Enhancing Light-Matter Interfaces via Collective Self-Organization

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The primary goal of this quantum nonlinear optics research program is to study a new type of light-matter interface, realized by laser driving cold atoms, that has very large coupling strength, low absorption, and long atomic coherence times. It arises due to the simultaneous action of Sisyphus cooling of the atoms and atomic bunching in wavelength-scale structures. Fields self-generated by the light-matter interaction have a large affect on the center-of-mass motion of the atoms in a single pass through the medium, giving rise to self-assembled spatial structures in the absence of a cavity. These structures act back on the fields, giving rise to long coherence times, slow light, and quantum optical patterns arising from an absolute instability (phase transition). The investigators are using this light-matter interface to: 1) Observe a low-light-level (potentially single-photon) nonlinear phase shift when the laser-driven gas is placed in an interferometer; 2) Measure the quantum statistical properties of the radiation scattered by the driven gas of atoms near the phase transition to test recent predictions of an associated Dicke-like model; 3) Measure spontaneous pattern formation in the driven gas and correlate to the atomic spatial reorganization; 4) Observe three-dimensional (3D) Sisyphus cooling when pumping the gas with counterpropagating Bessel beams, thereby dramatically increasing the quantum coherence time of the interaction; 5) Develop a self-consistent model of the light matter interaction that accounts for propagation of the optical fields, polarization of the atoms, center-of-mass atomic motion, and Sisyphus cooling in 3D; and 6) Extend the free-space Dicke-like model to account for the new physics found in this system. This work will provide new experimental and theoretical understanding of a unique physical system that has applications to quantum nonlinear optics, especially in the development of single-photon nonlinear interactions and the study of classical and quantum phase transitions in a well-controlled environment. The program has also has implications for the study of far-from equilibrium quantum phase transitions, cold-atom physics, and condensed matter physics. Broader Impact: From a broad perspective, the program has the potential to improve the performance of nonlinear optical devices by increasing the nonlinear optical sensitivity making it possible to shrink the size of the device and lower the power requirements. From an educational perspective, the program will results in the training of two graduate students in an interdisciplinary environment in both experimental and theoretical techniques in the enabling field of optical physics. It is noteworthy that the PI has been very effective in mentoring women and minority scientists and has undertaken substantial outreach in the local area elementary and middle schools to help attract more people to the science disciplines.