CAREER: The Effect of State-Mixing Interactions on the Rydberg Excitation Blockade

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The goal of this project is to study the "Rydberg excitation blockade." Atoms will be cooled to extremely low temperatures and put into high energy states called Rydberg states. In Rydberg states the outermost electron (or the negatively charged component of an atom) travels in extremely large orbits around the nucleus (or the core of an atom). Because of these large orbits, atoms in Rydberg states have properties which are exaggerated relative to the properties of atoms in their natural, or ground state. One such property is that Rydberg atoms interact strongly with each other when separated by large distances, even though they have no net charge. Normally, when a laser is shined on a group of atoms, the outermost electron in each atom is readily promoted to Rydberg states. However, the interactions among multiple Rydberg atoms causes this excitation to be suppressed, or "blocked," and leads to the creation of fewer Rydberg atoms than would otherwise be created. This suppression of excitation may help enable the use of single atoms as the "bits" in computer ("neutral atom quantum computing"). Quantum computers have the potential to revolutionize data security and encryption. The present project will focus on processes which make the Rydberg excitation blockade function less effectively (state-mixing interactions). Essentially, if one tries to put atoms into a given Rydberg state using a laser, the atoms will mix into other states. This mixing "breaks the blockade" and leads to an undesirably large number of Rydberg atoms. The goals of the present research are to quantify the extent to which state mixing interactions reduce the blockade efficiency, to understand the physical mechanism which gives rise to the mixing, and to study the experimental parameters which lead to the best excitation blockade. Understanding these issues will allow other researchers to use the blockade in a way that minimizes unwanted effects when developing a quantum computer. The project also involves a significant educational component. The PI will develop educational modules for a diverse group, ranging from general education students to advanced physics students. The PI will also study the impact of metacognitive exercises on problem solving performance in the introductory physics classroom. All work will be done at a primarily undergraduate university with a significant fraction of first-generation college students.The Rydberg excitation blockade, a process whereby strong interactions among highly-excited atoms suppress laser excitation, has been at the heart of an array of recent experimental achievements. It has been suggested that state-mixing interactions, which result from couplings among multi-particle Rydberg states near a Förster resonance, may compromise the effectiveness of the excitation suppression under otherwise favorable conditions. Experimentally, however, the extent to which the blockade is compromised has been unknown, as large amounts of state mixing have always accompanied an improved blockade near resonance. In this project, the extent to which state-mixing reduces the blockade efficiency will be quantified using state-selective field ionization spectroscopy of rubidium Rydberg atoms in a magneto-optical trap. This work will lead to a better understanding of the physical mechanism responsible for enhanced state-mixing. Additionally, the project will include a systematic study of the experimental conditions for the best blockade near a Förster resonance. The PI will design an eduational module on laser cooling and trapping for a general education course as well as an advanced laboratory experiment on characterizing an ultracold atom cloud in a magneto optical trap.