  The first thermal machines steered the industrial revolution, but their
quantum analogs have yet to prove useful. Here, we demonstrate a useful quantum
absorption refrigerator formed from superconducting circuits. We use it to
reset a transmon qubit to a temperature lower than that achievable with any one
available bath. The process is driven by a thermal gradient and is autonomous
-- requires no external control. The refrigerator exploits an engineered
three-body interaction between the target qubit and two auxiliary qudits
coupled to thermal environments. The environments consist of microwave
waveguides populated with synthesized thermal photons. The target qubit, if
initially fully excited, reaches a steady-state excited-level population of
$5\times10^{-4} \pm 5\times10^{-4}$ (an effective temperature of 23.5~mK) in
about 1.6~$\mu$s. Our results epitomize how quantum thermal machines can be
leveraged for quantum information-processing tasks. They also initiate a path
toward experimental studies of quantum thermodynamics with superconducting
circuits coupled to propagating thermal microwave fields.
