Decoherence due to the sudden coupling of an impurity to a metal

TL;DR

This paper studies how a quantum impurity loses coherence after sudden coupling to a metal, analyzing the transition from coherent oscillations to decoherence through analytical and numerical methods.

Contribution

It introduces a mixed discretization approach to suppress finite-size effects and provides a unified understanding of decoherence dynamics in impurity systems.

Findings

Finite systems show apparent coherence loss with revivals due to discrete spectra.

Mixed linear-logarithmic discretization suppresses finite-size artifacts.

Large lattices exhibit damping and relaxation, indicating irreversible decoherence.

Abstract

We investigate the nonequilibrium dynamics and loss of coherence in a quantum impurity system using the spinless resonant level model subject to sudden quenches of the hybridization between the impurity and the metal. The survival probability (fidelity) and impurity occupation are analyzed as probes of the dephasing induced by particle-hole excitations. For finite systems, the loss of coherence loss is only apparent, as discrete spectra lead to quasi-periodic dynamics and revivals when phases realign. We show that a mixed linear-logarithmic discretization suppresses these finite-size artifacts by rendering excitation energies incommensurate, thereby reducing revivals. Starting from the exactly solvable two-level limit exhibiting coherent Rabi oscillations, we extend the analysis to large lattices, where damping and relaxation emerge. Combining analytical and numerical results, we provide a unified picture of the crossover from coherent oscillations to effectively irreversible decoherence.