Quantum decoherence from complex saddle points

TL;DR

This paper proposes a novel approach to understanding quantum decoherence through complex saddle points in the Feynman path integral, supported by calculations in the Caldeira-Leggett model and potential extensions via Monte Carlo methods.

Contribution

It introduces a new perspective on quantum decoherence using complex saddle points, linking it to quantum tunneling and providing first-principle calculations.

Findings

Reproduces decoherence scaling with environment parameters

Demonstrates the use of complex saddle points in decoherence analysis

Suggests Monte Carlo methods to extend the approach

Abstract

Quantum decoherence is the effect that bridges quantum physics to well-understood classical physics. As such, it plays a crucial role in understanding the mysterious nature of quantum physics. Quantum decoherence is also a source of quantum noise that has to be well under control in quantum computing and in various experiments based on quantum technologies. Here we point out that quantum decoherence can be captured by $\textit{complex}$ saddle points in the Feynman path integral in much the same way as quantum tunneling can be captured by instantons. In particular, we present some first-principle calculations in the Caldeira-Leggett model, which reproduce the predicted scaling behavior of quantum decoherence with respect to the parameters of the environment, such as the temperature and the coupling to the system of interest. We also discuss how to extend our approach to general models by Monte Carlo calculations using a recently developed method to overcome the sign problem.