On-chip refrigeration for Kerr-cat qubits based on photon-assisted electron tunneling

A periodically-driven superconducting nonlinear resonator can implement a Kerr-cat qubit with a long lifetime. Pure dephasing of the resonator is a source of leakage error causing unwanted excitations outside the qubit subspace. To mitigate the error, a refrigeration technology which confines the system in the qubit subspace is desirable. We theoretically study on-chip cooling for Kerr-cat qubits with photon-assisted electron tunneling at tunneling junctions [1], which are called quantum circuit refrigerator (QCR) [2]. We show that rates of QCR-induced deexcitations of the system can be changed by more than four orders of magnitude by tuning a bias voltage across the tunneling junctions. Quantum interference in the tunneling process suppresses unwanted QCR-induced bit flips, and thus the long lifetime is preserved. The QCR can stabilize Kerr-cat qubits by acting as a tunable dissipation source.

[1] S. Masuda, et al., arXiv:2406.13957 (2024).

[2] K. Y. Tan, et al., Nat. Commun. 8, 15189 (2017).