Abstract
When a quantum system couples strongly to multiple baths, then it is generally no longer possible to describe the resulting system dynamics by simply adding the individual effects of each bath. However, capturing such multibath system dynamics typically requires approximations that can obscure some of the nonadditive effects. Here we present a numerically exact and efficient technique for tackling this problem that builds on the time-evolving matrix product operator (TEMPO) representation. We test the method by applying it to a simple model system that exhibits nonadditive behavior: a two-level dipole coupled to both a vibrational and an optical bath. Although not directly coupled, there is an effective interaction between the baths mediated by the system that can lead to population inversion in the matter system when the vibrational coupling is strong. We benchmark and validate multibath TEMPO against two approximate methods—one based on a polaron transformation, the other on an identification of a reaction coordinate—before exploring the regime of simultaneously strong vibrational and optical coupling where the approximate techniques break down. Here we uncover a new regime where the quantum Zeno effect leads to a fully mixed state of the electronic system.
- Received 17 September 2021
- Revised 21 December 2021
- Accepted 7 January 2022
DOI:https://doi.org/10.1103/PRXQuantum.3.010321
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Quantum systems that can be measured in the laboratory are never truly isolated. They interact with their surroundings, and this affects their behaviour. In many situations, this interaction is relatively strong - for example in the solid-state systems that might be used to build a quantum computer. Moreover, there is often more than one kind of environment, each consisting of a different collection of particles, and each of which changes the behaviour of the system in a different way. In this paper, an exact numerical technique is developed, able to capture their combined effect.
Importantly, these multiple environments cannot be treated separately - i.e. the changes in the system dynamics are not simply additive. Nor can they be treated through a direct solution of the Schroedinger equation: the number of particles is too large for any computer to represent directly. Rather, we develop a way of capturing only the most relevant information, through the use of tensor network techniques. In this way, we are able to obtain exact predictions for general models consisting of a quantum system and multiple environments.
The technique is illustrated by studying a two-level atom coupled to both photons (light particles) and phonons (lattice vibrations) and is able to look at what happens when the coupling to both environments is strong. This method paves the way for gaining a deeper insight into the non-equilibrium physics that naturally emerge in open quantum systems, and for understanding the behaviour of quantum devices being developed for future technologies.