States In Quantum Theory Research Articles

Progress in evaluation of human observer visual detection performance using the ROC curve approach

This perspective is focused on amide groups of peptides interacting with water. 2D IR spectroscopy has already enabled structural aspects of the peptide backbone to be determined through its ability to measure the coupling between different amide-I modes. Here we describe why nonlinear IR is emerging as the method of choice to examine the fast components of the water dynamics near peptides and how isotopically edited peptide links can be used to probe the local water at a residue level in proteins. This type of research necessarily involves an intimate mix of theory and experiment. The description of the results is underpinned by relatively well established quantum-statistical theories that describe the important manifestations of peptide vibrational frequency fluctuations.

Multiple spontaneous emissions and interference effects in resonance fluorescence

A QED calculation of the resonance fluorescence spectra of a two-level atom in a strong, nearly resonant field, is reported, taking into account multiple spontaneous emissions (in any order) and interference effects. The results of this calculation are compared with the results of the quantum statistical theories, and the role of the elementary processes analysed. At resonance, in the high-field limit, the exact agreement of the QED and statistical theories is demonstrated. It is pointed out that the interference effects are of the greatest importance.

Springer Tracts in Modern Physics Vol 70: Quantum Statistical Theories of Spontaneous Emission and their Relation to Other Approaches

G S Agarwal Berlin: Springer-Verlag 1974 pp ii + 135 price DM 77 The main argument of this little book is based on a quantum statistical master equation for the evolution of an excited state of a system. The advantage of this approach is that arrays of atoms can be treated more simply than in the conventional theories, and the role of the dynamical atomic coherence and field coherence can be studied more directly.

Facial aspect of superposition principle in algebraic quantum theory

A facial version of superposition principle is introduced in algebraic quantum theory; similar to the quantum logic approach it exhibits characteristic features of quantum theory. It is shown that any pair of primary states satisfy the superposition principle if and only if they are quasiequivalent. A coherent sector is then defined as a quasi-equivalent class of primary states, which holds for both pure states in quantum theory and pure thermodynamic phases in quantum statistical mechanics.

Application of general transport theories to model system

We consider a simple model, the two-site small-polaron system, and show that its properties can be characterized by a master equation which is in accordance with recent quantum statistical theories of macroscopic observables. It is shown by a combination of formal and numerical analyses that the model is an example of a system describable by the lowest-order term in the expansion of the kernel of the master equation in powers of the ratio of the average polaron-phonon interaction energy to the microscopic phonon energy. We discuss the relevance of the method to actual physical systems.

Nuclear Relaxation in Ferromagnetic Cobalt

Nuclear-magnetic spin-spin relaxation processes of ${\mathrm{Co}}^{59}$ have been studied in magnetically saturated particles of fcc cobalt. The transverse relaxation has been studied experimentally by observing the two-rf-pulse spin-echo envelope decay. This decay is initially oscillatory, with the oscillations damping in a time of order of the transverse-relaxation time ${T}_{2}$ into exponential decay. The oscillatory behavior is dependent on the pulse widths, and the relaxation time ${T}_{2}$, determined from the exponential decay rate, varies as the square root of the local field. Theory is presented which shows that the observed oscillatory behavior can be explained qualitatively by assuming that the dominant spin-spin interaction is of the Suhl-Nakamura type, with the resonance line broadened by microscopic inhomogeneities. The period of the oscillations gives the rms microscopic inhomogeneous linewidth 100 kHz. Using the correlation-function technique, the relaxation function has been derived for this system. This theory is similar to that of Kubo and Tomita for the exchange-narrowing problem, and agrees well with the observed nonoscillatory transverse relaxation. From the derived relaxation function and observed transverse-relaxation results, a model of the homogeneous line is deduced. The line is assumed to be Lorentzian, with a cutoff of the order of the second moment of the Suhl-Nakamura interaction. Using this model and the theory of quantum statistics of irreversible processes, a theory of spectral diffusion is derived. Spectral diffusion was studied experimentally by monitoring the decay of the three-rf-pulse-stimulated echo. The new theory presented here agrees well with these experimental results.

The Yukawa Theory of Nuclear Forces in the Light of Present Quantum Theory of Wave Fields

The Yukawa theory of nuclear forces1) has led to many successes and, owing to the present state of quantum theory, to some difficulties. Among the difficulties one remembers first the existence of the π-meson and the possibility of describing the spin dependency and the saturation of nuclear forces by means of simple vector fields or pseudo-scalar fields. Among the difficulties we mention the divergence of the interaction at small distances of the nucleons and the impossibility of getting the correct mass defect for heavy nuclei when one takes the constants of the Yukawa field from the mass defect of light nuclei.2) Furthermore, the existence of closed neutron and proton shells in the nucleus3) and the behaviour of the cross section for elastic collisions of nucleons at very high energies indicate, that the Yukawa potential is not correct at small distances of the nucleons.