Nonreciprocal Cavities and the Time-Bandwidth Limit

The time-bandwidth limit inherently relates the lifetime of a resonance and its spectral bandwidth, with direct implications for the maximum storage time of a pulse versus its frequency content. It has been recently argued that nonreciprocal cavities may overcome this constraint, by breaking the strict equality of their input and out-coupling coefficients. Here, we study the implications of nonreciprocity on resonant linear, time-invariant cavities and derive general relations, stemming from microscopic reversibility, that govern their dynamics. We show that nonreciprocal cavities do not provide specific advantages in terms of the time-bandwidth limit but enable other attractive properties for nanophotonic systems.