Rydberg units interfaced: Coherence and Entanglement

相干和纠缠是量子系统的基本性质，但随着与环境的耦合而逐渐丧失。如何在空间上传输纠缠和如何保护相干引起了人们的极大兴趣，特别是在量子信息处理中，读入和读出步骤强制将纠缠量子系统与不可避免地导致退相干的环境连接起来。另一方面，系统地研究有限量子系统与另一个量子系统(或与经典系统)的接口如何动态地改变其相干性是很少的。一个原因可能是很难找到允许调节这些相干性的实验测试系统。具有超原子和聚集体的超冷里德堡气体可以被设计成具有明确的相干性程度，从而缓解这种情况。这一提议的目的是表明它们的空间(微米)和时间(微秒)尺度允许人们以受控的方式将这些里德伯格量子系统与环境对接，从而可以相对容易地监测由此产生的相干性和纠缠性质的变化。因此，与之前的许多设置不同，我们希望能够提取和理解失去一致性和纠缠的相关机制。在这个方案中，我们将迈出第一步，并行研究两种相辅相成的场景：第一种是连接两个里德堡单元，其中我们指的是里德堡激发原子在受控位置和受控环境中的组装。虽然这种情况是完全对称的，系统和环境的作用可以互换，但第二种情况被刻意选择为非常不对称：我们通过将超冷里德堡气体耦合到机械的纳米级反射镜来创建光学机械系统，激光穿过里德伯格云并从镜面反射。通过改变激光参数，可以在这里和外部控制相干特性。

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.