We studied a qubit based on flux-pinning effects in ΔH=ΔB region of a superconductor. When volume defects are many enough in a superconductor, ΔH=ΔB region on M-H curve is formed, which is the region that increased applied magnetic field (ΔH) is the same as increasing magnetic induction (ΔB). Magnetization (M) is constant in the region by 4πM = B - H. Here we show that the behavior of fluxes in ΔH=ΔB 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 pick-out depinning state in which fluxes are moving in the superconductor. 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 ΔH=ΔB region and the behavior would be observed in M-H curve. The oscillation can be used for qubit by setting the pinning state at volume defects as ∣1⟩ and the depinned state as ∣0⟩. This method can operate at higher temperatures than that of using Josephson Junctions. In addition, it is expected that the device is quite simple and decoherences can be almost negligible.
@article{arxiv.2201.06016,
title = {Quantum Bit Behavior of Pinned Fluxes on Volume Defects in a Superconductor},
author = {H. B. Lee and G. C. Kim and Byeong-Joo Kim and Young Jin Sohn and Y. C. Kim},
journal= {arXiv preprint arXiv:2201.06016},
year = {2022}
}