Entanglement of orbital angular momentum states between an ensemble of cold atoms and a photon

Recently, atomic ensemble and single photons were successfully entangled by using collective enhancement [D. N. Matsukevich et al., Phys. Rev. Lett. 95, 040405 (2005)], where atomic internal states and photonic polarization states were correlated in a nonlocal manner. Here, we experimentally clarified that in an ensemble of atoms and a photon system, there also exists an entanglement concerned with spatial degrees of freedom. Generation of higher-dimensional entanglement between remote atomic ensemble and an application to condensed matter physics are also discussed.

Figure 1

(Color online) (a) Schematic of experimental setup. Write and read pulses propagate into a cloud of cold ${}^{87}\mathrm{Rb}$ atoms [magneto-optical trap (MOT)] and generate the correlated output pair of anti-Stokes (AS) and Stokes (S) photons. SMF1, 2, 3, and 4, single-mode fibers; H1 and H2, computer-generated holograms; D1 and D2, detectors; TIA, time-interval analyzer. (b) depicts the timing sequence for data acquisition.

Figure 2

(Color online) (a) Time-resolved coincidence counts, where the time resolution was set to $1.6\mathrm{ns}$. (b)–(d) are the coincidences in the various measurement bases.

Figure 3

(Color online) Graphical representation of the reconstructed density matrix. (a) is the real part and (b) is the imaginary part.