# Beating the limits with initial correlations

## TL;DR

This paper develops optimal protocols for resetting a qubit in open quantum systems, showing that initial correlations can enhance speed and accuracy without requiring entanglement.

## Contribution

It introduces a combined geometric and numerical control approach to derive optimal reset protocols, highlighting the benefits of initial correlations.

## Key findings

- Initial correlations enable faster qubit reset.
- Optimal reset speed is limited by maximum coupling strength.
- Entanglement is not required for improved reset performance.

## Abstract

Fast and reliable reset of a qubit is a key prerequisite for any quantum technology. For real world open quantum systems undergoing non-Markovian dynamics, reset implies not only purification, but in particular erasure of initial correlations between qubit and environment. Here, we derive optimal reset protocols using a combination of geometric and numerical control theory. For factorizing initial states, we find a lower limit for the entropy reduction of the qubit as well as a speed limit. The time-optimal solution is determined by the maximum coupling strength. Initial correlations, remarkably, allow for faster reset and smaller errors. Entanglement is not necessary.