Coalescence and anti-coalescence of surface plasmons on a lossy beamsplitter

TL;DR

This paper demonstrates quantum interference of surface plasmons on lossy beamsplitters, showing how losses can be exploited to control plasmon coalescence and anti-coalescence, advancing plasmonic quantum optics.

Contribution

It reports the first observation of two-plasmon interference on lossy beamsplitters, utilizing loss-induced phase control to observe coalescence and anti-coalescence effects.

Findings

Observed coalescence and anti-coalescence of plasmons

Losses enable control of interference phase

Demonstrated quantum interference with non-guided plasmons

Abstract

Surface plasma waves are collective oscillations of electrons that propagate along a metal-dielectric interface. In the last ten years, several groups have reproduced fundamental quantum optics experiments with surface plasmons. Observation of single-plasmon states, waveparticle duality, preservation of entanglement of photons in plasmon-assisted transmission, and more recently, two-plasmon interference have been reported. While losses are detrimental for the observation of squeezed states, they can be seen as a new degree of freedom in the design of plasmonic devices, thus revealing new quantum interference scenarios. Here we report the observation of two-plasmon quantum interference between two freely-propagating, non-guided SPPs interfering on lossy plasmonic beamsplitters. As discussed in the article "Quantum optics of lossy beam splitters" by Barnett et al. (Phys. Rev. A 57, 2134 (1998)) , the presence of losses (scattering or absorption) relaxes constraints on the reflection and transmission factors of the beamsplitter, allowing the control of their relative phase. By using this degree of freedom, we are able to observe either coalescence or anticoalescence of identical plasmons.