Quantum-limited tomographic detection of correlations in a strongly interacting atomic Fermi gas

物理学最大的挑战之一是实现具有可随意改变性质的材料。历史上，这一领域的研究主要是在凝聚态物理中进行的。这导致了性能由量子相关和强相互作用主导的复杂材料的发展。其中一些发现已经在我们的日常生活中得到了应用。主要的例子是用于医疗仪器和电信的高温超导性，以及彻底改变了计算机硬盘的巨磁电阻。然而，从基本的角度来看，往往缺乏对潜在机制的理解。没有这种理解，进一步优化或有针对性地搜索更先进的材料是相当困难的。近年来，一条研究强相关材料基本性质的新途径出现了：纳米开尔文温度下的原子气体——首先是玻色-爱因斯坦凝聚体，后来是简并的费米气体——实现了纯度和可调性空前的量子多体系统。具有复杂性质的材料现在可以用自下而上的方法从原子组装起来。在冷原子气体和固体物理之间建立特别好的概念关系的关键因素是光学晶格。光学晶格是由三对反向传播的激光束形成的光晶体。这种强激光光场的复杂排列为类似固体晶格的原子提供了周期势。光学晶格中的费米子原子气体模拟了固体中电子的物理性质，但却是一个非常好的控制模型系统。因此，它们为在更纯净甚至可调的条件下理解固体中电子的量子行为铺平了道路。例如，有人提出，光学晶格中的冷原子气体可以解开高温超导的物理原理。通过实验，我们将从第一性原理出发研究量子多体物理。我们计划在三维光学晶格中实现费米子原子的复杂量子相，包括高温超导相的模拟。这将有助于确定电子如何成为超导体对的机制，以及为什么高温超导体不同于金属或金属超导体。为了尽可能精确地表征强相关量子多体态，我们将执行一种新颖的单原子分辨率三维层析成像。这项新技术是基于过去十年来原子物理学的进步，实现了接近100%的单原子检测效率。有了这种实验能力，我们将能够在量子极限下发现最小的相关效应，以观察原子对的相关运动。这将明确地揭示新的超导态或磁有序态。

One of the greatest challenges of physics is the realisation of materials with properties that can be changed at will. Historically, this field of research was mainly pursued in condensed matter physics. This has lead to the development of complex materials whose performance is dominated by quantum correlations and strong interactions. Some of these discoveries have found their way into applications of our daily life. The prime examples are high-temperature superconductivity which is used in medical instrumentation and telecommunications and giant magneto-resistance which has revolutionized computer hard disks. However, from a fundamental perspective an understanding of the underlying mechanism is often lacking. Without this understanding a further optimization or targeted search for even more advanced materials is quite difficult.In recent years, a promising new route to study fundamental properties of strongly correlated materials has emerged: atomic gases at Nanokelvin temperatures - firstly Bose-Einstein condensates and later degenerate Fermi gases - realize quantum many-body systems of unprecedented purity and tunability. Materials with complex properties can now be assembled from atoms in a bottom-up approach. The key ingredient which allows for a particularly good conceptual relation between cold atomic gases and solid state physics is the optical lattice. Optical lattices are crystals of light formed by three pairs of counter-propagating laser beams. This complex arrangement of intense laser light fields provides a periodic potential for atoms resembling the crystal lattice of a solid. Fermionic atom gases in an optical lattice simulate the physics of electrons in a solid yet being an extremely well controlled model system. They thus pave the way to understand the quantum behaviour of electrons in a solid under much purer and even tunable conditions. For example, it has been proposed that cold atomic gases in optical lattices could unravel the physics underlying high-temperature superconductivity. With our experiments we will investigate quantum many-body physics from first principles. We plan to realize complex quantum phases of fermionic atoms in a three-dimensional optical lattice including the analogue of a high-temperature superconducting phase. This would allow to identify the mechanism of how the electrons in as superconductor pair and why high-temperature superconductors are different from metals or metallic superconductors. To characterize the strongly correlated quantum many-body state as precisely as possible we will perform a novel three-dimensional tomographic imaging with single atom resolution. This new technique is based on the progress in atomic physics over the past decade to achieve single atom detection of near 100% efficiency. Equipped with this experimental capability we will be able to uncover even the smallest correlation effects at the quantum limit to observe the correlated motion of pairs of atoms. This will unambiguously reveal novel superconducting or magnetically ordered states.