Search results for "semiclassical"
showing 10 items of 111 documents
Mean field methods in large amplitude nuclear collective motion
1984
The time dependent Hartree-Fock method (TDHF) is reviewed and its success and failure are discussed. It is demonstrated that TDHF is a semiclassical theory which is basically able to describe the time evolution of one-body operators, the energy loss in inclusive deep inelastic collisions, and fusion reactions above the Coulomb barrier. For genuine quantum mechanical processes as e.g. spontaneous fission, subbarrier fusion, phase shifts and the description of bound vibrations, the quantized adiabatic time dependent Hartree-Fock theory (quantized ATDHF) is suggested and reviewed. Realistic three-dimensional calculations for heavy ion systems of A1+A2<32 are presented. Applications to various …
Vacuum induced spin-1/2 Berry's phase.
2002
We calculate the Berry phase of a spin-1/2 particle in a magnetic field considering the quantum nature of the field. The phase reduces to the standard Berry phase in the semiclassical limit and eigenstate of the particle acquires a phase in the vacuum. We also show how to generate a vacuum induced Berry phase considering two quantized modes of the field which has a interesting physical interpretation.
Nonadiabatic quantum search algorithms
2007
7 pages, 4 figures.-- PACS nrs.: 03.67.Lx, 05.45.Mt, 72.15.Rn.-- ISI Article Identifier: 000251326400049.-- ArXiv pre-print available at: http://arxiv.org/abs/0706.1139
Classes of Exactly Solvable Generalized Semi-Classical Rabi Systems
2018
The exact quantum dynamics of a single spin-1/2 in a generic time-dependent classical magnetic field is investigated and compared with the quantum motion of a spin-1/2 studied by Rabi and Schwinger. The possibility of regarding the scenario studied in this paper as a generalization of that considered by Rabi and Schwinger is discussed and a notion of time-dependent resonance condition is introduced and carefully legitimated and analysed. Several examples help to disclose analogies and departures of the quantum motion induced in a generalized Rabi system with respect to that exhibited by the spin-1/2 in a magnetic field precessing around the $z$-axis. We find that, under generalized resonanc…
Quantum walks in weak electric fields and Bloch oscillations
2020
Bloch oscillations appear when an electric field is superimposed on a quantum particle that evolves on a lattice with a tight-binding Hamiltonian (TBH), i.e., evolves via what we will call an electric TBH; this phenomenon will be referred to as TBH Bloch oscillations. A similar phenomenon is known to show up in so-called electric discrete-time quantum walks (DQWs); this phenomenon will be referred to as DQW Bloch oscillations. This similarity is particularly salient when the electric field of the DQW is weak. For a wide, i.e., spatially extended initial condition, one numerically observes semi-classical oscillations, i.e., oscillations of a localized particle, both for the electric TBH and …
Dynamics of H2 molecule driven by an ultra-short laser field
2004
We describe, using a semiclassical approach, the molecular dynamics of a one-dimensional H2 molecule interacting with a laser, beyond the Born–Oppenheimer approximation. We observe and discuss different molecular behaviors, such as ionization and dissociation.
Use of three detuned lasers to generate isolated attosecond pulses
2010
The dynamics of a one-dimensional atom driven by three-laser fields is investigated. The total electric field is made up of a fundamental laser field of intensity W cm−2 and wavelength λ = 820 nm and two weak lasers with larger wavelengths. The intensity of the two weak fields is with k = 0.25. The frequencies of the weak fields are and , with and . The three lasers have a Gaussian envelope of 72 fs FWHM. It is shown, by numerical computation and using the semiclassical theory of high-harmonic generation, that the atom interacting with this combined field is able to emit an isolated attosecond burst of radiation.
Nuclear Molecular Dynamics Investigated by Using High Order Harmonic Generation Spectra
2009
In this paper we show how it is possible to investigate the nuclear dynamics of simple molecular ions and molecules by looking at the high-order harmonic generation spectra they emit in the presence of a laser field. In particular we investigate two different effects: the presence of sidebands in the emitted spectra around the usual odd harmonics and an isotopic effect which affects the height of the plateau lines. We further study the advantages and the limitations of the semiclassical approach.
Tunneling in a ?breathing? double well: Adiabatic and antiadiabatic limits and tunneling suppression
1995
Tunneling in a piecewise harmonic potential coupled to a harmonic oscillator is considered by means of the path integral technique. The reduced propagator for the tunneling particle is calculated explicitly and the tunneling splitting is found in semiclassical approximation. The result holds for arbitrary values of the parameters of the system. From this the adiabatic and antiadiabatic approximations are obtained as particular cases and compared with the results obtained differently. The limit of a strong interaction is also considered. It is found that for strong interaction or equivalently for the harmonic frequency tending to zero the preexponential factor in the tunneling splitting tend…
Focus on quantum Einstein gravity
2012
The gravitational asymptotic safety program summarizes the attempts to construct a consistent and predictive quantum theory of gravity within Wilson's generalized framework of renormalization. Its key ingredient is a non-Gaussian fixed point of the renormalization group flow which controls the behavior of the theory at trans-Planckian energies and renders gravity safe from unphysical divergences. Provided that the fixed point comes with a finite number of ultraviolet-attractive (relevant) directions, this construction gives rise to a consistent quantum field theory which is as predictive as an ordinary, perturbatively renormalizable one. This opens up the exciting possibility of establishin…