Photonic circuits for generating modal, spectral, and polarization entanglement

TL;DR

This paper designs photonic circuits using Ti:LiNbO3 waveguides to generate and control various forms of photon entanglement, including modal, spectral, and polarization, for quantum information applications.

Contribution

It introduces specific photonic circuit configurations capable of producing and manipulating multiple types of photon entanglement using integrated waveguide technology.

Findings

Circuits can generate frequency-degenerate and nondegenerate entangled photons.

Designs enable entanglement in frequency, polarization, and mode.

Conversion of entanglement types into path entanglement demonstrated.

Abstract

We consider the design of photonic circuits that make use of Ti:LiNbO$_{3}$ diffused channel waveguides for generating photons with various combinations of modal, spectral, and polarization entanglement. Down-converted photon pairs are generated via spontaneous optical parametric down-conversion (SPDC) in a two-mode waveguide. We study a class of photonic circuits comprising: 1) a nonlinear periodically poled two-mode waveguide structure, 2) a set of single-mode and two-mode waveguide-based couplers arranged in such a way that they suitably separate the three photons comprising the SPDC process, and, for some applications, 3) a holographic Bragg grating that acts as a dichroic reflector. The first circuit produces frequency-degenerate down-converted photons, each with even spatial parity, in two separate single-mode waveguides. Changing the parameters of the elements allows this same circuit to produce two nondegenerate down-converted photons that are entangled in frequency or simultaneously entangled in frequency and polarization. The second photonic circuit is designed to produce modal entanglement by distinguishing the photons on the basis of their frequencies. A modified version of this circuit can be used to generate photons that are doubly entangled in mode number and polarization. The third photonic circuit is designed to manage dispersion by converting modal, spectral, and polarization entanglement into path entanglement.