Diverging quantum speed limits: a herald of classicality

When is the quantum speed limit (QSL) really quantum?. Typically, a vanishing QSL time is an indicator of an emergent classicality. However, it is still not entirely understood what precise aspects of classicality lead to diverging quantum speeds. Here, we show that vanishing QSL times (or, equivalently, diverging quantum speeds) can be traced back to reduced uncertainty in quantum observables. We illustrate this mechanism by developing a QSL formalism for continuous variable 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. Finally, by studying the dynamics of open quantum systems and mixed states, we show that the addition of classical noise typically increases the QSL time.