Probing instantaneous quantum circuit refrigeration in the quantum regime

TL;DR

This paper demonstrates an instantaneous quantum circuit refrigerator capable of rapidly cooling superconducting resonators in the quantum regime, with experimental validation and theoretical modeling confirming its effectiveness at the single quantum level.

Contribution

The study introduces a time-resolved, quantum regime-compatible QCR and experimentally demonstrates its ability to rapidly reduce photon numbers in superconducting resonators.

Findings

QCR achieves approximately 300 aW cooling power.

QCR reduces photon number within 100 ns pulses below single quantum level.

Numerical models match experimental results accurately.

Abstract

Recent advancements in circuit quantum electrodynamics have enabled precise manipulation and detection of the single energy quantum in quantum systems. A quantum circuit refrigerator (QCR) is capable of electrically cooling the excited population of quantum systems, such as superconducting resonators and qubits, through photon-assisted tunneling of quasi-particles within a superconductor-insulator-normal metal junction. In this study, we demonstrated instantaneous QCR in the quantum regime. We performed the time-resolved measurement of the QCR-induced cooling of photon number inside the superconducting resonator by harnessing a qubit as a photon detector. From the enhanced photon loss rate of the resonator estimated from the amount of the AC Stark shift, the QCR was shown to have a cooling power of approximately 300 aW. Furthermore, even below the single energy quantum, the QCR can reduce the number of photons inside the resonator with 100 ns pulse from thermal equilibrium. Numerical calculations based on the Lindblad master equation successfully reproduced these experimental results.