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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导致了许多非凡的发现。最难液化的气体是氦，但这最终在世纪初实现了。这一突破导致了对超流现象的观察（一种没有摩擦力的液体，就像超导体中的电流没有阻力一样），现在氦制冷具有根本的技术重要性，例如对于牛津仪器等大型国际公司。在世纪末，新的技术被开发出来，使用激光来冷却原子（尽管这似乎违反直觉）和磁阱，将原子限制在一个非常好的真空区域。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至数十纳开尔文的极低温度。这使得第一次在弱相互作用的稀气体中观察到玻色-爱因斯坦凝聚（BEC），正如著名物理学家爱因斯坦和玻色所预测的那样。这种极其有趣的量子现象与以前对超流氦的研究有关，但这种液体比超冷的原子气体更难理解。使用为天文学和显微镜开发的最先进的照相机可以拍摄冷原子的非常详细的图像，这种直接看到量子流体中发生的事情的能力使得理解这些系统的进展非常迅速，并提供了丰富的新知识。这一点在BEC的第一个实验中就很明显了。在BEC实验中，从普通气体到量子态的相变被观察到了密度和形状的巨大变化。我们建造了一个新颖的装置，在该装置中，原子在磁场中运动时所经历的势能景观通过应用射频辐射以精确可控的方式进行调整。(The所施加的辐射改变了空间中特定位置处的原子的量子状态，从而改变了它们所感受到的电势。这已被证明是特别有用的二维系统和创造有趣的几何形状，如环陷阱（与量子相干的循环）。这种方法的一个很大的优点是，与用激光捕获原子产生干涉条纹相比，这种方法的电势非常平滑，没有缺陷。我们将这种新方法与时间平均相结合，以使陷阱中的电位范围更大，寿命更长。我们将继续开发和测试捕获原子的新方案，例如创建双环（原子在两个同心圆上）和在磁场中捕获原子，其中存在相互作用的共振增强（Fano-Feshbach共振）。我们将把这项技术应用于强关联系统的直接量子模拟，并探索在精密测量设备中的物质波干涉等应用。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·费曼的陈述，“因此，我相信，通过适当的量子机器，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，但它更直接地适用于可控量子系统的创建，在可控量子系统中，我们设计量子哈密顿量，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，量子力学被用于设计量子机器，即可控地创建多体量子态的装置，以与汽车力学用于创建车辆相同的方式。