Open quantum systems in thermal non-ergodic environments

TL;DR

This paper investigates how non-ergodic thermal environments with persistent correlations affect open quantum system dynamics, revealing conditions that prevent thermalization and introduce low-frequency noise relevant for quantum devices.

Contribution

It demonstrates that non-Harmonic environments can have non-decaying correlation offsets, challenging standard assumptions and linking environment structure to noise spectra in quantum systems.

Findings

Correlation functions may not decay to zero but to a positive offset.

Offset presence depends on environment eigenstate structure and thermalization hypothesis.

Realistic dye molecule environment exhibits offset linked to 1/f noise spectrum.

Abstract

The dynamics of an open system crucially depends on the correlation function of its environment, $C_B(t)$. We show that for thermal non-Harmonic environments $C_B(t)$ may not decay to zero but to an offset, $C_0>0$. The presence of such offset is determined by the environment eigenstate structure, and whether it fulfills or not the eigenstate thermalization hypothesis. Moreover, we show that a $C_0>0$ could render the weak coupling approximation inaccurate and prevent the open system to thermalize. Finally, for a realistic environment of dye molecules, we show the emergence of the offset by using matrix product states (MPS), and discuss its link to a 1/f noise spectrum that, in contrast to previous models, extends to zero frequencies. Thus, our results may be relevant in describing dissipation in quantum technological devices like superconducting qubits, which are known to be affected by such noise.