61 research outputs found
Pipeline model of a Fermi-sea electron pump
The use of a band offset between the two leads of an electron pump driven by
a local oscillating voltage is shown to increase the pump current dramatically.
The structure of the electron transmission suggests the existence of dominant
inelastic channels which we call pipelines. This permits the formulation of a
simple model that gives a physical account of the numerical results for a
realistic device. A spectral analysis reveals the pump current to be carried by
scattering states with initial energy deep within the Fermi sea and not at its
surface, thereby rendering the effect insensitive to temperature. We show this
is compatible with the current flowing near the Fermi surface in the leads.Comment: 6 pages in RevTex4 (beta4), 4 figures; status: accepted for
publication reason for replacement: A more detailed discussion of the
differences to Ref. [5] has been provided & new reference adde
Quasiclassical frustration
We study the dissipative properties of a harmonic oscillator subject to two
independent heat baths, one of which couples to its position and the other one
to its momentum. This model describes a large spin impurity in a ferromagnet.
We find that some effects of the two heat baths partially cancel each other.
Most notably, oscillations may remain underdamped for arbitrarily strong
coupling. This effect is a direct consequence of the mutually conjugate
character of position and momentum. For a single dissipative bath coupled
linearly to both position and momentum, no underdamped regime is possible for
strong coupling. The dynamics of purity loss for one and two wave packets is
also investigated
Perturbative analysis of coherent quantum ratchets in cold atom systems
We present a perturbative study of the response of cold atoms in an optical
lattice to a weak time- and space-asymmetric periodic driving signal. In the
noninteracting limit, and for a finite set of resonant frequencies, we show how
a coherent, long lasting ratchet current results from the interference between
first and second order processes. In those cases, a suitable three-level model
can account for the entire dynamics, yielding surprisingly good agreement with
numerically exact results for weak and moderately strong driving.Comment: 8 pages, 6 figure
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