We report on the observation of quantum interference of a collective single spin excitation with a spin ensemble of Natom=105 atoms. Detection of a single photon scattered from the atoms creates the single spin excitation, a Fock state embedded in the collective spin of the ensemble. The state of the atomic ensemble is then detected by tomography via a quantum non-demolition measurement of the collective spin. A macroscopic difference of the order of Natom in the marginal distribution of the collective spin state arises from the interference between the single excited spin and Natom atoms. The hybrid discrete-continuous processing of the collective spin pave the road towards generation of even more exotic states for quantum information processing, precision measurements and communication.
@article{arxiv.1309.2514,
title = {Quantum interference of a single spin excitation with a macroscopic atomic ensemble},
author = {S. L. Christensen and J. -B. Béguin and E. Bookjans and H. L. Sørensen and J. H. Müller and J. Appel and E. S. Polzik},
journal= {arXiv preprint arXiv:1309.2514},
year = {2014}
}