  We report anomalous heating in a colloidal system, the first observation of
the inverse Mpemba effect, where an initially cold system heats up faster than
an identical warm system coupled to the same thermal bath. For an overdamped,
Brownian colloidal particle moving in a tilted double-well potential, we find a
non-monotonic dependence of the heating times on the initial temperature of the
system, as predicted by an eigenfunction expansion of the associated
Fokker-Planck equation. By carefully tuning parameters, we also observe a
"strong" version of anomalous heating, where a cold system heats up
exponentially faster than systems prepared under slightly different conditions
