Experimental Quantum Physics

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Atom-Photon Entanglement

Entanglement between atomic systems and light is a promising approach for interfacing atomic quantum memories and photonic communication channels. In our project we work with single, optically trapped Rubidium atoms whose spin is entangled with the spin of single photons.

The starting point is a single Rb atom stored in an optical dipole trap. Entanglement is generated by exciting a short-lived upper state of the atom, from where it decays back emitting a single photon. The coherent superposition of the two decay channels provides an entangled state between the spin of the atom and the polarization of the emitted photon.
Characterization of the entangled state is performed by projective spin measurements on the atom and the photon. Combining those measurements we can perform complete quantum state tomography of the two-particle state. We obtain entanglement fidelity of up to 0.95.

picture of the experimental setup

Picture of the experimental setup (laser beams are visualized in false-color).


The new kind of entanglement opens new experimental possibilities. In particular we have demonstrated remote preparation of the atomic state via quantum teleportation. Furthermore, we are able to distribute the entanglement over long distance by exploiting long atomic coherence times together with implementation of a polarization-stabilized optical fiber link.

Currently we are working on establishing entanglement of two atoms independently trapped in two laboratories separated by 400 meters. With such a system of entangled atoms at a large distance a fundamental test of quantum mechanics comes into reach, the loophole-free test of Bell's inequality.


Selected publications:


Responsible for content: Wenjamin Rosenfeld