Rydberg units interfaced: Coherence and Entanglement

相干性和纠缠性是量子系统的基本特性，但随着量子系统与环境的耦合而逐渐丧失。研究如何在空间上传输纠缠以及如何保护相干性已经引起了相当大的兴趣，特别是在量子信息处理中，其中读取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相连接。另一方面，系统地研究一个有限量子系统与另一个有限量子系统（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整这些相干特性的实验测试系统。具有“超原子”和聚集体的超冷里德伯气体可以被设计成具有明确的相干度，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）尺度允许人们以一种可控的方式将这些里德堡-量子系统与环境连接起来，这样就可以相对容易地监测相干性和纠缠性的变化。因此，与许多先前的设置相反，我们希望能够提取和理解相干和纠缠丧失的相关机制。在这个提议中，我们将采取第一步，并行地研究两种相互补充的情况：第一个是将两个里德伯单元连接起来，我们指的是里德伯激发原子在受控位置和受控环境下的组装。虽然这种情况是完全对称的，系统和环境的作用可以交换，但第二种情况是故意选择非常不对称的：我们通过将超冷的里德伯气体与机械的纳米级镜子相结合来创建光力学系统，激光穿过里德伯云并从镜子反射。改变激光参数可以实现内部和外部对相干特性的控制。

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.