  We investigate coupled-qubit-based thermal machines powered by quantum
measurements and feedback. We consider two different versions of the machine:
1) a quantum Maxwell's demon where the coupled-qubit system is connected to a
detachable single shared bath, and 2) a measurement-assisted refrigerator where
the coupled-qubit system is in contant with a hot and cold bath. In the quantum
Maxwell's demon case we discuss both discrete and continuous measurements. We
find that the power output from a single qubit-based device can be improved by
coupling it to the second qubit. We further find that the simultaneous
measurement of both qubits can produce higher net heat extraction compared to
two setups operated in parallel where only single-qubit measurements are
performed. In the refrigerator case, we use continuous measurement and unitary
operations to power the coupled-qubit-based refrigerator. We find that the
cooling power of a refrigerator operated with swap operations can be enhanced
by performing suitable measurements.
