Generation of a squeezed state of an oscillator by stroboscopic back-action-evading measurement

TL;DR

This paper demonstrates the generation of a quadrature-squeezed state of an atomic ensemble oscillator through stroboscopic back-action-evading measurement, achieving noise reduction below the quantum zero-point level, advancing quantum sensing capabilities.

Contribution

The study experimentally realizes stroboscopic back-action-evading measurement to produce a squeezed state in an atomic ensemble oscillator, surpassing the standard quantum limit.

Findings

Achieved 2.2 dB noise reduction below zero-point fluctuations.

Prepared the atomic ensemble in a near-ground state with low thermal occupancy.

Demonstrated potential for enhanced quantum sensing applications.

Abstract

Continuous observation on an oscillator is known to result in quantum back-action which limits the knowledge acquired by the measurement. A careful balance between the information obtained and the back-action disturbance leads to a limit known as the standard quantum limit. The means to surpass this limit by modulating the measurement strength with the period proportional to half period of the oscillation has been proposed decades ago (Braginskii et al 1978 JETP Lett. 27 276; Thorne et al 1978 Phys. Rev. Lett. 40 667; Braginskii et al 1980 Science 209 547). Such modulated or stroboscopic observation leading to a squeezed state of one quadrature of the oscillator motion with the quantum noise below that of the zero-point fluctuations has been a long-standing goal. Here, we report on the generation of a quadrature-squeezed state of an oscillator by stroboscopic back-action evading measurement. The oscillator is the collective spin of an atomic ensemble precessing in magnetic field. It is initially prepared in nearly the ground state with an average thermal occupancy number $0.08 \pm 0.01$. The oscillator is coupled to the optical mode of a cavity, and the cavity output field detected with polarization homodyning serves as the meter. A back-action-evading measurement is performed by stroboscopically modulating the intensity of the light field at twice the Larmor frequency, resulting in a squeezed state conditioned on the light-polarization measurement with $2.2 \pm 0.3$ dB noise reduction below the zero-point fluctuations for the measured quadrature. The demonstrated squeezing holds promise for metrological advantage in quantum sensing.