Abstract: Techniques are described for coupling superconducting qubits, and for performing entangling operations on superconducting qubits, which simplify the control hardware for qubits while providing for high fidelity operations. Superconducting qubits may be coupled together via a tunable coupler that may be controlled to adjust the energy of one or more states of the coupler, allowing the extent to which states of the coupler couple to states of the qubits to be adjusted. For instance, the coupler may be controlled to turn the coupling between the qubits on and off. Moreover, entangling gates between the qubits may be performed by driving the coupler and/or the qubits between their different states.

Abstract: An apparatus comprises: an array of coupled quantum elements in a housing configured to provide a low-temperature environment, where at least one of the quantum elements comprises: a first fluxonium qubit circuit, and a qubit coupling circuit configured to couple the first fluxonium qubit circuit to a second fluxonium qubit circuit, where the qubit coupling circuit comprises a tunable superconducting circuit that has at least one tunable characteristic; and a control module configured to apply magnetic flux pulses to quantum elements in the array of coupled quantum elements based at least in part on digital control signals received from a digital signal interface providing the digital control signals into the housing.

Abstract: An apparatus comprises: an array of coupled quantum elements in a housing configured to provide a low-temperature environment, where one of the quantum elements comprises: a first fluxonium qubit circuit (FQC), and a qubit coupling circuit configured to couple the first FQC to a second FQC; and a control module configured to apply magnetic flux pulses to quantum elements in the array of coupled quantum elements based at least in part on signals received from a digital signal interface providing digital control signals into the housing, the control module comprising: a DAC module that comprises one or more SFQ circuits that receive a digital input and generate the magnetic flux pulses, and a control coupling circuit configured to provide mutual inductive coupling between at least one of the SFQ circuits and at least one of the first FQC, the second FQC, or the qubit coupling circuit.