Tightening Quantum Speed Limits for Almost All States

TL;DR

This paper introduces two new quantum speed limits for almost all states under unitary evolution, providing tighter bounds that are easier to compute and interpret geometrically, improving over traditional limits especially for mixed states.

Contribution

The authors derive two novel quantum speed limits that outperform traditional bounds for nearly all states, with simpler computation and a clear geometric interpretation.

Findings

New bounds outperform traditional limits for most states

Bounds are easier to compute and experimentally accessible

Geometric interpretation via generalized Bloch vectors

Abstract

Conventional quantum speed limits perform poorly for mixed quantum states: They are generally not tight and often significantly underestimate the fastest possible evolution speed. To remedy this, for unitary driving, we derive two quantum speed limits that outperform the traditional bounds for almost all quantum states. Moreover, our bounds are significantly simpler to compute as well as experimentally more accessible. Our bounds have a clear geometric interpretation; they arise from the evaluation of the angle between generalized Bloch vectors.