Coherence Control of Weak Localization in Cold Atoms

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In recent years, scientists have fine-tuned their ability to lower the temperature of some atoms and molecules to close to absolute zero on the Kelvin temperature scale. Atoms cooled down to this level, often referred to as “ultracold” atoms, behave differently than atoms at room temperature, especially when interacting with laser light. It is even possible to use laser light to hold atoms in place, countering the force of gravity. Such atoms are referred to as “trapped.” Trapped atoms can be studied as part of fundamental science investigations or used for real-world applications, like building very precise sensors or even deployed for a new class of computers known as “quantum computers.” Trapped atoms interacting with laser light can also be used to model other physical systems, for example, how electrons might travel in solids. This project explores how laser light, whose color is carefully controlled, scatters off of an ensemble of trapped, ultracold atoms. The experimental objectives of this project are twofold: 1) to study laser light scattering under conditions that have not been explored before to better understand the intricate details of the fundamental light scattering dynamics, and 2) to use additional lasers to actually control the light scattering process – not just to observe it. Accompanying these experiments in the laboratory will be an effort to refine the theoretical understanding of all of the observed physical phenomena so that the findings can be applied to other basic scientific and applied research problems. The project is directed towards investigation of unexplored areas of light scattering and transport in weakly disordered, ultracold atomic gases. In particular, coherent backscattering (CBS), an interference effect sometimes referred to as “weak-localization,” that results in enhanced scattering of light in the backwards direction, will be investigated in conjunction with electromagnetically-induced transparency-like conditions to explore potential control aspects to the light scattering process. Modification to the CBS effect will be measured, using light polarization, applied magnetic fields and atomic density as the principal “control knobs.” In a related project, the CBS effect will be investigated when the laser light is off-resonance from an atomic transition, and with variable polarization and applied magnetic fields. Here, an effect known as “anti-localization,” arising from hyperfine coherences that build up over time, is predicted – theoretically - to reduce the observed CBS signal. Beyond observation of this phenomena, of particular interest is measurement of the detuning dependence of the process to enable comparison to theoretical predictions and validate scattering models in this regime.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.