Single Impurity in a Dipolar Bose-Einstein Condensate

我的研究涉及使用冷原子气体来研究量子力学中奇怪的世界，在这个世界中，粒子的行为像波一样。在20世纪，正是对电子行为的量子本质的理解推动了计算机、iPhone和大多数现代技术的发展。然而，有许多量子现象还没有完全被理解。这是因为很难理解一个有这么多相互作用的粒子的系统。例如，一立方厘米的金属中的电子比可见宇宙中的恒星还多，而即使是超级计算机也难以模拟数百个以上的粒子。超冷原子气体在理解量子多体系统的探索中如此有用的原因是，它们可以在高度受控的环境中使用激光和磁场等工具进行操作。我想研究的特定系统是一个嵌入在超冷原子气体的量子浴中的单个杂质原子的系统。任何试图开车或穿过人群的人都会知道，个人与人群之间的互动会导致行为的重大变化(最明显的是，它会减慢人或车辆的速度！)同样的道理也适用于杂质粒子与粒子池的相互作用，以至于嵌入的粒子可以被认为是一个新的粒子-具有新性质的准粒子(例如，修改后的质量)。新粒子的性质既取决于它所处的浴液的性质，也取决于它与该浴液的相互作用方式。这个普遍的问题是一个丰富的多体范例，涉及从凝聚态物理到量子信息理论再到粒子物理的广泛领域。这笔赠款将允许我在我现有的铒冷原子机器(由EPSRC计划拨款资助)中添加一个杂质原子物种(钾)。铒原子具有长程偶极-偶极相互作用的特点，钾杂质物种的加入将产生一个独特的实验系统，对研究量子杂质问题具有明显的优势，这将增进我们对材料和量子信息技术的理解，使我们更好地发展21世纪的新技术。下面我将概述我计划进行的两个具体实验。首先，我将研究钾杂质原子与偶极浴的耦合如何改变其能量和质量。这与金属或半导体中的电子问题密切相关，因此可以提供见解，帮助我们解释和控制巨磁电阻(用于数据存储)和超导等现象。第二，将杂质设置为量子比特(量子比特)我计划研究与水库耦合的量子系统中的去相干物理，并探索一种称为非马尔科夫动力学的东西，通过这种动力学，信息可以从水库中恢复(而不仅仅是单向的信息流)。这既解决了量子力学中有趣的基本问题，也潜在地对量子信息处理产生了影响。

My research involves using cold atomic gases to study the strange world of quantum mechanics where particles behave as waves. In the 20th century, it was the understanding of the quantum nature of how electrons behave that enabled the development of computers, iPhones and most of modern technology. However, there are many quantum phenomena that are not fully understood. This is due to the difficulty of understanding a system with so many particles all interacting with each other. For example, there are more electrons in a cubic centimetre of metal than stars in the observable universe, while even super-computers struggle to simulate more than a few hundred particles. What makes ultracold atomic gases so useful in this quest to understand quantum many-body systems is that they can be manipulated using tools such as lasers and magnetic fields in a highly controlled environment. The particular system that I wish to study is that of a single impurity atom embedded in the 'quantum bath' of an ultracold atomic gas. Anybody who has tried to drive or walk through a crowd of people will know that the interactions between the individual and the crowd leads to significant changes of behaviour (most obviously it slows the person or vehicle down!). The same is true of an impurity particle interacting with a bath of particles, so much so that the embedded particle can be thought of as a 'new' particle - a quasiparticle which has new properties (for example a modified mass). The nature of the new particle depends on both the properties of the bath it which it sits and also on how it interacts with that bath. This general problem is a rich many-body paradigm that is relevant across a wide sweep of fields from condensed matter physics to quantum information theory to particle physics. This grant will allow me to add an impurity atomic species (potassium) to my existing erbium cold-atom machine (which was funded from an EPSRC programme grant). Erbium atoms have the special feature of long-range dipole-dipole interactions and the addition of a potassium impurity species will result in a unique experimental system with distinct advantages for the study of quantum impurity problems that will enhance our understanding of both materials and quantum information technology, making us better placed to develop the new technologies of the 21st century. Below I outline two specific experiments that I plan to carry out.First, I will investigate how the coupling of a potassium impurity atom to the dipolar bath changes both its energy and its mass. This is closely related to the problem of an electron in a metal or semiconductor and so could provide insights that help us to explain and control phenomena such as colossal magnetoresistance (used for data storage) and superconductivity.Second, setting up the impurity as a qubit (quantum bit) I plan to investigate the physics of de-coherence in quantum systems coupled to a reservoir and explore something known as non-Markovian dynamics whereby information can be recovered from the reservoir (rather than there just being a one-way information flow). This both addresses interesting fundamental questions in quantum mechanics as well as potentially having an impact on quantum information processing.