173 research outputs found
Measurements of Grain Motion in a Dense, Three-Dimensional Granular Fluid
We have used an NMR technique to measure the short-time, three-dimensional
displacement of grains in a system of mustard seeds vibrated vertically at 15g.
The technique averages over a time interval in which the grains move
ballistically, giving a direct measurement of the granular temperature profile.
The dense, lower portion of the sample is well described by a recent
hydrodynamic theory for inelastic hard spheres. Near the free upper surface the
mean free path is longer than the particle diameter and the hydrodynamic
description fails.Comment: 4 pages, 4 figure
Coherence of Nitrogen-Vacancy Electronic Spin Ensembles in Diamond
We present an experimental and theoretical study of electronic spin
decoherence in ensembles of nitrogen-vacancy (NV) color centers in bulk
high-purity diamond at room temperature. Under appropriate conditions, we find
ensemble NV spin coherence times (T_2) comparable to that of single NVs, with
T_2 > 600 microseconds for a sample with natural abundance of 13C and
paramagnetic impurity density ~10^15 cm^(-3). We also observe a sharp decrease
of the coherence time with misalignment of the static magnetic field relative
to the NV electronic spin axis, consistent with theoretical modeling of NV
coupling to a 13C nuclear spin bath. The long coherence times and increased
signal-to-noise provided by room-temperature NV ensembles will aid many
applications of NV centers in precision magnetometry and quantum information.Comment: 5 pages, 3 figures; v2 minor correction
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