Optimal cooling of a driven artificial atom in dissipative environment

TL;DR

This paper investigates microwave-driven cooling in superconducting flux qubits, analyzing how decoherence affects cooling efficiency and proposing an improved method to maintain high cooling performance under strong decoherence.

Contribution

It introduces an improved cooling technique that mitigates vibrational disturbances, enhancing cooling efficiency in the presence of strong decoherence in superconducting qubits.

Findings

Optimal microwave amplitude depends linearly on flux detuning.

Increased decoherence couples more vibrational modes, reducing cooling effectiveness.

The proposed method maintains high cooling efficiency despite strong decoherence.

Abstract

We study microwave-driven cooling in a superconducting flux qubit subjected to environment noises. For the weak decoherence, our analytical results agree well with the experimental observations near the degeneracy point and show that the microwave amplitude for optimal cooling should depend linearly on the dc flux detuning. With the decoherence increasing, more vibrational degrees of freedom couple in, making the ordinary cooling method less effective or even fail. We propose an improved cooling method, which can eliminate the perturbation of additional vibrational degrees of freedom hence keep high efficiency even under the strong decoherence. Furthermore, we point out that the decoherence will modulate the frequency where microwave-driven Landau-Zener transition reaches maximum in both methods, displaying the feature of incoherent dynamics which is important for the optimal cooling of qubits and other quantum systems.