Unveiling Quantum Interactions in Alkali Vapor - Photonic Integrated Circuits

As quantum technologies move towards deployable applications, there are significant benefits in moving away from large, infrastructure-heavy systems to compact and standalone platforms. This project focuses on one promising solution, in which alkali atomic vapors – gases of identical atoms that already power commercial devices like chip-scale atomic clocks and magnetometers – are merged with photonic integrated circuits (PICs), which are microchips designed to route and manipulate light. By directly integrating these systems, this research aims to create a compact, room-temperature platform capable of generating individual photons (particles of light) on demand. Such single-photon sources can serve as an essential building block for communications, simulations, and sensing approaches that harness quantum principles to outperform existing classical technologies. This effort directly supports the National Science Foundation's mission to promote the progress of science and advance national prosperity through its development of a scalable, deployable framework for quantum photonic devices. Beyond the technical milestones, the project provides value by training a student workforce in aspects of atomic physics, microfabrication, and photonics, equipping them with the vital skills needed in the emerging quantum economy. The technical objective of this project is to investigate interactions between single vapor-phase rubidium alkali atoms and single photons in a PIC microresonator. While this architecture enables exceptionally high coherent atom-photon coupling rates due to strongly confined evanescent fields, it faces critical challenges from Doppler broadening, ultra-short atomic transit times (~5 ns), and potential PIC degradation caused by adverse rubidium-surface interactions. To address these fundamental issues and achieve non-classical light emission, the project implements a three-part approach: first, tailoring air-clad silicon nitride PIC microresonators utilizing slot mode and photonic crystal concepts to maximize atom-photon interactions; second, developing advanced microfabricated atomic vapor cells that incorporate integrated beam collimators and methods to mitigate device degradation; and third, deploying fine-tooth electro-optic frequency comb technology to precisely track atom-cavity dynamics with high spectral and temporal resolution. This work will provide the underlying methodology and physical insights required to operate vapor-PIC platforms for high-performance quantum light sources and scalable quantum resources. 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. NSF Award ID: 2609932 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Kartik Srinivasan | Institution: University of Maryland, College Park, COLLEGE PARK, MD | Award Amount: $563,848 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2609932 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2609932.html