Four-dimensional entanglement distribution over 100 km

TL;DR

This paper demonstrates the distribution of four-dimensional time-bin entanglement over 100 km of optical fiber, enabling higher information capacity for quantum communication.

Contribution

It presents the first long-distance distribution of four-dimensional entanglement using scalable measurement techniques with cascaded interferometers.

Findings

Achieved over 1 bit of secure information capacity over 100 km

Successfully implemented high-dimensional entanglement measurement

Advances secure quantum communication in large Hilbert spaces

Abstract

High-dimensional quantum entanglement can enrich the functionality of quantum information processing. For example, it can enhance the channel capacity for linear optic superdense coding and decrease the error rate threshold of quantum key distribution. Long-distance distribution of a high-dimensional entanglement is essential for such advanced quantum communications over a communications network. Here, we show a long-distance distribution of a four-dimensional entanglement. We employ time-bin entanglement, which is suitable for a fibre transmission, and implement scalable measurements for the high-dimensional entanglement using cascaded Mach-Zehnder interferometers. We observe that a pair of time-bin entangled photons has more than 1 bit of secure information capacity over 100 km. Our work constitutes an important step towards secure and dense quantum communications in a large Hilbert space.