University of Sussex researchers have built and demonstrated a modular quantum sensor capable of recording brain signals. According to the researchers, their device is the first use a modular quantum sensor in the brain to detect a signal. The device uses ultrasensitive quantum sensors to pick up almost imperceptible magnetic fields within the brain to detect and map neural activity. “Our quantum sensor has to be exceptionally sensitive to pick up the magnetic fields in the brain, which are very weak indeed,” said Ph.D. student Thomas Coussens, who built the sensor. “To put it into context, the magnetic field of a brain is a trillion times lower than that of a fridge magnet.” The quantum magnetic sensor uses an optically pumped magnetometer inside a magnetic shield, itself used to reduce environmental magnetic fields so as to isolate those within the brain. The sensor itself works by putting a vapor into a quantum state, through which it then shines a laser. A photodetector component determines how much light has passed through. How the atomic vapor interacts with the laser light depends on the magnetic field. This is generated by the tiny electric currents in the neuron, even outside the brain, that the sensor ultimately picks up. “Because our device is so far unique in that it is modular — and we’ve shown the modularity works by connecting two sensors together — we now plan to scale up this project by building more sensors to turn this into an entire brain imaging system,” Coussens said. In tests, the team applied sensors to a volunteer’s scalp, close to the visual cortex. The volunteer was asked to open and close their eyes at 10- to 20-s intervals, which generated a signal that the device was able to pick up. “As our sensor works on a modular basis, we will now be able to scale it up to create much more detailed images of the brain or parts of the brain. You can’t do that with the current commercial product available,” said Peter Krüger, an experimental physicist and director of the Sussex Programme for Quantum Research. The sensor, he believes, is a large step toward further interdisciplinary studies with a variety of researchers, ranging from consciousness scientists and engineers to neuroscientists. The research is available in preprint on ariXiv (www.arxiv.org/abs/2106.05877). It is currently awaiting peer review.