Beating the limits with initial correlations

Abstract

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