Towards low-dimensional Bose-Fermi mixtures on a microchip

超低温下的原子会形成简并量子态，具体取决于它们的自旋，要么是玻色爱因斯坦凝聚态，要么是简并费米气体。当单个原子的波长与原子之间的距离相当时，就会发生玻色-爱因斯坦凝聚，因此整体的行为由波决定。这是量子力学预测的一个典型例子。作为极端多体系统的一种形式，简并量子气体本身就很有趣，并提供了对我们世界的基本组成部分的洞察。因为我们可以相对容易地控制这些系统，所以它们对于研究和建模其他控制不太好或更难以访问的系统也非常有用。例如，高温超导性、中子星物理学、重力模拟模型或黑洞和霍金辐射的模拟仍然是悬而未决的问题。模拟量子模拟器的符号由理查德·费曼 (Richard Feynman) 提出，他提出，与其尝试从理论上预测复杂系统的行为，不如用另一个量子系统对其行为进行建模。这样的模拟器正好可以通过冷原子混合实验来实现。我们在这里建议研究由玻色子（铯，具有整数自旋）和费米子（锂，具有半整数自旋）原子形成的两种超冷物质的混合物。这将首次允许在简并超流体背景（类似于晶体中的声子）中研究一维费米子原子（类似于固体中的电子）。我们将在微芯片上实现这些系统，这为研究超冷量子气体提供了一个特别稳定和可靠的环境。对于这些实验和相关实验，了解两种原子之间的相互作用也很重要，我们将在大范围的磁场中绘制出这些相互作用。对于原子-原子相互作用，可以存在所谓的费什巴赫共振，这使得能够将相互作用强度从强吸引力调整为非相互作用和强排斥，因此了解这种共振的位置和形状非常重要。因为一个物种可以充当另一种物种的背景介质，所以该系统也非常适合低维输运和非平衡物理的研究。 EPSRC 的物理大挑战强调了理解这些现象的重要性。

Atoms at ultra-low temperatures form degenerate quantum states, depending on their spin either a Bose-Einstein-Condensate or a degenerate Fermi gas. Bose-Einstein-Condensation occurs when the wavelength of an individual atom becomes comparable to the distance between the atoms and the behaviour of the ensemble is therefore dictated by the wave. This is a premier example for the predictions of quantum mechanics. As a form of an extreme many body system, degenerate quantum gases are fascinating on their own and provide insight into the fundamental building blocks of our world. Because we can control these systems comparatively easily they are also extremely useful to study and model other systems, which are less well controlled or more difficult to access. Examples are the still open problem of high-temperature superconductivity, the physics of neutron stars, analogue models for gravity or modelling of a black hole and Hawking radiation. The notation of an analogue quantum simulator was formed by Richard Feynman, where he proposed that instead of trying to theoretically predict the behaviour of a complex system one could model model its behaviour with another quantum system. Such a simulator would exactly be implemented by a cold atoms mixture experiment. We propose here to study mixtures of two ultracold species formed from bosonic (caesium, with integer spin) and fermionic (lithium, with half-integral spin) atoms. This will allow for the first time the study of one-dimensional fermionic atoms (similar to electrons in a solid) in a degenerate superfluid background (similar to the phonons in a crystal). We will implement these systems on a micro-chip, which provides a particularly stable and reliable environment for studying ultracold quantum gases.For these and related experiments it will also be relevant to know the interactions between the two sorts of atoms, which we will map out over a large range of magnetic-fields. For atom-atom interactions a so-called Feshbach-resonance can exist, which enables tuning of the interaction strength from strongly attractive to non-interacting and to strongly repulsive, knowing the position and shape of this resonance is therefore of great importance.Because one species can act as the background medium for the other, this system is also extremely well-suited to the investigation of transport and non-equilibrium physics in low-dimensions. The importance of understanding these phenomena has been highlighted in EPSRC's Physics Grand Challenges.