Feedback-enhanced parametric squeezing of mechanical motion

TL;DR

This paper introduces a feedback scheme that surpasses the 3 dB squeezing limit in mechanical systems, demonstrated with a micromechanical cantilever, achieving over 11 dB of squeezing without quantum-limited detection.

Contribution

The authors develop and experimentally validate a feedback method that exceeds the traditional squeezing limit in mechanical resonators, enabling greater control over quantum noise.

Findings

Achieved 11.5 dB squeezing in a micromechanical cantilever

Demonstrated squeezing beyond the 3 dB limit using feedback

Squeezing limited only by maximum parametric modulation

Abstract

We present a single-quadrature feedback scheme able to overcome the conventional 3 dB limit on parametric squeezing. The method is experimentally demonstrated in a micromechanical system based on a cantilever with a magnetic tip. The cantilever is detected at low temperature by a SQUID susceptometer, while parametric pumping is obtained by modulating the magnetic field gradient at twice the cantilever frequency. A maximum squeezing of 11.5 dB and 11.3 dB is observed, respectively in the response to a sinusoidal test signal and in the thermomechanical noise. The maximum squeezing factor is limited only by the maximum achievable parametric modulation. The proposed technique can be used to squeeze one quadrature of a mechanical resonator below the quantum noise level, even without the need for a quantum limited detector.