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Kasper Jensen*, Rima Budvytyte, Rodrigo A. Thomas, Tian Wang, Annette M. Fuchs, Mikhail V. Balabas, Georgios Vasilakis, Lars D. Mosgaard, Hans C. Stærkind, Thomas Heimburg, Søren-Peter Olesen, and Eugene S. Polzik

Niels Bohr Institute, University of Copenhagen.

Title: Non-invasive detection of nerve impulses with an optical magnetometer operating near quantum limited sensitivity

Abstract: Electromagnetic fields are generated by different sources inside the human body such as the heart, the brain and the nervous system. Detection of such fields is a keystone for medical diagnostics. We present a non-invasive technique for the detection of nerve impulses from a frog sciatic nerve using a room-temperature optical magnetometer. Our work [1] paves the road for implementing optical magnetometers operating at the quantum limits of sensitivity as practical devices for medical diagnostics. The magnetic field from a nerve impulse was first detected by Wikswo et al. [2]. They used a SQUID magnetometer combined with a pick-up coil in which the nerve had to be pulled through. Our magnetometer consists of a millimeter-sized cesium vapor cell kept at room- or human body temperature and lasers used for optical pumping and probing. The vapor cell is placed next to the nerve, and the nerve impulse can be detected non-invasively as the magnetic field extends outside the nerve. Our optical magnetometer operates in a small bias (< 1 microTesla) field, and can detect millisecond magnetic field pulses with high sensitivity. At 2 mm distance from the nerve, we measure a nerve impulse with 25 picoTesla peak-to-peak amplitude with a signal-to-noise ratio close to 1. The field decreases with larger distances, but remains detectable more than 5 mm away. We also show that our magnetometer is sensitive to the direction of the nerve impulse propagation. Future efforts will be put into developing a gradiometer consisting of two vapor cells. Differential measurements reduce the need for magnetic shielding and allow for enhanced sensitivity using quantum entanglement [3]. We will also develop a miniaturized and fiber-coupled device and investigate other applications such as fetal magnetocardiography. [1] K. Jensen et al. arXiv:1601.03273 (2016) [2] J. P. Wikswo et al. Science, 208(4439):53 (1980) [3] W. Wasilewski et al. Phys. Rev. Lett., 104:133601 (2010)

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