  We present a theoretical proposal for a microwave driven circuit composed of
superconducting resonators and qubits which shows a bistable behaviour, and we
present a simple mechanism that allows single- or few-photon microwave pulses
to work as Set- and Reset-signals that switch the circuit between its stable
modes. The resulting system constitutes an ultra-low-energy Set-Reset
flip-flop, and we show that its memory lifetime far exceeds the lifetime of
states stored in any of its separate components.
