Relaxation and decoherence in a resonantly driven qubit

TL;DR

This paper analytically investigates relaxation and decoherence in a resonantly driven qubit, revealing intrinsic and field-dependent components, and provides formulas applicable to experimental qubit systems like microwave-driven SQUID flux qubits.

Contribution

It introduces analytical expressions for relaxation and decoherence times of a driven qubit, distinguishing intrinsic and field-dependent effects, validated by numerical solutions.

Findings

Decoherence decomposes into intrinsic and field-dependent parts.

Analytical formulas match numerical master equation results.

Relations enable extraction of decoherence times from experimental measurements.

Abstract

Relaxation and decoherence of a qubit coupled to environment and driven by a resonant ac field are investigated by analytically solving Bloch equation of the qubit. It is found that the decoherence of a driven qubit can be decomposed into intrinsic and field-dependent ones. The intrinsic decoherence time equals to the decoherence time of the qubit in free decay while the field-dependent decoherence time is identical with the relaxation time of the qubit in driven oscillation. Analytical expressions of the relaxation and decoherence times are derived and applied to study a microwave-driven SQUID flux qubit. The results are in excellent agreement with those obtained by numerically solving the master equation. The relations between the relaxation and decoherence times of a qubit in free decay and driven oscillation can be used to extract the decoherence and thus dephasing times of the qubit by measuring its population evolution in free decay and resonantly driven oscillation.