147 research outputs found
Bilayer Graphene Interferometry : Phase Jump and Wave Collimation
We theoretically study the phase of the reflection amplitude of an electron
(massive Dirac fermion) at a lateral potential step in Bernal-stacked bilayer
graphene. The phase shows anomalous jump of , as the electron incidence
angle (relative to the normal direction to the step) varies to pass . The jump is attributed to the Berry phase associated with the
pseudospin-1/2 of the electron. This Berry-phase effect is robust against the
band gap opening due to the external electric gates generating the step. We
propose an interferometry setup in which collimated waves can be generated and
tuned. By using the setup, one can identify both the jump and the
collimation angle.Comment: 4 pages, 6 figure
Electron-tunneling-assisted non-Abelian braiding
It is common knowledge that fluctuations of fermion parity are harmful for
the demonstration of non-Abelian anyonic statistics. Here, we demonstrate a
striking exception in which such fluctuations are actively used. We present a
theory of coherent electron transport from a tunneling tip into a Corbino
geometry Josephson junction where four Majorana bound states (MBSs) rotate.
While the MBSs rotate, electron tunneling happens from the tip to one of the
MBSs thereby changing the fermion parity of the MBSs. The tunneling events in
combination with the rotation allow us to identify a novel braiding operator
that does not commute with the braiding cycles in the absence of tunneling,
revealing the non-Abelian nature of MBSs. The time-averaged tunneling current
exhibits resonances as a function of the tip voltage with a period that is a
direct consequence of the interference between the non-commuting braiding
operations. Our work opens up a possibility for utilizing parity non-conserving
processes to control non-Abelian states.Comment: Revised version: 7 pages, 3 figures + Supplemental material (10
pages, 3 figures
Vortex control in superconducting Corbino geometry networks
In superconductors, vortices induced by a magnetic field are nucleated where some random fluctuations determine the nucleation position, and then may be pinned by impurities or boundaries, impeding the development of vortex-based quantum devices. Here, we propose a superconducting structure, which allows to nucleate and control vortices on-demand by controlling magnetic fields and currents. Using time-dependent Ginzburg-Landau theory, we study a driven vortex motion in two-dimensional Corbino geometries of superconductor-normal metal-superconductor Josephson junctions. We remedy the randomness of nucleation by introducing normal conducting rails to the Corbino disk to guide the nucleation process and motion of vortices towards the junction. We elaborate on the consequences of rail-vortex and vortex-vortex interactions to the quantization of resistance across the junction. Finally, we simulate the nucleations and manipulations of two and four vortices in Corbino networks, and discuss its application to Majorana zero mode braiding operations. Our study provides a potential route towards quantum computation with non-Abelian anyon
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