Quantum Phases of Rotating Multipolar Molecules

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Birgitta Whaley of the University of California, Berkeley, is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry division to use ground state Quantum Monte Carlo techniques for the study of novel quantum phases formed by multipolar molecules. Professor Whaley and her research group study dipolar and quadrupolar molecules at densities where the interactions provide significant anisotropic orientational contributions to the energy, resulting in strongly interacting quantum molecular systems. Their goal is to determine the behavior and properties of these systems with special attention to the interplay between translational and rotational degrees of freedom in determining the quantum properties in the degenerate quantum regime, i.e., at the lowest possible temperatures. They are using a new path integral ground state Quantum Monte Carlo code developed by the researcher and her coworkers that incorporates full rotational and translational degrees of freedom with a high accuracy "any order'' propagator. The new high accuracy rotation/translation code allows exploration of the novel chemistry and physics of these systems without constraints on dipole orientation and allows calculation of off-diagonal matrix elements giving access to study of large scale quantum coherences in molecular systems, allowing them to investigate for the first time how molecular rotations might modify the well-known off-diagonal long range order of translational degrees of freedom in quantum gases and fluids. Recent growth of experimental methods that not only probe and reveal the microscopic behavior of quantum phases but also enable emulation of new phases in Feynman's original sense of quantum simulation, which makes theoretical research in novel molecular quantum phases an essential component of the chemical physics landscape for the near future. This research brings together molecular chemistry with quantum physics to extend the realm of molecular chemistry to cold molecules in strongly quantum regimes. It thus embodies the interdisciplinary view of science that is an essential aspect of scientific research in the twenty-first century. The anticipated results form a base for quantum simulation of biological and novel condensed phase materials and reveal opportunities for creating unusual materials with tailored quantum properties and diverse applications. The research involves students from chemistry and physics, and will be linked to education and outreach activities on the Berkeley campus.