  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.

Optics