Minimum resources for versatile continuous variable entanglement in integrated nonlinear waveguides

TL;DR

This paper demonstrates a resource-optimized integrated nonlinear waveguide device that generates versatile continuous-variable entanglement of bright and vacuum modes using second harmonic generation, without harmonic ancillas.

Contribution

It introduces a novel scheme exploiting second harmonic generation in coupled waveguides to produce entanglement efficiently without additional harmonic ancillas.

Findings

Efficient generation of bipartite and quadripartite entanglement.

Entanglement of bright and vacuum modes depending on propagation distance.

Device is simple, resource-efficient, and compatible with current technology.

Abstract

In a recent paper [Phys. Rev. A {\bf 96}, 053822 (2017)], we proposed a strategy to generate bipartite and quadripartite continuous-variable entanglement of bright quantum states based on degenerate down-conversion in a pair of evanescently coupled nonlinear $\chi^{(2)}$ waveguides. Here, we show that the resources needed for obtaining these features can be optimized by exploiting the regime of second harmonic generation: the combination of depletion and coupling among pump beams indeed supplies all necessary wavelengths and appropriate phase mismatch along propagation. Our device thus entangles the two fundamental classical input fields without the participation of any harmonic ancilla. Depending on the propagation distance, the generated harmonics are entangled in bright or vacuum modes. We also evidence two-color bipartite and quadripartite entanglement over the interacting modes. The proposed device represents a boost in continuous-variable integrated quantum optics since it enables a broad range of quantum effects in a very simple scheme, which optimizes the resources and can be easily realized with current technology.