Twisted photon entanglement through turbulent air across Vienna

TL;DR

This study demonstrates the successful distribution of quantum entanglement using twisted photons with orbital angular momentum over a 3-kilometer turbulent urban air link, enabling multiple quantum channels for advanced communication.

Contribution

It is the first to confirm entanglement of higher-order OAM states over a turbulent intra-city link, expanding the potential for high-capacity quantum communication.

Findings

Entanglement confirmed for OAM states ±1 and ±2.

Up to 11 quantum channels accessible via OAM.

Turbulence effects are manageable with current technology.

Abstract

Photons with a twisted phase front can carry a discrete, in principle unbounded amount of orbital angular momentum (OAM). The large state space allows for complex types of entanglement, interesting both for quantum communication and for fundamental tests of quantum theory. However, the distribution of such entangled states over large distances was thought to be infeasible due to influence of atmospheric turbulence, indicating a serious limitation on their usefulness. Here we show that it is possible to distribute quantum entanglement encoded in OAM over a turbulent intra-city link of 3 kilometers. We confirm quantum entanglement of the first two higher-order levels (with OAM=$\pm 1 \hbar$ and $\pm 2 \hbar$). They correspond to four new quantum channels orthogonal to all that have been used in long-distance quantum experiments so far. Therefore a promising application would be quantum communication with a large alphabet. We also demonstrate that our link allows access to up to 11 quantum channels of OAM. The restrictive factors towards higher numbers are technical limitations that can be circumvented with readily available technologies.