Molecules for Quantum simulation

为了在量子层面上全面了解宇宙，我们不能依赖经典计算机。这是因为物质太复杂了，例如，材料由大量相互作用的粒子组成，而计算这种系统的演化所需的计算机内存随着粒子的数量呈指数增长。一个更好的方法是用量子粒子来重建这个系统。在这个项目中，我们将使用超冷分子作为量子模拟器的基础。目前已有基于俘获离子、里德伯原子和超导电路的量子模拟器。每个平台都有自己的优点和缺点。分子，就像里德伯原子一样，为大量粒子提供了一条容易扩展的途径。然而，分子有很长的生命状态和丰富的内部结构。这种结构提供了不同的能量尺度，可以探索，超过4个数量级，以及增加额外合成维度的可能性。此外，超冷的受控分子可以用于基础物理测试和量子化学研究。本项目所展示的技术也将有助于这些领域。在过去的十年里，技术已经发展到可以制造非常冷的分子云，最近第一个分子被装载到单独的光学陷阱中——被称为镊子。我要建立一个新的实验，基于这些方法，在镊子中创建分子阵列。我将首次演示对镊子中分子运动的控制，使它们被固定在每个陷阱的最小值上。我还将控制分子的内部量子态——通过从分子的旋转中增加和减少能量。通过这样做，我将创造出所谓的旋转态叠加。叠加是一种量子力学现象，一个粒子可以同时以两种状态存在。在这样的叠加状态下，分子之间会产生强烈的相互作用，从而提供模拟系统所需的耦合。我将研究这种相互作用，称为偶极子-偶极子相互作用，并测量其对外部参数（如陷阱阵列的几何形状）的依赖性。为了真正从分子提供的优势中获益，我们希望将它们加载到光学晶格中，该晶格具有较小的位点间分离（低至捕获光波长的一半，即~400 nm），并且可以允许在位点之间隧穿以及偶极子-偶极子相互作用。这导致了其他平台无法访问的奇异阶段。这将是该项目的下一阶段，导致一个通用的，可编程的量子模拟器。

In order to fully understand the universe at a quantum level, we can't rely on classical computers. This is because matter is too complicated, for example, materials consist of large numbers of particles all interacting with one another and the computer memory required to calculate the evolution of such a system grows exponentially with the number of particles. A better route is to recreate the system using quantum particles. In this project we will be using ultracold molecules as the basis for a quantum simulator. There currently exist quantum simulators based on trapped ions, Rydberg atoms and superconducting circuits. Each platform has its own strengths and weaknesses. Molecules, much like Rydberg atoms, provide an easily scalable route to large numbers of particles. However, molecules have very long-lived states and a rich internal structure. This structure offers different energy scales which can be explored, over 4 orders of magnitude, and the possibility of adding an extra synthetic dimension. In addition, ultracold, controlled molecules can be used for tests of fundamental physics, and studies of quantum chemistry. The techniques demonstrated in this project will contribute to these fields as well.Over the last decade, techniques have been developed to create very cold clouds of molecules, and recently the first molecules were loaded into individual optical traps - known as tweezers. I am going to build a new experiment, based on these methods, to create arrays of molecules in tweezers. I am going to demonstrate control over the motion of the molecules in tweezers for the first time, such that they are pinned to the minimum of each trap. I will also control the internal quantum state of the molecule - by adding and removing energy from the rotation of the molecule. By doing this I will create what is known as a superposition of rotational states. A superposition is a quantum mechanical phenomenon where a particle can exist in two states at once. In such a superposition, molecules will interact strongly with one another providing the coupling required to simulate a system. I will study this interaction, called the dipole-dipole interaction, and measure its dependency on external parameters such as the geometry of the trap arrays. To truly benefit from the advantages offered by molecules, we want to load them into an optical lattice which has smaller intersite separation (down to half the wavelength of the trapping light i.e. ~400 nm) and can allow for tunnelling between sites as well as the dipole-dipole interaction. This leads to exotic phases which cannot be accessed by other platforms. This will be the next stage of the project, leading to a versatile, programmable quantum simulator.