Rydberg units interfaced: Coherence and Entanglement

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Coherence and entanglement are fundamental properties of quantum systems which are gradually lost through coupling to the environment. Investigations how to spatially transport entanglement and how to protect coherence have attracted considerable interest, particularly in quantum information processing where the read-in and read-out steps enforce to interface the entangled quantum system with an environment leading inevitably to decoherence. On the other hand, systematic studies how interfacing a finite quantum system with another one (or with a classical system) dynamically changes its coherence properties are scarce. A reason may be the difficulty to find experimental test systems that allow tuning these coherence properties. Ultracold Rydberg gases, with ``superatoms'' and aggregates can be designed to have a well defined degree of coherence and thus alleviate this situation.It is the aim of this proposal to show that their spatial (micrometer) and temporal (microsecond) scale allows one to interface these Rydberg-quantum-systems in a controlled way with an environment, such that the resulting change of coherence and entanglement properties can be monitored with relative ease. Thus, in contrast to many prior setups, we expect to be able to extract and understand the relevant mechanisms of loss of coherence and entanglement. Within this proposal we will take the first step and investigate in parallel two scenarios which supplement each other: The first one is to interface two Rydberg units, by which we refer to an assembly of Rydberg excited atoms at controlled positions and with controlled environment. While this scenario is completely symmetric and the role of system and environment can be exchanged, the second scenario is deliberately chosen to be very asymmetric: we create an optomechanical system by coupling an ultra cold Rydberg gas to a mechanical, nano-scale mirror with laser light passing through the Rydberg cloud and being reflected from the mirror. Changing the laser parameters allows here and external control of coherence properties.