859 research outputs found
Orbital entanglement and violation of Bell inequalities in the presence of dephasing
We discuss orbital entanglement in mesoscopic conductors, focusing on the
effect of dephasing. The entanglement is detected via violation of a Bell
Inequality formulated in terms of zero-frequency current correlations.
Following closely the recent work by Samuelsson, Sukhorukov and Buttiker, we
investigate how the dephasing affects the possibility to violate the Bell
Inequality and how system parameters can be adjusted for optimal violation.Comment: 9 pages, 2 figures. To appear in a special issue on "Quantum
Computation at the Atomic Scale" in Turkish Journal of Physic
Quantum Computation and Spin Electronics
In this chapter we explore the connection between mesoscopic physics and
quantum computing. After giving a bibliography providing a general introduction
to the subject of quantum information processing, we review the various
approaches that are being considered for the experimental implementation of
quantum computing and quantum communication in atomic physics, quantum optics,
nuclear magnetic resonance, superconductivity, and, especially, normal-electron
solid state physics. We discuss five criteria for the realization of a quantum
computer and consider the implications that these criteria have for quantum
computation using the spin states of single-electron quantum dots. Finally, we
consider the transport of quantum information via the motion of individual
electrons in mesoscopic structures; specific transport and noise measurements
in coupled quantum dot geometries for detecting and characterizing
electron-state entanglement are analyzed.Comment: 28 pages RevTeX, 4 figures. To be published in "Quantum Mesoscopic
Phenomena and Mesoscopic Devices in Microelectronics," eds. I. O. Kulik and
R. Ellialtioglu (NATO Advanced Study Institute, Turkey, June 13-25, 1999
Detection of non-Gaussian Fluctuations in a Quantum Point Contact
An experimental study of current fluctuations through a tunable transmission
barrier, a quantum point contact, are reported. We measure the probability
distribution function of transmitted charge with precision sufficient to
extract the first three cumulants. To obtain the intrinsic quantities,
corresponding to voltage-biased barrier, we employ a procedure that accounts
for the response of the external circuit and the amplifier. The third cumulant,
obtained with a high precision, is found to agree with the prediction for the
statistics of transport in the non-Poissonian regime.Comment: 4 pages, 4 figures; published versio
Multiparticle Interference, GHZ Entanglement, and Full Counting Statistics
We investigate the quantum transport in a generalized N-particle Hanbury
Brown--Twiss setup enclosing magnetic flux, and demonstrate that the Nth-order
cumulant of current cross correlations exhibits Aharonov-Bohm oscillations,
while there is no such oscillation in all the lower-order cumulants. The
multiparticle interference results from the orbital Greenberger-Horne-Zeilinger
entanglement of N indistinguishable particles. For sufficiently strong
Aharonov-Bohm oscillations the generalized Bell inequalities may be violated,
proving the N-particle quantum nonlocality.Comment: 4 pages, 1 figure, published versio
Counting Statistics and Dephasing Transition in an Electronic Mach-Zehnder Interferometer
It was recently suggested that a novel type of phase transition may occur in
the visibility of electronic Mach-Zehnder Interferometers. Here, we present
experimental evidence for the existence of this transition. The transition is
induced by strongly non-Gaussian noise that originates from the strong coupling
of a quantum point contact to the interferometer. We provide a transparent
physical picture of the effect, by exploiting a close analogy to the
neutrino-oscillations of particle physics. In addition, our experiment
constitutes a probe of the singularity of the elusive full counting statistics
of a quantum point contact.Comment: 7 pages, 4 figures (+Supplement 8 pages, 9 figures
Giant change in IR light transmission in La_{0.67}Ca_{0.33}MnO_{3} film near the Curie temperature: promising application in optical devices
Transport, magnetic, magneto-optical (Kerr effect) and optical (light
absorption) properties have been studied in an oriented polycrystalline
La_{0.67}Ca_{0.33}MnO_{3} film which shows colossal magneto-resistance. The
correlations between these properties are presented. A giant change in IR light
transmission (more than a 1000-fold decrease) is observed on crossing the Curie
temperature (about 270 K) from high to low temperature. Large changes in
transmittance in a magnetic field were observed as well. The giant changes in
transmittance and the large magneto-transmittance can be used for development
of IR optoelectronic devices controlled by thermal and magnetic fields.
Required material characteristics of doped manganites for these devices are
discussed.Comment: 7 pages, 7 figures, submitted to J. Appl. Phy
Classical simulation of squeezed light in optical waveguide arrays
We show that classical light diffraction in arrays of specially modulated coupled optical waveguides can simulate the quantum process of two-mode squeezing in nonlinear media, with the waveguide mode amplitudes corresponding the signal and idler photon n
Cascade Boltzmann - Langevin approach to higher-order current correlations in diffusive metal contacts
The Boltzmann - Langevin approach is extended to calculations of third and
fourth cumulants of current in diffusive-metal contacts. These cumulants result
from indirect correlations between current fluctuations, which may be
considered as "noise of noise". The calculated third cumulant coincides exactly
with its quantum-mechanical value. The fourth cumulant tends to its
quantum-mechanical value at high voltages and to a positive value
at V=0 changing its sign at .Comment: 6 pages, 2 eps figures, typo corrected, minor change
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