Fig. 2: Results of magnetometry.
a Spectra of the flux qubit with neurons measured at 12.5, 25, 50, 100, and 200 mK. The temperature was adjusted from low to high in the experiment. The in-plane magnetic field was fixed at 10 mT. The color scale indicates the switching probability (see Methods) of the SQUID [20% (blue), 50% (white), and 80% (red)]. The switching probability of 50% (20 and 80%) corresponds to the ground (excited) state of the qubit. The arrows referenced to gray dashed line indicate the reduced magnetization induced shifts from the spectra at 12.5 mK. b Temperature dependence of the magnetization with an in-plane magnetic field of 10 mT. The sample was first heated to 200 mK from base temperature (yellow squares). The sample was then cooled from 200 mK to verify the experimental results (purple circles). Magnetization signal of pure parylene-C film is also plotted for comparison (brown triangles). c In-plane magnetic field dependence of the magnetization for different temperatures. d Temperature and in-plane magnetic field dependence of the magnetization as a function of ∣B∥∣/T. Original dataset is the same as c. The black dashed line is simulated magnetic flux shift. e Calculated energy diagram of electron spins in neurons as a function of magnetic field. Here, h is the Planck’s constant. The direction of the magnetic field was +z for this calculation. f Effective spin temperature as a function of the cold plate temperature. The dashed line is a guide for the eye, which indicates that the spin temperature is equal to the cold plate temperature. Error bars (standard error of curve fitting) in b–d, and f are smaller than the symbols.
