Microscopic magnetometry of neurons using a superconducting flux qubit*

We have developed a microscopic magnetometer based on a superconducting flux qubit [1]. Using it, we have successfully obtained a magnetization signal from neurons. The neurons were cultured on parylene-C film in iron-rich medium to increase the number of spins in the cell. The film also worked as an insulator between the neurons and the flux qubit. The magnetization signal increased as a function of the inverse temperature and the Zeeman magnetic field. Considering that the control experiment without neurons showed no significant magnetization signal, this result strongly suggests that the signal originates from the spins in neurons. In the case of spins in neurons, because the spins distribute inhomogeneously in the cell, the contribution to the magnetization signal from the spins distant from the chip surface plays an important role, unlike the case of solid state spins [1]. To improve sensitivity to such widely distributed organic spins, a capacitively shunted flux qubit with a large loop size is developed and its design parameters are discussed [2]. [1] H. Toida et. al., Commun. Phys. 2, 33 (2019). [2] D. Marcos et. al., Phys. Rev. Lett. 105, 210501 (2010).