Entanglement of Three Cold Atomic Ensembles

Shau-Yu Lan

Bo Jing

Andrew R. Ferdinand

Correlated light generated from atomic ensembles can have a central role in prominent quantum information protocols, such as long-distance quantum communication. Here we present our studies on three topics involving the generation of correlated light with four-wave mixing (FWM) in a cold atomic ensemble for applications in quantum communications with high capacity. We experimentally investigate the generation of light with seeded FWM in cold cesium atoms and the time correlations of photon pairs generated with spontaneous FWM. We theoretically investigate the correlations in orbital angular momentum of photon pairs generated with spontaneous FWM for a range of experimental geometries. These studies represent foundational work toward the control and measurement of high-dimensional entanglement in the orbital angular momentum degree of freedom photon pairs for use in high-dimensional quantum communication.

Xu-Jie Wang, Sheng-Jun Yang, Peng-Fei Sun +5 more

A cold atomic ensemble suits well for optical quantum memories, and its entanglement with a single photon forms the building block for quantum networks that give promise for many revolutionary applications. Efficiency and lifetime are among the most important figures of merit for a memory. In this Letter, we report the realization of entanglement between an atomic ensemble and a single photon with subsecond lifetime and high efficiency. We engineer dual control modes in a ring cavity to create entanglement and make use of three-dimensional optical lattice to prolong memory lifetime. The memory efficiency is 38% for 0.1 s storage. We verify the atom-photon entanglement after 1 s storage by testing the Bell inequality with a result of S=2.36±0.14.

Hugues de Riedmatten, C. W. Chou, D. Felinto +3 more

Clara I. Osorio, S. Barreiro, Morgan W. Mitchell +1 more

Cold atomic ensembles can mediate the generation of entanglement between pairs of photons. Photons with specific directions of propagation are detected, and the entanglement can reside in any of the degrees of freedom that describe the whole quantum state of the photons: polarization, spatial shape, or frequency. We show that the direction of propagation of the generated photons determines the spatial quantum state of the photons and, therefore, the amount of entanglement generated. When photons generated in different directions are combined, this spatially distinguishing information can degrade the quantum purity of the polarization or frequency entanglement.