Figure 1

A schematic diagram of our experimental setup. Two cold atomic ensembles of ${}^{85}\mathrm{Rb}$, an unpolarized sample at site $A$, and a spin-polarized sample at site $B$, separated by 5.5 m, are connected by a single-mode fiber. The insets show the structure and the initial populations of the atomic levels for the two ensembles; for simplicity only couplings to the $m=-1$ state of level $|a⟩$ are shown at site $A$. An entangled state of a collective atomic qubit and a signal field (wavy blue line) is generated at site $A$ by Raman scattering of the write laser field (solid blue line). The orthogonal helicity states of the generated signal field are transmitted via optical fiber from site $A$ to site $B$, where they are converted to orthogonal collective atomic excitations, stored for a duration $T_s$, and subsequently converted into idler field $B$ (wavy blue line) by adiabatic variation of the control field amplitude. The atomic qubit at site $A$ is similarly converted into idler $A$ (wavy red line) by a read laser pulse, counterpropagating with respect to the write pulse. For polarization analysis, each idler field propagates through a quarter-wave plate (not shown), a half-wave plate ($\lambda /2$), and a polarizing beam splitter (PBS). Polarization correlations of the idler fields are recorded by photoelectric detection using the single photon detectors $D1–D4$.Reuse & Permissions

Figure 2

Measured coincidence fringes $C_{n3}({\theta }_A,{\theta }_B)$ as a function of ${\theta }_A$, for ${\theta }_B=135°$; $n=1$, diamonds; $n=2$, squares. The curves are sinusoidal fits to the data. Each point is acquired for 15 min. The effective repetition rate is 108 kHz, and each trial takes $1.1\mu \mathrm{s}$.Reuse & Permissions

Figure 3

Measured correlation function $E({\theta }_A,{\theta }_B)$ as a function of ${\theta }_A$. (a) ${\theta }_B=0°$, squares; and 90°, diamonds. (b) ${\theta }_B=45°$, squares,; and 135°, diamonds. The curves are sinusoidal fits to the data.Reuse & Permissions