Quantum decoherence reduction by increasing the thermal bath temperature

The well-known increase of the decoherence rate with the temperature, for a quantum system coupled to a linear thermal bath, holds no longer for a different bath dynamics. This is shown by means of a simple classical non-linear bath, as well as a quantum spin-boson model. The anomalous effect is due to the temperature dependence of the bath spectral profile. The decoherence reduction via the temperature increase can be relevant for the design of quantum computers

Non-Gaussian statistics and extreme waves in a nonlinear optical cavity

A unidirectional optical oscillator is built by using a liquid crystal light-valve that couples a pump beam with the modes of a nearly spherical cavity. For sufficiently high pump intensity, the cavity field presents a complex spatio-temporal dynamics, accompanied by the emission of extreme waves and large deviations from the Gaussian statistics. We identify a mechanism of spatial symmetry breaking, due to a hypercycle-type amplification through the nonlocal coupling of the cavity field

Bistability and macroscopic quantum coherence in a BEC of ^7Li

We consider a Bose-Einstein condensate (BEC) of $^7Li$ in a situation where the density undergoes a symmetry breaking in real space. This occurs for a suitable number of condensed atoms in a double well potential, obtained by adding a standing wave light field to the trap potential. Evidence of bistability results from the solution of the Gross-Pitaevskii equation. By second quantization, we show that the classical bistable situation is in fact a Schr\"odinger cat (SC) and evaluate the tunneling rate between the two SC states. The oscillation between the two states is called MQC (macroscopic quantum coherence); we study the effects of losses on MQC.Comment: 8 pages, 11 figures. e-mail: [email protected]

Spatiotemporal pulses in a liquid crystal optical oscillator

A nonlinear optical medium results by the collective orientation of liquid crystal molecules tightly coupled to a transparent photoconductive layer. We show that such a medium can give a large gain, thus, if inserted in a ring cavity, it results in an unidirectional optical oscillator. Dynamical regimes with many interacting modes are made possible by the wide transverse size and the high nonlinearity of the liquid crystals. We show the generation of spatiotemporal pulses, coming from the random superposition of many coexisting modes with different frequencies

Hydrogen-bonding interactions in T-2 toxin studies using solution and solid-state NMR

Open accessThe structure of T-2 toxin in the solid-state is limited to X-ray crystallographic studies, which lack sufficient resolution to provide direct evidence for hydrogen-bonding interactions. Furthermore, its solution-structure, despite extensive Nuclear Magnetic Resonance (NMR) studies, has provided little insight into its hydrogen-bonding behavior, thus far. Hydrogen-bonding interactions are often an important part of biological activity. In order to study these interactions, the structure of T-2 toxin was compared in both the solution- and solid-state using NMR Spectroscopy. It was determined that the solution- and solid-state structure differ dramatically, as indicated by differences in their carbon chemical shifts, these observations are further supported by solution proton spectral parameters and exchange behavior. The slow chemical exchange process and cross-relaxation dynamics with water observed between the hydroxyl hydrogen on C-3 and water supports the existence of a preferential hydrogen bonding interaction on the opposite side of the molecule from the epoxide ring, which is known to be essential for trichothecene toxicity. This result implies that these hydrogen-bonding interactions could play an important role in the biological function of T-2 toxin and posits towards a possible interaction for the trichothecene class of toxins and the ribosome. These findings clearly illustrate the importance of utilizing solid-state NMR for the study of biological compounds, and suggest that a more detailed study of this whole class of toxins, namely trichothecenes, should be pursued using this methodology.Ye

Metabolism of a hybrid algal galactan by members of the human gut microbiome

Native porphyran is a hybrid of porphryan and agarose. As a common element of edible seaweed, this algal galactan is a frequent component of the human diet. Bacterial members of the human gut microbiota have acquired polysaccharide utilization loci (PULs) that enable the metabolism of porphyran or agarose. However, the molecular mechanisms that underlie the deconstruction and use of native porphyran remains incompletely defined. Here, we have studied two human gut bacteria, porphyranolytic Bacteroides plebeius and agarolytic Bacteroidesuniformis, that target native porphyran. This reveals an exo-based cycle of porphyran depolymerization that incorporates a keystone sulfatase. In both PULs this cycle also works together with a PUL-encoded agarose depolymerizing machinery to synergistically reduce native porphyran to monosaccharides. This provides a framework for understanding the deconstruction of a hybrid algal galactan, and insight into the competitive and/or syntrophic relationship of gut microbiota members that target rare nutrients