Graphene as a source of entangled plasmons

TL;DR

This paper explores nonlinear optical processes in graphene to generate entangled plasmon pairs with higher efficiency than traditional sources, proposing experimental setups and analyzing stability conditions.

Contribution

It introduces novel schemes for entangled plasmon pair generation in graphene using second- and third-order nonlinearities, including practical experimental suggestions.

Findings

High plasmonic field concentration enhances pair-generation rates.

Spontaneous parametric down conversion enabled by dc electric fields.

Degenerate four-wave mixing can produce entangled plasmons without symmetry breaking.

Abstract

We analyze nonlinear optics schemes for generating pairs of quantum entangled plasmons in the terahertz-infrared range in graphene. We predict that high plasmonic field concentration and strong optical nonlinearity of monolayer graphene enables pair-generation rates much higher than those of conventional photonic sources. The first scheme we study is spontaneous parametric down conversion in a graphene nanoribbon. In this second-order nonlinear process a plasmon excited by an external pump splits into a pair of plasmons, of half the original frequency each, emitted in opposite directions. The conversion is activated by applying a dc electric field that induces a density gradient or a current across the ribbon. Another scheme is degenerate four-wave mixing where the counter-propagating plasmons are emitted at the pump frequency. This third-order nonlinear process does not require a symmetry-breaking dc field. We suggest nano-optical experiments for measuring position-momentum entanglement of the emitted plasmon pairs. We estimate the critical pump fields at which the plasmon generation rates exceed their dissipation, leading to parametric instabilities.