Interferometric distillation and determination of unknown two-qubit entanglement

We propose a scheme for both distilling and quantifying entanglement, applicable to individual copies of an arbitrary unknown two-qubit state. It is realized in a usual two-qubit interferometry with local filtering. Proper filtering operation for the maximal distillation of the state is achieved, by erasing single-qubit interference, and then the concurrence of the state is determined directly from the visibilities of two-qubit interference. We compare the scheme with full state tomography

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 $\pi$, as the electron incidence angle (relative to the normal direction to the step) varies to pass $\pm \pi/4$. 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 $\pi$ jump and the collimation angle.Comment: 4 pages, 6 figure

Spectator Behavior in a Quantum Hall Antidot with Multiple Bound Modes

We theoretically study Aharonov-Bohm resonances in an antidot system with multiple bound modes in the integer quantum Hall regime, taking capacitive interactions between the modes into account. We find the spectator behavior that the resonances of some modes disappear and instead are replaced by those of other modes, due to internal charge relaxation between the modes. This behavior is a possible origin of the features of previous experimental data which remain unexplained, spectator behavior in an antidot molecule and resonances in a single antidot with three modes.Comment: 4 pages, 3 figures, to be published in Physical Review Letter