2,875 research outputs found
Spectral properties of molecular oligomers. A non-Markovian quantum state diffusion approach
Absorption spectra of small molecular aggregates (oligomers) are considered.
The dipole-dipole interaction between the monomers leads to shifts of the
oligomer spectra with respect to the monomer absorption. The line-shapes of
monomer as well as oligomer absorption depend strongly on the coupling to
vibrational modes. Using a recently developed approach [Roden et. al, PRL 103,
058301] we investigate the length dependence of spectra of one-dimensional
aggregates for various values of the interaction strength between the monomers.
It is demonstrated, that the present approach is well suited to describe the
occurrence of the J- and H-bands
Room temperature photonic crystal defect lasers at near-infrared wavelengths in InGaAsP
Room temperature lasing from optically pumped single defects in a two-dimensional (2-D) photonic bandgap (PBG) crystal is demonstrated. The high-Q optical microcavities are formed by etching a triangular array of air holes into a half-wavelength thick multiquantum-well waveguide. Defects in the 2-D photonic crystal are used to support highly localized optical modes with volumes ranging from 2 to 3 (lambda/2n)(3). Lithographic tuning of the air hole radius and the lattice spacing are used to match the cavity wavelength to the quantum-well gain peak, as well as to increase the cavity Q. The defect lasers were pumped with 10-30 ns pulses of 0.4-1% duty cycle. The threshold pump power was 1.5 mW (approximate to 500 μW absorbed)
Parametric amplification of vacuum fluctuations in a spinor condensate
Parametric amplification of vacuum fluctuations is crucial in modern quantum
optics, enabling the creation of squeezing and entanglement. We demonstrate the
parametric amplification of vacuum fluctuations for matter waves using a spinor
F=2 Rb-87 condensate. Interatomic interactions lead to correlated pair creation
in the m_F= +/- 1 states from an initial unstable m_F=0 condensate, which acts
as a vacuum for m_F unequal 0. Although this pair creation from a pure m_F=0
condensate is ideally triggered by vacuum fluctuations, unavoidable spurious
initial m_F= +/- 1 atoms induce a classical seed which may become the dominant
triggering mechanism. We show that pair creation is insensitive to a classical
seed for sufficiently large magnetic fields, demonstrating the dominant role of
vacuum fluctuations. The presented system thus provides a direct path towards
the generation of non-classical states of matter on the basis of spinor
condensates.Comment: 5 pages, 4 figure
GANimation: anatomically-aware facial animation from a single image
The final publication is available at link.springer.comRecent advances in Generative Adversarial Networks (GANs) have shown impressive results for task of facial expression synthesis. The most successful architecture is StarGAN, that conditions GANs' generation process with images of a specific domain, namely a set of images of persons sharing the same expression. While effective, this approach can only generate a discrete number of expressions, determined by the content of the dataset. To address this limitation, in this paper, we introduce a novel GAN conditioning scheme based on Action Units (AU) annotations, which describes in a continuous manifold the anatomical facial movements defining a human expression. Our approach allows controlling the magnitude of activation of each AU and combine several of them. Additionally, we propose a fully unsupervised strategy to train the model, that only requires images annotated with their activated AUs, and exploit attention mechanisms that make our network robust to changing backgrounds and lighting conditions. Extensive evaluation show that our approach goes beyond competing conditional generators both in the capability to synthesize a much wider range of expressions ruled by anatomically feasible muscle movements, as in the capacity of dealing with images in the wild.Peer ReviewedAward-winningPostprint (author's final draft
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bitstream/item/126694/1/ID-7302.pd
Multi-resonant spinor dynamics in a Bose-Einstein condensate
We analyze the spinor dynamics of a Rb-87 F=2 condensate initially prepared
in the m_F=0 Zeeman sublevel. We show that this dynamics, characterized by the
creation of correlated atomic pairs in m_F=+/-1, presents an intriguing
multi-resonant magnetic field dependence induced by the trap inhomogeneity.
This dependence is directly linked to the most unstable Bogoliubov spin
excitations of the initial m_F = 0 condensate, showing that, in general, even a
qualitative understanding of the pair creation efficiency in a spinor
condensate requires a careful consideration of the confinement.Comment: 5 pages, 4 figure
Non-equilibrium Thermodynamics: Structural Relaxation, Fictive temperature and Tool-Narayanaswamy phenomenology in Glasses
Starting from the second law of thermodynamics applied to an isolated system
consisting of the system surrounded by an extremely large medium, we formulate
a general non-equilibrium thermodynamic description of the system when it is
out of equilibrium. We then apply it to study the structural relaxation in
glasses and establish the phenomenology behind the concept of the fictive
temperature and of the empirical Tool-Narayanaswamy equation on firmer
theoretical foundation.Comment: 20 pages, 1 figur
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