Polarization-encoded free-space Quantum Communication requires a quantum state source featuring fast polarization modulation, long-term stability and a low intrinsic error rate. Here we present a source based on a Sagnac interferometer and composed of polarization maintaining fibers, a fiber polarization beam splitter and an electro-optic phase modulator. The system generates predetermined polarization states with a fixed reference frame in free-space that does not require calibration neither at the transmitter nor at the receiver. In this way we achieve long-term stability and low error rates. A proof-of-concept experiment is also reported, demonstrating a Quantum Bit Error Rate lower than 0.2% for several hours without any active recalibration of the devices.
@article{arxiv.2004.11877,
title = {Stable, low-error and calibration-free polarization encoder for free-space quantum communication},
author = {Marco Avesani and Costantino Agnesi and Andrea Stanco and Giuseppe Vallone and Paolo Villoresi},
journal= {arXiv preprint arXiv:2004.11877},
year = {2020}
}