Polarization Drift Compensation in Fiber using Feedback from Correlated Measurements of Entangled Photons

Use of polarization entangled photons in fiber have been utilized for tests of Bell inequalities, teleportation, and quantum key distribution across kilometer scale distances [1,2]. All observations and applications of polarization entanglement require carefully coordinated polarization-resolved measurements between spatially separated observers. The uncontrolled thermal and mechanical variations in the fiber channels cause an unpredictable and time-varying transformation of the polarization state, which makes it hard to perform a stationary measurement of entanglement. Because a maximally entangled photon is statistically unpolarized, methods of polarization tracking based on single-channel measurements cannot be applied to stabilize the measurements. Instead, we employ feedback from coincidence measurements on a  entangled state, between spatially separate observers to experimentally stabilize the observation of entanglement. We implement several polarization drift compensation algorithms, and compare the convergence rate and tracking performance.

 

[1] Wengerowsky, S., Joshi, S. K., Steinlechner, F., ..., & Ursin, R. Proc. of the Nat. Acad. of Sciences, 116(14), 6684-6688 (2019)

[2] Bussières, F., Clausen, C., Tiranov, A., ..., & Gisin, N. Nature Photonics, 8(10), 775-778 (2014)