Cooling of mechanical mode at room temperature through frequency modulation

  We report a new cooling method of thermal modes of a nano-electromechanical system (NEMS). This technique doesn't require a cavity mode, neither condition like resolved sideband. We modulate frequency of mechanical mode of a low mass single layer graphene oscillator with a widely red detuned pump. The number of thermal phonons from that particular mode decreases with increasing modulation strength. Unlike other cooling methods, cooling rate also increases non-linearly as the number of phonons decreases. Amplitude of the thermal peak goes down following the 0th  order Bessel's function of the first kind.  Using this technique, we have reached from room temperature (300 K) to 54 K where thermal peak hits the noise floor of the detected spectrum. Our experiment is limited by thermal noise floor but predicts that at low temperature below single phonon limit can be reached easily. It is not limited to low mass oscillators. We also show that hybrid modes of graphene (low mass) and Silicon nitride (high mass) can be cooled following the same technique.