Dipolar quantum gases of strongly magnetic atoms

本项目旨在利用磁性原子的量子简并气体研究少体和多体物理中的偶极效应。更准确地说，我们的实验使用了原子铒，它是镧系元素家族的成员，是元素周期表中磁性最强的元素之一。选择铒具有将丰富的偶极-偶极相互作用与超冷原子气体群落的扩展知识以及镧系原子的特殊特征结合起来的优点。在接下来的几年里，我们将建立在这些系统上获得的知识和控制的基础上，并深化它们，目的是揭示偶极量子现象的新方面。我们的目标是研究两种非常不同类型的系统：一方面，我们将研究各向异性几何中的偶极玻色-爱因斯坦凝聚体（BECs）。在这里，我们的重点将放在这些系统的基本激发谱上，我们的目标是更好地理解与特殊激发有关的物理学，在大动量下形成能量最小值，即所谓的旋转模式。通过研究全谱，我们想揭示当相互作用被调整时，旋转模式是如何变软的，这是如何依赖于系统几何形状的，以及这是如何导致明显的超平均场效应的。我们还将研究BEC的激发谱如何与最近发现的偶极主导状态时的液滴状态的出现联系起来。在第一部分中，我们的总体目标是了解BEC是否可以以某种方式连接到特殊的基态，特别是有争议的超固态，同时显示出超流体和晶体的性质。另一方面，我们将关注由铒的两个费米子自旋态混合形成的量子系统。我们最近展示了我们制造这种混合物并调整它们相互作用的能力。我们现在的目标是在这个新系统中实现和研究超流体配对。通过调整相互作用，人们可以从沿Bardeen-Cooper-Schrieffer机制形成的离域对超流体过渡到由束缚费米子组成的BEC。虽然这种交叉已经在碱气中研究了多年，但铒带来了特殊的散射情况，包括偶极子-偶极子相互作用、各向异性短程相互作用和多通道共振散射。我们的目的是揭示这些少体特征如何在多体水平上改变费米子集合的行为。

This project aims at investigating dipolar effects in the few- and many-body physics using quantum degenerate gases of magnetic atoms. More precisely, our experiment uses atomic erbium, member of the lanthanide family, which counts among the most magnetic species of the periodic table. The choice of erbium has the advantage of combining the richness of the dipole-dipole interaction together with the extended knowhow of the ultracold atomic gas community, as well as the particular features of the lanthanide atoms. Within the next years, we will build on the knowledge and control gained on such systems, and deepen them, in the aim to unveil new aspects of dipolar quantum phenomena. We aim to investigate two very different types of systems: On the one hand, we will study dipolar Bose-Einstein condensates (BECs) in anisotropic geometries. Here our focus will be on the spectrum of elementary excitations of these systems and our aim a better understanding of the physics related to a special excitation, forming a minimum in energy at a large momentum, the so-called roton mode. By studying the full spectrum, we want to unveil how the roton mode softens when the interaction are tuned, how this depends on the system geometry and how this leads to distinct beyond-mean field effects does. We will also study how does the BEC’s excitation spectrum connects to the apparition of the recently discovered droplet states when reaching a dipolar dominated regime. Our overall goal in this first part is to understand if the BEC can connect in some way to special ground states, in particular the debated supersolid state, showing simultaneously superfluid and crystalline properties.On the other hand, we will focus on a quantum system formed by a mixture of two fermionic spin states of erbium. We have recently shown our ability to produce such mixtures and to tune their interactions. Our aim will now be to realize and study superfluid pairings in this new system. By tuning the interaction, one could cross from a superfluid of delocalized pairs formed along a Bardeen-Cooper-Schrieffer type of mechanism to a BEC of bound fermions. While such a crossover has been studied for years in alkali gases, erbium brings an exceptional scattering scenario, including dipole-dipole interactions, anisotropic short range interactions and multi-channel resonant scattering. Our aim is to reveal how these few-body features modify the behavior of the fermions assemblies at a many-body level.