Enhancement of quantum speed limit time due to cooperative effects in multilevel systems

TL;DR

This paper demonstrates that cooperative effects in multilevel quantum systems can significantly reduce the quantum speed limit time, surpassing two-level system predictions through optimized control fields.

Contribution

It reveals that cooperative interactions in multilevel systems enable faster quantum evolution, a novel insight achieved via quantum optimal control methods.

Findings

Optimal control fields reduce evolution time below two-level bounds

Cooperative effects between levels enhance quantum speed

Enhanced speed limit observed even with isolated avoided crossings

Abstract

Deriving minimum evolution times is of paramount importance in quantum mechanics. Bounds on the speed of evolution are given by the so called quantum speed limit (QSL). In this work we use quantum optimal control methods to study the QSL for driven many level systems which exhibit local two-level interactions in the form of avoided crossings (ACs). Remarkably, we find that optimal evolution times are proportionally smaller than those predicted by the well-known two-level case, even when the ACs are isolated. We show that the physical mechanism for such enhancement is due to non-trivial cooperative effects between the AC and other levels, which are dynamically induced by the shape of the optimized control field.