  The Mpemba effect is a counter-intuitive phenomena in which a hot system
reaches a cold temperature faster than a colder system, under otherwise
identical conditions. Here we propose a quantum analog of the Mpemba effect, on
the simplest quantum system, a qubit. Specifically, we show it exhibits an
inverse effect, in which a cold qubit reaches a hot temperature faster than a
hot qubit. Furthermore, in our system a cold qubit can heat up exponentially
faster, manifesting the strong version of the effect. This occurs only for
sufficiently coherent systems, making this effect quantum mechanical, i.e. due
to interference effects. We experimentally demonstrate our findings on a single
$^{88}\text{Sr}^+$ trapped ion qubit. The existence of this anomalous
relaxation effect in simple quantum systems reveals its fundamentality, and may
have a role in designing and operating quantum information processing devices.
