Quickly tunable refrigerator for superconducting qubits

The emerging quantum technological devices call for fast and accurate initialization of functional quantum degrees of freedom to a low-entropy state. Here, we theoretically study a recently demonstrated quantum-circuit refrigerator [1] in the case of superconducting qubits. We find that for typical parameters, the refrigerator is suitable for quickly cooling both transmon and flux qubits close to their ground states. The maximum refrigeration rate of transmon qubits is roughly an order of magnitude stronger than that of resonators [2], providing additional flexibility in the design criteria. The on/off ratio of the refrigerator assumes values above 10⁴ with typical experimental parameters. Thus the refrigerator is a promising tool for quantum technology and for studies of open quantum systems. Finally, we present an experimental realization based on transmon qubits and coupled qubit-resonator systems, which are the workhorses of quantum processors based on superconducting circuits.

[1] K. Y. Tan et.al., Nat. Commun. 8 15189 (2017)
[2] M. Silveri et.al., Phys. Rev. B 96, 094524 (2017)