We demonstrate deterministic generation of two distinct collective excitations in one atomic ensemble, and we realize the Hong-Ou-Mandel interference between them. Using Rydberg blockade we create single collective excitations in two different Zeeman levels, and we use stimulated Raman transitions to perform a beam-splitter operation between the excited atomic modes. By converting the atomic excitations into photons, the two-excitation interference is measured by photon coincidence detection with a visibility of 0.89(6). The Hong-Ou-Mandel interference witnesses an entangled NOON state of the collective atomic excitations, and we demonstrate its two times enhanced sensitivity to a magnetic field compared with a single excitation. Our work implements a minimal instance of Boson sampling and paves the way for further multi-mode and multi-excitation studies with collective excitations of atomic ensembles.
@article{arxiv.1608.03076,
title = {Hong-Ou-Mandel Interference between Two Deterministic Collective Excitations in an Atomic Ensemble},
author = {Jun Li and Ming-Ti Zhou and Bo Jing and Xu-Jie Wang and Sheng-Jun Yang and Xiao Jiang and Klaus Mølmer and Xiao-Hui Bao and Jian-Wei Pan},
journal= {arXiv preprint arXiv:1608.03076},
year = {2016}
}