Barnes co-developed (with Nottingham's Matt Brookes) OPM-MEG, the first wearable whole-head magnetoencephalography scanner: a helmet of optically-pumped magnetometer quantum sensors (spin-exchange-relaxation-free Rb vapour cells) that lets patients move naturally during a brain scan, inside an actively-nulled magnetically shielded room. His group has validated the system against cryogenic SQUID-MEG, deployed the UK's first paediatric OPM-MEG epilepsy clinic, and extended the technology to spinal-cord recording and naturalistic/VR paradigms -- a direct human-trials application of a quantum sensor whose femtotesla-scale sensitivity is comparable to the pT/sqrt(Hz)-class sensitivity sought from NV-ensemble magnetometry, but achieved with room-temperature atomic vapour cells rather than solid-state spin defects.