Self-guided method to search for EPR state correlations using uncalibrated polarization controllers in a plug-and-play optical system.*

Observing nonlocal correlations between entangled photons is a staple of many quantum information tasks. The measurement bases between two observers recording nonlocal correlations are often oriented with free space optical waveplates. Instead, we use uncalibrated piezoelectric actuator polarization controllers to align our observers’ measurement bases where the alignment is done through photon counting feedback and a stochastic gradient descent algorithm. This plug-and-play, fully fiber optic system eliminates many experimental complexities such as free-space optical component alignments and free-space-to-fiber couplings. We experimentally study the speed and stability of this alignment on a two-qubit entangled photon source with noise. We postulate on this method's ability to be used on future feedback Bell inequality experiments and the calibration of uncalibrated polarization controllers^[1]. This simplified experimental setup may be of use for automated alignment of future quantum information systems.

[1] L.K. Yang, G. Chen, W.-H. Zhang, X.-X. Peng, S. Yu, X.-J. Ye, C.-F. Li, and G.-C. Guo, Phys. Rev. A 96, 052310 (2017)