Microwave polarization reconstruction leading to self-calibrated vector magnetometry with atoms

There is need for sensitive magnetometers in both fundamental science and applications. Typical applications range from precision measurements and dark matter searches to timekeeping, biological imaging, and navigation.... [ view full abstract ]

There is need for sensitive magnetometers in both fundamental science and applications. Typical applications range from precision measurements and dark matter searches to timekeeping, biological imaging, and navigation. Whereas for some of these applications the measurement of only the magnetic field strength is sufficient, other applications require a full vector description.

As of today, atom magnetometers based on hot atomic vapor cells are the most sensitive scalar magnetometers - measuring magnetic fields below femto Tesla within a second. However, using such a system to measure the full three-dimensional field vector encounters the same problem many other (naturally scalar or vector) magnetometers exhibit; a missing stable and precise reference to calibrate drifts or uncertainties in the relative direction of the axes. We will present a proof-of-concept experiment in which we introduce the three-dimensional structure of a microwave field as such a reference.

Specifically, we use an array of single trapped atoms to first determine the full polarization ellipse of a microwave field (Figure: Polarization ellipse) using Rabi measurements [1]. Importantly, we show that all relevant systematics in the direction of an applied bias field - for example non-orthogonal coil orientations - can be calibrated based on the fundamental atomic response and electro-magnetic field structure. This immediately enables determining the direction of an a priori unknown magnetic field. In combination with a favorite technique to determine the length of the field - in our case simple Zeeman spectroscopy – one can perform full, self-calibrated vector magnetometry with atoms [2].

The magnetic field sensitivity we achieve is limited by the small numbers of atoms we trap. However, the technique is widely applicable to any atom-like system. We will present plans for increasing the sensitivity of our vector magnetometer using alkali atoms in hot vapor cells.

[1] J. Koepsell, T. Thiele, J. Deiglmayr, A. Wallraff, and F. Merkt: Phys. Rev. A 95, 053860 (2017)

[2] T. Thiele, Y. Lin, M. O. Brown, and C. A. Regal: ArXiv:1807.03619 (2018)