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 measuring the dispersive shift or linewidth of a resonator coupled to a qubit. In one aspect, a method includes the actions of: generating resonator response data, comprising, for each of two computational states of the qubit: for each of multiple qubit drive frequencies: for each of multiple resonator drive frequencies: preparing the qubit in the computational state; applying a first drive pulse with the resonator drive frequency to the resonator, applying a second drive pulse with the qubit drive frequency to the qubit; measuring the state of the qubit; and processing the generated resonator response data to determine the dispersive shift or linewidth of the resonator.

Abstract: Methods, systems, and apparatus for enhanced decoding using in-phase and quadrature information. In one aspect, a method includes obtaining in-phase and quadrature values for multiple measurement operations in a quantum error correction code for a quantum computation; classifying measurement outcomes of the multiple measurement operations using respective in-phase and quadrature values; generating a detector graph of nodes and edges, wherein the detector graph labels detection events that occur in the classified measurement outcomes; assigning weights to the edges of the detector graph using posterior probability distributions of the classified measurement outcomes to generate a weighted detector graph; and executing a decoding process on the weighted detector graph to compute a decoding output of the decoding process, wherein the decoding output predicts an occurrence of errors in the quantum computation.

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: Apparatus and methods for performing qubit readout. In one aspect, an apparatus includes a qubit that operates at a qubit frequency; a frequency controller that is configured to control the qubit frequency and that during a qubit measurement operation is configured to: determine a compensation pulse that when applied to the qubit, counteracts qubit frequency changes during the qubit measurement operation; and apply the determined compensation pulse to the qubit during the qubit measurement operation to maintain the qubit frequency.

Abstract: A detector for reading out a state of a qubit includes a flux qubit and a flux bias generator. The flux qubit includes an inductor and SQUID loop, in which the flux qubit is arranged to exhibit first and second flux states. The flux bias generator generates a first flux bias through the inductor and a second flux bias through the SQUID loop, such that, in response to a first value of the first flux bias, the energies of the first and the second flux states are substantially identical and, in response to a second value of the first flux bias, the energies of the first and the second flux states are different. In response to a first value of the second flux bias, the flux qubit couples to the qubit and, in response to a second value of the second flux bias, decouples from the qubit and suppresses tunneling.

Abstract: Apparatus and methods for performing qubit readout. In one aspect, an apparatus includes a qubit that operates at a qubit frequency; a frequency controller that is configured to control the qubit frequency and that during a qubit measurement operation is configured to: determine a compensation pulse that when applied to the qubit, counteracts qubit frequency changes during the qubit measurement operation; and apply the determined compensation pulse to the qubit during the qubit measurement operation to maintain the qubit frequency.

Abstract: Methods, systems, and apparatus for measuring the dispersive shift or linewidth of a resonator coupled to a qubit. In one aspect, a method includes the actions of: generating resonator response data, comprising, for each of two computational states of the qubit: for each of multiple qubit drive frequencies: for each of multiple resonator drive frequencies: preparing the qubit in the computational state; applying a first drive pulse with the resonator drive frequency to the resonator, applying a second drive pulse with the qubit drive frequency to the qubit; measuring the state of the qubit; and processing the generated resonator response data to determine the dispersive shift or linewidth of the resonator.

Abstract: A quantum computing device includes: a qubit; a single XYZ control line, in which the qubit and the single control line are configured and arranged such that, during operation of the quantum computing device, the single XYZ control line allows coupling of an XY qubit control flux bias, from the single XYZ control line to the qubit, over a first frequency range at a first predetermined effective coupling strength, and coupling of a Z qubit control flux bias, from the single XYZ control line to the qubit, over a second frequency range at a second predetermined effective coupling strength.

Abstract: Apparatus and methods for performing qubit readout. In one aspect, an apparatus includes a qubit that operates at a qubit frequency; a frequency controller that is configured to control the qubit frequency and that during a qubit measurement operation is configured to: determine a compensation pulse that when applied to the qubit, counteracts qubit frequency changes during the qubit measurement operation; and apply the determined compensation pulse to the qubit during the qubit measurement operation to maintain the qubit frequency.

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 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: Apparatus and methods for performing qubit readout. In one aspect, an apparatus includes a qubit that operates at a qubit frequency; a frequency controller that is configured to control the qubit frequency and that during a qubit measurement operation is configured to: determine a compensation pulse that when applied to the qubit, counteracts qubit frequency changes during the qubit measurement operation; and apply the determined compensation pulse to the qubit during the qubit measurement operation to maintain the qubit frequency.

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.