title: Quantum storage of photonic entanglement in a crystal.
abstract: Entanglement is the fundamental characteristic of quantum physics-much experimental effort is devoted to harnessing it between various physical systems. In particular, entanglement between light and material systems is interesting owing to their anticipated respective roles as 'flying' and stationary qubits in quantum information technologies (such as quantum repeaters and quantum networks). Here we report the demonstration of entanglement between a photon at a telecommunication wavelength (1,338 nm) and a single collective atomic excitation stored in a crystal. One photon from an energy-time entangled pair is mapped onto the crystal and then released into a well-defined spatial mode after a predetermined storage time. The other (telecommunication wavelength) photon is sent directly through a 50-metre fibre link to an analyser. Successful storage of entanglement in the crystal is proved by a violation of the Clauser-Horne-Shimony-Holt inequality by almost three standard deviations (S = 2.64 ± 0.23). These results represent an important step towards quantum communication technologies based on solid-state devices. In particular, our resources pave the way for building multiplexed quantum repeaters for long-distance quantum networks.
authors.affiliation: Group of Applied Physics, University of Geneva, CH-1211 Geneva 4, Switzerland.
authors.forename: Christoph
authors.initials: C
authors.lastname: Clausen
authors.forename: Imam
authors.initials: I
authors.lastname: Usmani
authors.forename: Félix
authors.initials: F
authors.lastname: Bussières
authors.forename: Nicolas
authors.initials: N
authors.lastname: Sangouard
authors.forename: Mikael
authors.initials: M
authors.lastname: Afzelius
authors.forename: Hugues
authors.initials: H
authors.lastname: de Riedmatten
authors.forename: Nicolas
authors.initials: N
authors.lastname: Gisin