We propose a versatile and efficient method to generate a broad class of complex entangled states of many atoms via the detection of a single photon. For an atomic ensemble contained in a strongly coupled optical cavity illuminated by weak single- or multi-frequency light, the atom-light interaction entangles the frequency spectrum of a transmitted photon with the collective spin of the atomic ensemble. Simple time-resolved detection of the transmitted photon then projects the atomic ensemble into a desired pure entangled state. This method can be implemented with existing technology, yields high success probability per trials, and can generate complex entangled states such as multicomponent Schr\"{o}dinger cat states with high fidelity.
@article{arxiv.1508.02457,
title = {Carving complex many-atom entangled states by single-photon detection},
author = {Wenlan Chen and Jiazhong Hu and Yiheng Duan and Boris Braverman and Hao Zhang and Vladan Vuletic},
journal= {arXiv preprint arXiv:1508.02457},
year = {2016}
}