Optical vortex knots - one photon at a time

TL;DR

This paper demonstrates the particle-wave duality of a three-dimensional optical field by generating a trefoil vortex knot with single photons, extending quantum interference principles to complex topological light structures.

Contribution

It is the first to show particle-wave duality in complex 3D optical fields formed by multi-path interference using single photons.

Findings

Particle-wave duality applies to 3D optical fields.

Interference occurs in space and time for complex modes.

Implications for quantum computing and topological states.

Abstract

Feynman described the double slit experiment as "a phenomenon which is impossible, absolutely impossible, to explain in any classical way and which has in it the heart of quantum mechanics". The double slit experiment, performed one photon at a time, dramatically demonstrates the particle-wave duality of quantum objects by generating a fringe pattern corresponding to the interference of light (a wave phenomenon) from two slits, even when there is only one photon (a particle) at a time passing through the apparatus. The particle-wave duality of light should also apply to complex three dimensional optical fields formed by multi-path interference, however, this has not been demonstrated. Here we observe particle-wave duality of a three dimensional field by generating a trefoil optical vortex knot - one photon at a time. This result demonstrates a fundamental physical principle, that particle-wave duality implies interference in both space (between spatially distinct modes) and time (through the complex evolution of the superposition of modes), and has implications for topologically entangled single photon states, orbital angular momentum multiplexing and topological quantum computing.