We demonstrate spectroscopy and thermometry of individual motional modes in a mesoscopic 2D ion array using entanglement-induced decoherence as a method of transduction. Our system is a ∼400 μm-diameter planar crystal of several hundred 9Be+ ions exhibiting complex drumhead modes in the confining potential of a Penning trap. Exploiting precise control over the 9Be+ valence electron spins, we apply a homogeneous spin-dependent optical dipole force to excite arbitrary transverse modes with an effective wavelength approaching the interparticle spacing (∼20 \nolinebreakμm). Center-of-mass displacements below 1 nm are detected via entanglement of spin and motional degrees of freedom.
@article{arxiv.1201.4415,
title = {Spectroscopy and Thermometry of Drumhead Modes in a Mesoscopic Trapped-Ion Crystal using Entanglement},
author = {Brian C. Sawyer and Joseph W. Britton and Adam C. Keith and C. -C. Joseph Wang and James K. Freericks and Hermann Uys and Michael J. Biercuk and John J. Bollinger},
journal= {arXiv preprint arXiv:1201.4415},
year = {2012}
}