Improving cooling performance in an optomechanical system using a nonlinear cavity – Part 3*

Operating massive mechanical resonators in the quantum regime requires precise control over its mechanical modes. The state of the art approach is to couple a high quality micromechanical resonator to a photonic mode. In our setup, we couple a magnetic cantilever as our mechanical object to a magnetic field sensitive microwave cavity. The field tunable sensitivity is provided by an embedded SQUID, which also makes the cavity nonlinear. We show, that the theory including the nonlinearity of the cavity is in very good agreement with the measurement data and we demonstrate one order of magnitude improvement in the cooling. As suggested by the theory, we show experimentally that even cooling above the bistability of the microwave cavity is possible. Currently, the cooling capabilities in the experiment are mostly limited by flux noise, which can be included in the model leading to even better theoretical agreement in those limits.