Controlling Nonclassical Atomic Spin Ensembles via Cavity-Enhanced Polarization Measurements

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Quantum Information Science (QIS) is an emerging field that will fuel the next digital information revolution. It is based on the revolutionary idea that when information is manipulated at the microscopic level of atoms and photons the strange laws of physics enable ultrafast computers, enhanced cyber security, and ultraprecise sensors. Accelerating progress in QIS is the goal of the National Quantum Initiative Act of 2018, to enhance the nation’s security and economic growth. This grant helps to achieve these goals by developing a new atom-photon interface with potential applications in quantum computing, communications, and sensing. It does so through basic research in theoretical atomic physics which is essential for the development of next-generation information processing technologies. The project involves the training of students who will create the new quantum-smart workforce. The goal of this project is to develop a new platform for an entangling atom-light interface that can be used to create nonclassical states of atomic spin ensembles for applications in metrology, quantum communication, quantum computation, and fundamental studies of complex many-body dynamics. This platform is based on a ring-cavity geometry that enables a strong birefringent dispersive interaction between atomic spins encoded in magnetically insensitive clock states of cesium atoms and the polarization of the light. Measurement of the light polarization at the cavity output port induces quantum backaction of the collective atomic spin. The project will explore both Gaussian (homodyne) measurements of the light to induce Gaussian entangled states of atoms (spin squeezing), nonGaussian (photon counting) measurements to induce nonGaussian atomic spin states (Dicke states), as well as hybrid approaches analogous to photon addition on a squeezed vacuum state. The group will develop new approaches to quantum state verification and tomography based on detailed understanding of continuous measurement quantum trajectories. Additionally, the group will develop a new approach to measurement-based feedback to create complex dynamical maps of the collective spins and enable studies of quantum chaos, the quantum-to-classical transition, and quantum simulation of many-body physics.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.