114 research outputs found
Coherent population oscillations with nitrogen-vacancy color centers in diamond
We present results of our research on two-field (two-frequency) microwave
spectroscopy in nitrogen-vacancy (NV-) color centers in a diamond. Both fields
are tuned to transitions between the spin sublevels of the NV- ensemble in the
3A2 ground state (one field has a fixed frequency while the second one is
scanned). Particular attention is focused on the case where two microwaves
fields drive the same transition between two NV- ground state sublevels (ms=0
-> ms=+1). In this case, the observed spectra exhibit a complex narrow
structure composed of three Lorentzian resonances positioned at the pump-field
frequency. The resonance widths and amplitudes depend on the lifetimes of the
levels involved in the transition. We attribute the spectra to coherent
population oscillations induced by the two nearly degenerate microwave fields,
which we have also observed in real time. The observations agree well with a
theoretical model and can be useful for investigation of the NV relaxation
mechanisms.Comment: 17 page
High-Excitation Hole States in the 24-Mg(p,d) Reaction
This work was supported by National Science Foundation Grants PHY 76-84033A01, PHY 78-22774, and Indiana Universit
Gamma Rays from Clusters and Groups of Galaxies: Cosmic Rays versus Dark Matter
Clusters of galaxies have not yet been detected at gamma-ray frequencies;
however, the recently launched Fermi Gamma-ray Space Telescope, formerly known
as GLAST, could provide the first detections in the near future. Clusters are
expected to emit gamma rays as a result of (1) a population of high-energy
primary and re-accelerated secondary cosmic rays (CR) fueled by structure
formation and merger shocks, active galactic nuclei and supernovae, and (2)
particle dark matter (DM) annihilation. In this paper, we ask the question of
whether the Fermi telescope will be able to discriminate between the two
emission processes. We present data-driven predictions for a large X-ray flux
limited sample of galaxy clusters and groups. We point out that the gamma ray
signals from CR and DM can be comparable. In particular, we find that poor
clusters and groups are the systems predicted to have the highest DM to CR
emission at gamma-ray energies. Based on detailed Fermi simulations, we study
observational handles that might enable us to distinguish the two emission
mechanisms, including the gamma-ray spectra, the spatial distribution of the
signal and the associated multi-wavelength emissions. We also propose optimal
hardness ratios, which will help to understand the nature of the gamma-ray
emission. Our study indicates that gamma rays from DM annihilation with a high
particle mass can be distinguished from a CR spectrum even for fairly faint
sources. Discriminating a CR spectrum from a light DM particle will be instead
much more difficult, and will require long observations and/or a bright source.
While the gamma-ray emission from our simulated clusters is extended,
determining the spatial distribution with Fermi will be a challenging task
requiring an optimal control of the backgrounds.Comment: revised to match resubmitted version, 35 pages, 16 figures: results
unchanged, some discussion added and unnecessary text and figures remove
Measurements of (p,pi Ì„) Reactions Near Zero Degrees
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
Ultralong Dephasing Times in Solid-State Spin Ensembles via Quantum Control
Quantum spin dephasing is caused by inhomogeneous coupling to the
environment, with resulting limits to the measurement time and precision of
spin-based sensors. The effects of spin dephasing can be especially pernicious
for dense ensembles of electronic spins in the solid-state, such as for
nitrogen-vacancy (NV) color centers in diamond. We report the use of two
complementary techniques, spin bath control and double quantum coherence, to
enhance the inhomogeneous spin dephasing time () for NV ensembles by
more than an order of magnitude. In combination, these quantum control
techniques (i) eliminate the effects of the dominant NV spin ensemble dephasing
mechanisms, including crystal strain gradients and dipolar interactions with
paramagnetic bath spins, and (ii) increase the effective NV gyromagnetic ratio
by a factor of two. Applied independently, spin bath control and double quantum
coherence elucidate the sources of spin dephasing over a wide range of NV and
spin bath concentrations. These results demonstrate the longest reported
in a solid-state electronic spin ensemble at room temperature, and
outline a path towards NV-diamond magnetometers with broadband femtotesla
sensitivity.Comment: PRX versio
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