We studied a qubit based on flux-pinning effects in \(\Delta H=\Delta B\) region of a superconductor. In the state that volume defects are many enough in a superconductor, \(\Delta\) H= \(\Delta\) B region on M–H curve would be evolved, which is the region that increased applied magnetic field ( \(\Delta\) H) is the same as increasing magnetic induction ( \(\Delta\) B). Magnetization (M) is constant in the region by 4 \(\pi\) M = B - H. Here we show the behavior of fluxes in \(\Delta\) H = \(\Delta\) B region can be a candidate of qubit. Pinned fluxes on volume defects would move as a bundle in the region by repeating flux-pinning and pick-out depinning process from the surface to the center of the superconductor. During the process, magnetic fluxes would exist as one of states that are flux-pinning state at volume defects and depinning state from the defect. A difference of diamagnetic property occurs between pinning state at volume defects and depinning state from the volume defects. Thus, diamagnetic properties of the superconductor would oscillate in \(\Delta\) H= \(\Delta\) B region and the behavior would be observed in M-H curve. The oscillation can be used for a qubit by setting the pinning state at volume defects as \(\mathinner {|{1}\rangle }\) and the depinning state as \(\mathinner {|{0}\rangle }\) . It is determined that the operating temperature as a qubit is up to 25 K if \(\hbox {MgB}_2\) is used as a base superconductor.
