Towards Understanding the Origin of Genetic Languages

Molecular biology is a nanotechnology that works--it has worked for billions of years and in an amazing variety of circumstances. At its core is a system for acquiring, processing and communicating information that is universal, from viruses and bacteria to human beings. Advances in genetics and experience in designing computers have taken us to a stage where we can understand the optimisation principles at the root of this system, from the availability of basic building blocks to the execution of tasks. The languages of DNA and proteins are argued to be the optimal solutions to the information processing tasks they carry out. The analysis also suggests simpler predecessors to these languages, and provides fascinating clues about their origin. Obviously, a comprehensive unraveling of the puzzle of life would have a lot to say about what we may design or convert ourselves into.Comment: (v1) 33 pages, contributed chapter to "Quantum Aspects of Life", edited by D. Abbott, P. Davies and A. Pati, (v2) published version with some editin

Efficient Energy Transport in Photosynthesis: Roles of Coherence and Entanglement

Recently it has been discovered---contrary to expectations of physicists as well as biologists---that the energy transport during photosynthesis, from the chlorophyll pigment that captures the photon to the reaction centre where glucose is synthesised from carbon dioxide and water, is highly coherent even at ambient temperature and in the cellular environment. This process and the key molecular ingredients that it depends on are described. By looking at the process from the computer science view-point, we can study what has been optimised and how. A spatial search algorithmic model based on robust features of wave dynamics is presented.Comment: 6 pages, 3 figures, to appear in the proceedings of the Symposium "75 Years of Quantum Entanglement: Foundations and Information Theoretic Applications", January 2011, Kolkata, Indi

The Quantum Density Matrix and its many uses: From quantum structure to quantum chaos and noisy simulators

The quantum density matrix generalises the classical concept of probability distribution to quantum theory. It gives the complete description of a quantum state as well as the observable quantities that can be extracted from it. Its mathematical structure is described, with applications to understanding quantum correlations, illustrating quantum chaos and its unravelling, and developing software simulators for noisy quantum systems with efficient quantum state tomography.Comment: (v1) 28 pages, 4 figures. Review article with some new results. Comments welcome. (v2) Version to be published. Subtitle added. Minor clarifications inserte

A Transverse Lattice QCD Model for Mesons

QCD is analysed with two light-front continuum dimensions and two transverse lattice dimensions. In the limit of large number of colours and strong transverse gauge coupling, the contributions of light-front and transverse directions factorise in the dynamics, and the theory can be analytically solved in a closed form. An integral equation is obtained, describing the properties of mesons, which generalises the 't Hooft equation by including spin degrees of freedom. The meson spectrum, light-front wavefunctions and form factors can be obtained by solving this equation numerically. These results would be a good starting point to model QCD observables which only weakly depend on transverse directions, e.g. deep inelastic scattering structure functions.Comment: Lattice 2003 (theory), 3 page

A derivation of Regge trajectories in large-N transverse lattice QCD

Large-N QCD is analysed in light-front coordinates with a transverse lattice at strong coupling. The general formalism can be looked up on as a d+n expansion with a stack of d-dimensional hyperplanes uniformly spaced in n transverse dimensions. It can arise by application of the renormalisation group transformations only in the transverse directions. At leading order in strong coupling, the gauge field dynamics reduces to the constraint that only colour singlet states can jump between the hyperplanes. With d=2, n=2 and large-N, the leading order strong coupling results are simple renormalisations of those for the 't Hooft model. The meson spectrum lies on a set of parallel trajectories labeled by spin. This is the first derivation of the widely anticipated Regge trajectories in a regulated systematic expansion in QCD.Comment: Lattice 2000 (spectrum), 5 pages, to appear in the proceeding

Quantum mechanics gives stability to a Nash equilibrium

We consider a slightly modified version of the Rock-Scissors-Paper (RSP) game from the point of view of evolutionary stability. In its classical version the game has a mixed Nash equilibrium (NE) not stable against mutants. We find a quantized version of the RSP game for which the classical mixed NE becomes stable.Comment: Revised on referee's criticism, submitted to Physical Review

I=2I=2 pion scattering amplitude with Wilson fermions

We present an exploratory calculation of the $I=2$ $\pi-\pi$ scattering amplitude at threshold using Wilson fermions in the quenched approximation, including all the required contractions. We find good agreement with the predictions of chiral perturbation theory even for pions of mass 560-700 MeV. Within the 10\% errors, we do not see the onset of the bad chiral behavior expected for Wilson fermions. We also derive rigorous inequalities that apply to 2-particle correlators and as a consequence show that the interaction in the antisymmetric state of two pions has to be attractive.Comment: This PS file includes 4 tables and figures 1-8 on 25 pages. Los Alamos Preprint Number LAUR-92-364

The Kaon BB-parameter with Wilson Fermions

We calculate the kaon $B$-parameter in quenched lattice QCD at $\beta=6.0$ using Wilson fermions at $\kappa=0.154$ and $0.155$. We use two kinds of non-local (``smeared'') sources for quark propagators to calculate the matrix elements between states of definite momentum. The use of smeared sources yields results with much smaller errors than obtained in previous calculations with Wilson fermions. By combining results for $\vec p =(0,0,0)$ and $\vec p =(0,0,1)$, we show that one can carry out the non-perturbative subtraction necessary to remove the dominant lattice artifacts induced by the chiral symmetry breaking term in the Wilson action. Our final results are in good agreement with those obtained using staggered fermions. We also present results for $B$-parameters of the $\Delta I = 3/2$ part of the electromagnetic penguin operators, and preliminary results for \bk\ in the presence of two flavors of dynamical quarks.Comment: 39 pages, including 9 PS figures (LA UR-91-3522