Diverging Quantum Speed Limits: A Herald of Classicality
Abstract
When is the quantum speed limit (QSL) really quantum? While vanishing QSL times often indicate emergent classical behavior, it is still not entirely understood what precise aspects of classicality are at the origin of this dynamical feature. Here, we show that vanishing QSL times (or, equivalently, diverging quantum speeds) can be traced back to reduced uncertainty in quantum observables and can thus be understood as a consequence of emerging classicality for these particular observables. We illustrate this mechanism by developing a QSL formalism for continuousvariable quantum systems undergoing general Gaussian dynamics. For these systems, we show that three typical scenarios leading to vanishing QSL times, namely large squeezing, small effective Planck's constant, and large particle number, can be fundamentally connected to each other. In contrast, by studying the dynamics of open quantum systems and mixed states, we show that the classicality that emerges due to incoherent mixing of states from the addition of classical noise typically increases the QSL time.
 Publication:

PRX Quantum
 Pub Date:
 December 2021
 DOI:
 10.1103/PRXQuantum.2.040349
 arXiv:
 arXiv:2107.06318
 Bibcode:
 2021PRXQ....2d0349P
 Keywords:

 Quantum Physics
 EPrint:
 7 pages + appendices, 3 figures