# Stuttgart 2012 – wissenschaftliches Programm

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# Q: Fachverband Quantenoptik und Photonik

## Q 58: Photonik 3

### Q 58.4: Vortrag

### Freitag, 16. März 2012, 11:30–11:45, V38.01

**Remote atom-atom entanglement** — •Michael Krug^{1}, Julian Hofmann^{1}, Norbert Ortegel^{1}, Lea Gérard^{1}, Kai Redeker^{1}, Florian Henkel^{1}, Wenjamin Rosenfeld^{1,2}, Markus Weber^{1}, and Harald Weinfurter^{1,2} — ^{1}Ludwig-Maximilians-Universität, München — ^{2}Max-Planck-Institut für Quantenoptik, Garching

Entanglement between atomic quantum memories at remote locations will be a key resource for future applications in quantum communication, especially for the quantum repeater. One possibility to generate such entanglement over large distances is entanglement swapping starting from two quantum memories each entangled with a photon. The photons can be transported easily to a Bell-state measurement where after the memories are projected onto an entangled state.

We have set up two independently operating atomic traps situated in two neighboring laboratories separated by 20 m. Via a spontaneous decay process each quantum memory, in our case a single ^{87}Rb atom, emits a single photon whose polarization is entangled with the atomic spin. For Bell state measurment interference of the two photons at a beam splitter is employed. Conditioned on the registration of particular two-photon coincidences the spin states of both atoms are measured. The observed correlations clearly prove the entanglement of the two remote atoms. This is a first step towards creating a basic node of a quantum communication network as well as a key prerequisite for
a future loophole-free test of Bell’s inequality with entangled pairs of neutral atoms.