Hidden non-Markovianity in open quantum systems

TL;DR

This paper demonstrates that certain open quantum systems can appear Markovian in their reduced dynamics despite being fundamentally non-Markovian, revealing that non-Markovianity can be hidden and undetectable through standard measurements.

Contribution

It introduces the concept of hidden non-Markovianity, showing that non-Markovian effects can be exactly masked in the system's observable dynamics, challenging previous assumptions.

Findings

Non-Markovianity can be perfectly hidden in quantum systems.

Reduced dynamics may appear Markovian despite underlying non-Markovian behavior.

Non-Markovianity is physically undecidable and can change unpredictably.

Abstract

We show that non-Markovian open quantum systems can exhibit exact Markovian dynamics up to an arbitrarily long time; the non-Markovianity of such systems is thus perfectly "hidden", i.e. not experimentally detectable by looking at the reduced dynamics alone. This shows that non-Markovianity is physically undecidable and extremely counterintuitive, since its features can change at any time, without precursors. Some interesting examples are discussed.