arXiv subjects

Ubaldo Tambini

Publications and source records attributed to Ubaldo Tambini.

7 recordsLinked to original sources

arXiv1997

Quantum Zeno Effect with the Feynman-Mensky Path-Integral Approach

A model for quantum Zeno effect based upon an effective Schrödinger equation originated by the path-integral approach is developed and applied to a two-level system simultaneously stimulated by a resonant perturbation. It is shown that inhibition of stimulated transitions between the two levels appears as a consequence of the influence of the meter whenever measurements of energy, either continuous or pulsed, are performed at quantum level of sensitivity. The generality of this approach allows to qualitatively understand the inhibition of spontaneous transitions as the decay of unstable particles, originally presented as a paradox of quantum measurement theory.

quant-ph↗

arXiv1997

Recoil effects on nucleon electromagnetic form factors

The electromagnetic form factors are computed using eigenstates of linear momentum for the nucleon. The latter is described in the framework of the chiral color-dielectric model, projecting the hedgehog ansatz on eigenstates of angular momentum and isospin. Form factors are well reproduced, with the exception of the magnetic one for the proton, up to $q^2 \simeq 0.5$ GeV$^2$. The effect of the removal of the spurious center-of-mass contributions shows up mainly in the electric form factor of the proton. A noticeable improvement is obtained with respect to the calculation without linear momentum projection.

nucl-th↗

arXiv1997

Finite Temperature Quark Matter and Supernova Explosion

We study the equation of state of quark matter at finite temperature, using a confinement model in which chiral symmetry remains broken in the deconfined phase. Implications for type II supernova explosion and for the structure and evolution of the proto-neutron star are discussed.

astro-ph↗

arXiv1996

Measurement quantum mechanics and experiments on quantum Zeno effect

Measurement quantum mechanics, the theory of a quantum system which undergoes a measurement process, is introduced by a loop of mathematical equivalencies connecting previously proposed approaches. The unique phenomenological parameter of the theory is linked to the physical properties of an informational environment acting as a measurement apparatus which allows for an objective role of the observer. Comparison with a recently reported experiment suggests how to investigate novel interesting regimes for the quantum Zeno effect.

cond-mat↗

arXiv1995

A Selective Relaxation Method for Numerical Solution of Schrödinger Problems

We propose a numerical method for evaluating eigenvalues and eigenfunctions of Schrödinger operators with general confining potentials. The method is selective in the sense that only the eigenvalue closest to a chosen input energy is found through an absolutely-stable relaxation algorithm which has rate of convergence infinite. In the case of bistable potentials the method allows one to evaluate the fundamental energy splitting for a wide range of tunneling rates.

quant-ph↗

arXiv1995

Quark Matter in the Chiral Color Dielectric Model

We study the equation of state (EOS) of quark matter at zero temperature, using the Color Dielectric Model (CDM) to describe confinement. Sensible results are obtained in the version of the CDM for which confinement is imposed {\it smoothly}. The two--phases version of the model turns out to give unrealistic results for the EOS. Chiral symmetry plays a marginal rôle and the quarks are massive till high densities. The deconfinement phase transition is smooth and unlikely to be first order. Instabilities of the quark matter and the gap equation are discussed.

hep-ph↗

arXiv1994

Dynamics of Quantum Collapse in Energy Measurements

The influence of continuous measurements of energy with a finite accuracy is studied in various quantum systems through a restriction of the Feynman path-integrals around the measurement result. The method, which is equivalent to consider an effective Schrödinger equation with a non-Hermitian Hamiltonian, allows one to study the dynamics of the wavefunction collapse. A numerical algorithm for solving the effective Schrödinger equation is developed and checked in the case of a harmonic oscillator. The situations, of physical interest, of a two-level system and of a metastable quantum-well are then discussed. In the first case the Zeno inhibition observed in quantum optics experiments is recovered and extended to nonresonant transitions, in the second one we propose to observe inhibition of spontaneous decay in mesoscopic heterostructures. In all the considered examples the effect of the continuous measurement of energy is a freezing of the evolution of the system proportional to the accuracy of the measurement itself.

cond-mat↗