Cooperative and Subradiant Phenomena in Quantum Optical Systems

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Quantum optical systems, consisting of ensembles of atoms that can be probed by laser light or by single light quanta, constitute a versatile platform for quantum technologies, with broad potential applications ranging from long-lived quantum memories for secure communication and robust quantum networks to quantum computation. The implementations resulting from the novel models in this project are relevant for applications such as atomic clocks or quantum simulation and quantum information processing, long before an impact from so-called "universal quantum computers" can be expected. Education of students from high school through doctoral level can particularly benefit from delving into these topics: quantum effects in general and quantum information science in particular are well-proven magnets for student learning and research involvement. This appeal will specifically be used to attract and retain underrepresented groups into academic research on quantum technologies. In addition, new teaching techniques that are largely based on recent physics education research will be tested on advanced physics classes to improve learning outcomes for classes that are not primary recipients for additional teaching resources. In ensemble-based quantum optics, the spontaneous emission of atoms into the vacuum modes of the environment and the subsequent loss of information into these undesired channels sets a fundamental performance limit. Such spontaneous emission is typically assumed to be an independent process for each atom. The goal of this project is to challenge this assumption; indeed, dissipation must be correlated to account for the interference between light emitted by different atoms. The nature of this correlated dissipation can be exquisitely controlled and engineered in systems such as gases in different geometries and ordered atomic arrays. For instance, it could lead to entire manifolds of protected - so-called "subradiant" - states whose decay rates approach zero with increasing system size. Alternatively, controlling the response of the atomic medium by combining spontaneous emission with strong, long-range interactions could enable the realization of collective or entangled many-body states across distant atoms. This project will address the following questions: (i) How can one efficiently describe such states, characterize them for various geometries, and how can one modify the calculation depending on system parameters and degree of entanglement? (ii) Looking at the particular example of two-dimensional arrays, how can subradiant states be accessed, used in the context of topological states, and how can this knowledge be potentially transferred to (experimentally easier-to-access) single-layer semiconductor states? (iii) How can this research be applied in order to control and probe cooperatively narrowed clock states, to create resource states for quantum information processing, or to utilize cooperative effects for molecule cooling?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.