FPGA-Based Adaptive Phase Control Reduces Noise by 30% and Stabilizes Fiber-Optic Interferometers for 600 Seconds

Phase noise represents a significant challenge to stable operation in long-distance fibre optic communication systems, particularly those employing time-bin encoded photons for robust data transmission. Researchers led by P. M. Berto, F. Campodónico, and A. A. Matoso, alongside colleagues S. Vergara, P. A. Coelho, and G. Lima, now demonstrate a fully digital solution to this problem, utilising an adaptive control system implemented on a field-programmable gate array. The team’s method actively stabilises the phase of correlated photons by responding to fluctuations in real time, achieving a substantial 70% reduction in response time and a 30% decrease in noise. This innovative approach sustains visibility improvements for over ten minutes, representing a major step towards practical, long-term phase stabilisation in advanced photonic systems.

Multi-Arm Interferometer Phase Noise Stabilization Algorithm

This research details the development of an adaptive Perturb-and-Observe (P and O) algorithm for stabilizing phase noise in complex fiber-optic interferometers, specifically multi-arm Mach-Zehnder interferometers. These interferometers are essential for quantum optics applications, but are vulnerable to environmental disturbances that cause phase fluctuations. The researchers addressed this challenge by developing an algorithm that dynamically adjusts its search for the optimal phase, utilizing a larger step size for faster exploration and a smaller step size for fine-tuning. The algorithm was implemented and tested on a fiber-based multi-arm MZI, using feedback control to adjust piezoelectric transducers that manipulate fiber length and thus the phase. Results demonstrate significantly improved performance compared to a fixed-step P and O algorithm, achieving faster convergence, reduced settling time, and enhanced stability in the presence of noise, paving the way for more advanced and reliable quantum optics experiments and applications.

Real-Time Phase Stabilization of Photon Pairs

Scientists engineered a fully digital system for stabilizing the phase of time-bin encoded photon pairs, crucial for long-distance quantum communication. The control signal derives directly from coincidence counts of correlated photon pairs, providing a self-referencing stabilization loop. The P and O algorithm does not require a precise mathematical model of the system, enabling robust operation even with nonlinearities and discontinuities in the optical phase response.

The team implemented incremental perturbations to the control input, observing corresponding changes in the system output to determine the optimal adjustment direction. This model-free strategy proves particularly effective in managing phase wrapping and nonlinear behavior. This innovative approach utilizes coincidence counts from correlated photon pairs to derive a control signal, enabling precise adjustments to maintain stable interference. Measurements confirm that the visibility improvements are sustained for over 600 seconds, demonstrating long-term stability crucial for practical applications. This breakthrough delivers a significant improvement over traditional phase stabilization techniques, paving the way for more reliable and efficient quantum communication networks.

Adaptive Phase Control Boosts Quantum Communication

Researchers have demonstrated an adaptive Perturb-and-Observe algorithm for stabilizing phase in time-bin quantum systems, a crucial advancement for long-distance quantum communication. This method, operating fully on coincidence counts, achieves a significant reduction in transient response time, up to 70%, and suppresses noise by more than 50% compared to conventional phase stabilization techniques. These improvements demonstrate faster convergence and enhanced stability. The developed system is notable for its autonomous operation, requiring no external reference signals, and its scalability, making it suitable for large-scale and field-deployable quantum communication networks.