Non-universality of quantum noise in optical amplifiers operating at exceptional points

TL;DR

This paper investigates the quantum noise characteristics of exceptional points-based optical amplifiers (EPOAs), revealing that their quantum noise performance varies significantly across different implementations and does not follow a universal pattern.

Contribution

It provides the first quantum noise analysis of various EPOA structures, highlighting their non-universal noise behavior and comparing them with traditional quantum-limited amplifiers.

Findings

Quantum noise varies across EPOA implementations.

Some EPOAs have noise comparable to traditional amplifiers.

Quantum noise does not follow a universal scaling law.

Abstract

The concept of exceptional points-based optical amplifiers (EPOAs) has been recently proposed as a new paradigm for miniaturizing optical amplifiers while simultaneously enhancing their gain-bandwidth product. While the operation of this new family of amplifiers in the classical domain provides a clear advantage, their performance in the quantum domain has not yet been evaluated. Particularly, it is not clear how the quantum noise introduced by vacuum fluctuations will affect their operation. Here, we investigate this problem by considering three archetypal EPOAs structures that rely either on unidirectional coupling, parity-time (PT) symmetry, or particle-hole symmetry for implementing the exceptional point (EP). By using the Heisenberg-Langevin formalism, we calculate the added quantum noise in each of these devices and compare it with that of a quantum-limited amplifier scheme that does not involve any exceptional points. Our analysis reveals several interesting results: most notably that while the quantum noise of certain EPOAs can be comparable to those associated with conventional amplifier systems, in general the noise does not follow a universal scaling as a function of the exceptional point but rather varies from one implementation to another.