5,071 research outputs found
Universal scaling in transport out of equilibrium through a single quantum dot using the noncrossing approximation
The universal scaling behavior is studied for nonequilibrium transport
through a quantum dot. To describe the dot we use the standard Anderson
impurity model and use the non-equilibrium non-crossing approximation in the
limit of infinite Coulomb repulsion. After solving de hamiltonian, we calculate
the conductance through the system as a function of temperature and bias
voltage in the Kondo and in the mixed valent regime. We obtain a good
scaling function in both regimes. In particular, in the mixed valent regime, we
find excellent agreement with recent experiments and previous theoretical
works.Comment: 6 pages, 5 figures, Accepted Physical Review
Cosmological perturbations from stochastic gravity
In inflationary cosmological models driven by an inflaton field the origin of
the primordial inhomogeneities which are responsible for large scale structure
formation are the quantum fluctuations of the inflaton field. These are usually
computed using the standard theory of cosmological perturbations, where both
the gravitational and the inflaton fields are linearly perturbed and quantized.
The correlation functions for the primordial metric fluctuations and their
power spectrum are then computed. Here we introduce an alternative procedure
for computing the metric correlations based on the Einstein-Langevin equation
which emerges in the framework of stochastic semiclassical gravity. We show
that the correlation functions for the metric perturbations that follow from
the Einstein-Langevin formalism coincide with those obtained with the usual
quantization procedures when the scalar field perturbations are linearized.
This method is explicitly applied to a simple model of chaotic inflation
consisting of a Robertson-Walker background, which undergoes a quasi-de-Sitter
expansion, minimally coupled to a free massive quantum scalar field. The
technique based on the Einstein-Langevin equation can, however, deal naturally
with the perturbations of the scalar field even beyond the linear
approximation, as is actually required in inflationary models which are not
driven by an inflaton field such as Starobinsky's trace-anomaly driven
inflation or when calculating corrections due to non-linear quantum effects in
the usual inflaton driven models.Comment: 29 pages, REVTeX; minor changes, additional appendix with an
alternative proof of the equivalence between stochastic and quantum
correlation functions as well as an exact argument showing that the
correlation function of curvature perturbations remains constant in time for
superhorizon modes, which clarifies a recent claim in arXiv:0710.5342v
Quantum Transport Through a Stretched Spin--1 Molecule
We analyze the electronic transport through a model spin-1 molecule as a
function of temperature, magnetic field and bias voltage. We consider the
effect of magnetic anisotropy, which can be generated experimentally by
stretching the molecule. In the experimentally relevant regime the conductance
of the unstretched molecule reaches the unitary limit of the underscreened
spin- 1 Kondo effect at low temperatures. The magnetic anisotropy generates an
antiferromagnetic coupling between the remaining spin 1/2 and a singular
density of quasiparticles, producing a second Kondo effect and a reduced
conductance. The results explain recent measurements in spin-1 molecules
[Science 328 1370 (2010)].Comment: 5 pages, 3 figures, minor changes, accepted for publication in EP
Comment on "Enhancing Acceleration Radiation from Ground-State Atoms via Cavity Quantum Electrodynamics"
This is a comment on [Phys. Rev. Lett. 91, 243004 (2003)] by Marlan O.
Scully, Vitaly V. Kocharovsky, Alexey Belyanin, Edward Fry and Federico Capasso
(quant-ph/0305178).Comment: 1 page, REVTeX
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