Quantum mechanical response to a driven Caldeira-Leggett bath

TL;DR

This paper investigates how a quantum system's response is affected when its environment, modeled as a Caldeira-Leggett bath, is driven externally, revealing qualitative changes in the system's dynamical susceptibility.

Contribution

It introduces a framework for analyzing quantum systems coupled to a driven Caldeira-Leggett bath, including explicit models and response characteristics.

Findings

Bath driving enhances low-frequency dispersion.

Susceptibility develops a zero-frequency maximum.

Qualitative changes are generic for driven quantum baths.

Abstract

We determine the frequency-dependent response characteristics of a quantum system to a driven Caldeira-Leggett bath. The bath degrees of freedom are explicitly driven by an external time-dependent force, in addition to the direct time-dependent forcing of the system itself. After general considerations of driven Caldeira-Leggett baths, we consider the Rubin model of a chain of quantum particles coupled by linear springs as an important model of a quantum dissipative system. We show that in the presence of time-dependent driving of the chain, this model can be mapped to a quantum system which couples to a driven Caldeira-Leggett bath. The effect of the bath driving is captured by a time-dependent force on the central system, which is, in principle, non-Markovian in nature. We study two specific examples, the exactly solvable case of a harmonic potential, and a quantum two-state system for which we assume a weak system-bath coupling. We evaluate the dynamical response to a periodic driving of the system and the bath. The dynamic susceptibility is shown to be altered qualitatively by the bath drive: The dispersive part is enhanced at low frequencies and acquires a maximum at zero frequency. The absorptive part develops a shoulder-like behavior in this frequency regime. These features seem to be generic for quantum systems in a driven Caldeira-Leggett bath.