Sub-kelvin optical cooling of a micromechanical resonator

Abstract

Micromechanical resonators, when cooled down to near their ground state, can be used to explore quantum effects such as superposition and entanglement at a macroscopic scale1,2,3. Previously, it has been proposed to use electronic feedback to cool a high frequency (10 MHz) resonator to near its ground state4. In other work, a low frequency resonator was cooled from room temperature to 18 K by passive optical feedback5. Additionally, active optical feedback of atomic force microscope cantilevers has been used to modify their response characteristics6, and cooling to approximately 2 K has been measured7. Here we demonstrate active optical feedback cooling to 135 ± 15 mK of a micromechanical resonator integrated with a high-quality optical resonator. Additionally, we show that the scheme should be applicable at cryogenic base temperatures, allowing cooling to near the ground state that is required for quantum experiments—near 100 nK for a kHz oscillator.