Curator's Take
This article demonstrates a crucial step toward practical quantum networks by successfully distributing high-quality entangled photons through real metropolitan fiber infrastructure in Vienna. The researchers achieved an impressive 93% quantum visibility over 30 kilometers of existing fiber, using time-bin encoding that cleverly sidesteps the polarization drift issues that plague long-distance quantum communication. What makes this particularly significant is their use of off-the-shelf components operating at GHz frequencies, suggesting this approach could be scaled and deployed in existing telecommunications infrastructure. This work bridges the gap between laboratory quantum communication experiments and the real-world quantum internet, where distributed entanglement will be essential for connecting quantum computers and enabling ultra-secure communications across cities.
— Mark Eatherly
Summary
Efficient generation and high-quality distribution of entanglement is becoming increasingly more relevant in the field of quantum technologies, with important applications such as multiparty computation as well as quantum key distribution (QKD) on the rise. Quantum communication protocols based on entanglement offer an inherent quantum based randomness for key generation and provide in general higher security compared to prepare and measure implementations. Moreover, the future quantum internet will also be based on the distribution of entanglement for securely connecting quantum computers in a network. In this work we show the feasibility of using sequential time-bin entangled states for quantum key distribution in metropolitan networks using off-the-shelf components. The time-bin encoding ensures high fidelity distribution robust against random polarisation fluctuations occuring in optical fibers. Modulated laser pulses in the GHz frequency range are used to generate time-bin entangled photon pairs. The entangled photons are then sent over an about 30km long (9.5dB loss) fiber link within the Vienna fiber network, showing high degree of distributed entanglement with a measured 93\% quantum visibility.