Interacting Bose-Einstein Condensates: Tunneling, Localization, and Beyond Mean-Field

锂原子表现出非常广泛的费什巴赫共振。Li-7的最低超精细亚能级的费什巴赫共振扩展在大约200高斯(G)的范围内，在那里它经历了一个斜率仅为0.1 ao/G的零交叉，其中ao为玻尔半径。我们的工作利用费什巴赫共振的性质来研究具有吸引、弱或强相互作用的玻色子。明亮物质波孤子的创造，先前证明了弱吸引Li-7原子，使探索基本量子现象成为可能。我们研究了单粒子隧穿，方法是在由光片形成的中心势垒存在的情况下，使孤子在一维光阱中执行偶极子振荡。这个系统可能显示出一个显著的相干重组，可以形成一个明亮的物质波孤子干涉仪的基础。长期目标是努力实现真正的宏观量子隧穿，以创建Schrödinger Cat状态。我们的第二个项目是研究由光学散斑产生的无序势对玻色-爱因斯坦凝聚体输运性质的影响。最近在凝聚态物质中提出了一种“超绝缘体”，其中在1D中导电状态和绝缘状态之间存在有限的温度转变，可以使用冷原子来实现。一个密切相关的课题是通过测量粒子间相互作用的局域化长度来理解相互作用在安德森局域化中的作用。最后，广泛的费什巴赫共振使我们能够进入强相互作用的领域，在那里玻色-爱因斯坦凝聚的平均场理论失效了。在扰动状态下，能量以许多次幂进行校正，散射长度的立方，以及强凝析油耗竭状态都在研究中。波粒二象性是量子物理学的核心。在非常低的温度下，我们发现通常作为致密固体的粒子表现得好像它们是波，也就是说，它们反射、衍射和干涉。原子的玻色-爱因斯坦凝聚（BECs）就是这种行为的典型例子。BEC是一组原子的集合，它们在低至绝对零度以上百万分之一度的温度下形成单个量子机械波。在这个项目中，我们创建了相互作用的锂原子的bec，并用它们来探索和测试量子力学的一些最基本的想法，包括粒子穿过其他不可穿透的障碍的隧道。这些实验是通过调节原子间相互作用的强度，甚至改变它们是排斥还是吸引的能力来实现的。通过使它们的吸引力变弱，bec形成了一个孤子，这是一个可以传播一段距离而不消散的波包。在某些条件下，BEC孤子可能表现得像一个单一的“超级原子”，从而将量子力学的领域扩展到更大的物体，就像著名的薛定谔猫一样。我们也将相互作用调整到相反的极端，相互作用是排斥的，而且非常强。这些bec被用来测试我们关于强相互作用物质的理论。这些实验将使我们对量子领域有更深入的了解，这将使我们能够在实际应用中利用量子现象，如超导性。

Lithium atoms exhibit extraordinarily broad Feshbach resonances. The Feshbach resonance for the lowest hyperfine sublevel of Li-7 extends over a range of approximately 200 Gauss (G), where it goes through a zero crossing with a slope of only 0.1 ao/G, where ao is the Bohr radius. Our work exploits the properties of this Feshbach resonance to study bosons with attractive, weak, or very strong interactions.The creation of bright matter wave solitons, previously demonstrated with weakly attracting Li-7 atoms, enables the exploration of fundamental quantum phenomena. We study single particle tunneling by causing the soliton to execute dipole oscillations in a one-dimensional optical trap in the presence of a central barrier formed from a light sheet. This system may show a remarkable coherent recombination that could form the basis for a bright matter wave soliton interferometer. Longer term goals are to work towards true macroscopic quantum tunneling in order to create a Schrödinger Cat state.Our second project is study of the effect of a disordered potential, created from optical speckle, on the transport properties of a Bose-Einstein condensate. Recent proposals in condensed matter to demonstrate a "superinsulator", in which there is a finite temperature transition between a conducting and insulating state in 1D may be realizable using cold atoms. A closely related topic is to understand the role of interactions in Anderson Localization by measuring the localization length as a function of interparticle interaction.Finally, the broad Feshbach resonance enables access to the regime of strong interactions where the mean-field theory of Bose-Einstein condensation breaks down. Both the perturbative regime, where the energy is corrected in powers of many time the cube of the scattering length and the regime of strong condensate depletion are being explored.Wave/particle duality is at the heart of quantum physics. At very low temperatures, we find that particles that ordinarily act as compact solid objects behave as if they are waves, that is, they reflect, diffract, and interfere. Bose-Einstein condensates (BECs) of atoms are iconic examples of such behavior. A BEC is a collection of atoms that become a single quantum mechanical wave at temperatures as low as one millionth of a degree above absolute zero. In this program, we create BECs of interacting lithium atoms and use them to explore and test some of the most fundamental ideas of quantum mechanics, including the tunneling of particles through otherwise impenetrable barriers. These experiments are enabled by the ability to tune the strength of the interatomic interactions and to even change whether they are repulsive or attractive. By making them weakly attractive, the BECs form a soliton, which is a packet of waves that can travel over a distance without dissipating. Under some conditions a BEC soliton may behave as a single "super-atom", thus stretching the realm of quantum mechanics to ever larger objects, much like the famous Schrodinger Cat. We also tune the interactions to the opposite extreme, where the interactions are repulsive and very strong. These BECs are being used to test our theories of strongly interacting matter. These experiments will give us a greater understanding of the quantum realm, which hopefully, will allow us to exploit quantum phenomena, such as superconductivity, for practical applications.