T1: Rotons and quantum droplets in dipolar Bose-Einstein condensates

偶极-偶极相互作用导致了偶极玻色-爱因斯坦凝聚体中丰富的新物理，最近的实验(特别是在E1和E2项目中)开始揭开这些新物理的面纱。最近，有两个主要话题引起了人们的极大关注：偶极粒子和量子偶极液滴。该项目将与研究股内的实验密切合作，调查这两种现象。最近在E2计划中首次创造的偶极轻子是有限动量的低能激发。在这个项目中，我们将研究旋子物理学中的有限尺寸效应。此外，偶极子激发和量子稳定性的结合，即在E1和E2中观察到的量子液滴形成的机制，有望导致丰富的基态和有限温度物理，我们也将对其进行研究。值得注意的是，这两种效应可能允许创建超固态，其实现和性质将被分析。对量子稳定至关重要的量子涨落在更低的维度上发生了根本性的变化。我们将与T2项目一起探索二维偶极凝聚的有趣案例，这可能允许创建特别强大的量子液滴。最后，我们还将研究最近在E2中创建的二元偶极混合物的基态性质和量子涨落。

Dipole-dipole interactions lead to a wealth of new physics in dipolar Bose-Einstein condensates that recent experiments (especially in projects E1 and E2) are starting to unveil. Two main topics have recently attracted a major attention: dipolar rotons and quantum dipolar droplets. This project will investigate both phenomena, in close collaboration with experiments within the Research Unit. Dipolar rotons, recently created for the first time in project E2, are finite-momentum low-energy excitations. Within this project we will study finite-size effects in the physics of rotons. Moreover, the combination of dipolar roton excitations and quantum stabilization, i.e. the mechanism behind the formation of quantum droplets observed in E1 and E2, is expected to lead to a rich ground-state and finite-temperature physics that we will investigate as well. Remarkably, these two effects may allow for the creation of a supersolid, whose realization and properties will be analyzed. Quantum fluctuations, crucial for quantum stabilization, change radically in lower dimensions. We will explore together with project T2 the interesting case of two-dimensional dipolar condensates, which may allow for the creation of particularly robust quantum droplets. Finally, we will investigate as well the ground-state properties and quantum fluctuations of binary dipolar mixtures, recently created in E2.