Teleportation of the polarization state of a coherent light pulse onto a single atom

Summary form only given. Quantum teleportation allows to transfer the quantum state of a particle to a remote location without sending the particle itself. This makes it a versatile tool for the distribution of quantum states over long distances or the remote preparation of quantum memories as they are necessary in various scenarios of quantum information processing and quantum communication. In this context atomic systems are often discussed as promising candidates for the storage and manipulation of qubit states whereas photonic qubit states are easy to prepare and to distribute. Hybrid systems of entangled atom-photon pairs can serve as an interface between those different carriers of quantum information. We utilize this property to perform teleportation of the polarization state of an attenuated laser pulse onto a single atom over a distance of 20m.Our experimental sequence consists of two steps. First the spin state of the single atom is entangled with the polarization state of a single photon in a spontaneous emission process [1]. The single photon is then sent to a second laboratory 20m away where an attenuated laser pulse with a well defined polarization state |Ψ) is prepared. In a second step a Bell-state measurement on the joint polarization state of the single photon from the atom and the attenuated laser pulse is performed (Fig. 1a). This is done via interference of the photon and the pulse at a fiber beam-splitter and subsequent coincidence detection of photons at the outputs of the beam-splitter (Fig. 1b). This teleports the input state |Ψ) onto the atom - up to a unitary tranformation depending on the outcome of the Bell-state measurement.need to be indistinguishable in all degrees of freedom except for their polarization. In particular, the temporal shape of the pulse was matched to that of the single photon using an arbitrary waveform generator and an AOM in a closed-loop feedback control. We performed this experiment with input sta- es |Ψ) = |H), |+45°) and |R) and evaluated the fidelity to find the atom in the correspondig output state. For |+45°) and |R) the fraction of coherent pulses containing two or more photons can cause the same signal as expected from a successful Bell-state projection which reduces the overall fidelity to 0.81 and 0.84, respectively. However, for |H) the fidelty is practically only limited by the precision of the atomic state readout and reaches a value of 0.93.