Efficient two-mode squeezing and quantum-state teleportation of macroscopic atomic ensembles

We present a protocol for deterministically generating an optimal two-mode-squeezed state of distant free-space atomic ensembles. The protocol relies on two passes of a single coherent pulse through two separate atomic ensembles placed in homogeneous magnetic fields. In contrast to previous single-pass schemes, our approach significantly enhances the degree of entanglement due to the exponential behavior of the Einstein-Podolsky-Rosen variance. We also provide an efficient scheme to perform Bell measurement of atomic states, enabling the implementation of high-fidelity atomic quantum teleportation.