Decoherence of a driven multilevel quantum system interacting with a multi-bath reservoir

TL;DR

This paper develops a comprehensive theory for decoherence in multilevel quantum systems interacting with multi-bath environments and driven by ac fields, with applications to SQUID flux qubits.

Contribution

It introduces a master equation approach that includes ac driving and leakage effects, applied specifically to 2D SQUID flux qubits, aligning well with experimental data.

Findings

Predicted decoherence times match experimental results.

Decoherence behavior depends on circuit parameters and temperature.

The theory enables optimization of qubit coherence properties.

Abstract

A general theory is presented for the treatment of decoherence of a multilevel quantum system (with many degrees of freedom) interacting with multi-bath reservoir and driven by ac fields. In this approach, the system is described by a reduced density operator and the multi-bath reservoir is characterized by a number of spectral densities. The reduced density operator is governed by the master equation in which the effect of ac driving fields and the leakage to non-computational states are included. The theory is applied to the study of decoherence of a two-dimensional (2D) SQUID flux qubit coupled to control and readout circuits. The predicted results are in very good agreement with available experimental results in the absence of driving fields and with the analytic results of a dissipative two-level system in the presence of weak driving fields. The relaxation and decoherence times versus the parameters and temperature of the control and readout circuits are also explored in details to facilitate the optimization of the 2D SQUID qubit.