Abstract

Magnetic fields generated by human and animal organs, such as the heart, brain and nervous system carry information useful for biological and medical purposes. These magnetic fields are most commonly detected using cryogenically-cooled superconducting magnetometers. Here we present the first detection of action potentials from an animal nerve using an optical atomic magnetometer. Using an optimal design we are able to achieve the sensitivity dominated by the quantum shot noise of light and quantum projection noise of atomic spins. Such sensitivity allows us to measure the nerve impulse with a miniature room-temperature sensor which is a critical advantage for biomedical applications. Positioning the sensor at a distance of a few millimeters from the nerve, corresponding to the distance between the skin and nerves in biological studies, we detect the magnetic field generated by an action potential of a frog sciatic nerve. From the magnetic field measurements we determine the activity of the nerve and the temporal shape of the nerve impulse. This work opens new ways towards implementing optical magnetometers as practical devices for medical diagnostics.

Highlights

  • We use the approach of ref. 9 for nerve impulse measurements

  • Projection noise dominated sensitivity can be reached by relatively straightforward steps, such as using multipass vapor cells[16], by modest heating or by employing a low finesse optical cavity[11]

  • Gradiometry with two cells with oppositely oriented spins allows for generation of nonclassical entangled states leading to sensitivity beyond the projection noise (PN) limit[9] as well as provides additional compensation of the ambient magnetic fields and classical fluctuations of the atomic spins

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Summary

Introduction

The magnetic field of the nerve Bnerve will create a transverse spin component J⊥ =(Jy, Jz) which afterwards will rotate in the y-z plane at the Larmor frequency Ω =Bx/γ [see Fig. 1(b)], where γ = 2.20 · 1010 rad/(s · T) is the cesium gyromagnetic ratio. We approach the SQL for the magnetic field measurement of nerve impulses whose frequency is much lower using the techniques described in the Supplementary Information.

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