Non-Markovianity: initial correlations and nonlinear optical measurements

TL;DR

This paper analytically links non-Markovianity in quantum systems to observable nonlinear optical responses, emphasizing the role of initial correlations and bath memory effects in quantum dynamics.

Contribution

It extends the response function approach to derive an expression for non-Markovianity, highlighting the importance of initial correlations and bath memory effects.

Findings

Memory effects are caused by bath fluctuations, not dissipation.

Initial system-bath correlations are crucial for understanding non-Markovianity.

Non-Markovianity can be connected to nonlinear optical measurements.

Abstract

By extending the response function approach developed in nonlinear optics, we analytically derive an expression for the non-Markovianity [Laine, et al, Phys. Rev. A 81, 062115 (2010)] in the time evolution of a system in contact with a quantum mechanical bath, and find a close connection with the directly observable nonlinear optical response. The result indicates that memory in the bath induced fluctuations rather than in the dissipation causes non-Markovianity. Initial correlations between states of the system and the bath are shown to be essential for a correct understanding of the non-Markovianity.