Molecules for Quantum simulation

为了在量子水平上充分理解宇宙，我们不能依赖经典计算机。这是因为物质太复杂了，例如，物质由大量相互作用的粒子组成，计算这样一个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。更好的方法是使用量子粒子重建系统。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。目前存在基于捕获离子、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势和劣势。分子，很像里德伯原子，提供了一个容易扩展的途径，以大量的粒子。然而，分子具有非常长的寿命状态和丰富的内部结构。这种结构提供了可以探索的不同能量尺度，超过4个数量级，以及增加额外合成维度的可能性。此外，超冷的受控分子可用于基础物理的测试和量子化学的研究。在过去的十年里，人们已经开发出了制造非常冷的分子云的技术，最近，第一批分子被装入了单独的光学陷阱--称为镊子。我将建立一个新的实验，基于这些方法，在镊子中创建分子阵列。我将第一次演示如何控制分子在镊子中的运动，使它们被固定在每个陷阱的最小值。我还将控制分子的内部量子态-通过增加和减少分子旋转的能量。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，其中粒子可以同时存在于两种状态中。在这样的叠加中，分子将彼此强烈地相互作用，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-偶极相互作用，并测量其对外部参数的依赖性，如陷阱阵列的几何形状。为了真正从分子提供的优势中受益，我们希望将它们加载到具有较小的位点间间隔（低至捕获光波长的一半，即~400 nm）的光学晶格中，并且可以允许位点之间的隧道效应以及偶极-偶极相互作用。这导致了其他平台无法访问的外来阶段。这将是该项目的下一阶段，将导致一个多功能的可编程量子模拟器。

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.