Antibunching and unconventional photon blockade with Gaussian squeezed states

TL;DR

This paper investigates photon antibunching phenomena in Gaussian states, clarifies the significance of intensity correlations, and demonstrates that unconventional photon blockade can be understood as optimized Gaussian squeezing.

Contribution

It derives a criterion to distinguish non-Gaussian fields from Gaussian ones based on $g^{(2)}(0)$ measurements and links unconventional photon blockade to Gaussian amplitude squeezing.

Findings

Gaussian antibunching with a degenerate parametric amplifier approaches ideal squeezing.

Unconventional photon blockade is a form of optimized Gaussian amplitude squeezing.

Abstract

Photon antibunching is a quantum phenomenon typically observed in strongly nonlinear systems where photon blockade suppresses the probability for detecting two photons at the same time. Antibunching has also been reported with Gaussian states, where optimized amplitude squeezing yields classically forbidden values of the intensity correlation, $g^{(2)}(0)<1$. As a consequence, observing antibunching is not necessarily a signature of photon-photon interactions. To clarify the significance of the intensity correlations, we derive a sufficient condition for deducing if a field is non-Gaussian based on a $g^{(2)}(0)$ measurement. We then show that the Gaussian antibunching obtained with a degenerate parametric amplifier is close to the ideal case reached using dissipative squeezing protocols. We finally shed light on the so-called unconventional photon blockade effect predicted in a driven two-cavity setup with surprisingly weak Kerr nonlinearities, stressing that it is a particular realization of optimized Gaussian amplitude squeezing.