%0 Journal Article
%D 2018
%T Spectrum estimation of density operators with alkaline-earth atoms
%A Michael E. Beverland
%A Jeongwan Haah
%A Gorjan Alagic
%A Gretchen K. Campbell
%A Ana Maria Rey
%A Alexey V. Gorshkov
%X We show that Ramsey spectroscopy of fermionic alkaline-earth atoms in a square-well trap provides an efficient and accurate estimate for the eigenspectrum of a density matrix whose *n *copies are stored in the nuclear spins of *n *such atoms. This spectrum estimation is enabled by the high symmetry of the interaction Hamiltonian, dictated, in turn, by the decoupling of the nuclear spin from the electrons and by the shape of the square-well trap. Practical performance of this procedure and its potential applications to quantum computing, quantum simulation, and time-keeping with alkalineearth atoms are discussed.

%V 120
%8 2018/01/09
%G eng
%U http://arxiv.org/abs/1608.02045
%N 025301
%R https://doi.org/10.1103/PhysRevLett.120.025301
%0 Journal Article
%J Physical Review A
%D 2015
%T Self-heterodyne detection of the \it in-situ phase of an atomic-SQUID
%A Ranchu Mathew
%A Avinash Kumar
%A Stephen Eckel
%A Fred Jendrzejewski
%A Gretchen K. Campbell
%A Mark Edwards
%A Eite Tiesinga
%X We present theoretical and experimental analysis of an interferometric measurement of the {\it in-situ} phase drop across and current flow through a rotating barrier in a toroidal Bose-Einstein condensate (BEC). This experiment is the atomic analog of the rf-superconducting quantum interference device (SQUID). The phase drop is extracted from a spiral-shaped density profile created by the spatial interference of the expanding toroidal BEC and a reference BEC after release from all trapping potentials. We characterize the interferometer when it contains a single particle, which is initially in a coherent superposition of a torus and reference state, as well as when it contains a many-body state in the mean-field approximation. The single-particle picture is sufficient to explain the origin of the spirals, to relate the phase-drop across the barrier to the geometry of a spiral, and to bound the expansion times for which the {\it in-situ} phase can be accurately determined. Mean-field estimates and numerical simulations show that the inter-atomic interactions shorten the expansion time scales compared to the single-particle case. Finally, we compare the mean-field simulations with our experimental data and confirm that the interferometer indeed accurately measures the {\it in-situ} phase drop.
%B Physical Review A
%V 92
%P 033602
%8 2015/09/03
%G eng
%U http://arxiv.org/abs/1506.09149v2
%N 3
%! Phys. Rev. A
%R 10.1103/PhysRevA.92.033602