Detecting high-dimensional time-bin entanglement in fiber-loop systems

TL;DR

This paper presents a method to certify high-dimensional time-bin entanglement in fiber-loop systems, enhancing quantum communication robustness and capacity without physical modifications to the setup.

Contribution

It introduces a certification technique using only two measurement bases, applicable to both two- and multiphoton states, adaptable to existing fiber-loop systems.

Findings

Method is robust against experimental noise.

Works effectively with limited measurement data.

Enables high-dimensional entanglement certification in fiber systems.

Abstract

Many quantum communication protocols rely on the distribution of entanglement between the different participating parties. One example is quantum key distribution (QKD), an application that has matured to commercial use in recent years. However, difficulties remain, especially with noise resilience and channel capacity in long-distance communication. One way to overcome these problems is to use high-dimensional entanglement, which has been shown to be more robust to noise and enables higher secret-key rates. It is therefore important to have access to certifiable high-dimensional entanglement sources to confidently implement these advanced QKD protocols. Here, we develop a method for certifying high-dimensional time-bin entanglement in fiber-loop systems. In these systems, entanglement creation and detection can utilize the same physical components, and the number of time bins, and thus the entanglement dimension, can be adapted without making physical changes to the setup. Our certification method builds on previous proposals for the certification of angular-momentum entanglement in photon pairs. In particular, measurements in only two experimentally accessible bases are sufficient to obtain a lower bound on the entanglement dimension for both two- and multiphoton quantum states. Numerical simulations show that the method is robust against typical experimental noise effects and works well even with limited measurement statistics, thus establishing time-bin encoded photons as a promising platform for high-dimensional quantum-communication protocols.