Landau-Zener transitions in a two-level system coupled to a finite-temperature harmonic oscillator

TL;DR

This paper investigates how a two-level quantum system's dynamics are affected by coupling to a finite-temperature harmonic oscillator, revealing complex behaviors in occupation probabilities across various regimes.

Contribution

It provides a detailed analysis of Landau-Zener transitions in a qubit coupled to a thermal oscillator, highlighting non-trivial effects of temperature and coupling strength.

Findings

Non-monotonic dependence of final populations on coupling strength.

Temperature influences transition probabilities in complex ways.

Different regimes show varied dynamical behaviors.

Abstract

We analyze the dynamics and final populations in a Landau-Zener problem for a two level system (or qubit) when this system interacts with one harmonic oscillator mode that is initially set to a finite-temperature thermal equilibrium state. The harmonic oscillator could represent an external mode that is strongly coupled to the qubit, e.g. an ionic oscillation mode in a molecule, or it could represent a prototypical uncontrolled environment. We analyze the qubit's occupation probabilities at the final time in a number of different regimes, varying the qubit and oscillator frequencies, their coupling strength and the temperature. In particular we find some surprising non-monotonic dependence on the coupling strength and temperature.