Observation of Atom-Photon Entanglement: Towards a Loophole-free test of Bells inequality
Markus Weber (LMU München, Sektion Physik)

Entanglement between atoms and photons [1,2] is a key resource for new applications in quantum communication and information because it combines the ability to store information (atom) with an effective communication channel (photon). Furthermore it enables one to entangle two atoms separated by large distances by the joint detection of the photons, coming from each of the atoms [1,3]. The space-like separation together with the high detection efficiency of the atoms finally should allow a loophole-free test of Bell´s inequality.

In our experiment we excite a single ⁸⁷Rb atom - stored in an optical dipole trap - by a short optical Pi-pulse and detect the subsequent spontaneously emitted single photon. Due to conservation of angular momentum the polarization of the emitted photon and the atomic magnetic quantum number are entangled. A STIRAP technique is used to analyze the atomic qubit in different measurement bases. Here we report the observation of strong atom-photon correlations in conjugate measurement bases resulting in an entanglement fidelity of F = 0.85.

[1] K. Saucke, Diploma thesis, University Munich, (2002).

[2] B. Blinov et al., Nature 428, 153 (2004).

[3] C. Simon et al., Phys. Rev. Lett. 91, 110405 (2003).