Towards low-dimensional Bose-Fermi mixtures on a microchip

原子在超低温下形成简并量子态，这取决于它们的自旋是玻色-爱因斯坦凝聚态还是简并费米气体。当单个原子的波长变得与原子之间的距离相当时，玻色-爱因斯坦凝聚就会发生，因此整体的行为由波决定。这是量子力学预言的一个主要例子。作为极端多体系统的一种形式，简并量子气体本身就很吸引人，并提供了对我们世界的基本构件的洞察。因为我们可以相对容易地控制这些系统，所以它们对研究和建模其他控制较差或更难访问的系统也非常有用。例如仍然悬而未决的高温超导问题、中子星物理学、引力的类比模型或黑洞和霍金辐射的模型。模拟量子模拟器的符号是由理查德·费曼提出的，他在其中提出，与其试图从理论上预测一个复杂系统的行为，不如用另一个量子系统来模拟它的行为。这样的模拟器完全可以通过冷原子混合实验来实现。在这里，我们建议研究由玻色子(铯，自旋为整数)和费米子(锂，自旋为半整)形成的两种超冷物种的混合物。这将首次允许在简并超流背景(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。对于这些和相关的实验，了解这两种原子之间的相互作用也将是相关的，我们将在大范围的磁场中绘制这些相互作用图。对于原子-原子相互作用，可以存在所谓的Feshbach共振，它使得相互作用的强度从强吸引到非相互作用再到强排斥，因此知道这种共振的位置和形状是非常重要的。因为一个物种可以作为另一个物种的背景介质，这个系统也非常适合于低维输运和非平衡物理的研究。理解这些现象的重要性在EPSRC的物理大挑战中得到了强调。

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.