Modal, Spectral, and Polarization Entanglement in Guided-Wave Parametric Down-Conversion

TL;DR

This paper investigates how photon pairs generated in nonlinear waveguides exhibit entanglement across modal, spectral, and polarization degrees of freedom, offering new ways to generate and control entangled states for quantum applications.

Contribution

It introduces methods to generate and distinguish entanglement in modal, spectral, and polarization degrees of freedom in waveguide-based parametric down-conversion, highlighting new entanglement configurations.

Findings

Modal, spectral, and polarization entanglement can be controlled via mode number, frequency, or polarization.

Efficient spectral or polarization entanglement can be generated by mode-based photon distinction.

Modal entanglement can serve as an alternative to polarization entanglement, especially in Type-0 processes.

Abstract

We examine the modal, spectral, and polarization entanglement properties of photon pairs generated in a nonlinear, periodically poled, two-mode waveguide (1-D planar or 2-D circular) via nondegenerate spontaneous parametric down-conversion. Any of the possible degrees of freedom -- mode number, frequency, or polarization -- can be used to distinguish the down-converted photons while the others serve as attributes of entanglement. Distinguishing the down-converted photons based on their mode numbers enables us to efficiently generate spectral or polarization entanglement that is either narrowband or broadband. On the other hand, when the generated photons are distinguished by their frequencies in a Type-0 process, modal entanglement turns out to be an efficient alternative to polarization entanglement. Moreover, modal entanglement in Type-II down-conversion may be used to generate a doubly entangled state in frequency and polarization.