Non-Markovian qubit decoherence during dispersive readout

TL;DR

This paper investigates non-Markovian qubit decoherence during dispersive readout, providing analytical and numerical insights into the transition from Markovian to Gaussian decay regimes under various coupling conditions.

Contribution

It introduces a comprehensive analysis of qubit decoherence including large detuning and quadratic coupling effects, extending beyond the Markov approximation.

Findings

Decoherence time derived analytically in the dispersive frame.

Identification of a crossover from Markovian to Gaussian decay.

Numerical validation of analytical results.

Abstract

We study qubit decoherence under generalized dispersive readout, i.e., we investigate a qubit coupled to a resonantly driven dissipative harmonic oscillator. We provide a complete picture by allowing for arbitrarily large qubit-oscillator detuning and by considering also a coupling to the square of the oscillator coordinate, which is relevant for flux qubits. Analytical results for the decoherence time are obtained by a transformation of the qubit-oscillator Hamiltonian to the dispersive frame and a subsequent master equation treatment beyond the Markov limit. We predict a crossover from Markovian decay to a decay with Gaussian shape. Our results are corroborated by the numerical solution of the full qubit-oscillator master equation in the original frame.