Steady-State Microwave Mode Cooling with a Diamond N- V Ensemble

All electronics are subject to thermal noise, which sets a minimum power to distinguish a signal from ambient background. Here quantum systems---in particular the nitrogen-vacancy center in diamond---show a path forward, as they can be laser-cooled to a quantum mechanical ground state while a device remains at ambient conditions. By placing an ensemble of N-$V$ centers inside a low-loss microwave cavity in which their spins strongly interact with gigahertz magnetic fields, the cold spins extract more energy than can leak in from the hot environment. The output voltage shows vastly reduced fluctuations at the cavity frequency; the effective temperature is lowered by 150 K.