Strongly quadrature-dependent noise in superconducting microresonators measured at the vacuum-noise limit

We measure frequency- and dissipation-quadrature noise in superconducting microresonators with sensitivity near the vacuum noise level using a Josephson parametric amplifier. At an excitation power of 100 nW, frequency noise rises orders of magnitude above the vacuum noise, but no excess dissipation-quadrature noise is observed above the vacuum noise level. Our results suggest that using quantum amplifiers in dissipation measurement may greatly improve the sensitivity of microresonator readout, which has important implications for applications such as detectors, qubits, and nanomechanical oscillators. (c) 2011 American Institute of Physics. [doi:10.1063/1.3597156]