arXiv subjects

T. W. Kornack

Publications and source records attributed to T. W. Kornack.

11 recordsLinked to original sources

arXiv2024

Long spin-1/2 noble gas coherence times in mm-sized anodically bonded batch-fabricated $^{3}$He-$^{129}$Xe-$^{87}$Rb cells

As the only stable spin-1/2 noble gas isotopes, $^{3}$He and $^{129}$Xe are promising systems for inertial rotation sensing and searches for exotic spin couplings. Spin-1/2 noble gases have intrinsic coherence times on the order of hours to days, which allows for incredibly low frequency error of free-precession measurements. However relaxation in miniature cells is dominated by interactions with the cell wall, which limits the performance of a chip-scale sensor that uses noble gases. While $^{129}$Xe wall relaxation times have previously been limited to 10's of seconds in mm-sized cells, we demonstrate the first anodically bonded batch-fabricated cells with dual $^{3}$He-$^{129}$Xe isotopes and $^{87}$Rb in a 6~mm$^3$ volume with $^{3}$He and $^{129}$Xe $T_2$ coherence times of, respectively, 4 h and 300 s. We use these microfabricated cells in a dual noble-gas comagnetometer and discuss its limits.

physics.atom-ph↗

arXiv2023

Large-scale, Multi-pass, Two-chamber RF Atomic Magnetometer

We describe one of the largest radio-frequency RF atomic magnetometers presently operating. A total atomic volume of 128 $\mathrm{cm^3}$, with correspondingly large number of $^{87}$Rb atoms, can reduce atom noise. A total of 44 passes of the probe beam reduces photon-shot noise. The atomic vapor is divided between two chambers allowing for pumping of the cells individually; doing so with opposite-helicity light enables use as an intrinsic gradiometer. In this configuration, common-mode noise sources including light-shift noise can be reduced. Magnetic tuning fields can also be applied to the chambers individually, allowing simultaneous measurement of two frequencies. An application of this is in the search for contraband materials using Nuclear Quadrupole Resonance (NQR), for which simultaneous measurement can significantly reduce search times. We demonstrate dual-frequency measurement on an effective range of 423-531 kHz, corresponding to the NQR frequencies of ammonium nitrate NH$_4$NO$_3$ at the lowest value and potassium chlorate KClO$_3$ at the highest. We explore fundamental, as well as instrumental, noise contributions to the sensitivity in this system.

physics.atom-ph↗

arXiv2021

Femtotesla nearly quantum-noise-limited pulsed gradiometer at Earth-scale fields

We describe a finite fields magnetic gradiometer using an intense pulsed laser to polarize a $^{87}$Rb atomic ensemble and a compact VCSEL probe laser to detect paramagnetic Faraday rotation in a single multipass cell. We report differential magnetic sensitivity of $14$ fT/Hz$^{1/2}$ over a broad dynamic range including Earth's field magnitude and common-mode rejection ratio higher than $10^4$. We also observe a nearly quantum-noise-limited behaviour of the gradiometer, by comparing the experimental standard deviation of the estimated frequency difference against the Cramér-Rao lower bound in the presence of white photon shot-noise, atomic spin noise and atomic diffusion.

physics.atom-ph↗

arXiv2021

Heading errors in all-optical alkali-vapor magnetometers in geomagnetic fields

Alkali-metal atomic magnetometers suffer from heading errors in geomagnetic fields as the measured magnetic field depends on the orientation of the sensor with respect to the field. In addition to the nonlinear Zeeman splitting, the difference between Zeeman resonances in the two hyperfine ground states can also generate heading errors depending on initial spin polarization. We examine heading errors in an all-optical scalar magnetometer that uses free precession of polarized $^{87}\text{Rb}$ atoms by varying the direction and magnitude of the magnetic field at different spin polarization regimes. In the high polarization limit where the lower hyperfine ground state $F = 1$ is almost depopulated, we show that heading errors can be corrected with an analytical expression, reducing the errors by two orders of magnitude in Earth's field. We also verify the linearity of the measured Zeeman precession frequency with the magnetic field. With lower spin polarization, we find that the splitting of the Zeeman resonances for the two hyperfine states causes beating in the precession signals and nonlinearity of the measured precession frequency with the magnetic field. We correct for the frequency shifts by using the unique probe geometry where two orthogonal probe beams measure opposite relative phases between the two hyperfine states during the spin precession.

physics.atom-ph↗

arXiv2020

Portable magnetometry for detection of biomagnetism in ambient environments

We present a method of optical magnetometry with parts-per-billion resolution that is able to detect biomagnetic signals generated from the human brain and heart in Earth's ambient environment. Our magnetically silent sensors measure the total magnetic field by detecting the free-precession frequency of highly spin-polarized alkali metal vapor. A first-order gradiometer is formed from two magnetometers that are separated by a 3 cm baseline. Our gradiometer operates from a laptop consuming 5 W over a USB port, enabled by state-of-the-art micro-fabricated alkali vapor cells, advanced thermal insulation, custom electronics, and laser packages within the sensor head. The gradiometer obtains a sensitivity of 16 fT/cm/Hz$^{1/2}$ outdoors, which we use to detect neuronal electrical currents and magnetic cardiography signals. Recording of neuronal magnetic fields is one of a few available methods for non-invasive functional brain imaging that usually requires extensive magnetic shielding and other infractructure. This work demonstrates the possibility of a dense array of portable biomagnetic sensors that are deployable in a variety of natural environments.

physics.med-ph↗

arXiv2018

Dipolar and scalar $^3$He and $^{129}$Xe frequency shifts in mm-sized cells

We describe a $^{3}$He-$^{129}$Xe comagnetometer operating in stemless anodically bonded cells with a 6 mm$^3$ volume and a $^{129}$Xe spin coherence time of 300 sec. We use a $^{87}$Rb pulse-train magnetometer with co-linear pump and probe beams to study the nuclear spin frequency shifts caused by spin polarization of $^{3}$He. By systematically varying the cell geometry in a batch cell fabrication process we can separately measure the cell shape dependent and independent frequency shifts. We find that a certain aspect ratio of the cylindrical cell can cancel the effects of $^3$He magnetization that limit the stability of vapor-cell comagnetometers. Using this control we also observe for the first time a scalar $^{3}$He-$^{129}$Xe collisional frequency shift characterized by an enhancement factor $κ_{\text{HeXe}} = -0.011\pm0.001$.

physics.atom-ph↗

arXiv2018

Characterization of the Global Network of Optical Magnetometers to search for Exotic Physics (GNOME)

The Global Network of Optical Magnetometers to search for Exotic physics (GNOME) is a network of geographically separated, time-synchronized, optically pumped atomic magnetometers that is being used to search for correlated transient signals heralding exotic physics. The GNOME is sensitive to nuclear- and electron-spin couplings to exotic fields from astrophysical sources such as compact dark-matter objects (for example, axion stars and domain walls). Properties of the GNOME sensors such as sensitivity, bandwidth, and noise characteristics are studied in the present work, and features of the network's operation (e.g., data acquisition, format, storage, and diagnostics) are described. Characterization of the GNOME is a key prerequisite to searches for and identification of exotic physics signatures.

physics.ins-det↗

arXiv2010

New limit on Lorentz and CPT-violating neutron spin interactions

We performed a search for neutron spin coupling to a Lorentz and CPT-violating background field using a magnetometer with overlapping ensembles of K and $^3$He atoms. The co-magnetometer is mounted on a rotary platform for frequent reversal of its orientation. We measure sidereal oscillations in the signal to search for anomalous spin coupling of extra-solar origin. We determine the equatorial components of the background field interacting with the neutron spin to be $\widetilde{b}^n_X = (0.1 \pm 1.6) \times 10^{-33}$ GeV and $\widetilde{b}^n_Y = (2.5 \pm 1.6) \times 10^{-33}$ GeV, improving on the previous limit by a factor of 30. This measurement represents the highest energy resolution of any spin anisotropy experiment.

physics.atom-ph↗

arXiv2010

Limits on new long range nuclear spin-dependent forces set with a K-3He co-magnetometer

A magnetometer using spin-polarized K and $^3$He atoms occupying the same volume is used to search for anomalous nuclear spin-dependent forces generated by a separate $^3$He spin source. We measure changes in the $^3$He spin precession frequency with a resolution of 18 pHz and constrain anomalous spin forces between neutrons to be less than $2 \times 10^{-8}$ of their magnetic or less than $2\times 10^{-3}$ of their gravitational interactions on a length scale of 50 cm. We present new limits on neutron coupling to light pseudoscalar and vector particles, including torsion, and constraints on recently proposed models involving unparticles and spontaneous breaking of Lorentz symmetry.

physics.atom-ph↗

arXiv2007

A low-noise ferrite magnetic shield

Ferrite materials provide magnetic shielding performance similar to commonly used high permeability metals but have lower intrinsic magnetic noise generated by thermal Johnson currents due to their high electrical resistivity. Measurements inside a ferrite shield with a spin-exchange relaxation-free atomic magnetometer reveal a noise level of 0.75 fT Hz^(-1/2), 25 times lower than what would be expected in a comparable mu-metal shield. The authors identify a 1/f component of the magnetic noise due to magnetization fluctuations and derive general relationships for the Johnson current noise and magnetization noise in cylindrical ferromagnetic shields in terms of their conductivity and complex magnetic permeability.

physics.atom-ph↗

arXiv2005

Nuclear spin gyroscope based on an atomic co-magnetometer

We describe a nuclear spin gyroscope based on an alkali-metal-noble-gas co-magnetometer. An optically pumped alkali-metal vapor is used to polarize the noble gas atoms and detect their gyroscopic precession. Spin precession due to magnetic fields as well as their gradients and transients can be cancelled in this arrangement. The sensitivity is enhanced by using a high-density alkali-metal vapor in a spin-exchange relaxation free (SERF) regime. With a K-3He co-magnetometer we demonstrate rotation sensitivity of 5 10^(-7) rad/sec/Hz^(1/2). The rotation signal can be increased by a factor of 10 using 21Ne due to its smaller magnetic moment and the fundamental rotation sensitivity limit for a 21Ne gyroscope with a 10 cm^3 measurement volume is about 2 10^(-10) rad/sec/Hz^(1/2).

physics.atom-ph↗