Quickly Tunable Refrigerator for Superconducting Quantum Circuits*

In the past decade, the research on superconducting quantum circuits has provided a great number of superior microwave components such as superconducting qubits, amplifiers, and sensors. Especially in the opertation of qubits, it is of utmost importance to be able to quickly remove any unwanted qubit excitations on demand for fast and accurate initialization. Furthermore, a reduction of excess photon population in qubit-coupled resonators is important in tackling shot-noise-induced dephasing. To this end, we recently introduced a device referred to as a quantum-circuit rerigerator [K. Y. Tan, et al., Nat. Commun. 8, 15189 (2017)]. It is a stand-alone component that can be integrated with most superconducting quantum electric devices without major compromises in their other design criteria. In our experiments, we show how we can tune the dissipation of a superconducting resonator by orders of magnitude just by applying a bias voltage on the refrigerator. The time scale for switching the dissipation on and off is in the nanosecond range. We also observe a tunable Lamb shift owing to the dissipation induced by the refrigirator.