# Preparations and Weak Quantum Control can Witness non-Markovianity

## TL;DR

This paper demonstrates how weak quantum control techniques can be used to detect initial system-environment correlations and identify non-Markovian dynamics in quantum systems.

## Contribution

It introduces a method combining weak quantum controllability with quantum preparations to witness initial correlations and non-Markovianity.

## Key findings

- Weak quantum control can detect initial system-environment correlations.
- Weak field phase control can identify when the quantum regression formula fails.
- The approach provides a practical way to characterize non-Markovian dynamics.

## Abstract

The dynamics of a system that is initially correlated with an environment is almost always non-Markovian. Hence it is important to characterise such initial correlations experimentally and witness them in physically realistic settings. One such setting is weak-field phase control, where chemical reactions are sought to be controlled by the phase of shaped weak laser pulses. In this manuscript, we show how weak quantum controllability can be combined with quantum preparations to witness initial correlations between the system and the environment. Furthermore we show how weak field phase control can be applied to witness when the quantum regression formula does not apply.