Insightful Approach to Quantum Noise Suppression Below the Standard Quantum Limit Using a Single Mirror and Beam Splitter

TL;DR

This paper demonstrates a method to reduce quantum noise below the standard quantum limit using a beam splitter and a mirror, with potential applications in quantum noise control.

Contribution

It introduces a novel setup with a mirror at the beam splitter's unused port to manipulate vacuum fluctuations and suppress quantum noise below the standard limit.

Findings

Vacuum fluctuations can be periodically reduced to zero at the beam splitter output.

Vacuum noise can be suppressed below the quantum limit using the proposed setup.

Feedback mechanisms enable further suppression of electromagnetic field fluctuations.

Abstract

When a coherent electromagnetic wave passes through a beam splitter (BS), it is divided equally into two parts. However, the quantum noise associated with the resulting coherent states, despite being reduced in amplitude by half, remains fundamentally constrained by the quantum noise limit, independent of the intensity. By placing a mirror at the unused input port of the BS, a standing wave is formed in the vicinity of the mirror, which influences the vacuum fluctuations of the coherent state at the BS output. Using semi-classical and quantum mechanical approaches, we calculate the vacuum fluctuations induced by the mirror and demonstrate that the vacuum noise originating from the mirror side periodically reaches zero at the BS output. Leveraging this effect, we show that the vacuum fluctuations of the light split by the BS can be readily reduced below the quantum noise limit. Furthermore, through feedback mechanisms, the vacuum fluctuations of the electromagnetic field at the other output port can also be suppressed below the quantum noise limit. These findings provide a pivotal insight into the manipulation of electromagnetic noise, with broad implications for all experiments involving quantum noise control.