disposed adjacent to at least a portion of the inner surface of the ground layer. For example, in some embodiments, the inner surface of the ground layer can be combined with the outer surface of the dielectric layer. Further, in some embodiments, the inner surfaces of two dielectric layers can be combined with the signal line disposed therebetween.

[0059] The flexible circuit board 306 may include one or more signal lines. The one or more signal lines can be disposed on the surface (e.g., inner surface) of at least one dielectric layer. As an example, in some implementation forms, the one or more signal lines can be disposed between the opposing inner surfaces of two dielectric layers. The signal lines may be or include any suitable conductive material. In some embodiments, the signal lines may be superconducting signal lines including a superconducting material such as a superconducting material that achieves superconductivity at a temperature of less than about 3 Kelvin, such as about 1 Kelvin, such as about 20 millikelvin, or may include superconducting signal lines. By way of example, the signal lines may be or include niobium, tin, aluminum, molybdenum disulfide, BSCCO, and / or other suitable superconducting materials. Additionally and / or alternatively, the signal lines may be or include a material having high signal transmission performance characteristics. By way of example, the signal lines may be or include copper, gold, and / or other suitable materials having high signal transmission performance characteristics. Additionally and / or alternatively, the signal lines may be or include a material having desirable thermal characteristics, such as, for example, copper, copper alloy, etc., or may include them.

[0060] In some embodiments, the flexible circuit board 306 may include one or more vias. For example, the vias may extend through a ground layer, a dielectric layer, and / or a signal line. The vias help to improve the separation of the signal lines. In some embodiments, the vias can be plated with a via plate extending along the vias. In some embodiments, the via plate may be or include a conductive material such as copper.

[0061] For example, in some embodiments, the quantum computing system 300 may include quantum hardware 304 that communicates data with one or more classical processors 302. For example, the quantum hardware 304 can use qubits to represent and / or manipulate information. A qubit may be any suitable quantum device, or may include, for example, a superposition of multiple states, such as both the "0" and "1" states. As an example, a qubit may be, or may include, a unit of a superconducting material, such as a superconducting material that achieves superconductivity at a temperature below about 3 Kelvin, such as about 20 millikelvin, such as about 1 Kelvin. In some embodiments, the quantum computing system 300 may include one or more multi-level quantum subsystems, such as a register of qubits. In some implementations, the multi-level quantum subsystem may include superconducting qubits, such as flux qubits, charge qubits, transmon qubits, gmon qubits, and the like.

[0062] The classical processor 302 may be a binary processor such as a processor that operates on data represented as a plurality of bits. As an example, a bit can be represented by a voltage difference between a low voltage (e.g., 0V) and a high voltage (e.g., 5V) at a reference point such as a memory cell, a circuit node, etc. The low voltage can be associated with the "0" state, and the high voltage can be associated with the "1" state. In addition to any other suitable functions of the classical processor 302, the classical processor 302 can be configured to control the quantum hardware 304. For example, the classical processor 302 can be coupled to the quantum hardware 304 (e.g., by signal lines included in the flexible circuit board 306 according to an exemplary aspect of the present disclosure), and / or can be configured to send control signals for performing quantum operations using the quantum hardware 304. As an example, the classical processor 302 can be configured to send control signals for performing quantum gate operations on the quantum hardware 304 (e.g., by a control device). Additionally and / or alternatively, the classical processor 302 can be configured to send control signals that cause the quantum hardware 304 to perform a quantum state measurement and / or provide the quantum state measurement value to the classical processor 302 (e.g., by a readout device). For example, the classical processor 302 can receive measurement values of a quantum system that can be interpreted by the classical processor 302.

[0063] According to an exemplary aspect of the present disclosure, the quantum computing system 300 may include one or more flexible circuit boards 306 including one or more signal lines. The classical processor 302 can be coupled to at least one first flexible circuit board. For example, the classical processor 302 may be coupled to the first flexible circuit board 314 by a classical flexible interconnect 332. The classical flexible interconnect 332 can convert from a classical signal transmission medium (e.g., a coaxial cable) 312 to the first flexible circuit board 314.

[0064] As an example, the classical flex interconnect 332 may be a compression interposer or may include a compression interposer. The compression interposer may include an array of spring pads (e.g., a two-dimensional array). A connector that receives signals from the classical processor 302, such as via one or more coaxial cables 312 (e.g., one coaxial cable 312 per signal line), may be compressed against the compression interposer to form signal communication between the spring pad and the connector (e.g., the coaxial cable). Each spring pad may be coupled to a signal line on the first flex circuit board 314 and can transmit signals from the classical processor 302 (e.g., the coaxial cable) to the signal line. The compression interposer enables connecting a signal transmission medium 312 having a relatively low space density, such as a coaxial cable, to a signal transmission medium having a relatively high space density, such as signal lines embedded in the first flex circuit board 314 provided according to an exemplary aspect of the present disclosure, where the amount of space occupied per cable can be relatively large. Further, the compression interposer can achieve high separation between signal lines and / or low reflectivity along the signal lines, which is suitable for quantum computing applications.

[0065] In some embodiments, the first flex circuit board 314 may be or may include the first flex circuit board material in the ground layer and / or signal lines. The first flex circuit board material may be selected to provide high signal transmission performance characteristics. By way of example, the first flex circuit board material may be or may include copper, brass, gold, and / or other suitable materials having high signal transmission performance characteristics. For example, the first flex circuit board 314 may include copper signal lines and / or a ground layer to provide high signal transmission performance characteristics.

[0066] The first flexible circuit board 314 can pass through an airtight seal 352 disposed at an end (e.g., an inlet) of a vacuum chamber such as a cap 307. For example, a flexible circuit board (e.g., the first flexible circuit board 314) can be configured such that a first portion of the flexible circuit board (e.g., the first flexible circuit board 314) is disposed within the vacuum chamber and a second portion of the flexible circuit board (e.g., the first flexible circuit board 314) is disposed outside the vacuum chamber, while the airtight seal 352 is configured to pass through the airtight seal 352 so as to form a vacuum seal of the vacuum chamber. The airtight seal 352 can allow the first flexible circuit board 314 to enter the vacuum chamber without (e.g., substantially) breaking the vacuum generated by the vacuum chamber. As an example, the airtight seal 352 may include a mating seal for each first flexible circuit board 314. The mating seal can receive the first flexible circuit board 314 and form a vacuum seal with the surface of the first flexible circuit board 314. Further, the airtight seal 352 may include one or more seal slots configured to receive the mating seal and / or the first flexible circuit board 314. For example, the mating seal can form a vacuum seal with the seal slot while allowing the first flexible circuit board 314 to pass through the seal slot and enter the vacuum chamber. In this way, the flexible circuit board 306 can enter the vacuum chamber without experiencing signal disruption due to damage to the circuit board, since the substrate can continuously enter the vacuum chamber. In some embodiments, the airtight seal 352 may include a fastening system that fixes the mating seal to the seal slot and / or forms a vacuum seal, such as screws, bolts, seal rings, O-rings, etc. In some embodiments, the airtight seal 352 can form a vacuum seal without the need for an adhesive material (e.g., an adhesive, resin, etc.) such that, for example, residual adhesive material does not contaminate the flexible circuit board 306.

[0067] The first flexible circuit board 314 can be coupled to at least one second flexible circuit board 316. The first flexible circuit board 314 can be coupled to the second flexible circuit board 316 by at least one flex-flex interconnect 334. For example, the flex-flex interconnect 334 can couple (structurally and / or electrically) a ground layer, a dielectric layer, and / or signal lines of the first flexible circuit board 314 to the second flexible circuit board 316. By way of example, the flex-flex interconnect 334 can be formed by soldering, welding, and / or fusing components of the first flexible circuit board 314 to the second flexible circuit board 316. The flex-flex interconnect 334 can be any suitable interconnect of the two flexible circuit boards 306, such as a butted joint, an overlap joint, and / or any other suitable interconnect, or can include the same.

[0068] The second flexible circuit board 316 may have a material composition that is at least different from that of the first flexible circuit board 314. In some embodiments, the second flexible circuit board 316 may be or include a second flexible circuit board material in the ground layer and / or signal lines. The second flexible circuit board material can be selected to provide high signal transmission performance characteristics and / or a reduction in thermal conductivity. By way of example, the second flexible circuit board material may be or include a copper alloy and / or other suitable materials having desirable thermal properties. For example, the second flexible circuit board 316 can include a copper alloy signal line and / or ground layer, which can reduce the thermal conductivity from the top of the vacuum chamber (e.g., the first circuit board 314), and / or can expel heat generated by subsequent components such as the surface mount attenuator 354.

[0069] In some embodiments, the second flexible circuit board 316 can be coupled to at least one surface mount attenuator board 318. For example, the second flexible circuit board 316 can be coupled to the surface mount attenuator board 318 by at least one flex-flex interconnect 336. For example, the flex-flex interconnect 336 can couple (structurally and / or electrically) the ground layer, dielectric layer, and / or signal lines of the second flexible circuit board 316 to the surface mount attenuator board 318. By way of example, the flex-flex interconnect 336 can be formed by soldering, welding, and / or fusing components of the second flexible circuit board 316 to the surface mount attenuator board 318. The flex-flex interconnect 336 can be any suitable interconnect of the two flexible circuit boards 306, such as a butted joint, an overlap joint, and / or any other suitable interconnect, or can include them.

[0070] The surface mount attenuator board 318 may be a flexible printed circuit board. In some embodiments, the surface mount attenuator board 318 may be or include a surface mount attenuator board material in the ground layer and / or signal lines. The surface mount attenuator board material can be selected to provide high signal transmission performance characteristics. By way of example, the surface mount attenuator board material may be or include copper, brass, gold, and / or other suitable materials having high signal transmission performance characteristics. For example, the surface mount attenuator board may include copper signal lines and / or a ground layer to provide high signal transmission performance characteristics.

[0071] The surface mount attenuator substrate 318 may include one or more surface mount attenuators 354. The surface mount attenuator 354 may be configured to attenuate or block thermal photon interference. In some embodiments, the surface mount attenuator substrate 318 and / or the surface mount attenuator 354 can be placed at a sufficiently low temperature so that the surface mount attenuator 354 does not generate thermal photons. In some embodiments, the surface mount attenuator 354 can be placed within a separation plate. The separation plate can be configured to separate one or more surface mount attenuators. The separation plate can be attached to the surface mount attenuator substrate 318. In some embodiments, the insulating plate can be attached to and / or grounded to the ground layer. The separation plate may include one or more cavities configured to separate a first surface mount attenuator from a second surface mount attenuator. For example, the cavity can surround the first surface mount attenuator in the direction of the second surface mount attenuator and block crosstalk between the attenuators.

[0072] The quantum computing system 300 may include at least one third flexible circuit board 320. For example, the surface mount attenuator substrate 318 can be coupled to the third flexible circuit board 320 by at least one flex-flex interconnect 338. For example, the flex-flex interconnect 338 can couple (structurally and / or electrically) the ground layer, dielectric layer, and / or signal lines of the surface mount attenuator substrate 318 to the third flexible circuit board 320. By way of example, the flex-flex interconnect 338 can be formed by soldering, welding, and / or fusing components of the surface mount attenuator substrate 318 to the third flexible circuit board 320. The flex-flex interconnect 338 may be or include any suitable interconnect of two flexible circuit boards 306, such as a butted joint, an overlap joint, and / or any other suitable interconnect.

[0073] The third flexible circuit board 320 can be placed at a point within a vacuum chamber where the cooling gradient cools sufficiently so that some materials exhibit superconductivity. For example, at least a portion of the third flexible circuit board 320 may have a temperature of less than about 3 Kelvin.

[0074] In some embodiments, the third flexible circuit board 320 may be or include the material of the third flexible circuit board in the ground layer and / or signal lines. The material of the third flexible circuit board 320 can be selected such that at least a portion of the third flexible circuit board 320 becomes superconducting at a temperature at which it experiences superconductivity. By way of example, the material of the third flexible circuit board 320 may be or include niobium, tin, aluminum, and / or other suitable superconducting materials. For example, the third flexible circuit board 320 may include copper-plated niobium signal lines and / or a ground layer to provide superconductivity. For example, the copper plating on a copper-plated niobium substrate may be useful for interfacing with superconducting niobium, which can provide improved signal transmission characteristics. In some embodiments, the copper-plated niobium substrate can be formed by first applying a layer of niobium, then an adhesion layer (e.g., a thin copper layer) to prevent oxide formation, and then applying a thicker layer of copper.

[0075] In some embodiments, the third flexible circuit board 320 can be coupled to at least one fourth flexible circuit board 322. The third flexible circuit board 320 can be coupled to the fourth flexible circuit board 322 by at least one flex-flex interconnect 340. For example, the flex-flex interconnect 340 can couple (structurally and / or electrically) a ground layer, a dielectric layer, and / or signal lines of the third flexible circuit board 320 to the fourth flexible circuit board 322. By way of example, the flex-flex interconnect 340 can be formed by soldering, welding, and / or fusing components of the third flexible circuit board 320 to the fourth flexible circuit board 322. The flex-flex interconnect 340 can be any suitable interconnect between two flexible circuit boards 306, such as a butt joint, an overlap joint, and / or any other suitable interconnect, or can include it.

[0076] The fourth flexible circuit board 322 can couple the third flexible circuit board 320 to the quantum hardware 304. For example, a connector 342 at an end of the fourth flexible circuit board 322 can be attached to a port that signal communicates with the quantum hardware 304. As an example, the connector can be a T-junction connector, such as a T-junction connector including a superconducting material (e.g., tin). Additionally and / or alternatively, the connector 342 can be a planar spring array.

[0077] In some embodiments, the fourth flexible circuit board 322 may be or may include a material of the fourth flexible circuit board for a ground layer and / or signal lines. The material of the fourth flexible circuit board 322 may be selected to provide high signal transmission performance characteristics. By way of example, the material of the fourth flexible circuit board 322 may be or may include copper, brass, gold, and / or other suitable materials having high signal transmission performance characteristics. For example, the fourth flexible circuit board 322 may include copper signal lines and / or a ground layer to provide high signal transmission performance characteristics. Additionally and / or alternatively, the material of the fourth flexible circuit board 322 may be selected such that at least a portion of the fourth flexible circuit board 322 becomes superconducting at the temperature at which it operates. By way of example, the material of the fourth flexible circuit board 322 may be or may include niobium, tin, aluminum, molybdenum disulfide, BSCCO, and / or other suitable superconducting materials.

[0078] In some embodiments, the fourth flexible circuit board 322 may be or may include a filter 356, such as an XYZ and / or IR filter 356. For example, the filter 356 may be configured to reduce the effects of noise, thermal photons, and / or other potential sources of interference. As an example, the filter 356 may include, in the fourth flexible circuit board 322, a cavity filled with a filter material, such as a particulate suspension, to provide XYZ / IR filtering. In some examples, the filter material may provide less attenuation for signals of a first frequency and greater attenuation for signals of a second, higher frequency. For example, some filter materials provide attenuation that increases substantially monotonically with an increase in at least some signal frequencies in a target frequency band. In some embodiments, the form of the filter material may be configured for low-pass and / or band-pass operation.

[0079] In some embodiments, the filter 356 can be defined by one or more boundaries of cavities (e.g., cavities within a dielectric material) within the fourth flexible circuit board 322. For example, the cavities within the fourth flexible circuit board 322 can be filled with a filter material (e.g., a magnetically loaded polymer). In some embodiments, when the filter material is in any injectable, pourable, and / or moldable state (e.g., flowing particles, soft / plasticized material, gel, slurry, paste, foam, uncured thermosetting resin, softened / melted thermoplastic resin, etc.), the cavities can be (e.g., partially or completely) filled with the filter material via access within the fourth flexible circuit board 322. In some embodiments, the cavities can be filled with a substantially solid-state filter material (e.g., by press-fitting into the cavities, etc.).

[0080] FIG. 4 shows a cross-sectional view of an exemplary flexible circuit board 400 according to an exemplary embodiment of the present disclosure. The flexible circuit board 400 may include one or more signal lines 406. The flexible circuit board 400 may be configured to transmit signals by one or more signal lines 406 via a vacuum chamber or the like in order to couple one or more classical processors to quantum hardware. The flexible circuit board 400 may include a plurality of signal lines 406, and in addition to providing improved isolation, reduced thermal conductivity, and / or improved scalability, can provide a significantly improved signal line density. For example, by including a flexible circuit board 400 according to an exemplary aspect of the present disclosure to couple a classical processor to quantum hardware, an infrastructure can be provided that can reliably scale to an increasing number of qubits achieved in current quantum computing systems and / or expected in future quantum computing systems.

[0081] As used herein, a "flex circuit board" refers to a substrate that includes at least one substantially planar substrate (e.g., a laminated substrate), or one or more signal lines 406 are formed or otherwise disposed thereon, and includes another support having flexibility in at least one plane. As used herein, "flexibility" refers to the ability to deform without breaking (e.g., being subjected to mechanical stress, etc.). For example, the rectangular flex circuit board 400 may have flexibility along the largest surface of the rectangular flex circuit board 400. The rectangular flex circuit board 400 may have flexibility and / or rigidity along at least a portion of its edge. Flexibility may be achieved as a property of the material of which the flex circuit board 400 and / or the layers of the flex circuit board 400 are formed (e.g., metals such as copper, copper alloy, niobium, aluminum, dielectric materials, non-metals, polymers, rubber, etc.), or by hinges and / or segmentation of the flex circuit board 400 (e.g., hinges and / or segmentation of rigid portions), and / or by any other suitable method. The substrate may be strictly planar (e.g., having a substantially linear cross-section over its length and width), and / or in the sense of representing a shape that is curved, wrinkled, or otherwise non-linear in at least one cross-section, but overall has a depth that is significantly smaller (e.g., less than about 10%) than its length and width, and may be substantially planar.

[0082] In some embodiments, the flexible circuit board 400 may include at least one ground layer 402. The ground layer 402 may form the outer surface of the flexible circuit board 400, such as the outer surface along the maximum surface. In some embodiments, the flexible circuit board 400 may include two ground layers 402, such as two parallel and spaced-apart ground layers 402. For example, the two ground layers 402 may form the maximum outer surfaces on both sides of the flexible circuit board 400. The ground layer 402 may function as an electrical isolation layer to separate the signal lines 406 on one side of the ground layer 402 from interfering signals (e.g., from signal lines 406 in other layers, other boards, the environment, etc.) on the other side of the ground layer 402. For example, the ground layer 402 may be coupled to ground and / or other suitable grounds.

[0083] The ground layer 402 may be or include any suitable conductive material. In some embodiments, the ground layer 402 may be or include a superconducting ground layer 402 that includes a superconducting material that achieves superconductivity at a temperature less than about 3 kelvin, such as about 20 millikelvin, such as about 1 kelvin. By way of example, the ground layer 402 may be or include niobium, tin, aluminum, and / or other suitable superconducting materials. Additionally and / or alternatively, the ground layer 402 may be or include a material having high signal transmission performance characteristics such as low resistance, low reflectivity, low distortion, etc., such that the signal does not substantially change by passing through the signal line. By way of example, the ground layer 402 may be or include copper, gold, and / or other suitable materials having high signal transmission performance characteristics. Additionally and / or alternatively, the ground layer 402 may be or include a material having desirable thermal characteristics such as appropriately high and / or low heat transfer, such as copper, copper alloy, etc.

[0084] In some embodiments, the flexible circuit board 400 may include at least one dielectric layer 404. The dielectric layer 404 may be or may include any suitable dielectric material such as a dielectric polymer. In some embodiments, the dielectric layer 404 may be or may include a flexible dielectric material. By way of example, the dielectric layer 404 may be or may include polyimide. At least a portion of the dielectric layer 404 may be formed on or otherwise disposed proximate at least a portion of the inner surface of the ground layer 402. For example, in some embodiments, the inner surface of the ground layer 402 may be combined with the outer surface of the dielectric layer 404. Further, in some embodiments, the inner surfaces of two dielectric layers 404 may be combined with signal lines 406 disposed therebetween.

[0085] The flexible circuit board 400 may include one or more signal lines 406. The one or more signal lines 406 may be disposed on the surface (e.g., inner surface) of at least one dielectric layer 404. As an example, in some implementation forms, the one or more signal lines 406 may be disposed between the opposing inner surfaces of two dielectric layers 404. The signal line 406 may be or include any suitable conductive material. In some embodiments, the signal line 406 may be or include a superconducting signal line including a superconducting material that achieves superconductivity at a temperature of less than about 1 kelvin, such as less than about 20 millikelvins, such as less than about 3 kelvins. As an example, the signal line 406 may be or include niobium, tin, aluminum, and / or other suitable superconducting materials. Additionally and / or alternatively, the signal line 406 may be or include a material having high signal transmission performance characteristics. As an example, the signal line 406 may be or include copper, gold, and / or other suitable materials having high signal transmission performance characteristics. Additionally and / or alternatively, the signal line 406 may be or include a material having desirable thermal characteristics, such as copper, copper alloy, etc.

[0086] FIG. 5 shows a cross-sectional view of an exemplary flexible circuit board 500 according to an exemplary embodiment of the present disclosure. The flexible circuit board 500 may include various components discussed with reference to the flexible circuit board 400 of FIG. 4, such as, for example, a ground layer 402, a dielectric layer 404, and / or signal lines 406. Further, the flexible circuit board 500 may include one or more vias 502. For example, the via 502 may extend through the ground layer 402, the dielectric layer 404, and / or the signal lines 406. The via may function to improve the separation of the signal lines 406. In some embodiments, the via 502 may be plated with a via plate 504 that extends along the via 502. The via plate 504 may be any suitable material. For example, in some embodiments, the via plate 504 may be or may include a conductive material such as copper.

[0087] FIG. 6 shows a cross-sectional view of an exemplary flexible circuit board 600 according to an exemplary embodiment of the present disclosure. The flexible circuit board 600 may include various components described with reference to the flexible circuit board 400 of FIG. 4, such as, for example, a ground layer 402, a dielectric layer 404, and / or signal lines 406. Further, the flexible circuit board 600 may include interconnect pads 602. The interconnect pads 602 may be coupled to conductive materials on the flexible circuit board 600 such as the ground layer 402 and / or the signal lines 406. Additionally and / or alternatively, the vias 604 of the flexible circuit board 600 may be plated with a via plate 606. The via plate 606 may be formed of the same material and / or may be formed simultaneously with the interconnect pads 602.

[0088] In some embodiments, the ground layer 402 and / or the signal line 406 may be a superconducting material, and the interconnect pad 602 may be a material such as copper that provides improved interfacing with the superconducting ground layer 402 and / or the superconducting signal line 406. For example, this can solve some problems related to interfacing with the superconducting material and / or interfacing between superconducting materials. In some embodiments, an adhesive layer (not shown) can be included between the interconnect pad 602 and the conductive material (e.g., the ground layer 402 and / or the signal line 406). In some embodiments, the adhesive layer may be a material that can be different from the materials of the ground layer 402 and / or the signal line 406 and / or the interconnect pad 602, such as titanium. In some embodiments, the interconnect pad 602 and / or the via plate 606 can be formed from deposited copper and then electroplated copper. For example, a portion of the interconnect pad 602 and / or the via plate 606 can first be deposited as a metal film (e.g., in addition to the adhesive layer in some embodiments), and then the remainder of the interconnect pad 602 and / or the via plate 606 can be electroplated. The interconnect pad 602 and / or the via plate 606 may be deposited in a vacuum to prevent contamination of the interfacing between the interconnect pad 602 and the flexible circuit board 600.

[0089] In some embodiments, at least one superconducting layer (e.g., the ground layer 402 and / or the signal line 406) may have a first end and an opposite second end. The first interconnect pad 602 may be disposed at the first end of the at least one superconducting layer. The second interconnect pad 602 may be disposed at the second end of the at least one superconducting layer.

[0090] FIG. 7 shows a flexible circuit board at various stages 710, 720, 730 of a manufacturing process 700 according to an exemplary embodiment of the present disclosure. In the manufacturing process 700, more or fewer steps than those shown in FIG. 7 can be performed. In some embodiments, steps 710, 720, and 730 can be performed sequentially. Steps 710, 720, and 730 can be performed without exposing the superconducting layer to oxygen. For example, each of steps 710, 720, and 730 can be performed in a vacuum without breaking the vacuum between steps. In this way, the formation of oxides and / or other contaminants at the interfaces (e.g., interconnect pads) of the flexible circuit board can be reduced.

[0091] For example, a first step 710 of the manufacturing process 700 can include depositing a metal film 716 on a superconducting layer 704. For example, the metal film 716 can be deposited on a surface of the superconducting layer 704 that is larger than the final metal structure 738, such as over the entire surface of the superconducting layer 704. In some embodiments, the metal film 716 can be deposited proximate to an edge of the superconducting layer 704. The superconducting layer 704 can be formed or otherwise disposed on a dielectric layer 702. For example, in some embodiments, the superconducting layer 704 can be deposited on the dielectric layer 702 prior to step 710. Although the metal film 716 is shown as being deposited on the surface of the superconducting layer 704, it should be understood that the metal film 716 can be deposited on vias that extend through at least the superconducting layer 704 and / or the dielectric layer 702.

[0092] The second step 720 of the manufacturing process 700 can include the step of etching the metal film 716 to form the metal film 726. For example, the metal film 716 can be etched to remove at least the removed portion of the metal film 716. The remaining portion of the metal film 716 can form the metal film 726. For example, the remaining portion of the metal film 716 (e.g., the metal film 726) can be approximately the same size as the final metal structure 738. In some embodiments, the metal film 726 can be or include an adhesive layer. For example, the metal film 726 may include a first layer of a first material (e.g., titanium) and / or a second layer of a second material (e.g., copper). In some embodiments, one of the first or second layers may be of the same material (e.g., copper) as the metal structure 738 such that the metal film 726 forms at least a part of the metal structure 738.

[0093] The third step 730 of the manufacturing process 700 can include the step of electroplating the metal structure 738 onto the metal film 726. For example, in some embodiments, a part of the metal structure 738 can first be deposited as the metal film 726 onto the superconducting layer 704. The remaining portion of the metal structure 738 can be electroplated following the deposition and etching of the metal film 726. In this way, the metal film 726 can function as an adhesive layer to fix the metal structure 738 to the superconducting layer 704. Further, the metal structure 738 and / or the metal film 726 can provide a high-quality electrical contact (e.g., a non-contaminated electrical contact) to the superconducting layer 704 that can assist in interfacing with the superconducting layer 704. The metal structure 738 can be an interconnect pad, a via plate, and / or any other suitable metal structure for interfacing with the superconducting layer 704.

[0094] FIG. 8 shows an example of a method 800 for creating a flexible circuit board used when transmitting signals in a quantum computing system. FIG. 8 shows steps executed in a specific order for illustration and explanation purposes. Those skilled in the art will understand that, using the disclosure provided herein, various steps of any of the methods disclosed herein can be adapted, modified, executed simultaneously, omitted, rearranged, including steps not illustrated, and / or extended in various ways without departing from the scope of this disclosure.

[0095] Method 800 may include, at 802, depositing a superconducting layer (e.g., a first superconducting layer) on a first surface of a dielectric layer (e.g., a first dielectric layer). For example, in some embodiments, the superconducting layer may be a superconducting signal line layer including a ground layer and / or one or more signal lines. The superconducting layer may be a superconducting material such as a material that superconducts at a temperature of less than about 3 Kelvin, such as about 20 millikelvin, such as about 1 Kelvin, or may include such a material. As an example, the superconducting material may be niobium or may include niobium. The dielectric layer may be any suitable dielectric material, such as a flexible dielectric material such as polyimide.

[0096] Method 800 may include, at 804, depositing a metal film (e.g., a first metal film) on the superconducting layer. For example, the metal film may be deposited over an area wider than the final metal structure, such as over the entire surface of the superconducting layer. The metal film may include at least one layer. As an example, the metal film may be the same material as the final metal structure. As an example, the metal film may be copper or may include copper. For example, the metal film may be a first portion of the final metal structure formed by deposition. The metal film may function to prevent the formation of contaminants (e.g., oxides) and / or to adhere the metal structure to the superconducting layer. Additionally and / or alternatively, the metal film may include an additional adhesion layer having a material different from the final metal structure, such as titanium. The additional adhesion layer may improve the adhesion of the metal structure and / or the metal film to the superconducting layer.

[0097] Method 800 may include, at 806, etching a metal film to remove a removed portion of the metal film (e.g., a first removed portion) and leaving a remaining portion of the metal film (e.g., a first remaining portion). For example, the remaining portion of the metal film can be masked so that only the removed portion of the metal film is etched. The removed portion of the metal film may be etched such that the remaining portion of the metal film has approximately the same size, shape, and / or area as the metal structure. For example, the etching can remove unwanted regions of the metal film.

[0098] Method 800 may include, at 808, electroplating a metal structure (e.g., a first metal structure) on the remaining portion of the metal film. For example, a first portion of the metal structure can first be formed as a metal film, and a second portion of the metal structure can be formed by electroplating on top of the metal film. In this way, the metal structure can be attached to the superconducting material within the superconducting layer, thereby improving the interfacing with the superconducting layer. The metal structure can be formed of any suitable material such as copper. The metal structure may be, for example, an interconnect pad, a via plate, and / or any other suitable metal structure.

[0099] Method 800 may be repeated for any suitable number of layers within the flexible circuit board. As an example, method 800 may further include depositing a second superconducting layer on a second side of the first dielectric layer. For example, the first superconducting layer may be a ground layer and the second superconducting layer may be a signal line layer. The second side of the first dielectric layer may be on the opposite side of the first side of the first dielectric layer. Method 800 may further include depositing a second metal film on the second superconducting layer. Method 800 may further include etching the second metal film to remove a second removed portion of the second metal film and leaving a second remaining portion of the second metal film. Method 800 may further include electroplating a second metal structure on the second remaining portion of the second metal film disposed on the second superconducting layer. Method 800 may further include depositing a second dielectric layer on the second superconducting layer. Method 800 may further include depositing a third superconducting layer on the second dielectric layer. For example, the third superconducting layer may be a second ground layer. Method 800 may further include depositing a third metal film on the third superconducting layer. Method 800 may further include etching the third metal film to remove a third removed portion of the third metal film and leaving a third remaining portion of the third metal film. Method 800 may further include electroplating a third metal structure on the third remaining portion of the third metal film disposed on the third superconducting layer. In this way, method 800 can provide a superconducting flexible circuit board including interconnect pads and / or via plates for each of the two ground layers and signal line layers.

[0100] In some embodiments, to provide a metal structure for a via, method 800 may include etching a via through each layer (e.g., dielectric layer, ground layer, and / or signal line) and depositing a metal film on the inner surface of the via. A metal structure (e.g., a via plate) can then be electroplated on the metal film on the inner surface of the via. In this way, the metal film and / or the metal structure can extend through each layer.

[0101] In some embodiments, method 800 can be performed without exposing the flexible circuit board to oxygen. For example, in some embodiments, the step of depositing the first metal film on the superconducting layer is performed without exposing the superconducting layer to oxygen. As an example, a flexible circuit board including a superconducting layer and a dielectric layer can be placed in a vacuum before depositing the first metal film. The vacuum can be maintained until the risk of oxygen contamination is removed, for example, until the metal structure is successfully electroplated.

[0102] FIG. 9 shows an exemplary method of operating a quantum computing system including a flexible circuit board according to an exemplary embodiment of the present disclosure. Method 900 can be implemented using any suitable quantum computing system, such as quantum computing system 100 or 300 shown in FIGS. 1-3. FIG. 9 shows steps performed in a particular order for illustration and explanation. One of ordinary skill in the art will understand that, using the disclosure provided herein, various steps of any of the methods disclosed herein can be adapted, modified, performed simultaneously, omitted, rearranged, including steps not illustrated, and / or extended in various ways without departing from the scope of the present disclosure.

[0103] Method 900 may include, at 902, transmitting a control pulse to one or more signal lines. For example, the control pulse may be transmitted by one or more classical processors coupled to the signal lines. The control pulse may be a classical (e.g., binary) computer-readable signal data such as a voltage signal, and / or a signal implementable by a quantum computing device, or may include them. The signal lines may be disposed on one or more flexible circuit boards. The flexible circuit board may include at least one metal structure electroplated on at least one superconducting signal line, as described herein. For example, the flexible circuit board may be any suitable flexible circuit board discussed herein, such as the flexible circuit boards 400, 500, and / or 600 of FIGS. 4-6. The flexible circuit board may be disposed in any suitable quantum computing system, such as the quantum computing systems 100 and / or 300 of FIGS. 1-3.

[0104] Method 900 may include, at 904, transmitting the control pulse to one or more quantum computing devices via one or more flexible circuit boards. For example, the control pulse may be transmitted to the quantum computing device via the signal lines of one or more flexible circuit boards. The control pulse may be transmitted by the signal lines via a temperature gradient in a vacuum chamber. For example, the signal lines carrying the control pulse may gradually decrease in temperature from a classical processor (e.g., at room temperature and / or a temperature of about 100 Kelvin) to a quantum computing device (e.g., at a temperature less than about 1 Kelvin, such as about 10 mK).

[0105] Method 900 may include, at 906, applying a control pulse and performing at least one quantum operation based at least in part on the control pulse. As an example, in some embodiments, the quantum operation may be or may include obtaining a state measurement of a quantum computing device. For example, the control pulse may direct the quantum computing device to measure a quantum state and / or decompose the quantum state into a basis state representation. Further, the measured quantum state may be transmitted to a classical processor (e.g., via a signal line).

[0106] As another example, in some embodiments, the quantum operation may be or may include performing at least one quantum gate operation by and / or on a quantum computing device. For example, the control pulse may represent a microwave pulse applied to a quantum computing device (e.g., a qubit) to perform a quantum gating operation. Exemplary quantum gating operations include, but are not limited to, Hadamard gates, controlled NOT (CNOT) gates, controlled phase gates, T gates, multi-qubit quantum gates, coupler quantum gates, and the like.

[0107] The digital and / or quantum subject matter described in this specification, as well as implementations of digital functional operations and quantum operations, may be implemented in digital electronic circuitry, appropriate quantum circuitry, or, more generally, specifically implemented digital and / or quantum computer software or firmware, a quantum computing system in digital and / or quantum computer hardware, or one or more combinations thereof, including the structures disclosed herein and structural equivalents thereof. The term "quantum computing system" may include, but is not limited to, a quantum computer / computing system, a quantum information processing system, a quantum cryptographic system, or a quantum simulator.

[0108] The digital and / or quantum subject matter implementations described herein can be implemented as one or more digital and / or quantum computer programs, i.e., one or more modules of digital and / or quantum computer program instructions encoded on a tangible, non-transitory storage medium for execution by, or to control the operation of, a data processing apparatus. The digital and / or quantum computer storage medium may be a machine-readable storage device, a machine-readable storage substrate, a random or serial access memory device, one or more qubit / qubit structures, or a combination of one or more thereof. Alternatively or additionally, the program instructions may be encoded in an artificially generated propagated signal (e.g., a machine-generated electrical, optical, or electromagnetic signal) that can encode digital and / or quantum information generated to encode digital and / or quantum information for transmission to a suitable receiving device for execution by a data processing apparatus.

[0109] The terms quantum information and quantum data refer to information or data carried by, held in, or stored by a quantum system, and the smallest significant system is a qubit, i.e., a system that defines a unit of quantum information. It is understood that the term "qubit" encompasses all quantum systems that can be suitably approximated as two-level systems in the corresponding context. Such quantum systems can include, for example, multi-level systems having two or more levels. By way of example, such systems may include atoms, electrons, photons, ions, or superconducting qubits. In many implementations, the computational basis states are identified with the ground state and the first excited state, but it is understood that other setups are possible where the computational states are identified with higher-level excited states (e.g., qutrits).

[0110] The term "data processing apparatus" refers to digital and / or quantum data processing hardware, and includes, by way of example, programmable digital processors, programmable quantum processors, digital computers, quantum computers, or multiple digital and quantum processors or computers, and any kind of apparatus, device, and machine for processing digital and / or quantum data, including combinations thereof. The apparatus may also be, or further include, dedicated logic circuitry such as, for example, an FPGA (Field Programmable Gate Array), or an ASIC (Application Specific Integrated Circuit), or a quantum simulator, i.e., a quantum data processing apparatus designed to simulate or generate information about a particular quantum system. In particular, a quantum simulator is a dedicated quantum computer that does not have the function of performing universal quantum computing. The apparatus may optionally include, in addition to the hardware, code that creates an execution environment for digital and / or quantum computer programs, such as code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.

[0111] A digital computer program, which may also be referred to or described as a program, software, software application, module, software module, script, or code, can be written in any form of programming language, including a compiled or interpreted language, or a declarative or procedural language, and can be deployed in any form, such as as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a digital computing environment. A quantum computer program, which may also be called or described as a program, software, software application, module, software module, script, or code, can be written in any form of programming language, including a compiled or interpreted language, or a declarative or procedural language, and can be converted into a suitable quantum programming language or written in a quantum programming language such as QCL, Quipper, Cirq, etc.

[0112] A digital and / or quantum computer program may correspond to a file in a file system, but it is not necessarily so. A program can be stored as part of a file that holds other programs or data. For example, it can be stored in one or more scripts stored in a markup language document, a single file dedicated to the program in question, or multiple coordinated files, such as files that hold one or more modules, subprograms, or portions of code. A digital and / or quantum computer program can be deployed to be executed on one digital or one quantum computer, or on multiple digital and / or quantum computers located at one site or distributed across multiple sites and interconnected by a digital and / or quantum data communication network. A quantum data communication network is understood to be a network that can transmit quantum data using a quantum system such as qubits. Generally, a digital data communication network cannot transmit quantum data, but a quantum data communication network can transmit both quantum data and digital data.

[0113] The processes and logic flows described in this specification may, as necessary, be executed by one or more digital and / or quantum processors operating on one or more digital and / or quantum computers, manipulating input digital and quantum data, and generating outputs by executing one or more digital and / or quantum computer programs that perform functions. The processes and logic flows may also be executed by dedicated logic circuits such as FPGAs and ASICs, or quantum simulators, or by a combination of dedicated logic circuits or quantum simulators and one or more programmed digital and / or quantum computers, and the apparatus may also be implemented as such.

[0114] For a system of one or more digital and / or quantum computers or processors to be "configured" or "operable" to perform a particular operation or action means that the system has software, firmware, hardware, or a combination thereof installed that causes the system to perform the operation or action during operation. For one or more digital and / or quantum computer programs to be configured to perform a particular operation or action means that the one or more programs include instructions that, when executed by a digital and / or quantum data processing apparatus, cause the apparatus to perform the operation or action. A quantum computer can receive instructions from a digital computer that cause the apparatus to perform an operation or action when executed by the quantum computing apparatus.

[0115] Digital and / or quantum computers suitable for the execution of digital and / or quantum computer programs can be based on general-purpose or special-purpose digital and / or quantum microprocessors or both, or any other kind of central digital and / or quantum processing unit. Generally, the central digital and / or quantum processing unit receives instructions and digital and / or quantum data from read-only memory, random access memory, or a quantum system suitable for transmitting quantum data such as photons, or a combination thereof.

[0116] Some exemplary elements of a digital and / or quantum computer are a central processing unit for executing or performing instructions and one or more memory devices for storing instructions and digital and / or quantum data. The central processing unit and the memory can be complemented or incorporated by dedicated logic circuits or quantum simulators. Generally, a digital and / or quantum computer also includes one or more mass storage devices for storing digital and / or quantum data, such as magnetic, magneto-optical disks, optical disks, or a quantum system suitable for storing quantum information, or is operatively coupled to receive, or transmit, or both digital and / or quantum data. However, a digital and / or quantum computer need not include such devices.

[0117] Digital and / or quantum computer program instructions and digital and / or quantum computer-readable media suitable for storing digital and / or quantum data include all forms of non-volatile digital and / or quantum memory, media, and memory devices, such as semiconductor memory devices like EPROM, EEPROM, and flash memory devices, magnetic disks (such as internal hard disks and removable disks), magneto-optical disks, CD-ROM and DVD-ROM disks, and quantum systems such as trapped atoms and electrons. Quantum memory is understood to be a device that can store quantum data with high fidelity and efficiency for a long time, for example, an optical-matter interfacing where light is used for transmission and matter is used to store and preserve the quantum properties of quantum data such as superposition and quantum coherence.

[0118] The control of the various systems described in this specification or a portion thereof can be implemented as a digital and / or quantum computer program product stored on one or more non-transitory machine-readable storage media and including instructions executable by one or more digital and / or quantum processing devices. The systems described in this specification or a portion thereof can each be implemented as an apparatus, method, or electronic system that includes one or more digital and / or quantum processing devices and memory for storing executable instructions for performing the operations described in this specification.

[0119] Although this specification contains many details of particular implementations, these should not be construed as limitations on the scope of the claims, but rather as descriptions of features that may be specific to particular implementation forms. The particular features described in this specification in the context of individual implementation forms may also be implemented in combination in a single implementation form. Conversely, the various features described in the context of a single implementation form may also be implemented individually, or in any suitable sub-combination, in multiple implementations. Furthermore, features may be described above as acting in a particular combination and may even initially be claimed as such, but one or more features from the claimed combination may in some cases be removed from the combination, and the claimed combination may be directed to a sub-combination or a variation of a sub-combination.

[0120] Similarly, operations are shown in the drawings in a particular order, but this should not be understood as requiring that such operations be performed in the particular order or sequence shown, or that all of the illustrated operations be performed, in order to achieve the desired result. In certain circumstances, multitasking and parallel processing may be advantageous. Furthermore, the separation of the various system modules and components in the above implementations should not be understood as requiring such separation in all implementation forms, and it is necessary to understand that the described program components and systems can generally be integrated into a single software product and packaged into multiple software products.

[0121] Particular implementation forms of the subject matter are described. Other implementation forms are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve the desired result. As an example, the process shown in the accompanying figures does not necessarily require the particular order or sequence shown to achieve the desired result. In some cases, multitasking and parallel processing may be advantageous.

Description of the Reference Numerals

[0122] 100, 300 Quantum Computing System 102, 304 Quantum Hardware 104, 302 Classical Processor 106 Physical Control Parameter Value 108 Measurement Result 110 Quantum System 112 Control Device 114 Reading Device 120, 406 Signal Line 130 Ultra-Low Temperature Cooling System 306, 500, 600 Flexible Circuit Board 307 Cap 308 Chamber Mount 312 Classical Signal Transmission Medium (Coaxial Cable) 314 First Flexible Circuit Board 316 Second Flexible Circuit Board 318 Surface Mount Attenuator Board 320 Third Flexible Circuit Board 322 Fourth Flexible Circuit Board 332 Classical Flexible Interconnection 336, 340 Flexible-Flexible Interconnection 342 Connector 352 Hermetic Seal 354 Surface Mount Attenuator 402 Ground Layer 404 Dielectric Layer 502, 604 Via 504, 606 Via Plate 602 Interconnection Pad

Claims

1. A flexible circuit board used for transmitting signals in a quantum computing system, wherein the flexible circuit board comprises: at least one dielectric layer; at least one superconducting layer disposed on the surface of the at least one dielectric layer, wherein the at least one superconducting layer contains a superconducting material, and the superconducting material superconducts at a temperature below 3 Kelvin; and the flexible circuit board has at least one metal structure electroplated on the at least one superconducting layer, the at least one metal structure being configured to couple the at least one superconducting layer to another structure outside the flexible circuit board, the at least one metal structure being a via plate, and the via plate covering a via extending through at least the at least one dielectric layer and the at least one superconducting layer; Flexible circuit board.

2. The flexible circuit board according to claim 1, wherein the superconducting material contains niobium.

3. The flexible circuit board according to claim 1, wherein the at least one dielectric layer contains polyimide.

4. The flexible circuit board according to claim 1, wherein the at least one metal structure contains copper.

5. The at least one superconducting layer comprises: a first ground layer; a second ground layer; a signal line layer disposed between the first ground layer and the second ground layer and containing one or more signal lines; and the at least one dielectric layer comprises: a first dielectric layer disposed between the first ground layer and the signal line layer; a second dielectric layer disposed between the second ground layer and the signal line layer; and The flexible circuit board according to claim 1.

6. The flexible circuit board according to claim 1, further comprising at least one adhesive layer disposed between the at least one superconducting layer and the at least one metal structure.

7. The flexible circuit board according to claim 6, wherein the at least one adhesive layer is formed by etching a deposited metal film.

8. The flexible circuit board according to claim 6, wherein the at least one adhesive layer contains titanium.

9. The flexible circuit board according to claim 6, wherein the at least one adhesive layer contains copper.

10. A method of manufacturing a flexible circuit board used for transmitting signals in a quantum computing system, comprising: depositing a first superconducting layer on a first side surface of a first dielectric layer; depositing a first metal film on the first superconducting layer; etching the first metal film to remove a first removed portion of the first metal film and leave a first remaining portion of the first metal film; electroplating a metal structure on the first remaining portion of the first metal film disposed on the first superconducting layer; wherein the metal structure is configured to couple the first superconducting layer to another structure outside the flexible circuit board, the metal structure is a via plate, and the via plate covers a via extending through at least the first dielectric layer and the first superconducting layer. **Claim 11** depositing a second superconducting layer on a second side surface of the first dielectric layer, wherein the second side surface of the first dielectric layer is on the opposite side of the first side surface of the first dielectric layer; depositing a second metal film on the second superconducting layer; etching the second metal film to remove a second removed portion of the second metal film and leave a second remaining portion of the second metal film; electroplating a second metal structure on the second remaining portion of the second metal film disposed on the second superconducting layer; The method according to claim 10, further comprising: **Claim 12** depositing a second dielectric layer on the second superconducting layer; depositing a third superconducting layer on the second dielectric layer; depositing a third metal film on the third superconducting layer; etching the third metal film to remove a third removed portion of the third metal film and leave a third remaining portion of the third metal film; electroplating a third metal structure on the third remaining portion of the third metal film disposed on the third superconducting layer; The method according to claim 11, further comprising: **Claim 13** The method according to claim 10, wherein the step of depositing the first metal film on the first superconducting layer is performed without exposing the first superconducting layer to oxygen. **Claim 14** A method of operating a quantum computing system including a flexible circuit board, comprising: Transmitting control pulses to one or more superconducting signal lines by one or more classical processors, wherein the one or more superconducting signal lines are disposed on one or more flexible circuit boards, and the one or more flexible circuit boards include at least one metal structure electroplated on the one or more superconducting signal lines; Transmitting the control pulses to one or more quantum computing devices via the one or more flexible circuit boards by the one or more signal lines; Applying the control pulses by the one or more quantum computing devices to perform at least one quantum operation based at least in part on the control pulses; comprising; The at least one metal structure is configured to couple the one or more superconducting signal lines to another structure external to the flexible circuit board, the at least one metal structure is a via plate, and the via plate covers vias extending through at least the one or more superconducting signal lines.

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