Abstract: A flex circuit board can be used in transmitting signals in a quantum computing system. The flex circuit board 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 can include a superconducting material. The superconducting material can be superconducting at a temperature less than about 3 kelvin. The flex circuit board can have at least one metal structure electroplated onto the at least one superconducting layer.

Abstract: A laminated circuit assembly for filtering signals in one or more signal lines in, for instance, a quantum computing system is provided. In one example, the laminated circuit assembly includes one or more signal lines disposed within a substrate in a first direction. The laminated circuit assembly includes a dielectric portion of the substrate. The laminated circuit assembly includes a filter portion of the substrate extending in a first direction and containing a frequency absorbent material providing less attenuation to a first signal of a first frequency than to a second signal of a second, higher frequency. The filter portion is configured to attenuate infrared signals passing through the one or more signal lines.

Abstract: An interconnection for flex circuit boards used, for instance, in a quantum computing system are provided. In one example, the interconnection can include a first flex circuit board having a first side and a second side opposite the first side. The interconnection can include a second flex circuit board having a third side and a fourth side opposite the third side. The first flex circuit board and the second flex circuit board are physically coupled together in an overlap joint in which a portion of the second side for the first flex circuit board overlaps a portion of the third side of the flex circuit board. The interconnection can include a signal pad structure positioned in the overlap joint that electrically couples a first via in the first flex circuit board and a second via in the second flex circuit board.

Abstract: A T-joint connector can be useful for connecting one or more flex circuit boards to quantum hardware including one or more qubits. The T-joint connector can include one or more flex circuit boards. Each of the one or more flex circuit boards can include one or more signal lines and one or more spring interconnects including a superconducting material. The one or more spring interconnects can be coupled to the one or more signal lines. The one or more spring interconnects can be configured to couple the one or more signal lines to one or more signal pads disposed on a mounting circuit board associated with the quantum hardware. The superconducting material can be superconducting at a temperature less than about 3 kelvin.

Abstract: Interconnections for connecting flex circuit boards in classical and/or quantum computing systems can include a first flex circuit board having a removed portion that exposes one or more signal lines and a second flex circuit board having a removed portion that exposes one or more other signal lines. The flex circuit boards can be aligned at the removed portions to form a signal trace gap near the exposed signal lines. Exposed signal lines of the first flex circuit board can be coupled with exposed signal lines of the second flex circuit board. A ground support layer can be coupled to the first flex circuit board and the second flex circuit board along the same side. An isolation plate at least partially covering the signal trace gap can be coupled to the first flex circuit board and/or the second flex circuit board on a side opposite of the ground support layer.

Abstract: Methods and apparatus for estimating the fidelity of quantum hardware. In one aspect, a method includes accessing a set of quantum gates; sampling a subset of quantum gates from the set of quantum gates, wherein the subset of quantum gates defines a quantum circuit; applying the quantum circuit to a quantum system and performing measurements on the quantum system to determine output information of the quantum system; calculating output information of the quantum system based on application of the quantum circuit to the quantum system; and estimating a fidelity of the quantum circuit based on the determined output information and the calculated output information of the quantum system.

Abstract: Methods, systems, and apparatus for operating a system of qubits. In one aspect, a method includes operating a first qubit from a first plurality of qubits at a first qubit frequency from a first qubit frequency region, and operating a second qubit from the first plurality of qubits at a second qubit frequency from a second first qubit frequency region, the second qubit frequency and the second first qubit frequency region being different to the first qubit frequency and the first qubit frequency region, respectively, wherein the second qubit is diagonal to the first qubit in a two-dimensional grid of qubits.

Abstract: A qubit device includes an elongated thin film uninterrupted by Josephson junctions, a quantum device in electrical contact with a proximal end of the elongated thin film, and a ground plane that is co-planar with the elongated thin film and is in electrical contact with a distal end of the elongated thin film, in which the thin film, the quantum device, and the ground plane comprise a material that is superconducting at a designed operating temperature.

Abstract: Methods, systems, and apparatus for operating a system of qubits. In one aspect, a method includes operating a first qubit from a first plurality of qubits at a first qubit frequency from a first qubit frequency region, and operating a second qubit from the first plurality of qubits at a second qubit frequency from a second first qubit frequency region, the second qubit frequency and the second first qubit frequency region being different to the first qubit frequency and the first qubit frequency region, respectively, wherein the second qubit is diagonal to the first qubit in a two-dimensional grid of qubits.

Abstract: Methods, systems, and apparatus for operating a system of qubits. In one aspect, a method includes operating a first qubit from a first plurality of qubits at a first qubit frequency from a first qubit frequency region, and operating a second qubit from the first plurality of qubits at a second qubit frequency from a second first qubit frequency region, the second qubit frequency and the second first qubit frequency region being different to the first qubit frequency and the first qubit frequency region, respectively, wherein the second qubit is diagonal to the first qubit in a two-dimensional grid of qubits.

Abstract: A method includes generating a bias signal from a first device, and applying the bias signal to a second device, the first device having (a) a superconducting trace and (b) a superconducting quantum interference device (SQUID), in which a first terminal of the SQUID is electrically coupled to a first end of the superconducting trace, and a second terminal of the SQUID is electrically coupled to a second end of the superconducting trace, where generating the bias signal from the first device includes: applying a first signal ?1 to a first sub-loop of the SQUID; and applying a second signal ?2 to a second sub-loop of the SQUID, in which the first signal ?1 and the second signal ?2 are applied such that a value of a superconducting phase of the first device is incremented or decremented by a non-zero integer multiple n of 2?.

Abstract: A qubit device includes an elongated thin film uninterrupted by Josephson junctions, a quantum device in electrical contact with a proximal end of the elongated thin film, and a ground plane that is co-planar with the elongated thin film and is in electrical contact with a distal end of the elongated thin film, in which the thin film, the quantum device, and the ground plane comprise a material that is superconducting at a designed operating temperature.

Abstract: Methods, systems, and apparatus for operating a system of qubits. In one aspect, a method includes operating a first qubit from a first plurality of qubits at a first qubit frequency from a first qubit frequency region, and operating a second qubit from the first plurality of qubits at a second qubit frequency from a second first qubit frequency region, the second qubit frequency and the second first qubit frequency region being different to the first qubit frequency and the first qubit frequency region, respectively, wherein the second qubit is diagonal to the first qubit in a two-dimensional grid of qubits.

Abstract: Methods, systems, and apparatus for nonlinear calibration of quantum computing apparatus. In one aspect, elements in a set of experimental data correspond to a respective configuration of control biases for the quantum computing apparatus. An initial physical model comprising one or more model parameters of the quantum computing apparatus is defined. The model is iteratively adjusted to determine a revised physical model, where at each iteration: a set of predictive data corresponding to the set of experimental data is generated, and elements in the predictive data represent a difference between the two smallest eigenvalues of a Hamiltonian characterizing the system qubits for the previous iteration, and are dependent on at least one model parameter of the physical model for the previous iteration; and the model for the previous iteration is adjusted using the obtained experimental data and the generated set of predictive data for the iteration.

Abstract: Methods and systems for performing a surface code error detection cycle. In one aspect, a method includes initializing and applying Hadamard gates to multiple measurement qubits; performing entangling operations on a first set of paired qubits, wherein each pair comprises a measurement qubit coupled to a neighboring data qubit in a first direction; performing entangling operations on a second set of paired qubits, wherein each pair comprises a measurement qubit coupled to a neighboring data qubit in a second or third direction, the second and third direction being perpendicular to the first direction, the second direction being opposite to the third direction; performing entangling operations on a third set of paired qubits, wherein each pair comprises a measurement qubit coupled to a neighboring data qubit in a fourth direction, the fourth direction being opposite to the first direction; applying Hadamard gates to the measurement qubits; and measuring the measurement qubits.

Abstract: The subject matter of the present disclosure may be embodied in devices, such as flexible wiring, that include: an elongated flexible substrate; multiple electrically conductive traces arranged in an array on a first side of the elongated flexible substrate; and an electromagnetic shielding layer on a second side of the elongated flexible substrate, the second side being opposite the first side, in which the elongated flexible substrate includes a fold region between a first electronically conductive trace and a second electrically conductive trace such that the electromagnetic shielding layer provides electromagnetic shielding between the first electronically conductive trace and the second electrically conductive trace.

Abstract: Methods, systems, and apparatus for performing an entangling operation on a system of qubits. In one aspect, a method includes operating the system of qubits, wherein the system of qubits comprises: a plurality of first qubits, a plurality of second qubits, a plurality of qubit couplers defining nearest neighbor interactions between the first qubits and second qubits, wherein the system of qubits is arranged as a two dimensional grid and each qubit of the multiple first qubits is coupled to multiple second qubits through respective qubit couplers, and wherein operating the system of qubits comprises: pairing multiple first qubits with respective neighboring second qubits; performing an entangling operation on each paired first and second qubit in parallel, comprising detuning each second qubit in the paired first and second qubits in parallel.

Abstract: A qubit device includes an elongated thin film uninterrupted by Josephson junctions, a quantum device in electrical contact with a proximal end of the elongated thin film, and a ground plane that is co-planar with the elongated thin film and is in electrical contact with a distal end of the elongated thin film, in which the thin film, the quantum device, and the ground plane comprise a material that is superconducting at a designed operating temperature.

Abstract: A qubit device includes an elongated thin film uninterrupted by Josephson junctions, a quantum device in electrical contact with a proximal end of the elongated thin film, and a ground plane that is co-planar with the elongated thin film and is in electrical contact with a distal end of the elongated thin film, in which the thin film, the quantum device, and the ground plane comprise a material that is superconducting at a designed operating temperature.

Abstract: A method includes generating a bias signal from a first device, and applying the bias signal to a second device, the first device having (a) a superconducting trace and (b) a superconducting quantum interference device (SQUID), in which a first terminal of the SQUID is electrically coupled to a first end of the superconducting trace, and a second terminal of the SQUID is electrically coupled to a second end of the superconducting trace, where generating the bias signal from the first device includes: applying a first signal ?1 to a first sub-loop of the SQUID; and applying a second signal ?2 to a second sub-loop of the SQUID, in which the first signal ?1 and the second signal ?2 are applied such that a value of a superconducting phase of the first device is incremented or decremented by a non-zero integer multiple n of 2?.