Verification of conditional mechanical squeezing for a mg-scale pendulum near quantum regimes

TL;DR

This paper demonstrates conditional quantum squeezing of a milligram-scale pendulum near quantum regimes, showing potential for quantum control of massive objects and tests of quantum mechanics at macroscopic scales.

Contribution

It presents the first experimental verification of conditional squeezing in a mg-scale pendulum near quantum regimes using continuous measurement and quantum state prediction.

Findings

Achieved position and momentum standard deviations of 36 and 89 times the zero-point amplitudes.

Demonstrated squeezing level about 5 times closer to zero-point motion.

Showed potential for quantum control of massive objects and testing quantum mechanics.

Abstract

In quantum mechanics, measurement can be used to prepare a quantum state. This principle is applicable even for macroscopic objects, which may enable us to see classical-quantum transition. Here, we demonstrate conditional mechanical squeezing of a mg-scale suspended mirror (i.e. the center-of-mass mode of a pendulum) near quantum regimes, through continuous linear position measurement and quantum state prediction. The experiment involved the pendulum interacting with photon coherent fields in a detuned optical cavity, which creates an optical spring. Futhermore, the detuned cavity allows us to perform linear position measurement by direct photo-detection of the reflected light. We experimentally verify the conditional squeezing using the theory combining prediction and retrodiction based on the causal and anti-causal filters. As a result, the standard deviation of position and momentum are respectively given by 36 times the zero-point amplitude of position $q_{\rm zpf}$ and 89 times the zero-point amplitude of momentum $p_{\rm zpf}$. The squeezing level achieved is about 5 times closer to the zero-point motion, despite that the mass of the mechanical oscillator is approximately 7 orders of magnitude greater, compared to the previous study. Thus, our demonstration is the first step towards quantum control for massive objects whose mass-scale is high enough to measure gravitational interactions. Such quantum control will pave the way to test quantum mechanics using the center-of-mass mode of massive objects.