Harmonic oscillations and rotations in quantum theory

Carlo Jacoboni

Zahid Zakir

The states of a planar oscillator are separated to a vibrational mode, containing a zero-point energy, and a rotational mode without the zero-point energy, but having a conserved angular momentum.On the basis of the analysis of properties of models of rigid and semirigid rotators, the theory of soft rotators is formulated where the harmonic attractive force is balanced only by the centrifugal force.As examples a Coulomb rotator (the Bohr model) and a magneto-harmonic rotator (the Fock-Landau levels) are considered.Disappearance of the radial speed in the model of a magneto-harmonic rotator is taken as a defining property of a pure rotational motion in the harmonic potential.After the exception of energies of the magnetic and spin decompositions, specific to magnetic fields, one turns to a simple and general model of a plane harmonic rotator (circular oscillator without radial speed) where kinetic energy is reduced to the purely rotational energy.Energy levels of the harmonic rotator have the same frequency and are twice degenerate, the energy spectrum is equidistant.In the ground state there is no zeropoint energy from rotational modes, and the zero-point energy of vibrational modes can be compensated by spin effects or symmetries of the system.In this case the operators of observables vanish the ground state, i.e. are "strongly" normally ordered.In a chain of harmonic rotators collective rotations around a common axis lead to transverse waves, at quantization of which there appear quasi-particles and holes carrying an angular momentum.In the chain SU (2) appears as a group of symmetry of a rotator.

Shigemi Araki

Mohsen Daeimohammad

The aim of the present study is to investigate the effect of the counter-rotating terms on the quantum dynamics of a harmonic oscillator in the presence of a deformed bath. We first obtain the Langevin equation of motion for damped oscillator with and without the rotating-wave approximation (RWA). Then, we study the effect of the counter-rotating terms on the diffusion coefficients. Then, we obtain the equation of motion for the harmonic oscillator correlation function with and without the RWA. Finally, we investigate the influence of the counter-rotating terms on the oscillator correlation function.

Shigemi Araki

Masatoshi Yamamura

A description of the rotator is given as an example of large amplitude oscillation. The basic idea is a quasi-harmonic approximation proposed by the present author. Classical solution is quantized in the framework of the old quantum theory. The results are qualitatively consistent with the exact ones in the region from the small to the large amplitude.