Molecules for Quantum simulation

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.