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Register a new userSuppression of nonlinear Zeeman effect and heading error in earth-field-range alkali-vapor magnetometers
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The nonlinear Zeeman effect can induce splitting and asymmetries of magnetic-resonance lines in the geophysical magnetic field range. This is a major source of heading error for scalar atomic magnetometers. We demonstrate a method to suppress the nonlinear Zeeman effect and heading error based on spin locking. In an all-optical synchronously pumped magnetometer with separate pump and probe beams, we apply a radio-frequency field which is in-phase with the precessing magnetization. In an earth-range field, a multi-component asymmetric magnetic-resonance line with ? 60 Hz width collapses into a single peak with a width of 22 Hz, whose position is largely independent of the orientation of the sensor. The technique is expected to be broadly applicable in practical magnetometry, potentially boosting the sensitivity and accuracy of earth-surveying magnetometers by increasing the magnetic resonance amplitude, decreasing its width and removing the important and limiting heading-error systematic.
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When optically pumped magnetometers are aimed for the use in Earths magnetic field, the orientation of the sensor to the field direction is of special importance to achieve accurate measurement result. Measurement errors and inaccuracies related to the heading of the sensor can be an even more severe problem in the case of special operational configurations, such as for example the use of strong off-resonant pumping. We systematically study the main contributions to the heading error in systems that promise high magnetic field resolutions at Earths magnetic field strengths, namely the non-linear Zeeman splitting and the orientation dependent light shift. The good correspondence of our theoretical analysis to experimental data demonstrates that both of these effects are related to a heading dependent modification of the interaction between the laser light and the dipole moment of the atoms. Also, our results promise a compensation of both effects using a combination of clockwise and counter clockwise circular polarization.
The nonlinear Zeeman effect can induce splittings and asymmetries of magnetic-resonance lines in the geophysical magnetic-field range. We demonstrate a scheme to suppress the nonlinear Zeeman effect all optically based on spin locking. Spin locking is achieved with an effective oscillating magnetic field provided by the AC Stark-shift of an intensity-modulated and polarization-modulated laser beam. This results in the collapse of the multi-component asymmetric magnetic-resonance line with about 100 Hz width in the Earth-field range into a peak with a central component width of 25Hz. The technique is expected to be broadly applicable in practical magnetometry, potentially boosting the sensitivity and accuracy of Earth-surveying magnetometers by increasing the magnetic-resonance amplitude and decreasing its width. Advantage of an all-optical approach is the absence of cross-talk between nearby sensors when these are used in a gradiometric or in an array arrangement.
Precession frequencies measured by optically pumped scalar magnetometers are dependent on the relative angle between the sensor and the external magnetic field. This dependence is known to be induced mainly by the nonlinear Zeeman effect and the orientation-dependent light shift, resulting in the so-called heading errors if the magnetic field orientation is not well known or is not stable. In this work, we find that the linear nuclear Zeeman effect has also a significant impact on the heading errors. It not only shifts the precession frequency but causes asymmetry: the heading error for sensors orienting in the upper-half plane with respect to the external field is different from the case when the sensors work in the lower-half plane. This heading error also depends on the relative direction of the probe laser to the driving magnetic field. With a left-handed circularly-polarized pump laser, when the probe laser is parallel to the driving field, the angular dependence of the precession frequency is smaller when the sensor is in the upper plane. Otherwise, when they are perpendicular to each other, the heading error is smaller when the sensor is in the lower plane. Furthermore, to suppress the heading error, we propose to utilize a small magnetic field along the propagation direction of the pump laser. By tuning the magnitude of this auxiliary field, the heading-error curve is flattened around different angles, which can increase the accuracy in practice when the magnetometer works around a certain orientation angle.
We realize simultaneous quantum degeneracy in mixtures consisting of the alkali and alkalineearth-like atoms Li and Yb. This is accomplished within an optical trap by sympathetic cooling of the fermionic isotope 6Li with evaporatively cooled bosonic 174Yb and, separately, fermionic 173Yb.Using cross-thermalization studies, we also measure the elastic s-wave scattering lengths of both Li-Yb combinations, |a6Li-174Yb| = 1.0pm0.2 nm and |a6Li-173Yb| = 0.9pm0.2 nm. The equality of these lengths is found to be consistent with mass-scaling analysis. The quantum degenerate mixtures of Li and Yb, as realized here, can be the basis for creation of ultracold molecules with electron spin degrees of freedom, studies of novel Efimov trimers, and impurity probes of superfluid systems.
We report on widefield microwave vector field imaging with sub um resolution using a microfabricated alkali vapor cell. The setup can additionally image dc magnetic fields, and can be configured to image microwave electric fields. Our camera-based widefield imaging system records 2D images with a 6x6 mm2 field of view at a rate of 10 Hz. It provides up to 50 um spatial resolution, and allows imaging of fields as close as 150 um above structures, through the use of thin external cell walls. This is crucial in allowing us to take practical advantage of the high spatial resolution, as feature sizes in near-fields are on the order of the distance from their source, and represents an order of magnitude improvement in surface-feature resolution compared to previous vapor cell experiments. We present microwave and dc magnetic field images above a selection of devices, demonstrating a microwave sensitivity of 1.4 uT/sqrt-Hz per 50x50x140 um3 voxel, at present limited by the speed of our camera system. Since we image 120x120 voxels in parallel, a single scanned sensor would require a sensitivity of at least 12 nT/sqrt-Hz to produce images with the same sensitivity. Our technique could prove transformative in the design, characterisation, and debugging of microwave devices, as there are currently no satisfactory established microwave imaging techniques. Moreover, it could find applications in medical imaging.
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