1,548 research outputs found
Nonlinear transport and oscillating magnetoresistance in double quantum wells
We study the evolution of low-temperature magnetoresistance in double quantum
wells in the region below 1 Tesla as the applied current density increases. A
flip of the magneto-intersubband oscillation peaks, which occurs as a result of
the current-induced inversion of the quantum component of resistivity, is
observed. We also see splitting of these peaks as another manifestation of
nonlinear behavior, specific for the two-subband electron systems. The
experimental results are quantitatively explained by the theory based on the
kinetic equation for the isotropic non-equilibrium part of electron
distribution function. The inelastic scattering time is determined from the
dependence of the inversion magnetic field on the current.Comment: 20 pages, 10 figure
Measurement of miniband parameters of a doped superlattice by photoluminescence in high magnetic fields
We have studied a 50/50\AA superlattice of GaAs/AlGaAs
composition, modulation-doped with Si, to produce
cm electrons per superlattice period. The modulation-doping was tailored
to avoid the formation of Tamm states, and photoluminescence due to interband
transitions from extended superlattice states was detected. By studying the
effects of a quantizing magnetic field on the superlattice photoluminescence,
the miniband energy width, the reduced effective mass of the electron-hole
pair, and the band gap renormalization could be deduced.Comment: minor typing errors (minus sign in eq. (5)
Resonance oscillations of magnetoresistance in double quantum wells
We present experimental and theoretical studies of the magnetoresistance
oscillations induced by resonance transitions of electrons between
tunnel-coupled states in double quantum wells. The suppression of these
oscillations with increasing temperature is irrelevant to the thermal
broadening of the Fermi distribution and reflects the temperature dependence of
the quantum lifetime of electrons. The gate control of the period and amplitude
of the oscillations is demonstrated.Comment: 5 pages 4 figures, to be published in the Physical Review
Nonlinear transport and oscillating magnetoresistance in double quantum wells
The nonlinear regime of low-temperature magnetoresistance of double quantum wells in the region of magnetic fields below 1 T is studied both experimentally and theoretically. The observed inversion of the magnetointersubband oscillation peaks with increasing electric current and splitting of these peaks are described by the theory based on the kinetic equation for the isotropic nonequilibrium part of electron distribution function. The inelastic-scattering time of electrons is determined from the current dependence of the inversion field
Performance of a multigap RPC prototype for the LHCb muon system
Several technologies are under consideration for the muon system of the LHCb experiment. Resistive Plate Chambers (RPCs) are one of the favourite candidates for the outer areas where the particle fluxes are expected to be at most some kHz/cm/sup 2/. This work describes the results obtained with a multigap RPC prototype under various beam conditions at the CERN facilities. (9 refs)
Field-driven femtosecond magnetization dynamics induced by ultrastrong coupling to THz transients
Controlling ultrafast magnetization dynamics by a femtosecond laser is
attracting interest both in fundamental science and industry because of the
potential to achieve magnetic domain switching at ever advanced speed. Here we
report experiments illustrating the ultrastrong and fully coherent light-matter
coupling of a high-field single-cycle THz transient to the magnetization vector
in a ferromagnetic thin film. We could visualize magnetization dynamics which
occur on a timescale of the THz laser cycle and two orders of magnitude faster
than the natural precession response of electrons to an external magnetic
field, given by the Larmor frequency. We show that for one particular
scattering geometry the strong coherent optical coupling can be described
within the framework of a renormalized Landau Lifshitz equation. In addition to
fundamentally new insights to ultrafast magnetization dynamics the coherent
interaction allows for retrieving the complex time-frequency magnetic
properties and points out new opportunities in data storage technology towards
significantly higher storage speed.Comment: 25 page
Multi-photon, multi-mode polarization entanglement in parametric down-conversion
We study the quantum properties of the polarization of the light produced in
type II spontaneous parametric down-conversion in the framework of a multi-mode
model valid in any gain regime. We show that the the microscopic polarization
entanglement of photon pairs survives in the high gain regime (multi-photon
regime), in the form of nonclassical correlation of all the Stokes operators
describing polarization degrees of freedom
Quantum Hall ferromagnet in a parabolic well
We report the observation of an anomalous magnetoresistance peak in a tilted magnetic field corresponding to filling factor of 2 in several parabolic wells of different width. This phenomenon is due to the unpolarizedferromagnetic transitions in quantum Hall ferromagnets. The domain formation induced by the random impurity potential is responsible for this magnetoresistance peak. The shift of the peak position with the tilt angle is attributed to the magnetic-field dependence of the exchange-correlation energy across the transition
Long distance quantum teleportation of qubits from photons at 1300 nm to photons at 1550 nm wavelength
Elementary 2-dimensional quantum states (qubits) encoded in 1300 nm
wavelength photons are teleported onto 1550 nm photons. The use of
telecommunication wavelengths enables to take advantage of standard optical
fibre and permits to teleport from one lab to a distant one, 55 m away,
connected by 2 km of fibre. A teleportation fidelity of 81.2 % is reported.
This is large enough to demonstrate the principles of quantum teleportation, in
particular that entanglement is exploited. This experiment constitutes a first
step towards a quantum repeater.Comment: 7 pages, 5 figures, Extended version of Nature lette
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