1,249 research outputs found
Tunnel spectroscopy in ac-driven quantum dot nanoresonators
Electronic transport in a triple quantum dot shuttle device in the presence
of an ac field is analyzed within a fully quantum mechanical framework. A
generalized density matrix formalism is used to describe the time evolution for
electronic state occupations in a dissipative phonon bath. In the presence of
an ac gate voltage, the electronic states are dressed by photons and the
interplay between photon and vibrational sidebands produces current
characteristics that obey selection rules. Varying the ac parameters allows to
tune the tunneling current features. In particular, we show that coherent
destruction of tunneling can be achieved in our device
AC-driven double quantum dots as spin pumps and spin filters
We propose and analyze a new scheme of realizing both spin filtering and spin
pumping by using ac-driven double quantum dots in the Coulomb blockade regime.
By calculating the current through the system we demonstrate that the spin
polarization of the current can be controlled by tuning the parameters
(amplitude and frequency) of the ac field. We also discuss spin relaxation and
decoherence effects in the pumped current.Comment: 5 pages, 4 figure
Spin filtering through excited states in double quantum dot pumps
Recently it has been shown that ac-driven double quantum dots can act as spin
pumps and spin filters. By calculating the current through the system for each
spin polarization, by means of the time evolution of the reduced density matrix
in the sequential tunneling regime (Born-Markov approximation), we demonstrate
that the spin polarization of the current can be controlled by tuning the
parameters (amplitude and frequency) of the ac field. Importantly, the pumped
current as a function of the applied frequency presents a series of peaks which
are uniquely associated with a definite spin polarization. We discuss how
excited states participating in the current allow the system to behave as a
bipolar spin filter by tuning the ac frequency and intensity. We also discuss
spin relaxation and decoherence effects in the pumped current and show that
measuring the width of the current vs frequency peaks allows to determine the
spin decoherence time .Comment: 10 pages. 5 figure
Cosmological simulations using a static scalar-tensor theory
We present CDM -body cosmological simulations in the framework of
a static general scalar-tensor theory of gravity. Due to the influence of the
non-minimally coupled scalar field, the gravitational potential is modified by
a Yukawa type term, yielding a new structure formation dynamics. We present
some preliminary results and, in particular, we compute the density and
velocity profiles of the most massive group.Comment: 4 pages, 6 figures, to appear in Journal of Physics: Conference
Series: VII Mexican School on Gravitation and Mathematical Physics. 26
November to 1 December 2006, Playa del Carmen, Quintana Roo, Mexic
Remote Sensing of Ocean Color in the High Arctic
With four years of NASA SeaWiFS funding I established a completely new capability and expertise for in-water optical measurements nearly from scratch and with very little optical background. My first-year budget included only capital for a profiling spectral radiometer. Over the next 30 months we conducted six cruises and collected almost 300 optical profiles in challenging environments; many were collected from 21' launches. I also changed institutions during this period: it is very disruptive to move, set up a new lab, and hire and train new people, etc. We also did not have access to NASA funds for almost a year during the move because of difficulties in subcontracting and/or transferring funds. Nevertheless, we delivered data sets from six bio-optical cruises from three high latitude regions, although only two or three cruises from two areas were promised for our SeaWiFS research. The three Canadian Arctic field programs comprise the most comprehensive high latitude bio-optical and biogeochemical data sets in existence. Optical and pigment data from all six cruises have been submitted to NASA and are being included in the algorithm development test set. Additional data are still being submitted
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