Broken Symmetry and Coherence of Molecular Vibrations in Tunnel Transitions

We examine the Breit-Wigner resonances that ensue from field effects in molecular single electron transistors (SETs). The adiabatic dynamics of a quantum dot elastically attached to electrodes are treated in the Born-Oppenheimer approach. The relation between thermal and shot noise induced by the source-drain voltage $V_{bias}$ is found when the SET operates in a regime tending to thermodynamic equilibrium far from resonance. The equilibration of electron-phonon subsystems produces broadening and doublet splitting of transparency resonances helping to explain a negative differential resistance (NDR)of current versus voltage (I-V) curves. Mismatch between the electron and phonon temperatures brings out the bouncing-ball mode in the crossover regime close to the internal vibrations mode. The shuttle mechanism occurs at a threshold $V_{bias}$ of the order of the Coulomb energy $U_c$. An accumulation of charge is followed by the Coulomb blockade and broken symmetry of a single or double well potential. The Landau bifurcation cures the shuttling instability and the resonance levels of the quantum dot become split because of molecular tunneling. We calculate the tunnel gaps of conductivity and propose a tunneling optical trap (TOT) for quantum dot isolation permitting coherent molecular tunneling by virtue of Josephson oscillations in a charged Bose gas. We discuss experimental conditions when the above theory can be tested.Comment: 45 pages, 18 figures; The talk presented at Workshop "Decoherence, Entanglement and Information Protection in Complex Quantum Systems", Les Houches, April 25 -30, 2004. Corrected typos and minor grammatical and stylistic changes; Editors: V. M. Akulin, A. Sarfati, G. Kurizki and S. Pellegrin Publisher: Kluwer Academic Publisher, Boston / Dordrecht / London: to appear in 2005 (February / March

Principal basis for enzyme power

The reaction rate enhancement that enzymes produce had not been fully appreciated. The object of the article is to present the mechanism of the enormous catalytic power of the enzymes. I conclude that during substrate conversion to product the enzyme transfers firstly some additional small reactant group that must be initially presented in the active site of the enzyme to bound substrate (i) ; the enzyme regenerates during second substrate group transfer (ii); the active enzyme acts as a reactant of the enzymatic reaction (iii). The detailed chemical mechanisms of enzymatic reactions, such as a the well-studied reaction of the serine proteases family, the peptide bond hydrolysis catalyzed by α-chymotrypsin, and the glyceraldehyde-3-phosphate interconversion step in glycolysis, are in accordance with my conclusion

Photon echoes of molecular photoassociation

Revivals of optical coherence of molecular photoassociation driven by two ultrashort laser pulses are addressed in the Condon approach. Based on textbook examples and numerical simulation of KrF excimer molecules, a prediction is made about an existence of photon echo on free-bound transitions. Delayed rise and fall of nonlinear polarization in the half-collisions are to be resulted from the resonant quantum states interference whether it be in gas, liquid or solid phases.Comment: 15 pages and 5 figures presented at ICONO '98'(Moscow, 1998): Fundamental Aspects of Laser-Matter Interaction, New Nonlinear Optical Materials and Physics of Low-Dimensional Structure