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Measuring Magnetic Fields with Magnetic-Field-Insensitive Transitions


  Yotam Shapira [1]  ,  Yehonatan Dallal [1]  ,  Roee Ozeri [1]  ,  Ady Stern [2]  
 [1] Department of Physics of Complex Systems, Weizmann Institute of Science
[2] Department of Condensed Matter Physics, Weizmann Institute of Science

The prevalent approach to atomic sensing is to measure an accumulating dynamical phase, which appears due to the dependence of the energy on the quantity to be sensed [1,2].  Specifically, high-sensitivity atomic-based magnetometers always operate by tracking and accumulating the phase difference between Zeeman-split atomic states [3].

Here we make use of clock states, i.e. atomic states that have a magnetic-field insensitive energy difference and are therefore commonly used in atomic clocks. Naively one would expect that these states would be useless for magnetic field sensing, since a superposition of these states does not accumulate a magnetic field dependent dynamical phase. We show that, surprisingly, these clock states can indeed acquire a phase, which is proportional to the magnetic field magnitude. We demonstrate this effect on an ensemble of laser-cooled trapped 87 Rb atoms, and propose a new method for magnetic field sensing which uses magnetic-field-insensitive transitions. Our findings have recently been published on Phys. Rev. Lett. [4].

Furthermore, we investigate our method’s sensitivity and show that it scales inversely with the coherence time of the clock subspace, which is typically much longer than in a Zeeman-split subspace [5]. This implies that our proposed method may be used to improve upon the sensitivity of Zeeman-splitting based magnetometry methods. In addition, we show that this magnetic dependent phase shift can also act as a source for systematic errors in contemporary atomic clocks.

References:

[1] J. Kitching, S. Knappe, and A. Donley, Atomic sensors—A review, IEEE Sens. J. 11, 1749 (2011).

[2] C. L. Degen, F. Reinhard, and P. Cappellaro, Quantum sensing, Rev. Mod. Phys. 89, 035002 (2017).

[3] D. Budker and M. Romalis, Optical magnetometry, Nat. Phys. 3, 227 (2007).

[4] Y. Shapira, Y. Dallal, R. Ozeri, and A. Stern, Measuring Magnetic Fields with Magnetic-Field-Insensitive Transitions, Phys. Rev. Lett. 123, 133204 (2019).

[5] G. Kleine Büning, J. Will, W. Ertmer, E. Rasel, J. Arlt, C. Klempt, F. Ramirez-Martinez, F. Piéchon, and P. Rosenbusch, Extended Coherence Time on the Clock Transition of Optically Trapped Rubidium, Phys. Rev. Lett. 106, 240801 (2011).