Nonuniversality of quantum noise in optical amplifiers operating at exceptional points

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 EPOA structures that rely either on unidirectional coupling, parity-time symmetry, or particle-hole symmetry for implementing the exceptional point. 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.Received 19 April 2022Revised 18 August 2022Accepted 22 August 2022DOI:https://doi.org/10.1103/PhysRevResearch.4.033226Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasPhoton statisticsQuantum description of light-matter interactionQuantum fluctuations & noisePhysical SystemsDevicesNon-Hermitean systemsOptical microcavitiesWaveguidesTechniquesNonperturbative methodsQuantum InformationAtomic, Molecular & OpticalCondensed Matter, Materials & Applied Physics