Spatial multimode entanglement within one laser beam

TL;DR

This paper demonstrates the generation and measurement of entanglement between different spatial modes within a single laser beam, simplifying quantum communication setups by avoiding multiple sources and complex optical components.

Contribution

It introduces a novel method to create and detect spatial multimode entanglement within one beam using lenses, beam rotation, and a multi-pixel detector, reducing system complexity.

Findings

Entanglement achieved between orthogonal spatial modes within one beam.

Single source produces squeezed light in two modes.

Quantum correlations measured directly with a multi-pixel detector.

Abstract

Optical entanglement is a key requirement for many quantum communication protocols. Conventionally entanglement is formed between two distinct beams, with the quantum correlations being measured at separate locations. We show entanglement between the modes within one beam. Our technique is particularly elegant and a major advance towards practical systems with minimum complexity. We demonstrate three major experimental achievements: (i) only one source is required to produce squeezed light in two orthogonal spatial modes, (ii) the entanglement is formed through lenses and beam rotation, without the need of a beam splitter and (iii) the quantum correlations are measured directly and simultaneously using a multi pixel, quadrant detector.