Reduction of quantum noise in optical interferometers using squeezed light

TL;DR

This paper investigates how injecting squeezed vacuum states into optical interferometers can reduce quantum noise in photon counting, especially in the dark port configuration, without amplifying the signal, thus improving gravitational wave detection sensitivity.

Contribution

It demonstrates that squeezed vacuum injection reduces photon counting noise in dark port interferometers without amplifying the signal, clarifying the limits of quantum noise reduction techniques.

Findings

Photon counting noise decreases with higher squeezing factors.

Signal strength remains dependent solely on laser beam intensity.

No signal amplification occurs despite noise reduction.

Abstract

We study the photon counting noise in optical interferometers used for gravitational wave detection. In order to reduce quantum noise a squeezed vacuum state is injected into the usually unused input port. Here, we specifically investigate the so called `dark port case', when the beam splitter is oriented close to 90{\deg} to the incoming laser beam, such that nearly all photons go to one output port of the interferometer, and only a small fraction of photons is seen in the other port (`dark port'). For this case it had been suggested that signal amplification is possible without concurrent noise amplification [R.Barak and Y.Ben-Aryeh, J.Opt.Soc.Am.B25(361)2008]. We show that by injection of a squeezed vacuum state into the second input port, counting noise is reduced for large values of the squeezing factor, however the signal is not amplified. Signal strength only depends on the intensity of the laser beam.