SINGLE IMPURITY IN A DIPOLAR BOSE-EINSTEIN CONDENSATE

单个杂质与量子浴相互作用是一个简单（陈述）但丰富的多体范例，它与从凝聚态物理学到量子信息理论再到粒子物理学的广泛领域有关。这个项目的目的是创造一个高度可控的环境来研究这种物理学。这些研究的平台将是现有的铒冷原子机器。超冷铒原子将被限制在一个均匀的准二维几何结构中，该几何结构是利用沿着垂直方向的强谐波限制和在水平面上的盒陷阱产生的。铒原子的特殊之处在于其大的磁偶极矩，除了在冷原子系统中更常见的短程接触相互作用之外，还会产生长程和各向异性的偶极-偶极相互作用。在这个项目中，我们将在这个实验中加入第二个杂质原子种类。由此产生的系统将有几个优势，目前的国家的最先进的，并将开辟许多途径的探索，但对于这个项目，我们有两个主要的主题/目标，将是我们的重点。偶极BEC中极化子的形成。极化子，如最初设想的那样，是当电子在晶格中移动时被声子修饰而形成的准粒子。杂质原子浸入简并玻色气体中是研究极化子物理的一个可调谐的环境。虽然在过去的十年中，BEC中的杂质一直是重要的实验研究的主题，但直到最近才清楚地观察到玻色极化子（与费米极化子相反，费米极化子在浴是费米气体时出现）。至少对于弱杂质浴相互作用的玻色极化子预计将很好地描述Frohlich模型，该模型认为杂质与声子相互作用（在BEC的情况下是长波长的Bogoliubov激发）。杂质与偶极BEC相互作用的情况由于以下几个原因而进一步丰富：（i）偶极模式变得各向异性，（ii）我们有第二种低能激发（即圆形），也应该打扮杂质，和（iii）旋转模的软化也导致量子涨落的增强作用和甚至对于弱杂质进入强耦合区的可能性。浴互动。我建议探索这个问题，通过测量这异国情调的极化子的静态和输运性质。虽然理论上研究了很多非马尔可夫行为只是最近才被实验探索-到目前为止，主要是在光子系统。最近的一项建议表明，一种可能的方式来实现这样一个非马尔可夫水库将与准2D BEC的偶极原子;事实上，它是在激发光谱中的旋转状的功能，在这样的特点的结果。我建议实现这种情况，并测试信息流的性质（使用杂质原子作为量子比特）作为BEC激发光谱的形式发生变化。此外，研究如何通过增加浴的温度来破坏非马尔可夫行为，这对于理解量子信息的存储也是有趣的，也是重要的。将非马尔可夫行为的研究扩展到原子系统将是开放量子系统研究的关键一步，并可能对量子信息技术产生重要影响，例如增强自旋压缩和可控耗散。更一般地说，与工程库可控耦合的量子系统可能能够解决关于叠加和纠缠以及量子-经典交叉的基本问题。

A single impurity interacting with a quantum bath is a simple (to state) yet rich many-body paradigm that is relevant across a wide sweep of fields from condensed matter physics to quantum information theory to particle physics. The aim of this project is to create a highly controllable setting in which to study this physics. The platform for these studies will be ann existing erbium cold-atom machine. The ultracold erbium atoms will be confined in a homogeneous quasi-2D geometry generated using strong harmonic confinement along the vertical direction and box trap in the horizontal plane. The special feature of erbium atoms is their large magnetic dipole moments which result in long-range and anisotropic dipole-dipole interactions in addition to the short-range contact interactions more normally seen in cold atom systems. In this project we will add a second, impurity, atomic species to this experiment. The resulting system will have several advantages over the current state-of-the-artand will open up many avenues for exploration, but for this project we have two main themes/objectives that will be our focus. Polaron' formation in a dipolar BEC. A polaron, as originally conceived, is the quasiparticle formed when an electron is dressed by phonons as it moves through a crystal lattice. An impurity atom immersed in a degenerate Bose gas is a tuneable setting in which to study polaron physics. While impurities in a BEC have been the topic of significant experimental investigation in the past decade it is only very recently that the Bose polaron (so named in contrast to Fermi polarons which occur when the bath is a Fermi gas) have been clearly observed. At least for weak impurity-bath interactions the Bose-polaron is expected to be well described by a Frohlich model which considers an impurity interacting with phonons (which in the case of a BEC are long-wavelength Bogoliubov excitations). The case of an impurity interacting with a dipolar BEC is enriched further for several reasons: (i) the dipole modes become anisotropic, (ii) we have a second type of low-energy excitation (namely the roton) which should also dress the impurity, and (iii) the softening of the roton mode also leads to an enhanced role for quantum fluctuations and the possibility to enter the strong-coupling regime even for weak impurity - bath interactions. I propose to explore this problem by measuring both the static and transport properties of this exotic polaron.While much studied theoretically non-Markovian behaviour is only recently being explored experimentally - so far mainly in photonic systems. A recent proposal has suggested that one possible way to realise such a non-Markovian reservoir would be with a quasi- 2D BEC of dipolar atoms; indeed it is the roton-like feature in the excitation spectrum that results in such characteristics. I propose to realise such a situation and test the nature of information flow (using an impurity atom as the qubit) as the form of the BEC excitation spectrum is changed. Also it would be interesting, and important for understanding the storage of quantum information, to investigate how easily the non-Markovian behaviour is destroyed by increasing the temperature of the bath. Extending the studies of non-Markovian behaviour to atomic systems would represent a key step in the study of open quantum systems and could have important consequences for quantum information technology for example in enhanced spin squeezing and controllable dissipation. Even more generally, a quantum system with a controllable coupling to an engineered reservoir may be able to address fundamental questions about superposition and entanglement and the quantum-classical crossover.