New techniques for nanokelvin condensed matter physics

纳开尔文凝聚态物理新技术

基本信息

批准号：
EP/J008028/1
负责人：
Christopher Foot
金额：
$ 40.76万
依托单位：
University of Oxford
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2011
资助国家：
英国
起止时间：
2011 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FJ008028%2F1
关键词：
New techniques nanokelvin condensed matter

项目摘要

The quest for colder and colder temperatures has led to many remarkable discoveries. The most difficult gas to liquify is helium but this was finally achieved at the beginning of the 20th century. That breakthrough led the observation of the intriguing phenomena of superfluidity (a liquid that flows without friction just like the current in a superconductor flows without resistance) and nowadays refrigeration with helium is of fundamental technological importance, e.g. for large international companies such as Oxford Instruments. At end of the the 20th century new techniques were developed that used laser light to cool atoms (although this may seem counterintuitive) and magnetic traps that confine the atoms in a region of very good vacuum. This new technology allowed dilute vapours of alkali metal atoms to be prepared a low temperatures. Amazingly this atoms of metal do no clump together (to form molecules) and evaporation cools the cloud further to extremely low temperatures of tens of nanokelvin. This allowed the first experimental observation of Bose-Einstein condensation (BEC) in a weakly interacting dilute gas, as predicted by the famous physicists Einstein and Bose. This extremely interesting quantum phenomenon has links with previous work on superfluid helium but the liquid is more complicated to understand than the ultra-cold atomic gases. Wonderfully detailed images of the cold atoms can be taken using state-of-the-art cameras developed for astronomy and microscopy and this ability to see directly what is going on in quantum fluids has allowed very rapid progress in understanding these systems and provided a wealth of new knowledge. This was evident in the very first experiment on BEC where the phase transition from an ordinary gas to the quantum regime was observed as a dramatic change in the density and shape.We have built a novel apparatus in which in the the potential energy landscape that atoms experience as they move through the magnetic field is tailored in a precisely controllable way by the application of radio-frequency radiation. (The applied radiation changes the quantum state of the atoms at particular positions in space hence changing the potential they feel.) This has proven to be particularly useful for two-dimensional systems and for creating interesting geometries such as ring traps (with quantum coherence around the loop). A great advantage of this approach is that the potential is very smooth and free from defects, as compared to trapping atoms with laser light where interference fringes arise. We have combined this new approach with time-averaging to allow an even greater range of potentials and long lifetimes in the traps. We shall continue to develop and test new schemes for trapping atoms, such as the create of double rings (atoms on two concentric circles) and trapping atoms at magnetic fields where there is resonant enhancement of the interactions (Fano-Feshbach resonance). We shall apply this technology to the direct quantum simulation of strongly correlated systems, and explore applications such a matter-wave interferometry for precision measuring devices. This progress in cooling atomic gases to nanokelvin temperatures now allows us to fulfill the statement of Richard Feynman,``I therefore believe it's true that with a suitable class of quantum machines you could imitate any quantum system, including the physical world''. This is often quoted in the context of quantum information processing but it applies more directly to the creation of controllable quantum systems in which we engineer the quantum Hamiltonian so that it looks the same as that of the physical system of interest. This is the underlying principle of our work on Direct Quantum Simulation. In this context quantum mechanics is used to design a quantum machine, i.e. an apparatus to controllably create many-body quantum states, in the same way that automotive mechanics is used in the creation of vehicles.

对越来越冷的温度的追求带来了许多非凡的发现。最难液化的气体是氦气，但这终于在 20 世纪初实现了。这一突破导致了人们对超流动性（一种无摩擦流动的液体，就像超导体中的电流无阻力流动一样）的有趣现象的观察，而如今，氦制冷具有根本性的技术重要性，例如制冷。适用于牛津仪器等大型国际公司。 20 世纪末，新技术被开发出来，使用激光来冷却原子（尽管这似乎违反直觉）和磁阱，将原子限制在真空度非常高的区域。这项新技术可以在低温下制备碱金属原子的稀蒸气。令人惊讶的是，这些金属原子不会聚集在一起（形成分子），并且蒸发将云进一步冷却到数十纳开尔文的极低温度。正如著名物理学家爱因斯坦和玻色所预测的那样，这使得首次在弱相互作用的稀气体中实验观察到玻色-爱因斯坦凝聚（BEC）。这种极其有趣的量子现象与之前关于超流氦的工作有关，但这种液体比超冷原子气体更难以理解。可以使用为天文学和显微镜开发的最先进的相机拍摄冷原子的精美详细图像，这种直接观察量子流体中发生的情况的能力使得人们在理解这些系统方面取得了非常快的进展，并提供了丰富的知识。新知识。这在 BEC 的第一个实验中很明显，其中从普通气体到量子态的相变被观察为密度和形状的巨大变化。我们建立了一种新颖的装置，其中原子在势能景观中通过应用射频辐射，以精确可控的方式定制它们在磁场中移动时的体验。（所施加的辐射改变了空间中特定位置处原子的量子态，从而改变了它们感受到的电势。）这已被证明对于二维系统和创建有趣的几何形状特别有用，例如环陷阱（在周围具有量子相干性）循环）。与用激光捕获原子（会出现干涉条纹）相比，这种方法的一大优点是电势非常平滑且没有缺陷。我们将这种新方法与时间平均相结合，以允许陷阱具有更大范围的潜力和更长的寿命。我们将继续开发和测试捕获原子的新方案，例如创建双环（两个同心圆上的原子）以及在相互作用共振增强（法诺-费什巴赫共振）的磁场中捕获原子。我们将将该技术应用于强相关系统的直接量子模拟，并探索物质波干涉测量等在精密测量装置中的应用。将原子气体冷却到纳开尔文温度的这一进展现在使我们能够实现理查德·费曼的说法，“因此，我相信，使用合适的量子机器，你可以模仿任何量子系统，包括物理世界”。这经常在量子信息处理的背景下被引用，但它更直接地应用于可控量子系统的创建，在该系统中我们设计了量子哈密顿量，使其看起来与感兴趣的物理系统相同。这是我们直接量子模拟工作的基本原则。在这种情况下，量子力学用于设计量子机器，即可控地创建多体量子态的装置，就像汽车力学用于制造车辆一样。