  Quantum heat transport devices are currently intensively studied in theory.
Experimental realization of quantum heat transport devices is a challenging
task. So far, they have been mostly investigated in experiments with ultra-cold
atoms and single atomic traps. Experiments with superconducting qubits have
also been carried out and heat transport and heat rectification has been
studied in two terminal devices. The structures with three independent
terminals offer additional opportunities for realization of heat transistors,
heat switches, on-chip masers and even more complicated devices. Here we report
an experimental realization of a three-terminal photonic heat transport device
based on a superconducting quantum circuit. Its central element is a flux qubit
made of a superconducting loop containing three Josephson junctions, which is
connected to three resonators terminated by resistors. By heating one of the
resistors and monitoring the temperatures of the other two, we determine
photonic heat currents in the system and demonstrate their tunability by
magnetic field at the level of 1 aW. We determine system parameters by
performing microwave transmission measurements on a separate nominally
identical sample and, in this way, demonstrate clear correlation between the
level splitting of the qubit and the heat currents flowing through it. Our
experiment is an important step in the development of on-chip quantum heat
transport devices. On the one hand, such devices are of great interest for
fundamental science because they allow one to investigate the effect of quantum
interference and entanglement on the transport of heat. On the other hand, they
also have great practical importance for the rapidly developing field of
quantum computing, in which management of heat generated by qubits is a
problem.
