Quantum vortices of strongly interacting photons

TL;DR

This paper demonstrates the creation of quantum vortices through strong photon-photon interactions in a nonlinear optical medium, revealing complex multi-photon topological structures with potential quantum computing applications.

Contribution

It reports the first experimental realization of quantum vortices resulting from strong photon-photon interactions, including vortex-antivortex pairs and vortex lines in multi-photon states.

Findings

Quantum vortices observed in two-photon wavefunctions.

Formation of vortex lines and rings in three-photon states.

Conditional phase shift of π per photon enabling quantum logic.

Abstract

Vortices are a hallmark of topologically nontrivial dynamics in nonlinear physics and arise in a huge variety of systems, from space and atmosphere to condensed matter and quantum gases. In optics, vortices manifest as phase twists of the electromagnetic field, commonly formed by the interaction of light and matter. Formation of vortices by effective interaction of light with itself requires strong optical nonlinearity and has therefore been confined, until now, to the classical regime. Here we report on the realization of quantum vortices resulting from a strong photon-photon interaction in a quantum nonlinear optical medium. The interaction causes faster phase accumulation for co-propagating photons. Similarly to a plate pushing water, the local phase accumulation produces a quantum vortex-antivortex pair within the two-photon wavefunction. For three photons, the formation of vortex lines and a central vortex ring attests to a genuine three-photon interaction. The wavefunction topology, governed by two- and three-photon bound states, imposes a conditional phase shift of $\pi$-per-photon, a potential resource for deterministic quantum logic operations.