Observing the steady-state visual evoked potentials with a compact quad-channel spin exchange relaxation-free magnetometer**Project supported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0300600 and 2016YFA0301500), the Strategic Priority Research Program of Chinese Academy of Sciences (Grant Nos. XDB07030000 and XDBS32000000), the National Natural Science Foundation of China (Grant Nos. 11474347 and 31730039), and the Fund

Abstract

We observed the steady-state visually evoked potential (SSVEP) from a healthy subject using a compact quad-channel potassium spin exchange relaxation-free (SERF) optically pumped magnetometer (OPM). To this end, 30 s of data were collected, and SSVEP-related magnetic responses with signal intensity ranging from 150 fT to 300 fT were observed for all four channels. The corresponding signal to noise ratio (SNR) was in the range of 3.5–5.5. We then used different channels to operate the sensor as a gradiometer. In the specific case of detecting SSVEP, we noticed that the short channel separation distance led to a strongly diminished gradiometer signal. Although not optimal for the case of SSVEP detection, this set-up can prove to be highly useful for other magnetoencephalography (MEG) paradigms that require good noise cancellation. Considering its compactness, low cost, and good performance, the K-SERF sensor has great potential for biomagnetic field measurements and brain-computer interfaces (BCI).