We report a simple scheme for direct generation of frequency-bin entangled photon pairs via spontaneous parametric downconversion. Our fabricated nonlinear optical crystal with two different poling periods can simultaneously satisfy two different, spectrally symmetric nondegenerate quasi-phase-matching conditions, enabling the direct generation of entanglement in two discrete frequency-bin modes. Our produced photon pairs exhibited Hong-Ou-Mandel interference with high-visibility beating oscillations, a signature of two-mode frequency-bin entanglement. Moreover, we demonstrate deterministic entanglement-mode conversion from frequency-bin to polarization modes, with which our source can be more versatile for various quantum applications. Our scheme can be extended to direct generation of high-dimensional frequency-bin entanglement, and thus will be a key technology for frequency-multiplexed optical quantum information processing.
@article{arxiv.1810.02052,
title = {Direct generation of frequency-bin entangled photons via two-period quasi-phase-matched parametric downconversion},
author = {Fumihiro Kaneda and Hirofumi Suzuki and Ryosuke Shimizu and Keiichi Edamatsu},
journal= {arXiv preprint arXiv:1810.02052},
year = {2019}
}