Decoherence by a spin-chain environment: the universal regime

CECILIA CORMICK; JUAN PABLO PAZ

Paraty

Workshop; International School and Workshop on Quantum Information; 2007

This work analyzes the decoherence induced on a single qubit by the interaction with a spin chain with nontrivial internal dynamics ͑XY-type interactions͒. The aim of the paper is to study the existence and prop-erties of the so-called universal regime, in which the decoherence time scale becomes independent of the strength of the coupling with the environment. It is shown that, although such a regime does exist, as previously established by Cucchietti et al. ͓Phys. Rev. A 75, 032337 ͑2007͔͒, it is not a clear signature of a quantum phase transition in the environment. In fact, this kind of universality also exists in the absence of quantum phase transitions. A universal regime can be related to the existence of an energy scale separation between theHamiltonian of the environment and the one characterizing the system-environment interaction. The results presented also indicate that in the strong-coupling regime the quantum phase transition does not produce an enhancement of decoherence ͑as opposed to what happens in the weak-coupling regime͒.