Generation and Measurement of Entangled Atomic Ensembles with an Optical Cavity

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015.Cataloged from PDF version of thesis.Includes bibliographical references (pages 103-109).Atomic interferometers have a resolution limit set by the projection noise in measurements on ensembles of uncorrelated atoms. To overcome this classical limit and extend precision measurements into the quantum regime, we need to generate complex entangled states of large atomic ensembles and measure the atomic states with high-quality detection. This thesis describes two experiments in this context. The first experiment demonstrates single-atom resolution and detection sensitivity more than 20 dB below the projection noise limit for hyperfine-state-selective measurements on mesoscopic ensembles containing 100 or more atoms. The measurement detects the atom-induced shift of the resonance frequency of an optical cavity containing the ensemble. The second experiment generates entangled states of 3,000 atoms with non-Gaussian spin distributions. Atoms interact with a weak cavity field, and the heralded detection of a single photon with certain polarization prepares the entangled states. By measuring the non-Gaussian spin distributions using the atom-cavity interaction, we construct a negative Wigner function, manifestly demonstrating that the atoms are entangled. We also show that nearly all of 3000 atoms are involved in the entanglement using an entanglement measure known as the entanglement depth.by Hao Zhang.Ph. D