  We uncover an unforeseen asymmetry in relaxation -- for a pair of
thermodynamically equidistant temperature quenches, one from a lower and the
other from a higher temperature, the relaxation at the ambient temperature is
faster in case of the former. We demonstrate this finding on hand of two
exactly solvable many-body systems relevant in the context of single-molecule
and tracer-particle dynamics. We prove that near stable minima and for all
quadratic energy landscapes it is a general phenomenon that also exists in a
class of non-Markovian observables probed in single-molecule and
particle-tracking experiments. The asymmetry is a general feature of reversible
overdamped diffusive systems with smooth single-well potentials and occurs in
multi-well landscapes when quenches disturb predominantly intra-well
equilibria. Our findings may be relevant for the optimization of stochastic
heat engines.
