Ultracold molecules for quantum simulation: rotational coherences in CaF and RbCs

Polar molecules offer a new platform for quantum simulation of systems with long-range interactions, based on the electrostatic interaction between their electric dipole moments. Here, we report the development of coherent quantum state control using microwave fields in 40 Ca 19 F and 87 Rb 133 Cs molecules, a crucial ingredient for many quantum simulation applications. We perform Ramsey interferometry measurements with fringe spacings of 1 kHz and investigate the dephasing time of a superposition of N=0 and N=1 rotational states when the molecules are confined. For both molecules, we show that a judicious choice of molecular hyperfine states minimises the impact of spatially varying transition-frequency shifts across the trap. For magnetically trapped 40 Ca 19 F we use a magnetically insensitive transition and observe a coherence time of 0.61(3)ms. For optically trapped 87 Rb 133 Cs we exploit an avoided crossing in the AC Stark shifts and observe a maximum coherence time of 0.75(6)ms. Since Lloyd's proof that evolving a controllable quantum system in small time steps can allow efficient simulation of any quantum many-body Hamiltonian [1], the field of quantum simulation has grown enormously. This growth has been driven by the prospect of understanding complex physical systems, such as high-temperature superconductors [2, 3] or warm, dense nuclear matter In this context, the role of the quantum simulator is to implement a model of a physical system, and to measure observables that can be compared to real systems of interest Currently, a number of experimental platforms are under exploration, each in essence attempting to address Cirac and Zoller's criteria to qualify as a quantum simulator [6] through different paths