Rydberg crystals and supersolids

高温超导体是强关联量子系统的一个重要技术例子。它们奇异的电子特性归功于电子之间的相互作用，从而产生关联行为。强关联材料很难建模--它们位于电子之间--电子相互作用，因此不能被描述为单个粒子，但强相互作用也意味着我们不能用“为了弥补简单模型和真实的材料之间的差距，人们越来越感兴趣的是使用激光冷却原子来模拟强关联行为，每个原子的内部和外部状态都可以被完全控制。最近，通过使用激光脉冲将最外层的电子激发到高激发态（或里德伯态），已经有可能将这种控制扩展到相互作用。这会开启偶极-偶极相互作用，其强度比基态原子之间的强12个数量级。相互作用完全控制了冷原子（5微开尔文）的动能，系统变得强相关。在这个提议中，我们将利用锶里德伯原子的独特性质来探索这些强相互作用如何导致空间相关性。特别是，我们将研究这些相关性和超流性之间的相互作用。第一个挑战是开发一种对里德伯原子成像的技术。为此，我们将开发一种新的扫描显微镜，利用锶原子有两个价电子的事实。接下来，我们将使用这种新技术来观察相互作用如何导致"里德堡晶体“的动态形成，其中里德堡激发形成有序晶格。然后，为了将这些强相互作用与超流性联合收割机结合起来，我们将使用与里德伯态的弱耦合，以少量的里德伯特征“装扮”处于基态的原子。通过将这种“里德伯敷料”与玻色-爱因斯坦凝聚相结合，我们将能够可控地将空间相关性引入超流体，为研究强相关系统的物理学提供一个新的实验室。最近的理论建议表明，这可能导致观察到“里德伯超固体”，其中晶体空间分布可以与超流体流动共存-类似于40多年前预测存在于固体氦中的相。

High-temperature superconductors are a technologically important example of a strongly correlated quantum system. They owe their exotic electronic properties to interactions between the electrons, which give rise to correlated behaviour.Strongly correlated materials are very difficult to model they lie in between - the electrons interact, and so can't be described as individual particles, but the strong interactions also mean that we can't use a ``bulk'' description based on average properties either.To bridge the gap between simple models and real materials, there is growing interest in simulating strongly correlated behaviour using laser cooled atoms, where the external and internal state of each atom can be completely controlled. Recently it has become possible to extend this control to the interactions, by exciting the outermost electron to a highly excited (or Rydberg state) using a laser pulse. This switches on a dipole-dipole interaction which is 12 orders of magnitude stronger than that between the ground state atoms. The interactions completely dominate the kinetic energy of the cold (5 microKelvin) atoms, and the system becomes strongly correlated. In this proposal, we will exploit the unique properties of strontium Rydberg atoms to explore how these strong interactions lead to spatial correlations. In particular we will examine the interplay between these correlations and superfluidity. The first challenge is to develop a technique for imaging the Rydberg atoms. To do this, we will develop a new kind of scanning microscopy that exploits the fact that strontium atoms have two valence electrons.Next, we will use this new technique to observe how the interactions lead to the dynamical formation of ``Rydberg crystals'' where the Rydberg excitations form an ordered lattice. Then, to combine these strong interactions with superfluidity, we will use a weak coupling to the Rydberg state to ``dress'' atoms in their ground state with a small amount of Rydberg character. By combining this ``Rydberg dressing'' with a Bose-Einstein condensate, we will be able to controllably introduce spatial correlations into a superfluid, providing a new laboratory for studying the physics of strongly correlated systems. Recent theoretical proposals have suggested that this could lead to the observation of a ``Rydberg supersolid'', where a crystalline spatial distribution can coexist with superfluid flow - similar to a phase predicted to exist in solid helium over 40 years ago.