D. F. Jackson Kimball

Nonlinear magneto-optical rotation with frequency-modulated light in the geophysical field range

Recent work investigating resonant nonlinear magneto-opticalrotation (NMOR) related to long-lived (tau_rel approx 1s) ground-stateatomic coherences has demonstrated potential magnetometric sensitivitiesexceeding (10-11 G Hz-1/2) for small (<1 micro G) magnetic fields. Inthe present work, NMOR using frequency-modulated light (FM NMOR) isstudied in the regime where the longitudinal magnetic field is in thegeophysical range (sim 500mG), of particular interest for manyapplications. In this regime a splitting of the FM NMOR resonancedue tothe nonlinear Zeeman effect is observed. At sufficiently high lightintensities, there is also a splitting of the FM NMOR resonances due toac Stark shifts induced by the optical field, as well as evidence ofalignment-to-orientation conversion type processes. The consequences ofthese effects for FM-NMOR-based atomic magnetometry in the geophysicalfield range are considered.

Controlling atomic vapor density in paraffin-coated cells using light-induced atomic desorption

Atomic-vapor density change due to light induced atomic desorption (LIAD) is studied in paraffincoated rubidium, cesium, sodium and potassium cells. In the present experiment, low-intensity probe light is used to obtain an absorption spectrum and measure the vapor density, while light from an argon-ion laser, array of light emitting diodes, or discharge lamp is used for desorption. Potassium is found to exhibit significantly weaker LIAD from paraffin compared to Rb and Cs, and we were unable to observe LIAD with sodium. A simple LIAD model is applied to describe the observed vapor-density dynamics, and the role of the cell’s stem is explored through the use of cells with lockable stems. Stabilization of Cs vapor density above its equilibrium value over 25 minutes is demonstrated. The results of this work could be used to assess the use of LIAD for vapor-density control in magnetometers, clocks, and gyroscopes utilizing coated cells.

Investigation of anti-Relaxation coatings for alkali-metal vapor cells using surface science techniques

Many technologies based on cells containing alkali-metal atomic vapor benefit from the use of antirelaxation surface coatings in order to preserve atomic spin polarization. In particular, paraffin has been used for this purpose for several decades and has been demonstrated to allow an atom to experience up to 10 000 collisions with the walls of its container without depolarizing, but the details of its operation remain poorly understood. We apply modern surface and bulk techniques to the study of paraffin coatings in order to characterize the properties that enable the effective preservation of alkali spin polarization. These methods include Fourier transform infrared spectroscopy, differential scanning calorimetry, atomic force microscopy, near-edge x-ray absorption fine structure spectroscopy, and x-ray photoelectron spectroscopy. We also compare the light-induced atomic desorption yields of several different paraffin materials. Experimental results include the determination that crystallinity of the coating material is unnecessary, and the detection of C[Double Bond]C double bonds present within a particular class of effective paraffin coatings. Further study should lead to the development of more robust paraffin antirelaxation coatings, as well as the design and synthesis of new classes of coating materials.

Influence of magnetic-field inhomogeneity on nonlinear magneto-optical resonances

In this work, a sensitivity of the rate of relaxation of ground-state atomic coherences to magnetic-field inhomogeneities is studied. Such coherences give rise to many interesting phenomena in light-atom interactions, and their lifetimes are a limiting factor for achieving better sensitivity, resolution, or contrast in many applications. For atoms contained in a vapor cell, some of the coherence-relaxation mechanisms are related to magnetic-field inhomogeneities. We present a simple model describing relaxation due to such inhomogeneities in a buffer-gas-free antirelaxation-coated cell. A relation is given between relaxation rate and magnetic-field inhomogeneities including the dependence on cell size and atomic species. Experimental results, which confirm predictions of the model, are presented. Different regimes, in which the relaxation rate is equally sensitive to the gradients in any direction and in which it is insensitive to gradients transverse to the bias magnetic field, are predicted and demonstrated experimentally.

Pump-probe nonlinear magneto-optical rotation with frequency-modulated light

Specific types of atomic coherences between Zeeman sublevels can be generated and detected using a method based on nonlinear magneto-optical rotation with frequency-modulated light. Linearly polarized, frequency-modulated light is employed to selectively generate ground-state coherences between Zeeman sublevels for which m=2 and m=4 in 85 Rb and 87 Rb atoms, and additionally m=6 in 85 Rb. The atomic coherences are detected with a separate, unmodulated probe light beam. Separation of the pump and probe beams enables independent investigation of the processes of creation and detection of the atomic coherences. With the present technique the transfer of the Zeeman coherences, including high-order coherences, from excited to ground state by spontaneous emission has been observed.

Production and detection of atomic hexadecapole at Earth’s magnetic field

Optical magnetometers measure magnetic fields with extremely high precision and without cryogenics. However, at geomagnetic fields, important for applications from landmine removal to archaeology, they suffer from nonlinear Zeeman splitting, leading to systematic dependence on sensor orientation. We present experimental results on a method of eliminating this systematic error, using the hexadecapole atomic polarization moment. In particular, we demonstrate selective production of the atomic hexadecapole moment at Earths magnetic field and verify its immunity to nonlinear Zeeman splitting. This technique promises to eliminate directional errors in all-optical atomic magnetometers, potentially improving their measurement accuracy by several orders of magnitude.

Electric-field-induced change of the alkali-metal vapor density in paraffin-coated cells

Alkali vapor cells with antirelaxation coating (especially paraffin-coated cells) have been a central tool in optical pumping and atomic spectroscopy experiments for 50 years. We have discovered a dramatic change of the alkali vapor density in a paraffin-coated cell upon application of an electric field to the cell. A systematic experimental characterization of the phenomenon is carried out for electric fields ranging in strength from 0-8 kV/cm for paraffin-coated cells containing rubidium and cells containing cesium. The typical response of the vapor density to a rapid (duration < 100 ms) change in electric field of sufficient magnitude includes (a) a rapid (duration of < 100 ms) and significant increase in alkali vapor density followed by (b) a less rapid (duration of ~ 1 s) and significant decrease in vapor density (below the equilibrium vapor density), and then (c) a slow (duration of ~ 100 s) recovery of the vapor density to its equilibrium value. Measurements conducted after the alkali vapor density has returned to its equilibrium value indicate minimal change (at the level of < 10%) in the relaxation rate of atomic polarization. Experiments suggest that the phenomenon is related to an electric-field-induced modification of the paraffin coating.

Searching for axion stars and

Light (pseudo-)scalar fields are promising candidates to be the dark matter in the Universe. Under certain initial conditions in the early Universe and/or with certain types of self-interactions, they can form compact dark-matter objects such as axion stars or Q-balls. Direct encounters with such objects can be searched for by using a global network of atomic magnetometers. It is shown that for a range of masses and radii not ruled out by existing observations, the terrestrial encounter rate with axion stars or Q-balls can be sufficiently high (at least once per year) for a detection. Furthermore, it is shown that a global network of atomic magnetometers is sufficiently sensitive to pseudoscalar couplings to atomic spins so that a transit through an axion star or Q-ball could be detected over a broad range of unexplored parameter space.

Q

There are numerous recent and ongoing experiments employing a variety of atomic species to search for couplings of atomic spins to exotic fields. In order to meaningfully compare these experimental results, the coupling of the exotic field to the atomic spin must be interpreted in terms of the coupling to electron, proton, and neutron spins. Traditionally, constraints from atomic experiments on exotic couplings to neutron and proton spins have been derived using the single-particle Schmidt model for nuclear spin. In this model, particular atomic species are sensitive to either neutron or proton spin couplings, but not both. More recently, semi-empirical models employing nuclear magnetic moment data have been used to derive new constraints for non-valence nucleons. However, comparison of such semi-empirical models to detailed large-scale nuclear shell model calculations and analysis of known physical effects in nuclei show that existing semi-empirical models cannot reliably be used to predict the spin polarization of non-valence nucleons. The results of our re-analysis of nuclear spin content are applied to searches for exotic long-range monopole–dipole and dipole–dipole couplings of nuclei leading to significant revisions of some published constraints.

-balls with a terrestrial magnetometer network

A comparison between existing measurements and calculated cross sections for spin exchange between alkali-metal atoms and noble gases (specifically sodium and helium) is used to constrain anomalous spin-dependent forces between nuclei at the atomic scale ({approx}10{sup -8} cm). Combined with existing stringent limits on anomalous short-range, spin-dependent couplings of the proton, the dimensionless coupling constant for an axial vector interaction of the neutron arising from exchange of a boson of mass < or approx. 100 eV is constrained to be g{sub A}{sup n}/{radical}(4{pi}({h_bar}/2{pi})c)<2x10{sup -3}. Constraints are established for a velocity- and spin-dependent interaction {proportional_to}(I{center_dot}v)(K{center_dot}v), where I and K are the nuclear spins of He and Na, respectively, and v is the relative velocity of the atoms. Constraints on torsion gravity are also considered.