  Since the the first studies of thermodynamics, heat transport has been a
crucial element for the understanding of any thermal system. Quantum mechanics
has introduced new appealing ingredients for the manipulation of heat currents,
such as the long-range coherence of the superconducting condensate. The latter
has been exploited by phase-coherent caloritronics, a young field of
nanoscience, to realize Josephson heat interferometers, which can control
electronic thermal currents as a function of the external magnetic flux. So
far, only one output temperature has been modulated, while multi-terminal
devices that allow to distribute the heat flux among different reservoirs are
still missing. Here, we report the experimental realization of a phase-tunable
thermal router able to control the heat transferred between two terminals
residing at different temperatures. Thanks to the Josephson effect, our
structure allows to regulate the thermal gradient between the output electrodes
until reaching its inversion. Together with interferometers, heat diodes and
thermal memories, the thermal router represents a fundamental step towards the
thermal conversion of non-linear electronic devices, and the realization of
caloritronic logic components.
