Search

In our recent companion paper [arXiv:2106.00022], we pointed out a novel signature of ultralight kinetically mixed dark-photon dark matter. This signature is a quasi-monochromatic, time-oscillating terrestrial magnetic field that takes a particular pattern over the surface of the Earth. In this work, we present a search for this signal in existing, unshielded magnetometer data recorded by geographically dispersed, geomagnetic stations. The dataset comes from the SuperMAG Collaboration and consists of measurements taken with one-minute cadence since 1970, with $\mathcal{O}(500)$ stations contributing in all. We aggregate the magnetic field measurements from all stations by projecting them onto a small set of global vector spherical harmonics (VSH) that capture the expected vectorial pattern of the signal at each station. Within each dark-photon coherence time, we use a data-driven technique to estimate the broadband background noise in the data, and search for excess narrowband power in this set of VSH components; we stack the searches in distinct coherence times incoherently. Following a Bayesian analysis approach that allows us to account for the stochastic nature of the dark-photon dark-matter field, we set exclusion bounds on the kinetic mixing parameter in the dark-photon dark-matter mass range $2\times10^{-18}\,\text{eV} \lesssim m_{A'} \lesssim 7\times10^{-17}\,\text{eV}$ (corresponding to frequencies $6\times 10^{-4}\,\text{Hz}\lesssim f_{A'} \lesssim 2\times 10^{-2}\,\text{Hz}$). These limits are complementary to various existing astrophysical constraints. Although our main analysis also identifies a number of candidate signals in the SuperMAG dataset, these appear to either fail or be in tension with various additional robustness checks we apply to those candidates. We report no robust and significant evidence for a dark-photon dark-matter signal in the SuperMAG dataset., Comment: 41 pages, 11 figures. Published version

Results of a search for a long-range monopole-dipole coupling between the mass of the Earth and rubidium (Rb) nuclear spins are reported. The experiment simultaneously measures the spin precession frequencies of overlapping ensembles of $^{85}$Rb and $^{87}$Rb atoms contained within an evacuated, antirelaxation-coated vapor cell. The nuclear structure of the Rb isotopes makes the experiment particularly sensitive to spin-dependent interactions of the proton. The spin-dependent component of the gravitational energy of the proton in the Earth's field is found to be smaller than $3 \times 10^{-18}~{\rm eV}$, improving laboratory constraints on long-range monopole-dipole interactions by over three orders of magnitude., 10 pages, 8 figures

New constraints on exotic dipole-dipole interactions between electrons at the micrometer scale are established, based on a recent measurement of the magnetic interaction between two trapped $^{88}$Sr$^+$ ions. For light bosons (mass $\le$ 0.1 eV) we obtain a $90\%$ confidence interval on axial-vector mediated interaction strength of $\left|g_A^eg_A^e/4\pi\hbar c\right|\le 1.2\times 10^{-17}$. Assuming CPT invariance, this constraint is compared to that on anomalous electron-positron interactions, derived from positronium hyperfine spectroscopy. We find that the electron-electron constraint is six orders of magnitude more stringent than the electron-positron counterpart. Bounds on pseudo-scalar mediated interaction as well as on torsion gravity are also derived and compared with previous work performed at different length scales. Our constraints benefit from the high controllability of the experimental system which contained only two trapped particles. It therefore suggests a useful new platform for exotic particle searches, complementing other experimental efforts., Comment: 5 pages, 1 figure

In this article, we review the history, current status, physical mechanisms, experimental methods, and applications of nonlinear magneto-optical effects in atomic vapors. We begin by describing the pioneering work of Macaluso and Corbino over a century ago on linear magneto-optical effects (in which the properties of the medium do not depend on the light power) in the vicinity of atomic resonances, and contrast these effects with various nonlinear magneto-optical phenomena that have been studied both theoretically and experimentally since the late 1960s. In recent years, the field of nonlinear magneto-optics has experienced a revival of interest that has led to a number of developments, including the observation of ultra-narrow (1-Hz) magneto-optical resonances, applications in sensitive magnetometry, nonlinear magneto-optical tomography, and the possibility of a search for parity- and time-reversal-invariance violation in atoms., 51 pages, 23 figures, to appear in Rev. Mod. Phys. in Oct. 2002, Figure added, typos corrected, text edited for clarity

The dynamics of resonant light propagation in rubidium vapor in a cell with antirelaxation wall coating are investigated. We change the polarization of the input light and measure the time dependence of the polarization after the cell. The observed dynamics are shown to be analogous to those in electromagnetically induced transparency. Spectral dependence of light pulse delays is found to be similar to that of nonlinear magneto-optic rotation. Delays up to [approx]13 ms are observed, corresponding to a 8 m/s group velocity. Fields of a few microgauss are used to control the group velocity. [copyright] [ital 1999] [ital The American Physical Society ]

Results of an investigation of collisional deexcitation of the metastable $6s6p{}^{3}{P}_{0}$ state in atomic ytterbium by helium and neon buffer gases are reported. We find upper limits for the quenching cross sections to be ${\ensuremath{\sigma}}_{\mathrm{He}}l13\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}{\mathrm{cm}}^{2}$ and ${\ensuremath{\sigma}}_{\mathrm{Ne}}l8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}{\mathrm{cm}}^{2}.$ The small cross sections may allow an ytterbium parity nonconservation experiment to be performed in a vapor cell. We have also measured the pressure broadening and shift of the $6s6p{}^{3}{P}_{0}\ensuremath{\rightarrow}6s7s{}^{3}{\mathrm{S}}_{1}$ and ${6s}^{2}{}^{1}{S}_{0}\ensuremath{\rightarrow}6s6p{}^{3}{P}_{1}$ transitions by helium and neon.

The relaxation of atomic polarization in buffer-gas-free, paraffin-coated cesium vapor cells is studied using a variation on Franzen's technique of ``relaxation in the dark'' [Franzen, Phys. Rev. {\bf 115}, 850 (1959)]. In the present experiment, narrow-band, circularly polarized pump light, resonant with the Cs D2 transition, orients atoms along a longitudinal magnetic field, and time-dependent optical rotation of linearly polarized probe light is measured to determine the relaxation rates of the atomic orientation of a particular hyperfine level. The change in relaxation rates during light-induced atomic desorption (LIAD) is studied. No significant change in the spin relaxation rate during LIAD is found beyond that expected from the faster rate of spin-exchange collisions due to the increase in Cs density., 14 pages, 14 figures

Using laser optical pumping, widths and frequency shifts are determined for microwave transitions between ground-state hyperfine components of {sup 85}Rb and {sup 87}Rb atoms contained in vapor cells with alkane anti-relaxation coatings. The results are compared with data on Zeeman relaxation obtained in nonlinear magneto-optical rotation (NMOR) experiments, a comparison important for quantitative understanding of spin-relaxation mechanisms in coated cells. By comparing cells manufactured over a forty-year period we demonstrate the long-term stability of coated cells, an important property for atomic clocks and magnetometers.

Observation of nonthermal, light-induced desorption of Cs and Rb atoms from paraffin coating is reported. Buffer-gas-free paraffin-coated cells containing Cs and Rb were exposed to laser light of various intensities and frequencies, and the change of the vapor densities as a function of time was investigated. Because atomic polarization relaxes very slowly in paraffin-coated cells (spin-relaxation times can be $\ensuremath{\gtrsim}1\mathrm{s}),$ they are applied in a variety of precision measurements (e.g., magnetometry, discrete symmetry tests, etc.). Light-induced desorption may be useful in such measurements as a method to control atomic density without changing the temperature of the cell.

Optical pumping of an atomic sample with narrow-band light can create sub-Doppler features, known as Bennett structures, in the velocity distribution of state populations. In the presence of static magnetic or electric fields, the corresponding sub-Doppler features in the index of refraction can cause nonlinear optical rotation and induced ellipticity of resonant light propagating through the atomic medium. Physical mechanisms causing Bennett-structure-related nonlinear electro- and magneto-optical effects are discussed in detail for transitions involving states with low angular momenta. Measurements of Bennett-structure-related nonlinear magneto-optical rotation and electric-field-induced ellipticity for the Rb D2 line are performed and compared to density-matrix calculations. The latter effect can he used for measuring electric fields applied to atoms.

A new scheme to measure parity-nonconserving effects in atomic ytterbium is proposed. This method entails measuring parity-nonconserving optical rotation on the $1.28 \ensuremath{\mu}\mathrm{m} 6s6p{ }^{3}{P}_{0}\ensuremath{\rightarrow}6s6p{}^{1}{P}_{1}$ transition, for which optical rotation per unit absorption length is predicted to be an order of magnitude larger than that for transitions experimentally studied in thallium, lead, and bismuth. In the proposed experiment using a vapor cell filled with buffer gas, the lifetime of the lower metastable $6s6p{ }^{3}{P}_{0}$ state is limited by collisional de-excitation. Atoms are excited to the lower metastable state by, e.g., short $(\ensuremath{\sim}10 \mathrm{ns})$ near-resonant light pulses and spurious optical rotation is subtracted on a pulse by pulse basis. The potential sensitivity of this technique may enable precise measurements of electroweak parameters.

Self-rotation (SR) of elliptically polarized light resonant with atoms in a collision-free vapor is investigated experimentally and theoretically. Results of density matrix calculations are compared to measurements of SR on the Rb D1 and D2 lines. It is noted that SR eects involving individual hyperne transitions are suppressed due to Doppler broadening, and so previously unrecognized eects arising from the interaction of light with multiple hyperne transitions can become dominant. PACS. 42.50.Gy, 42.50.Hz, 32.80.Bx Interaction with an elliptically polarized light eld can cause an initially isotropic medium to become dichroic and birefringent. The resultant circular birefringence and linear dichroism induce rotation of the polarization ellipse of the light. In the present work, we investigate this eect, known as self-rotation (SR), occurring in a rubidium vapor in which the eect of collisions can be neglected. The vapor is subject to narrow-band cw light near-resonant with the Rb D1 (795 nm, 2 S 1 ! 2 P 1 ) and D2 (780 nm, 2 S 1 ! 2 P 3 ) transitions. Under these conditions, as we discuss below, the previously unrecognized

Application of nonlinear magneto-optical (Faraday) rotation to magnetometry is investigated. Our experimental setup consists of a modulation polarimeter that measures rotation of the polarization plane of a laser beam resonant with transitions in Rb. Rb vapor is contained in an evacuated cell with antirelaxation coating that enables atomic ground-state polarization to survive many thousand wall collisions. This leads to ultranarrow features $(\ensuremath{\sim}{10}^{\ensuremath{-}6} \mathrm{G})$ in the magnetic-field dependence of optical rotation. The potential sensitivity of this scheme to sub-$\ensuremath{\mu}\mathrm{G}$ magnetic fields as a function of atomic density, light intensity, and light frequency is investigated near the $D1$ and $D2$ lines of ${}^{85}\mathrm{Rb}.$ It is shown that through an appropriate choice of parameters the shot-noise-limited sensitivity to small magnetic fields can reach $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12} \mathrm{G}/\sqrt{\mathrm{Hz}}.$