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Ultracold Molecules in Optical Trap Arrays

Periodic Reporting for period 1 - UMOTA (Ultracold Molecules in Optical Trap Arrays)

Reporting period: 2018-06-01 to 2020-05-31

Quantum systems can be in superposition states. For example, the spin of one electron can be in three possible quantum states: up, down, or simultaneously up AND down. With each electron we add, the number of possible joint quantum states including superpositions doubles. Amazingly, the memory required to store the state of just a 35-electron system exceeds the total storage capacity of all computers worldwide. A normal computer is clearly incapable of simulating many-particle quantum systems, which exhibit remarkable phenomena, such as high-temperature superconductivity. As a result, very little is understood about these systems and simulating their properties is one of the greatest unsolved problems in physics. Richard Feynman identified this bottleneck in 1982 and suggested an elegant workaround: rather than using a normal computer, we should simulate complicated quantum systems using another, more controllable quantum system. It took until recently for technology to catch up and such quantum simulators are slowly being realized using photons, atoms, ions and superconducting circuits. Each of these has advantages, but struggle with simulation of collective many-body behaviour. Over the course of the UMOTA project I pursued Feynman’s idea by designing and constructing a new and unique apparatus for quantum simulation with ultracold polar molecules. Unlike the systems used so far, polar molecules interact over long distances through their electric dipole moments, facilitating simulation of systems with long-range interactions. The new experiment will allow me to confine laser cooled polar molecules to the sites of a configurable optical tweezer array and entangle the molecules via their dipole-dipole interactions. I will be able to implement a two-molecule quantum gate, which is the basic building block of my quantum simulator, and also of a quantum computer. In the future, the system will be able to mimic up to 49 interacting electrons and solve problems intractable to classical computers.
Over the course of the two-year UMOTA project, I designed and setup a completely new apparatus to magnetically transport, optically trap and image small numbers of laser cooled Calcium Monofluoride (CaF) molecules in optical dipole traps. The setup is capable of trapping single CaF molecules in sub-micrometre optical tweezers traps, cooling them to the ground state of the trap, and coherently manipulating them with optical and microwave radiation. The optical imaging and trapping system was developed in collaboration with the secondment host group at Durham University. The magnetic transport link allows me to shuttle atoms or molecules over a distance of 40cm into a dedicated vacuum chamber for the optical tweezer experiments. During the lab shutdown, I developed a Monte Carlo simulation code to investigate trapping a cloud of molecules in a dipole trap and found the right experimental parameters to implement this in the UMOTA experiment. Since the lab re-opening I have demonstrated optical dipole trapping of Rubidium atoms in the apparatus. I disseminated the results of my work at three major atomic and molecular physics conferences, and many meetings with our collaboration partners in Durham. I also shared my research with the general public, showcasing a dipole trapping experiment at two science festivals, which were attended by thousands of people.
The one-of-a-kind apparatus that I developed as a MSCA fellow will allow me to perform novel quantum simulation experiments with ultracold polar molecules. First tests with laser cooled Rubidium atoms indicate that the experiment is functional and promise the investigation of dipolar physics with ultracold polar molecules in the near future.