Weak coupling study of decoherence of a qubit in disordered magnetic environments

TL;DR

This paper investigates how a qubit's decoherence is affected by weak coupling to disordered magnetic environments, revealing complex, non-Markovian decay behaviors influenced by the bath's phase diagram and initial state.

Contribution

It provides new insights into the decoherence dynamics of a qubit coupled to frustrated spin baths, highlighting the impact of bath phase and initial conditions on decoherence behavior.

Findings

Decoherence varies significantly with the phase of the spin bath.

Unexpected non-Markovian decay observed in the quantum transverse Ising bath.

Decoherence behavior is sensitive to the initial thermal state of the environment.

Abstract

We study the decoherence of a qubit weakly coupled to frustrated spin baths. We focus on spin-baths described by the classical Ising spin glass and the quantum random transverse Ising model which are known to have complex thermodynamic phase diagrams as a function of an external magnetic field and temperature. Using a combination of numerical and analytical methods, we show that for baths initally in thermal equilibrium, the resulting decoherence is highly sensitive to the nature of the coupling to the environment and is qualitatively different in different parts of the phase diagram. We find an unexpected strong non-Markovian decay of the coherence when the random transverse Ising model bath is prepared in an initial state characterized by a finite temperature paramagnet. This is contrary to the usual case of exponential decay (Markovian) expected for spin baths in finite temperature paramagnetic phases, thereby illustrating the importance of the underlying non-trivial dynamics of interacting quantum spinbaths.