Session M6: Atomic Magnetometry

A $^3$He-$^{129}$Xe co-magnetometer probed by alkali metal atoms

We report the recent progress in the development of a new co-magnetometer using $^3$He and $^{129}$Xe nuclear spins. The co-magnetometer is run as a clock by measuring the precession frequencies of the two nuclear spin species ''in the dark'', with Rb atoms used only to measure the initial and final phases of nuclear spin precession. Using this system we investigated several general classes of systematic effects affecting gas co-magnetometers. We studied the effect of thermal diffusion, which results in a non-uniform relative concentration of $^3$He and $^{129}$Xe in the presense of a temperature gradient. We also investigated the effects of linear and quadratic magnetic field gradients and develped a new theory to model the effects of arbitrary magnetic field gradients on the frequency shifts and nuclear spin relaxation rates. We will present the latest results on the precision and accuracy in the measurements of the ratio between the two nuclear spin precession frequencies. This co-magnetometer has potential applications for many precision measurements, such as searches for spin-gravity couplings, electric dipole moments and nuclear spin gyroscopes.   

A Nuclear-Electronic Spin Gyro-Comagnetometer

We have started a project aiming to fully characterize a new generation of atomic gyroscope very promising for applications requiring miniature sensors with high performances. Our experiment is based on the detection of a nuclear spin orientation with an alkali magnetometer [1]. The key element of the device is a spherical gas cell filled with an alkali gas (Rb) with an electronic spin and a noble gas ($^{129}$Xe) with a nuclear spin and heated at about 110 $^{\circ}$C and shielded from parasite magnetic fields. The first step of our project was the conception of the atomic spin gyroscope. The second step was the realization and the validation of the filling system. The gas mixture filled into the spherical cells was checked by the study of the collisional broadening and frequency shift of the D1 lines of the Rb. We are currently analyzing the $^{129}$Xe polarization by NMR and measuring the spin-exchange and relaxation parameters to estimate the future gyroscope performances. In parallel, the realization and of a first prototype of atomic spin gyroscope is in progress.\\[4pt] [1] T.W. Kornack, et al., ``Nuclear Spin Gyroscope Based on an Atomic Comagnetometer,'' PRL, vol. 95, 230801, 2005.   

All-optical vector atomic magnetometer

Alkali-vapor magnetometers are among the most precise magnetic sensors today, reaching sensitivities on the scale of fT/$\sqrt{\textrm{Hz}}$. In general, alkali-vapor magnetometers operating in finite fields can only measure the scalar magnitude of the field (not its direction or projection). In this work we demonstrate an all-optical \emph{vector} cesium magnetometer with $0.2\:\textrm{pT}/\sqrt{\textrm{Hz}}$ sensitivity to the field magnitude and $4\:\textrm{mrad}/\sqrt{\textrm{Hz}}$ angular precision in the field direction. Although this can be accomplished by applying orthogonal magnetic fields to the sensor and measuring the change in Larmor frequency, in our sensor we employ the vector light shift induced by orthogonal laser beams to achieve the same effect. We will present results from such a sensor operating in a 10 mG magnetic field and discuss its applications to fundamental physics experiments and remote magnetometry.   

The Global Network of Optical Magnetometers to search for Exotic physics (GNOME)

Construction of a network of geographically separated, time-synchronized ultrasensitive atomic comagnetometers to search for correlated transient signals heralding new physics is underway [S. Pustelny et al., Annalen der Physik 525(8-9), 659-670 (2013)]. The {\textbf{G}}lobal {\textbf{N}}etwork of {\textbf{O}}ptical {\textbf{M}}agnetometers to search for {\textbf{E}}xotic physics (GNOME) would be sensitive to nuclear and electron spin couplings to various exotic fields generated by astrophysical sources. To date, no such search has ever been carried out, making the GNOME a novel experimental window on new physics. A specific example of new physics detectable with the GNOME, presently unconstrained by astrophysical observations and laboratory experiments, is a network of domain walls of light pseudoscalar fields [M. Pospelov et al., Phys. Rev. Lett. 110, 021803 (2013)].   

Remote Atmospheric Magnetometry

We are investigating an optical technique for remotely measuring nanotesla variations in the Earth's magnetic field ($\sim$ 0.5G). This technique uses a frequency-modulated, circularly polarized laser ($\lambda = $ 760 nm) to spin polarize the ground state of molecular oxygen at atmospheric conditions. The Earth's magnetic field splits the magnetic sublevels of molecular oxygen's ground state leading to spin depolarization. The molecule's fluorescence depends on the spin depolarization and consequently on the Earth's magnetic field. The time-dependent fluorescence will be extracted by heterodyning with the laser's frequency modulation. We will discuss limiting physical processes such as collisional dephasing, Doppler broadening, and molecular oxygen's magnetic dipole transition strength. This research is being funded by ONR.   

Super-resolution high sensitivity AC Magnetic Field Imaging with NV Centers in Diamond

The Nitrogen-Vacancy center in diamond (NV center), a defect consisting of a nitrogen atom next to a missing atom, has become increasingly popular in the last few years. It has been successfully applied as magnetic field sensor, electric field sensor, nanoscale thermometer, fluorescence marker, and single photon emitter. We will present our work on subdiffraction imaging of NV centers and simultaneous sensing of AC magnetic fields with high sensitivity. To demonstrate the applicability of super-resolution magnetic field imaging, we resolve several NV centers within the confocal volume of our setup with an optical resolution smaller than 20 nm and measure the gradient of a magnetic field from a wire. Additionally, we demonstrate the detection of magnetic field signals from $^1H$ protons with subdiffraction image resolution. Our technique paves the way to implement NV centers as a nanoscale electric and magnetic field sensor.   

A cryogenic quantum gas scanning magnetic microscope

Improved measurements of strongly correlated and topologically non-trivial systems open the path to a better fundamental understanding of these materials as well as the possibility for predictive design of new materials. We are working to demonstrate atom chip trapping of quantum gases to enable single-shot, large area imaging of electronic transport through these materials via detection of magnetic flux at the $10^{-7}$ flux quantum level and below. Using the exquisite sensitivity of ultracold atoms in the form of either an atomic clock or Bose-Einstein condensate, the cryogenic atom chip technology we have recently demonstrated [1] will provide a magnetic flux detection capability that surpasses other techniques while allowing sample temperatures spanning $<10$ K to room temperature. We will report on experimental progress toward developing this novel quantum gas scanning magnetic microscope and describe our recent proposal to image topologically protected transport through a non-ideal topological insulator in a relatively model-independent fashion.\\[4pt] [1] M. A. Naides, R. W. Turner, R. A. Lai, J. M. DiSciacca, and B. L. Lev, Trapping ultracold gases near cryogenic materials with rapid reconfigurability, Appl. Phys. Lett. 103, 251112 (2013) (2013).   

Measurement of the Magnetic Interaction Between Two Electrons

In this talk we will report on the first measurement of the magnetic interaction between two electronic spins. While the dipolar magnetic interaction between different spin systems, such as an electron and its nucleus or several multi-electron spin complexes, were experimentally studied, the magnetic interaction between two isolated electronic spins was never observed. We will explain why the Coulomb exchange forces on the one hand, and magnetic field noise on the other hand, make the electron-electron magnetic interaction measurement a challenging one. This challenge was resolved by the use of Quantum Information techniques. In our experiment, we used the ground state valence electrons of two $^{88}$Sr$^+$ ions, co-trapped in an electric Paul trap and separated by more than two micrometers. We measured a weak, millihertz scale, magnetic interaction between their electronic spins, in the presence of magnetic noise that was six orders of magnitude larger than the respective fields the electrons apply on each other. Spin dynamics was restricted to a Decoherence Free Subspace where a coherent evolution of 15 seconds led to spin-entanglement. Finally, by varying the separation between the ions, we were able to recover the inverse cubic distance dependence of the interaction.   

Sub-Wavelength Microwave Electric Field Imaging using Rydberg Atoms

It is clearly important to pursue atomic standards for quantities like electromagnetic fields, time, length and gravity. We have recently shown that Alkali atoms in a vapor cell can serve as a standard for microwave electric field strength and that vector electrometry is also feasible. Here, we demonstrate, for the first time, that microwave electrometry using Rydberg atom electromagnetically induced transparency can be used to image microwave microwave electric fields with unprecedented precision. The spatial resolution of the method is sub-wavelength $\lambda$/1933. We present new data demonstrating the utility of the method. Our calculations using High Frequency Structural Simulator (Hfss) agree well with the pattern of the field measured by our experiment.