Rydberg crystals and supersolids

高温超导体是强相关量子系统在技术上的重要例子。它们的奇异电子特性是由于电子之间的相互作用，从而产生了相关行为。强相关材料很难建模，因为它们介于两者之间——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使用基于平均性质的“整体”描述。为了弥合简单模型和真实材料之间的差距，人们对使用激光冷却原子模拟强相关行为越来越感兴趣，其中每个原子的外部和内部状态可以完全控制。最近，通过使用激光脉冲将最外层的电子激发到高度激发态（或里德伯态），将这种控制扩展到相互作用已经成为可能。这开启了偶极-偶极相互作用，比基态原子之间的相互作用强12个数量级。这种相互作用完全支配了冷原子（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。我们将特别研究这些相关性和超流动性之间的相互作用。第一个挑战是开发一种成像里德伯原子的技术。为了做到这一点，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“里德伯晶体”的动态形成，里德伯激发形成有序晶格。然后，为了将这些强相互作用与超流动性结合起来，我们将使用与里德伯态的弱耦合来“装扮”处于基态的原子，使其具有少量的里德伯特征。通过将这种“里德伯修饰”与玻色-爱因斯坦凝聚相结合，我们将能够在超流体中可控地引入空间相关性，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“里德堡超固体”，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.