Abstract: Apparatus and methods for removing leakage from a qubit. In one aspect, an apparatus includes one or more qubits, wherein each qubit facilitates occupation of at least one of a plurality of qubit levels, the qubit levels including two computational levels and one or more non-computational levels that are each higher than the computational levels, wherein the qubit facilitates transitions between qubit levels associated with a corresponding transition frequency; a cavity, wherein the cavity defines a cavity frequency; one or more couplers coupling each qubit to the cavity; one or more couplers coupling the cavity to an environment external to the one or more qubits and the cavity; a frequency controller that controls the frequency of each qubit such that, for each qubit, the frequency of the qubit is adjusted relative to the cavity frequency such that a population of a non-computational level is transferred to the cavity.

Abstract: A device includes: a substrate; a superconducting quantum interference device (SQUID) including a superconductor trace arranged on an upper surface of the substrate and having at least one Josephson junction interrupting a path of the superconductor trace, in which the superconductor trace includes a first superconductor material that exhibits superconducting properties at or below a corresponding superconducting critical temperature; and a dielectric capping layer on an upper surface of the SQUID, in which the dielectric capping layer covers a majority of the superconductor trace of the SQUID, and the capping layer includes an opening through which a first region of the SQUID is exposed, the first region of the SQUID including a first Josephson junction.

Abstract: Apparatus and methods for removing leakage from a qubit. In one aspect, an apparatus includes one or more qubits, wherein each qubit facilitates occupation of at least one of a plurality of qubit levels, the qubit levels including two computational levels and one or more non-computational levels that are each higher than the computational levels, wherein the qubit facilitates transitions between qubit levels associated with a corresponding transition frequency; a cavity, wherein the cavity defines a cavity frequency; one or more couplers coupling each qubit to the cavity; one or more couplers coupling the cavity to an environment external to the one or more qubits and the cavity; a frequency controller that controls the frequency of each qubit such that, for each qubit, the frequency of the qubit is adjusted relative to the cavity frequency such that a population of a non-computational level is transferred to the cavity.

Abstract: A method of fabricating a circuit element, such as a quantum computing circuit element, including obtaining a lithography mask write file that includes mask information characterizing one or more mask features, obtaining a uniformity function that is configured to modify the mask information to compensate for a non-uniform deposition process, applying the uniformity function to the lithography mask write to obtain a modified lithography mask write file, and performing lithography as directed by the modified lithography mask write file.

Abstract: Apparatus and methods for removing leakage from a qubit. In one aspect, an apparatus includes one or more qubits, wherein each qubit facilitates occupation of at least one of a plurality of qubit levels, the qubit levels including two computational levels and one or more non-computational levels that are each higher than the computational levels, wherein the qubit facilitates transitions between qubit levels associated with a corresponding transition frequency; a cavity, wherein the cavity defines a cavity frequency; one or more couplers coupling each qubit to the cavity; one or more couplers coupling the cavity to an environment external to the one or more qubits and the cavity; a frequency controller that controls the frequency of each qubit such that, for each qubit, the frequency of the qubit is adjusted relative to the cavity frequency such that a population of a non-computational level is transferred to the cavity.

Abstract: Apparatus and methods for removing leakage from a qubit. In one aspect, an apparatus includes one or more qubits, wherein each qubit facilitates occupation of at least one of a plurality of qubit levels, the qubit levels including two computational levels and one or more non-computational levels that are each higher than the computational levels, wherein the qubit facilitates transitions between qubit levels associated with a corresponding transition frequency; a cavity, wherein the cavity defines a cavity frequency; one or more couplers coupling each qubit to the cavity; one or more couplers coupling the cavity to an environment external to the one or more qubits and the cavity; a frequency controller that controls the frequency of each qubit such that, for each qubit, the frequency of the qubit is adjusted relative to the cavity frequency such that a population of a non-computational level is transferred to the cavity.

Abstract: Methods, systems, and apparatus for individual qubit excitation control. In one aspect, a method includes accessing a quantum system that comprises a plurality of qubits; a plurality of qubit frequency control lines, each qubit frequency control line corresponding to an individual qubit and controlling the frequency of the qubit; a driveline; a plurality of couplers, each coupler coupling a corresponding qubit to the driveline so that a plurality of qubits are coupled to the driveline; determining one or more qubits that require a rotation operation; for each qubit requiring a rotation operation: tuning the qubit frequency to the corresponding driveline frequency of the rotation operation; performing the rotation operation using a microwave pulse on the excitation drive; and tuning the qubit away from the driveline frequency of the rotation operation.

Abstract: Apparatus and methods for removing leakage from a qubit. In one aspect, an apparatus includes one or more qubits, wherein each qubit facilitates occupation of at least one of a plurality of qubit levels, the qubit levels including two computational levels and one or more non-computational levels that are each higher than the computational levels, wherein the qubit facilitates transitions between qubit levels associated with a corresponding transition frequency; a cavity, wherein the cavity defines a cavity frequency; one or more couplers coupling each qubit to the cavity; one or more couplers coupling the cavity to an environment external to the one or more qubits and the cavity; a frequency controller that controls the frequency of each qubit such that, for each qubit, the frequency of the qubit is adjusted relative to the cavity frequency such that a population of a non-computational level is transferred to the cavity.