The classic paradoxes of quantum theory

This paper contains four new dialogues among Simplicio, Salviati, and Sagredo, on the fate of Schrödinger's cat, the existence of physical quantities, the paradigm of Einstein, Podolsky, and Rosen, and why a watched kettle may boil, after all.Dedicated to Nathan Rosen, teacher and friend, on the occasion of his 75th birthday.     

Hyperfine coupling tensors of the benzosemiquinone radical anion from Car-Parrinello molecular dynamics.

Based on Car-Parrinello ab initio molecular dynamics simulations of the benzosemiquinone radical anion in both aqueous solution and the gas phase, density functional calculations provide the currently most refined EPR hyperfine coupling (HFC) tensors of semiquinone nuclei and solvent protons. For snapshots taken at regular intervals from the molecular dynamics trajectories, cluster models with different criteria for inclusion of water molecules and an additional continuum solvent model are used to analyse the HFCs. These models provide a detailed picture of the effects of dynamics and of different intermolecular interactions on the spin-density distribution and HFC tensors. Comparison with static calculations allows an assessment of the importance of dynamical effects, and of error compensation in static DFT calculations. Solvent proton HFCs depend characteristically on the position relative to the semiquinone radical anion. A point-dipolar model works well for in-plane hydrogen-bonded protons but deviates from the quantum chemical values for out-of-plane hydrogen bonding.     

Synthesis of Highly Charged, Monodisperse Polystyrene Colloidal Particles for the Fabrication of Photonic Crystals

We have developed a series of emulsion polymerization recipes for the synthesis of highly charged, monodisperse polystyrene colloids of diameters between 100-400 nm. These spherical colloidal particles were crosslinked with divinyl benzene and functionalized with 1-allyloxy-2-hydroxypropane sulfonate. These highly charged, monodisperse colloidal particles readily self-assemble into robust three-dimensionally ordered crystalline colloidal arrays (CCAs). These CCAs operate as photonic crystals that Bragg diffract light in the ultraviolet, visible, and infrared regions of the spectrum. Copyright 2000 Academic Press.     

A copper(II)–pyrazole complex cation with imposed symmetry

The reaction of Cu(ClO₄)₂·6H₂O, NaAsF₆ and excess pyrazole yields hexakis­(pyrazole‐κN²)copper(II) bis­(hexa­fluoroarsenate), [Cu(C₃H₄N₂)₆](AsF₆)₂ or [Cu(pzH)₆](AsF₆)₂ (pzH is pyrazole), (I). The analogous hexakis­(pyrazole‐κN²)copper(II) hexafluorophosphate perchlorate complex, [Cu(C₃H₄N₂)₆](PF₆)_1.29(ClO₄)_0.71 or [Cu(pzH)₆](PF₆)_1.29(ClO₄)_0.71, (II), is obtained in a similar fashion, using KPF₆ in place of NaAsF₆. Both compounds contain the hitherto unknown [Cu(pzH)₆]²⁺ complex cation, in which the copper(II) ion lies at the center of a regular octahedron of coordinated N atoms. The cation has crystallographically imposed symmetry. The X‐ray data indicate that the lack of the expected distortion can be accounted for by the presence of either static Jahn–Teller disorder or dynamic Jahn–Teller distortion.     

Stereochemistry of retro-diel-salder fragmentation in gas-phase ions formed by chemical ionization

Retro Diels Alder fragmentation is highly stereospecific in the diones 1 under chemical ionization conditions, both with methane and isobutane as the reagent gases. Only the cis-isomers yield abundant protonated diene and quinone ions. The isotope effect indicates preferential protonation on a CO oxygen, and a subsequent H-migration prior to the formation of the protonated diene cations in the cis isomers.     

Einstein,Gödel,Bohr

Linear combinations of elements of reality, as defined by Einstein, Podolsky, and Rosen, may not be themselves elements of reality. There are questions which can be formulated (and unambiguously answered) in the ordinary language of experimental physics, but cannot be represented in the mathematical framework of quantum theory in a nontrivial way.     

Error Symmetrization in Quantum Computers

Errors in quantum computers are of two kinds:sudden perturbations to isolated qubits, and slow,random drifts of all the qubits. Isolated errors can becorrected by using quantum codewords that represent a logical qubit in a redundant way, by severalphysical qubits. On the other hand, slow drifts can bereduced, but not completely eliminated, by means ofsymmetrization, namely by using many replicas of the computer, and forcing their joint quantumstate to be completely symmetric. Several symmetrizationstrategies are examined and analyzed.     

Improving IRMPD in a quadrupole ion trap

A focused laser is used to make infrared multiphoton photodissociation (IRMPD) more efficient in a quadrupole ion trap mass spectrometer. Efficient (up to 100%) dissociation at the standard operating pressure of 1 × 10⁻³ Torr can be achieved without any supplemental ion activation and with shorter irradiation times. The axial amplitudes of trapped ion clouds are measured using laser tomography. Laser flux on the ion cloud is increased six times by focusing the laser so that the beam waist approximates the ion cloud size. Unmodified peptide ions from 200 Da to 3 kDa are completely dissociated in 2.5–10 ms at a bath gas pressure of 3.3 × 10⁻⁴ Torr and in 3–25 ms at 1.0 × 10⁻³ Torr. Sequential dissociation of product ions is increased by focusing the laser and by operating at an increased bath gas pressure to minimize the size of the ion cloud.     

UV raman examination of alpha-helical peptide water hydrogen bonding

UV resonance Raman spectra (UVRS) of an alpha-helical, 21 residue, mainly Ala peptide (AP) in the dehydrated solid state were compared to those in aqueous solution at different temperatures. The UVRS amide band frequencies of a dehydrated solid alpha-helix peptide show frequency shifts compared to those in aqueous solution due to the loss of amide backbone hydrogen bonding to water; the amide II and amide III bands of the solid alpha-helix downshift, while the amide I band upshifts. The shifts are identical in direction but smaller than those that occur for alpha-helices in aqueous solution as the temperature increases; water hydrogen bonding strengths decrease as the temperature increases. The UV Raman amide band frequency shifts can be used to monitor alpha-helix hydrogen bonding.     

Suppression of thermal lensing effects in intra-cavity coherent combining of lasers

An efficient approach to suppress thermal lensing, when coherently combining several laser distributions, is presented. It is based on incorporating a compensating lens inside the laser cavity. The results reveal that with compensation the overall efficiencies can be more than 80% when combining four laser distributions and more than 90% when combining two laser distributions even at relatively high pulse repetition rates. A model for analyzing coherent combining is developed, where predicted results are in good agreement with the experimental results.