Laser Spectroscopy of Isolated Molecules and Complex Systems: Structure, Dynamics and Analysis

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Full-scale quantum computers will require large ensembles of qubits in protected states of sustained coherence. This presents a challenge. Isolated quantum systems of macroscopic size normally conform with the Eigenstate Thermalization Hypothesis. Here, quantum statistical mechanics applies, and eigenstate superpositions just evolve ergodically at a temperature defined by the energy density.   But, in a development with great significance for the field of quantum materials, theory has found conditions under which disordered quantum many-body systems avoid decoherence, preserve spatial order and localize energy in superpositions of states. A small number of highly engineered experiments probing the dynamics of ultracold atoms confirm the principle of many-body localization (MBL) in optical lattices. In new research, we have changed the paradigm, offering a straightforward route to a state with all the hallmarks of MBL. We study Rydberg gases in which electron-impact avalanche ionization followed by shaped hydrodynamic expansion quenches the system to form an ultracold neutral plasma. Here, local integrals of motion (LIOM) govern the propagation of particle and energy density in a strongly disordered landscape. These LIOM create locally emergent conservation laws that guide the spontaneous formation of a global many-body localized state. Like lattice-based quantum many-body systems composed of ultracold atoms, the localized state of a quenched ultracold plasma offers promise as an analog quantum simulator, or a protected regime in which to embed discrete atomic or molecular qubits.   New work will build on our preliminary observations of these quantum dynamics. We will further investigate the quenching and localization dynamics of nitric oxide and other ultracold plasmas. We will use a high-resolution digital synthesizer of mm-wave radiation to probe for localized (Poisson) versus delocalized (Wigner-Dyson) level-spacing statistics. The mechanics of avalanche and quench create a narrow distribution of particle distances.  This may play a role in the quantum dynamics of arrested relaxation. We propose to study plasmas of NO and other molecules for the development of spatial correlation by means of coherent diffractive imaging with visible light.   Interferometric imaging will also figure in a parallel program of Discovery Grant research on the sub-micron analysis and classification of complex materials by high-resolution interferometric backscattering (iSCAT) - Raman microscopy.  We will develop multivariate analysis strategies that determine nanoparticle size distributions in real time, and probe three-dimensional structure in native samples. We illuminate a wide field by the acousto-optical deflection of a diffraction-limited focus. Frequency resolving this image affords a confocal Raman map as wide as 100 x 100 µm.  We will build on these unique instrumental capabilities in a context of active local and international collaborations.