Storage and distribution of quantum information are key elements of quantum information processing and quantum communication. Here, using atom-photon entanglement as the main physical resource, we experimentally demonstrate the preparation of a distant atomic quantum memory. Applying a quantum teleportation protocol on a locally prepared state of a photonic qubit, we realized this so-called remote state preparation on a single, optically trapped 87 Rb atom. We evaluated the performance of this scheme by the full tomography of the prepared atomic state, reaching an average fidelity of 82%.Quantum teleportation[1] and quantum cryptography [2] were the first quantum communication methods experimentally demonstrated. Meanwhile, first devices for secure communication became already commercially available. For the next step of quantum information processing, new methods and technologies are required. Many new concepts of quantum information science, for example the quantum repeater [3] or quantum networks, all the way towards distributed quantum computing, require a device interfacing photonic quantum channels and matter-based quantum memories and processors. So far, there are two methods experimentally investigated. The first employs atomic ensembles to momentarily store quantum states of light. Recently, qubits encoded on single photons or qunits encoded in the quantum state of an electromagnetic field have been transferred to the collective state of atoms and vice versa [4,5]. An impressive experimental demonstration of a first quantum communication protocol, the quantum teleportation of coherent states of light, was reported very recently [6]. In the second method the desired interface to a photonic communication channel can be realized using the recently achieved entanglement between a single atom and a single photon [7,8]. This method applies directly to well-studied single quantum systems like trapped neutral atoms or ions. For linear ion chains and neutral atoms in optical lattices, various methods of quantum information storage and processing were already demonstrated, e.g. entanglement of up to 8 ions [9,10], creation of a cluster state involving tens of neutral atoms [11] or manipulations on a neutral atom quantum shift register [12]. Furthermore, this interface concept can be adopted to other qubit systems, like optically addressed quantum dots [13,14,15] or superconducting QED-systems [16], stimulating novel applications in these areas as well.Here we report the first experimental realization of a quantum communication protocol based on atom-photon entanglement. We perform full remote preparation of an atomic quantum memory via teleportation of an arbitrarily prepared quantum state of a single photon, using matter-light entanglement as the interface between the memory device and the communication channel. This method uses expansion of the Hilbert space of one particle of the entangled pair with subsequent complete Bell-state analysis. Being formally equivalent to quantum teleportation [17,18] it enables t...
