A Stable Quantum Gas of Fermionic Polar Molecules

费米子极性分子的稳定量子气体

基本信息

批准号：
EP/N007085/1
负责人：
Simon Cornish
金额：
$ 126.74万
依托单位：
Durham University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2016
资助国家：
英国
起止时间：
2016 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FN007085%2F1
关键词：
Stable Quantum Gas Fermionic Polar

项目摘要

The theory of quantum mechanics provides an excellent description of isolated atoms and has allowed us to develop our understanding of the physics of such systems to unprecedented levels. The same quantum physics ultimately governs all matter, even in bulk materials, and leads to many important and interesting phenomena, such as high temperature superconductivity and exotic forms of magnetism. However, in solid materials individual atoms are no longer isolated from one another and commonly experience strong long-range interactions with many other particles in the material. In this case, the nature of quantum mechanics means that an exact solution of the many-body system is usually impossible. Instead we must develop a simple model of the system which captures the essential physics and then try to solve this model for a finite number of particles. However, even this approach becomes intractable on a classical computer for more than 10 to 100 particles. An alternative strategy, originally proposed by Richard Feynman, is to use another quantum system to 'simulate' the model or Hamiltonian describing the system of interest. Developing such 'quantum simulators' has become a major theme of research, as they have the potential to change the way we understand new materials and could ultimately impact on future devices and technologies of benefit to all of society.The development of laser cooling has allowed us to cool atomic gases to temperatures less than a millionth of a degree above absolute zero where the quantum mechanical nature of particles dominates over their thermal motion. In this regime new states of matter emerge in the form of Bose-Einstein condensates and Fermi-degenerate gases. Such gases are highly controllable and offer a promising platform to implement quantum simulation protocols. In particular, ultracold heteronuclear molecules possess the controllable long-range interactions needed to engineer an important class of problems relevant to condensed-matter physics. Moreover, the crystalline structures of real materials can easily be replicated using standing waves of laser light to confine the molecules in optical lattices.The laser cooling and trapping techniques developed for atoms do not generally work, however, for molecules due to their complex internal rotational and vibrational structure. Nevertheless, they can still be exploited by carefully assembling ultracold molecules from ultracold atoms. This approach has proved remarkably successful, with a number of different molecules having been created. The technique uses two distinct steps to associate the molecules. First, weakly bound molecules are formed using a collision resonance, known as a Feshbach resonance, which couples the free atoms into a near threshold molecular state. Secondly, the molecules are transferred to the absolute ground state using a two-photon optical transfer process, known as stimulated Raman adiabatic passage (STIRAP). Remarkably, the overall conversion process can be highly efficient with negligible heating so that the temperature and density of the resulting molecular quantum gas mirror the initial parameters of the atomic mixture. The goal of this proposal is to realise a gas of ultracold fermionic KCs molecules by associating pre-cooled atoms of K and Cs. This molecule has the advantage over other bi-alkali molecules of being stable against reactive collisions and offers both fermionic and bosonic isotopes. By confining the molecules in an array of two-dimensional pancake traps we will deliver a test platform for quantum simulation applications. To achieve this ambitious objective we propose to combine state-of-the-art experiments in synergy with world leading theoretical support into a transformative program of research that stands to cement the UK's position at the forefront of an exciting international field.

量子力学理论提供了对孤立原子的出色描述，并使我们能够将对此类系统的物理学的理解发展到前所未有的水平。同样的量子物理学最终控制着所有物质，甚至是散装材料，并导致许多重要且有趣的现象，例如高温超导和奇异形式的磁性。然而，在固体材料中，单个原子不再彼此隔离，并且通常会与材料中的许多其他粒子发生强烈的长程相互作用。在这种情况下，量子力学的本质意味着多体系统的精确解通常是不可能的。相反，我们必须开发一个简单的系统模型来捕获基本物理原理，然后尝试针对有限数量的粒子求解该模型。然而，对于超过 10 到 100 个粒子的经典计算机来说，即使这种方法也变得棘手。另一种策略最初由理查德·费曼提出，是使用另一个量子系统来“模拟”模型或描述感兴趣系统的哈密顿量。开发这种“量子模拟器”已成为研究的一个主要主题，因为它们有可能改变我们理解新材料的方式，并最终影响未来造福全社会的设备和技术。激光冷却的发展使得我们将原子气体冷却到绝对零以上不到百万分之一度的温度，其中粒子的量子力学性质主导其热运动。在这种状态下，新的物质状态以玻色-爱因斯坦凝聚态和费米简并气体的形式出现。这种气体是高度可控的，并为实施量子模拟协议提供了一个有前途的平台。特别是，超冷异核分子具有解决与凝聚态物理相关的一类重要问题所需的可控长程相互作用。此外，使用激光驻波将分子限制在光学晶格中，可以轻松复制真实材料的晶体结构。然而，针对原子开发的激光冷却和捕获技术通常不适用于分子，因为分子具有复杂的内部旋转和振动结构。尽管如此，仍然可以通过从超冷原子仔细组装超冷分子来利用它们。事实证明，这种方法非常成功，已经创建了许多不同的分子。该技术使用两个不同的步骤来关联分子。首先，使用称为费什巴赫共振的碰撞共振形成弱结合分子，它将自由原子耦合成接近阈值的分子状态。其次，使用双光子光学转移过程（称为受激拉曼绝热通道（STIRAP））将分子转移到绝对基态。值得注意的是，整个转化过程可以非常高效，加热可以忽略不计，从而所得分子量子气体的温度和密度反映了原子混合物的初始参数。该提案的目标是通过缔合预冷的 K 原子和 Cs 原子来实现超冷费米子 KCs 分子气体。与其他双碱分子相比，该分子的优点是对反应性碰撞稳定，并提供费米子和玻色子同位素。通过将分子限制在一系列二维薄饼陷阱中，我们将为量子模拟应用提供一个测试平台。为了实现这一雄心勃勃的目标，我们建议将最先进的实验与世界领先的理论支持相结合，形成一项变革性的研究计划，以巩固英国在令人兴奋的国际领域的前沿地位。