Harnessing room-temperature quantum-dot-like states in 2D materials for nanoscale non-classical light sources

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Nontechnical SummaryLight-based quantum technologies rely on the creation and manipulation of individual photons, the discrete fundamental packets of energy that constitute light. Engineers and scientists who are seeking to use light for quantum technologies require “single-photon emitter” devices that produce just a single photon with a flip of a switch. Such devices, however, need single-photon emitting materials that are hard to come by because they also need to be compatible with modern semiconductor engineering and fabrication techniques. Recently, a new class of single-photon emitters was discovered in ultrathin two-dimensional materials and was greeted with much excitement because, among other advantages, two-dimensional materials can be more easily integrated into devices than most other single-photon emitting materials. However, the underlying material properties and physical phenomena that lead to the single-photon emission in two-dimensional materials remain unknown: it is known that single-photon emitters exist, but it is not known why. This project aims to answer this critical question by combining highly sophisticated optical microscopy techniques to study single-photon emitters in two-dimensional materials on ultrasmall length scales. The experimental studies are complemented by the development of theoretical models to better predict their behavior and identify ways to improve their performance for quantum technologies. These research activities include strong components of quantum-centered education and workforce training, including highly interdisciplinary Ph.D. research, integrated undergraduate research opportunities, curriculum development, and public and K-12 outreach activities.Technical SummaryLight-based quantum technologies necessitate quantum emitters to produce single photons or entangled photon pairs on demand. The discovery of single-photon emitters (SPEs) in monolayer WSe2 (1L-WSe2) ushered in a revolutionary class of solid-state quantum emitters with new opportunities for deterministic positioning, facile emitter control, and integrability into photonic architectures. However, the physical mechanisms giving rise to these promising states are still unknown, hindering their development. Using state-of-the-art theoretical modeling with advanced experimental characterization, a new mechanism of strain-induced exciton localization in 1L-WSe2 was previously identified. It upends the understanding of strain localization of excitons in two-dimensional semiconductors and may be the mechanism that underlies many SPEs in 1L-WSe2. With an overarching goal of developing an understanding of SPE phenomena in 1L-WSe2 that will guide their development into controllable quantum photonic devices, this project is focused on (1) investigating whether the newly discovered states are room-temperature SPEs; (2) establishing the roles of these states in known low-temperature SPEs; and (3) exploring new routes for engineering the creation and active control of SPEs in 1L-WSe2 and other two-dimensional materials. The research strategy combines nano-optical characterization with low-temperature quantum optical measurements and theory, and it is integrated with educational efforts emphasizing mentoring and hands-on learning about photonic materials, quantum optical characterization techniques, and the fundamentals of quantum information science for students in high school through graduate school.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.