14 research outputs found
Cosmic Axion Spin Precession Experiment (CASPEr)
We propose an experiment to search for QCD axion and axion-like-particle
(ALP) dark matter. Nuclei that are interacting with the background axion dark
matter acquire time-varying CP-odd nuclear moments such as an electric dipole
moment. In analogy with nuclear magnetic resonance, these moments cause
precession of nuclear spins in a material sample in the presence of an electric
field. Precision magnetometry can be used to search for such precession. An
initial phase of this experiment could cover many orders of magnitude in ALP
parameter space beyond the current astrophysical and laboratory limits. And
with established techniques, the proposed experimental scheme has sensitivity
to QCD axion masses m_a < 10^-9 eV, corresponding to theoretically
well-motivated axion decay constants f_a > 10^16 GeV. With further
improvements, this experiment could ultimately cover the entire range of masses
m_a < 10^-6 eV, complementary to cavity searches.Comment: 11 pages, 2 figures, 1 table. v2: Reordered sections and minor
modifications to agree with published versio
Detection of a single cobalt microparticle with a microfabricated atomic magnetometer
We present magnetic detection of a single, 2 {\mu}m diameter cobalt
microparticle using an atomic magnetometer based on a microfabricated vapor
cell. These results represent an improvement by a factor of 105 in terms of the
detected magnetic moment over previous work using atomic magnetometers to
detect magnetic microparticles. The improved sensitivity is due largely to the
use of small vapor cells. In an optimized setup, we predict detection limits of
0.17 {\mu}m^3.Comment: 3 pages, 3 figure
Near-zero-field nuclear magnetic resonance
We investigate nuclear magnetic resonance (NMR) in near-zero-field, where the
Zeeman interaction can be treated as a perturbation to the electron mediated
scalar interaction (J-coupling). This is in stark contrast to the high field
case, where heteronuclear J-couplings are normally treated as a small
perturbation. We show that the presence of very small magnetic fields results
in splitting of the zero-field NMR lines, imparting considerable additional
information to the pure zero-field spectra. Experimental results are in good
agreement with first-order perturbation theory and with full numerical
simulation when perturbation theory breaks down. We present simple rules for
understanding the splitting patterns in near-zero-field NMR, which can be
applied to molecules with non-trivial spectra.Comment: 5 pages, 5 figure
Long-lived heteronuclear spin-singlet states
We report observation of long-lived spin-singlet states in a 13C-1H spin pair
at zero magnetic field. In 13C-labeled formic acid, we observe spin-singlet
lifetimes as long as 37 seconds, about a factor of three longer than the T1
lifetime of dipole polarization in the triplet state. We also observe that the
lifetime of the singlet-triplet coherence, T2, is longer than T1. Moreover, we
demonstrate that this singlet states formed by spins of a heteronucleus and a
1H nucleus, can exhibit longer lifetimes than the respective triplet states in
systems consisting of more than two nuclear spins. Although long-lived
homonuclear spin-singlet states have been extensively studied, this is the
first experimental observation of analogous spin-singlets consisting of a
heteronucleus and a proton.Comment: 5 pages, 4 figure
Measurement of Untruncated Nuclear Spin Interactions via Zero- to Ultra-Low-Field Nuclear Magnetic Resonance
Zero- to ultra-low-field nuclear magnetic resonance (ZULF NMR) provides a new
regime for the measurement of nuclear spin-spin interactions free from effects
of large magnetic fields, such as truncation of terms that do not commute with
the Zeeman Hamiltonian. One such interaction, the magnetic dipole-dipole
coupling, is a valuable source of spatial information in NMR, though many terms
are unobservable in high-field NMR, and the coupling averages to zero under
isotropic molecular tumbling. Under partial alignment, this information is
retained in the form of so-called residual dipolar couplings. We report zero-
to ultra-low-field NMR measurements of residual dipolar couplings in
acetonitrile-2-C aligned in stretched polyvinyl acetate gels. This
represents the first investigation of dipolar couplings as a perturbation on
the indirect spin-spin -coupling in the absence of an applied magnetic
field. As a consequence of working at zero magnetic field, we observe terms of
the dipole-dipole coupling Hamiltonian that are invisible in conventional
high-field NMR. This technique expands the capabilities of zero- to
ultra-low-field NMR and has potential applications in precision measurement of
subtle physical interactions, chemical analysis, and characterization of local
mesoscale structure in materials.Comment: 6 pages, 3 figure
Fundamental Aspects of Parahydrogen Enhanced Low-Field Nuclear Magnetic Resonance
We report new phenomena in low-field 1H nuclear magnetic resonance (NMR) spectroscopy using parahydrogen induced polarization (PHIP), enabling determination of chemical shift differences, δν, and the scalar coupling constant J. NMR experiments performed with thermal polarization in millitesla magnetic fields do not allow the determination of scalar coupling constants for homonuclear coupled spins in the inverse weak coupling regime (δν<J). We show here that low-field PHIP experiments in the inverse weak coupling regime enable the precise determination of δν and J. Furthermore we experimentally prove that observed splittings are related to δν in a nonlinear way. Naturally abundant 13C and 29Si isotopes lead to heteronuclear J-coupled 1H-multiplet lines with amplitudes significantly enhanced compared to the amplitudes for thermally prepolarized spins. PHIP-enhanced NMR in the millitesla regime allows us to measure characteristic NMR parameters in a single scan using samples containing rare spins in natural abundance
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Long-lived heteronuclear spin-singlet states
We report observation of long-lived spin-singlet states in a 13C-1H spin pair
at zero magnetic field. In 13C-labeled formic acid, we observe spin-singlet
lifetimes as long as 37 seconds, about a factor of three longer than the T1
lifetime of dipole polarization in the triplet state. We also observe that the
lifetime of the singlet-triplet coherence, T2, is longer than T1. Moreover, we
demonstrate that this singlet states formed by spins of a heteronucleus and a
1H nucleus, can exhibit longer lifetimes than the respective triplet states in
systems consisting of more than two nuclear spins. Although long-lived
homonuclear spin-singlet states have been extensively studied, this is the
first experimental observation of analogous spin-singlets consisting of a
heteronucleus and a proton
High-Resolution Zero-Field NMR <i>J</i>‑Spectroscopy of Aromatic Compounds
We report the acquisition and interpretation
of nuclear magnetic
resonance (NMR) <i>J</i>-spectra at zero magnetic field
for a series of benzene derivatives, demonstrating the analytical
capabilities of zero-field NMR. The zeroth-order spectral patterns
do not overlap, which allows for straightforward determination of
the spin interactions of substituent functional groups. Higher-order
effects cause additional line splittings, revealing additional molecular
information. We demonstrate resonance linewidths as narrow as 11 mHz,
permitting resolution of minute frequency differences and precise
determination of long-range <i>J</i>-couplings. The measurement
of <i>J</i>-couplings with the high precision offered by
zero-field NMR may allow further refinements in the determination
of molecular structure and conformation
High-Resolution Zero-Field NMR <i>J</i>‑Spectroscopy of Aromatic Compounds
We report the acquisition and interpretation
of nuclear magnetic
resonance (NMR) <i>J</i>-spectra at zero magnetic field
for a series of benzene derivatives, demonstrating the analytical
capabilities of zero-field NMR. The zeroth-order spectral patterns
do not overlap, which allows for straightforward determination of
the spin interactions of substituent functional groups. Higher-order
effects cause additional line splittings, revealing additional molecular
information. We demonstrate resonance linewidths as narrow as 11 mHz,
permitting resolution of minute frequency differences and precise
determination of long-range <i>J</i>-couplings. The measurement
of <i>J</i>-couplings with the high precision offered by
zero-field NMR may allow further refinements in the determination
of molecular structure and conformation
High-Resolution Zero-Field NMR <i>J</i>‑Spectroscopy of Aromatic Compounds
We report the acquisition and interpretation
of nuclear magnetic
resonance (NMR) <i>J</i>-spectra at zero magnetic field
for a series of benzene derivatives, demonstrating the analytical
capabilities of zero-field NMR. The zeroth-order spectral patterns
do not overlap, which allows for straightforward determination of
the spin interactions of substituent functional groups. Higher-order
effects cause additional line splittings, revealing additional molecular
information. We demonstrate resonance linewidths as narrow as 11 mHz,
permitting resolution of minute frequency differences and precise
determination of long-range <i>J</i>-couplings. The measurement
of <i>J</i>-couplings with the high precision offered by
zero-field NMR may allow further refinements in the determination
of molecular structure and conformation