Optical Stability in Quantum Networks

Matthew E. Grein, Mark L. Stevens, Nicholas D. Hardy +1 more

We implemented an active feedback scheme to stabilize an ∼84 km deployed optical fiber between Lincoln Laboratory and MIT Campus. The residual fluctuations of less than 193 attoseconds RMS enable quantum networking and quantum secure communications.

Päivi Törmä, Stig Stenholm, Igor Jex

Ian R. Petersen

Arian Stolk, J.J.B. Biemond, Kian L. van der Enden +3 more

Entanglement generation between remote qubit systems is the central tasks for quantum communication. Future quantum networks will have to be compatible with low-loss telecom bands and operate with large separation between qubit nodes. Single-click heralding schemes can be used to increase entanglement rates at the cost of needing an optically phase-synchronized architecture. In this paper we present such a phase synchronization scheme for a metropolitan quantum network, operating in the low-loss telecom L band. To overcome various challenges such as communication delays and optical power limitations, the scheme consists of multiple tasks that are individually stabilized. We characterize each task, identify the main noise sources, motivate the design choices, and describe the synchronization schemes. The performance of each of the tasks is quantified by a transfer-function measurement that investigates the frequency response and feedback bandwidth. Finally we investigate the resulting optical phase stability of the fully deployed system over a continuous period of 10 h, reporting a short-term stability standard deviation of σ ≈ 30 ∘ and a long-term stability of the average optical phase to within a few degrees. The scheme presented served as a key enabling technology for a nitrogen-vacancy-center-based metropolitan quantum link. This scheme is of interest for other quantum network platforms that benefit from an extendable and telecom-compatible phase-synchronization solution.

Nicholas V. Nardelli, Dileep V. Reddy, Michael B. Grayson +5 more

We demonstrate the distribution of single-photon-level pulses from a mode-locked laser source over a phase-stable fiber link, achieving an optical timing jitter of less than 100 as over 10 minutes of data accumulation. This stability enables a fidelity greater than 0.998 between two stabilized 2.1 km long deployed fiber links. Building on time and frequency metrology techniques traditionally used for high-stability optical atomic clock signal distribution, we use time and frequency multiplexing to achieve an isolation of quantum and classical channels of 8×10 10 . Our results mark a necessary step towards scalable, high-rate quantum networks with a provable quantum advantage.

J. I. CIRAC S. J. VAN ENK