Decoherence as a signature of an excited state quantum phase transition

TL;DR

This paper investigates how a qubit's decoherence is significantly affected by the environment undergoing an excited state quantum phase transition, revealing maximal decoherence at critical points.

Contribution

It demonstrates that excited state quantum phase transitions in the environment cause dramatic changes in qubit decoherence, highlighting a new signature of such transitions.

Findings

Decoherence peaks at critical energy levels of the environment.

Fidelity tends to zero with finite size scaling at the transition.

Decoherence dynamics change dramatically at the phase transition.

Abstract

We analyze the decoherence induced on a single qubit by the interaction with a two-level boson system with critical internal dynamics. We explore how the decoherence process is affected by the presence of quantum phase transitions in the environment. We conclude that the dynamics of the qubit changes dramatically when the environment passes through a continuous excited state quantum phase transition. If the system-environment coupling energy equals the energy at which the environment has a critical behavior, the decoherence induced on the qubit is maximal and the fidelity tends to zero with finite size scaling obeying a power-law.