Interferometer readout-noise below the Standard Quantum Limit of a membrane

TL;DR

This paper demonstrates a Michelson-Sagnac interferometer achieving readout noise below the Standard Quantum Limit for membrane motion detection, surpassing previous nano-wire experiments and advancing quantum measurement techniques.

Contribution

The work presents a cavity-free interferometer with readout noise 16 dB below the SQL, enabling more precise membrane motion measurements than prior methods.

Findings

Readout noise spectral density of 3E-16 m/√Hz at 100 kHz

Readout noise exceeds 16 dB below the membrane's SQL

Neither current nor previous experiments reach the total noise spectral density of the SQL

Abstract

Here we report on the realization of a Michelson-Sagnac interferometer whose purpose is the precise characterization of the motion of membranes showing significant light transmission. Our interferometer has a readout noise spectral density (imprecision) of 3E-16 m/sqrt(Hz) at frequencies around the fundamental resonance of a SiN_x membrane at about 100 kHz, without using optical cavities. The readout noise demonstrated is more than 16 dB below the peak value of the membrane's standard quantum limit (SQL). This reduction is significantly higher than those of previous works with nano-wires [Teufel et al., Nature Nano. 4, 820 (2009); Anetsberger et al., Nature Phys. 5, 909 (2009)]. We discuss the meaning of the SQL for force measurements and its relation to the readout performance and conclude that neither our nor previous experiments achieved a total noise spectral density as low as the SQL.