1,721,032 research outputs found
Bilayer Graphene Interferometry: Phase Jump and Wave Collimation
No full textWe 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 an anomalous jump of pi, as the electron incidence angle (relative to the normal direction to the step) varies to pass +/-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.This work is supported by NRF (2009-0078437)
pi Berry phase and Veselago lens in a bilayer graphene np junction
No full textKlein tunneling in gapless bilayer graphene, perfect reflection of electrons injecting normal to a pn junction, is expected to disappear in the presence of energy band gap induced by external gates. We theoretically show that the Klein effect still exists in gapped bilayer graphene, provided that the gaps in the n and p regions are balanced such that the polarization of electron pseudospin has the same normal component to the bilayer plane in the regions. We attribute the Klein effect to pi Berry phase (rather than the conventional value 2 pi of bilayer graphene) and to electron-hole and time-reversal symmetries. The Klein effect and the pi Berry phase can be identified in an electronic Veselago lens, an important component of graphene-based electron optics
Three-particle Hanbury Brown-Twiss interferometer
No full textWe investigate a three-particle Hanbury Brown-Twiss effect in mesoscopic systems, where three electrons together can enclose a loop while neither single electron nor two electrons do so. This leads to the three-particle interference effect which manifests itself in the periodic oscillations of the third-order cumulant of current cross correlations as a function of the total phase accumulated by three electrons along the loop. Bosons such as photons also show a similar interference effect. (c) 2006 Elsevier B.V. All rights reserved.We thank APCTP focus program on Quantum effects in
nanosystems. HSS was supported by grants from the Korea
Research Foundation (KRF-2005-003-C00071) and from the
Ministry of Science and Technology (MOST) of Korea.
Negative Excess Shot Noise by Anyon Braiding
No full textAnyonic fractional charges e* have been detected by autocorrelation shot noise at a quantum point contact (QPC) between two fractional quantum Hall edges. We find that the autocorrelation noise can also show a fmgerprint of Abelian anyonic fractional statistics. We predict the noise of the electrical tunneling current I at the QPC of the fractional-charge detection setup, when anyons are dilutely injected, from an additional edge biased by a voltage, to the setup in equilibrium. At large voltages, the nonequilibrium noise is reduced below the thermal equilibrium noise by the value 2e*I. This negative excess noise is opposite to the positive excess noise 2e*I of the conventional fractional-charge detection and also to the usual positive autocorrelation noises of electrical currents. This is a signature of Abelian fractional statistics, resulting from the effective braiding of an anyon thermally excited at the QPC around another anyon injected from the additional edge.
Interferometric distillation and determination of unknown two-qubit entanglement
No full textWe 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.We thank J. B. Altepeter, N. Gisin, Hee Su Park, and
Tzu-Chieh Wei for valuable discussions, and especially the
group of P. G. Kwiat for the numerical code for the tomography.
This work was supported by KAIST-HRHRP
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