38 research outputs found
Absolute chiral sensing in dielectric metasurfaces with signal reversals
Sensing molecular chirality at the nanoscale has been a long-standing
challenge due to the inherently weak nature of chiroptical signals, and
nanophotonic approaches have proven fruitful in accessing these signals.
However, in most cases, absolute chiral sensing of the total chiral refractive
index has not been possible, while the strong inherent signals from the
nanostructures themselves obscure the weak chiroptical signals. Here, we
propose a dielectric metamaterial system that overcomes these limitations and
allows for absolute measurements of the total chirality, and the possibility
for a crucial signal reversal that enables chirality measurements without the
need for sample removal. As proof of principle, we demonstrate
signal-enhancements by a factor of 200 for ultrathin, sub-wavelength, chiral
samples over a uniform and accessible area.Comment: 5 pages, 4 figure
Search for ultralight scalar dark matter with atomic spectroscopy
We report new limits on ultralight scalar dark matter (DM) with dilaton-like
couplings to photons that can induce oscillations in the fine-structure
constant alpha. Atomic dysprosium exhibits an electronic structure with two
nearly degenerate levels whose energy splitting is sensitive to changes in
alpha. Spectroscopy data for two isotopes of dysprosium over a two-year span is
analyzed for coherent oscillations with angular frequencies below 1 rad/s. No
signal consistent with a DM coupling is identified, leading to new constraints
on dilaton-like photon couplings over a wide mass range. Under the assumption
that the scalar field comprises all of the DM, our limits on the coupling
exceed those from equivalence-principle tests by up to 4 orders of magnitude
for masses below 3 * 10^-18 eV. Excess oscillatory power, inconsistent with
fine-structure variation, is detected in a control channel, and is likely due
to a systematic effect. Our atomic spectroscopy limits on DM are the first of
their kind, and leave substantial room for improvement with state-of-the-art
atomic clocks.Comment: 5 pages, 4 figures; v2: references adde
Microwave-free magnetometry with nitrogen-vacancy centers in diamond
We use magnetic-field-dependent features in the photoluminescence of
negatively charged nitrogen-vacancy centers to measure magnetic fields without
the use of microwaves. In particular, we present a magnetometer based on the
level anti-crossing in the triplet ground state at 102.4 mT with a demonstrated
noise floor of 6 nT/, limited by the intensity noise of the
laser and the performance of the background-field power supply. The technique
presented here can be useful in applications where the sensor is placed closed
to conductive materials, e.g. magnetic induction tomography or magnetic field
mapping, and in remote-sensing applications since principally no electrical
access is needed.Comment: 5 pages, 4 figure
Nondestructive in-line sub-picomolar detection of magnetic nanoparticles in flowing complex fluids
Over the last decades, the use of magnetic nanoparticles in research and
commercial applications has increased dramatically. However, direct detection
of trace quantities remains a challenge in terms of equipment cost, operating
conditions and data acquisition times, especially in flowing conditions within
complex media. Here we present the in-line, non-destructive detection of
magnetic nanoparticles using high performance atomic magnetometers at ambient
conditions in flowing media. We achieve sub-picomolar sensitivities measuring
30 nm ferromagnetic iron and cobalt nanoparticles that are suitable for
biomedical and industrial applications, under flowing conditions in water and
whole blood. Additionally, we demonstrate real-time surveillance of the
magnetic separation of nanoparticles from water and whole blood. Overall our
system has the merit of inline direct measurement of trace quantities of
ferromagnetic nanoparticles with so far unreached sensitivities and could be
applied in the biomedical field (diagnostics and therapeutics) but also in the
industrial sector
Diamond magnetic microscopy of malarial hemozoin nanocrystals
Magnetic microscopy of malarial hemozoin nanocrystals was performed using
optically detected magnetic resonance imaging of near-surface diamond
nitrogen-vacancy centers. Hemozoin crystals were extracted from
--infected human blood cells and studied alongside
synthetic hemozoin crystals. The stray magnetic fields produced by individual
crystals were imaged at room temperature as a function of applied field up to
350 mT. More than 100 nanocrystals were analyzed, revealing the distribution of
their magnetic properties. Most crystals () exhibit a linear dependence
of stray field magnitude on applied field, confirming hemozoin's paramagnetic
nature. A volume magnetic susceptibility is inferred
using a magnetostatic model informed by correlated scanning electron microscopy
measurements of crystal dimensions. A small fraction of nanoparticles (4/82 for
-produced and 1/41 for synthetic) exhibit a saturation behavior
consistent with superparamagnetism. Translation of this platform to the study
of living malaria-infected cells may shed new light on hemozoin formation
dynamics and their interaction with antimalarial drugs.Comment: Main text: 8 pages and 5 figures, Supplemental Information: 9 pages
and 8 figure