Single Impurity in a Dipolar Bose-Einstein Condensate

我的研究包括使用冷原子气体来研究量子力学的奇怪世界，在量子力学中，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，仍有许多量子现象尚未被完全理解。这是因为很难理解一个有这么多粒子相互作用的系统。例如，一立方厘米金属中的电子比可观测宇宙中的恒星还要多，而即使是超级计算机也很难模拟出几百个以上的粒子。在了解量子多体系统的探索中，超冷原子气体之所以如此有用，是因为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。我希望研究的特殊系统是嵌入在超冷原子气体的“量子浴”中的单个杂质原子。任何试图开车或步行穿过人群的人都知道，个人和人群之间的相互作用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！）杂质粒子与一群粒子的相互作用也是如此，以至于嵌入的粒子可以被认为是一种“新”粒子——一种具有新性质的准粒子（例如，质量改变了）。新粒子的性质既取决于它所在的池子的性质，也取决于它如何与池子相互作用。这个一般性问题是一个丰富的多体范式，涉及从凝聚态物理到量子信息理论到粒子物理的广泛领域。这笔拨款将允许我在我现有的铒冷原子机器（由EPSRC项目拨款资助）中添加杂质原子物种（钾）。铒原子具有远距离偶极-偶极相互作用的特点，钾杂质的加入将形成一个独特的实验系统，对量子杂质问题的研究具有明显的优势，这将增强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。下面我概述了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槽的耦合如何改变它的能量和质量。这与金属或半导体中的电子问题密切相关，因此可以提供帮助我们解释和控制诸如巨磁阻（用于数据存储）和超导性等现象的见解。其次，将杂质设置为量子位（量子比特），我计划研究耦合到储层的量子系统中的脱相干物理，并探索所谓的非马尔可夫动力学，即信息可以从储层中恢复（而不仅仅是单向信息流）。这既解决了量子力学中有趣的基本问题，也可能对量子信息处理产生影响。

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.