24 research outputs found
Photo-induced spin filtering in a double quantum dot
We investigate the spin-resolved electron dynamics in a double quantum dot
driven by ultrafast asymmetric electromagnetic pulses. Using a analytical model
we show that applying an appropriate pulse sequence allows to control
coherently the spin degree of freedom on the femtosecond time scale. It can be
achieved that the spin-up state is localized in a selected quantum dot while
the spin-down state remains in the other dot. We show that this photo-induced
spin-dependent separation can be maintained for a desired period of time.Comment: shortened, revised version 2 article published at Appl. Phys. Let
Spin-orbit-coupled quantum memory of a double quantum dot
The concept of quantum memory plays an incisive role in the quantum
information theory. As confirmed by several recent rigorous mathematical
studies, the quantum memory inmate in the bipartite system can
reduce uncertainty about the part , after measurements done on the part .
In the present work, we extend this concept to the systems with a spin-orbit
coupling and introduce a notion of spin-orbit quantum memory. We
self-consistently explore Uhlmann fidelity, pre and post measurement
entanglement entropy and post measurement conditional quantum entropy of the
system with spin-orbit coupling and show that measurement performed on the spin
subsystem decreases the uncertainty of the orbital part. The uncovered effect
enhances with the strength of the spin-orbit coupling. We explored the concept
of macroscopic realism introduced by Leggett and Garg and observed that POVM
measurements done on the system under the particular protocol are
non-noninvasive. For the extended system, we performed the quantum Monte Carlo
calculations and explored reshuffling of the electron densities due to the
external electric field.Comment: accepted in Phys. Rev.
The Crab pulsar and its red knot in the near-infrared
We present near-infrared observations obtained with ISAAC on the VLT of the
Crab pulsar and its environment. Photometry of the pulsar in Js, H and Ks shows
the pulsar spectrum to extend fairly smoothly from the UV/optical regime. PSF
subtraction of the pulsar allows us to study its immediate neighborhood in some
detail. In particular, the knot positioned just 0.6 arcsec from the pulsar has
been revealed in the IR. Using also archival HST data for the knot, we have
measured its broad band spectrum to rise steeply into the IR, in contrast to
the spectrum of the pulsar itself.Comment: Accepted by A&
Pulsed radiation from neutron star winds
The radiation of a pulsar wind is computed assuming that at roughly 10 to 100
light cylinder radii from the star, magnetic energy is dissipated into particle
energy. The synchrotron emission of heated particles appears periodic, with, in
general, both a pulse and an interpulse. The predicted spacing agrees well with
the Crab and Vela pulse profiles.Using parameters appropriate for the Crab
pulsar (magnetisation parameter at the light cylinder ,
Lorentz factor ) agreement is found with the observed total pulsed
luminosity. This suggests that the high-energy pulses from young pulsars
originate not in the corotating magnetosphere within the light cylinder (as in
all other models) but from the radially directed wind well outside it.Comment: 4 pages, 2 figures, accepted for publication in A&A Letter
Ultrafast optically induced resonant and non-resonant current generation in atoms and nanostructures: role of the photons orbital angular momentum
side from technological applications, steering non-equilibrium currents in electronic matter delivers information on the system electric and magnetic properties and their relation to electronic correlation and the underlying symmetry of the electrons’ confinement. This theoretical study demonstrates that optical vortices are a versatile tool for spatio-temporal generation of charge currents via resonant and stimulated Raman-type processes for semi-conductor-based nanostructures as well as for atoms, thereby the orbital angular momentum associated with the optical vortex plays a key role