Decoherence from spin environments: Loschmidt echo and quasiparticle excitations

TL;DR

This paper investigates how a qubit's decoherence is influenced by its spin environment, revealing that quasiparticle excitations, not proximity to quantum phase transitions, primarily determine decoherence rates.

Contribution

It demonstrates that propagating quasiparticles in spin environments are key to qubit decoherence, challenging previous assumptions about phase transition proximity effects.

Findings

Decoherence correlates with quasiparticle propagation.

Proximity to quantum phase transitions is not necessary for fast decoherence.

Different spin liquid phases affect decoherence dynamics.

Abstract

We revisit the problem of decoherence of a qubit centrally coupled to an interacting spin environment, here modeled by a quantum compass chain or an extended XY model in a staggered magnetic field. These two models both support distinct spin liquid phases, adding a new element to the problem. By analyzing their Loschmidt echoes when perturbed by the qubit we find that a fast decoherence of the qubit is conditioned on the presence of propagating quasiparticles which couple to it. Different from expectations based on earlier works on central spin models, our result implies that the closeness of an environment to a quantum phase transition is neither a sufficient nor a necessary condition for an accelerated decoherence rate of a qubit.