  In miniaturising electrical devices down to nanoscales, heat transfer has
turned into a serious obstacle but also potential resource for future
developments, both for conventional and quantum computing architectures.
Controlling heat transport in superconducting circuits has thus received
increasing attention in engineering microwave environments for circuit quantum
electrodynamics (cQED) and circuit quantum thermodynamics experiments (cQTD).
While theoretical proposals for cQTD devices are numerous, the experimental
situation is much less advanced. There exist only relatively few experimental
realisations, mostly due to the difficulties in developing the hybrid devices
and in interfacing these often technologically contrasting components. Here we
show a realisation of a quantum heat rectifier, a thermal equivalent to the
electronic diode, utilising a superconducting transmon qubit coupled to two
strongly unequal resonators terminated by mesoscopic heat baths. Our work is
the experimental realisation of the spin-boson rectifier proposed by Segal and
Nitzan.
