Polarization engineering in photonic crystal waveguides for spin-photon entanglers

TL;DR

This paper analyzes how phase influences light-matter interaction in photonic crystal waveguides, enabling unidirectional emission and entangled photon sources, with implications for quantum devices and fundamental physics.

Contribution

It reveals the critical role of phase in symmetry and directionality of light-matter interactions in photonic crystal waveguides with quantum dots, introducing new control mechanisms.

Findings

Phase affects symmetry of light-matter interaction.

Unidirectional emission and entanglement are achievable.

Quantum entanglement can reverse photon propagation.

Abstract

By performing a full analysis of the projected local density of states (LDOS) in a photonic crystal waveguide, we show that phase plays a crucial role in the symmetry of the light-matter interaction. By considering a quantum dot (QD) spin coupled to a photonic crystal waveguide (PCW) mode, we demonstrate that the light-matter interaction can be asymmetric, leading to unidirectional emission and a deterministic entangled photon source. Further we show that understanding the phase associated with both the LDOS and the QD spin is essential for a range of devices that that can be realised with a QD in a PCW. We also show how quantum entanglement can completely reverse photon propagation direction, and highlight a fundamental breakdown of the semiclassical dipole approximation for describing light-matter interactions in these spin dependent systems.