A mechanical degenerate parametric amplifier has been devised which greatly increases the motional response of a microcantilever for small harmonic force excitations. The amplifier can improve force detection sensitivity for measurements dominated by sensor noise or backaction effects and can also produce mechanical squeezed states. In an initial squeezing demonstration, the thermal noise (Brownian motion) of the cantilever was reduced in one phase by 4.9 dB.

/pdf/mechanical-parametric-amplification-and-thermomechanical-21lz91afqb.pdf

Mechanical parametric amplification and thermomechanical noise squeezing.

Significant advances in the field of sensors and the need for improving the resolution in the measurement of physical, chemical and biological quantities, are increasing the importance of the characterization of the noise sources in sensors. The noise in fact limits the ultimate performances that can be obtained from a given device in terms of signal to noise ratio. After a brief review of the fundamental noise sources, particular attention is dedicated to some examples of specific sensors for which noise aspects are presented and discussed. Noise considerations will concern temperature, gas, displacement, weak force and photon sensors.

Noise in sensors

We review a scheme for performing a backaction-evading measurement of one mechanical quadrature in an optomechanical setup. The experimental application of this scheme has been limited by parametric instabilities caused in general by a slight dependence of the mechanical frequency on the electromagnetic energy in the cavity. We find that a simple modification to the optical drive can effectively eliminate the parametric instability even at high intracavity power, allowing realistic devices to achieve sub-zero-point uncertainties in the measured quadrature.

/pdf/optomechanical-backaction-evading-measurement-without-1n1kz4eoor.pdf

Optomechanical backaction-evading measurement without parametric instability

The basic principles of electromechanical transduction are reviewed with an emphasis on applications relevant to gravitational-wave detectors. In any apparatus where feeble forces are measured, certain fundamental limits are imposed by the quantum nature of the measurement. After filtering out all sources of noise whose origins are external to the apparatus, the noise sources that remain are intrinsic to the measurement itself. The origin of three major noise sources are identified. These are: (i) Brownian noise due to the energy exchange with the surrounding thermal reservoir, (ii) the noise injected into the apparatus by the amplifier, and (iii) the noise of the amplifier itself. It is shown how the contribution of these noise sources are affected in the transduction mechanism. A general strategy is suggested where a parametric transducer strongly coupled to a gravity-wave antenna reduces the back-action of noisy amplifiers to negligible amounts. A strong electromechanical coupling and the attendant increase in the bandwidth facilitates rapid energy transfer between antenna and transducer. As a result, with a sufficiently low dissipative antenna, the remaining Brownian noise can be reduced by using short sampling intervals. This strategy is illustrated using, as an example, a tunnelling transducer. Along with other technological improvements, quite possibly a similar strategy may be necessary to lower the sensitivity of future Weber-type gravity-wave detectors.

Fundamental noise, electromechanical transduction and their role in resonant gravitational-wave detectors

Generalized back-action evasion schemes for the detection of weak classical forces.

A technique is proposed to improve the squeezing of the mechanical noise in a back-action evasion measurement. The scheme is based on the use of a parametric multipump system and, in the limit of many pump components, approaches a stroboscopic measurement. A simple model of the back-action evasion effect for this scheme is developed. Experimental evidence of a significant increase in the squeezing with respect to the two-pump scheme and in accordance with the model is reported.

Multisqueezing of mechanical states and back-action evasion measurements.

Multisqueezing of mechanical states and back-action evasion measurements

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Generalized back-action evasion schemes for the detection of weak classical forces.

Multisqueezing of mechanical states and back-action evasion measurements.

Multisqueezing of mechanical states and back-action evasion measurements