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We propose an experiment to search for QCD axion and axionlike-particle 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 axionlike-particle parameter space beyond the current astrophysical and laboratory limits. And with established techniques, the proposed experimental scheme has sensitivity to QCD axion masses ma≲10−9eV , corresponding to theoretically well-motivated axion decay constants fa≳1016GeV . With further improvements, this experiment could ultimately cover the entire range of masses ma≲μeV , complementary to cavity searches.

Scalar couplings between covalently bound nuclear spins are a ubiquitous feature in nuclear magnetic resonance (NMR) experiments, imparting valuable information to NMR spectra regarding molecular structure and conformation. Such couplings arise due to a second-order hyperfine interaction, and, in principle, the same mechanism should lead to scalar couplings between nuclear spins in unbound van der Waals complexes. Here, we report the first observation of scalar couplings between nuclei in van der Waals complexes. Our measurements are performed in a solution of hyperpolarized ¹²⁹Xe and pentane, using superconducting quantum interference devices to detect NMR in 10 mG fields, and are in good agreement with calculations based on density functional theory. van der Waals forces play an important role in many physical phenomena. The techniques presented here may provide a new method for probing such interactions.

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.

Here we report progress toward the measurement of a permanent electric dipole moment (EDM) in hyperpolarized liquid 129Xe which violates invariance under both parity and time reversal. The standard model (SM) predicts atomic EDMs well beyond current experimental limits while many natural extensions to the SM predict EDMs within the expected sensitivity of current experiments. Hence the search for a non-zero EDM is viewed as an ideal test for new physics. Liquid 129Xe is an attractive medium in which to perform such a search because it has a high number density and a high electric field breakdown strength. For experimentally realizable parameters it should be possible to achieve a sensitivity of ∼10−32 e-cm for one day of integration; several orders of magnitude beyond current experimental limits on EDMs. In preparation for performing a search for an EDM in liquid xenon, we have conducted a thorough experimental and theoretical investigation of the spin dynamics of hyperpolarized liquid 129Xe. In a highly polarized liquid magnetic dipolar interactions can strongly influence spin precession. For small tip angles of the magnetization away from the holding field, the system is insensitive to perturbations, leading to extended free induction decays. For large tip angles the system develops a dynamical instability so that spin precession due to a small magnetic field gradient is amplified exponentially relative to the non-interacting case. In principle; this amplification can be quite large, leading to enhanced sensitivity of spin precession measurements when noise in the detection system is much greater than spin-projection noise. Experimentally, we have achieved amplification of spin precession due to a small applied field gradient by a factor of 9.5 relative to the non-interacting case in the large tip angle regime. Considerable improvement is expected with further optimization of high order gradients. In the small tip angle regime we have realized an extension of the free induction decay by up to a factor of 100 compared to the non-interacting case. We discuss how these two different regimes can be used in a search for an EDM in liquid xenon and analyze the expected sources of systematic effects.

A comparison between existing measurements and calculations of the scalar spin-spin interaction (J-coupling) in deuterated molecular hydrogen (HD) yields stringent constraints on anomalous spin-dependent potentials between nucleons at the atomic scale (\\({\\rm \\sim 1 \\AA}\\)). The dimensionless coupling constant \\(g_P^pg_P^{N}/4\\pi\\) associated with exchange of pseudoscalar (axion-like) bosons between nucleons is constrained to be less than \\(5\\times 10^{-7}\\) for boson masses in the range of \\(5 {\\rm keV}\\). This represents improvement by a factor of about 100 over constraints placed by measurements of the dipole-dipole interaction in molecular \\({\\rm H_2}\\). The dimensionless coupling constant \\(g_A^pg_A^N/4 \\pi\\) associated with exchange of a heretofore undiscovered axial-vector boson between nucleons is constrained to be \\(g_A^pg_A^N/4 \\pi < 2 \\times 10^{-19}\\) for bosons of mass \\(\\lesssim 1000 {\\rm eV}\\), improving constraints at this distance scale by a factor of 100 for proton-proton couplings and more than 8 orders of magnitude for neutron-proton couplings. This limit is also a factor of 100 more stringent than recent constraints obtained for axial-vector couplings between electrons and nucleons obtained from comparison of measurements and calculations of hyperfine structure.

We propose solid-state gyroscopes based on ensembles of negatively charged nitrogen-vacancy (\\({\\rm NV^-}\\)) centers in diamond. In one scheme, rotation of the nitrogen-vacancy symmetry axis will induce Berry phase shifts in the \\({\\rm NV^{-}}\\) electronic ground-state coherences proportional to the solid angle subtended by the symmetry axis. We estimate sensitivity in the range of \\(5\\times10^{-3} {\\rm rad/s/\\sqrt{Hz}}\\) in a 1 \\({\\rm mm^3}\\) sensor volume using a simple Ramsey sequence. Incorporating dynamical decoupling to suppress dipolar relaxation may yield sensitivity at the level of \\(10^{-5} {\\rm rad/s/\\sqrt{Hz}}\\). With a modified Ramsey scheme, Berry phase shifts in the \\({\\rm ^{14}N}\\) hyperfine sublevels would be employed. The projected sensitivity is in the range of \\(10^{-5} {\\rm rad/s/\\sqrt{Hz}}\\), however the smaller gyromagnetic ratio reduces sensitivity to magnetic-field noise by several orders of magnitude. Reaching \\(10^{-5} {\\rm rad/s/\\sqrt{Hz}}\\) would represent an order of magnitude improvement over other compact, solid-state gyroscope technologies.

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.

Scalar couplings between covalently bound nuclear spins are a ubiquitous feature in nuclear magnetic resonance (NMR) experiments, imparting valuable information to NMR spectra regarding molecular structure and conformation. Such couplings arise due to a second-order hyperfine interaction, and, in principle, the same mechanism should lead to scalar couplings between nuclear spins in unbound van der Waals complexes. Here, we report the first observation of scalar couplings between nuclei in van der Waals molecules. Our measurements are performed in a solution of hyperpolarized \\({\\rm ^{129}Xe}\\) and pentane, using superconducting quantum interference devices to detect NMR in 10 mG fields, and are in good agreement with calculations based on density functional theory. van der Waals forces play an important role in many physical phenomena, and hence the techniques presented here may provide a new method for probing such interactions.

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-\\(^{13}\\)C aligned in stretched polyvinyl acetate gels. This represents the first investigation of dipolar couplings as a perturbation on the indirect spin-spin \\(J\\)-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.

We demonstrate lifetimes of atomic populations and coherences in excess of 60 seconds in alkali vapor cells with inner walls coated with an alkene material. This represents two orders of magnitude improvement over the best paraffin coatings. Such anti-relaxation properties will likely lead to substantial improvements in atomic clocks, magnetometers, quantum memory, and enable sensitive studies of collisional effects and precision measurements of fundamental symmetries.