Three-electron correlations in strong laser field ionization.

Strong field processes involving several active electrons reveal unambiguous dynamical signatures of the Pauli principle importance even in the nonrelativistic regime. We exemplify this statement studying three active electrons model atoms interacting with strong pulsed radiation, using an ab-initio time-dependent Schrödinger equation on a grid. In our restricted dimensionality model we are able to analyze momenta correlations of the three outgoing electrons using Dalitz plots. The different symmetries of the electronic wavefunctions, directly related to the initial state spin components, appear clearly visible.

Fidelity susceptibility in Gaussian random ensembles.

The fidelity susceptibility measures the sensitivity of eigenstates to a change of an external parameter. It has been fruitfully used to pin down quantum phase transitions when applied to ground states (with extensions to thermal states). Here, we propose to use the fidelity susceptibility as a useful dimensionless measure for complex quantum systems. We find analytically the fidelity susceptibility distributions for Gaussian orthogonal and unitary universality classes for arbitrary system sizes. The results are verified by a comparison with numerical data.

Stochastic resonance in bistable spin-crossover compounds with light-induced transitions.

This article presents a theoretical prediction of stochastic resonance in spin-crossover materials. The analysis of stochastic resonance phenomenon in a spin-crossover system is performed in the framework of the phenomenological kinetic model with light-induced transition described by dynamical potential in terms of the Lyapunov functions. By using numerical simulation of stochastic trajectories with white- and colored-noise action, the evaluation of stochastic resonance is carried out by signal-to-noise ratio of the system output. The corresponding signal-to-noise ratio features a two-peak behavior which is related to the asymmetric shape of the dynamic potential. For the case of the Ornstein-Uhlenbeck process, the variations of resonance condition with respect to different autocorrelation times are additionally studied.

Study of pressure influence on thermal transition in spin-crossover nanomaterials.

The thermal transition accompanied by the variation of the molecular volume in nanoparticles of spin-crossover materials has been studied on the basis of microscopic Ising-like model solved using Monte Carlo methods. For considered model, we examined the spin-crossover phenomenon with applied hydrostatic pressure and thus was shown the possibility to shift transition temperature toward its room value. The obtained results of numerical simulations are in agreement with the experimental ones.

Stochastic kinetics of photoinduced phase transitions in spin-crossover solids.

We study the stochastic macroscopic kinetics of photoinduced phase transitions in spin-crossover compounds assisted by white and colored Ornstein-Uhlenbeck noise. By using a phenomenological master equation obtained in the mean-field approach, the phase diagram is constructed based on the associated Lyapunov function. The stochastic behavior is then analyzed in the Langevin framework and the corresponding Fokker-Planck equations. Both additive and multiplicative and white and colored types of noise are considered and the stationary probability densities are found along with the noise-assisted light induced hysteretic loops. By using the Kramers formalism, we also focus our attention on the escape time problem in these noise perturbed systems. A detailed study of the relative escape time dependence on various noise characteristics is performed and the main features are compared for different types of noise.

Optically induced switching in spin-crossover compounds: microscopic and macroscopic models and their relationship.

We present the examination of light induced behavior of spin-crossover compounds. We focus on the switching phenomena between low-spin and high-spin states of the system. The connection between the Ising-like model and the macroscopic evolution equation has been analyzed. By means of numerical simulations, we found the dynamical potential changes, the corresponding light induced hysteresis, and the transient regimes. The statistical properties of the system in contact with a heat bath are shown in a stationary probability distribution.

Noise effects in a finite-size Ising-like model.

We study finite-size effects on properties of stationary state and also transient process of a bistable system with long range interaction. We adopt an Ising-like model with infinite range interaction (Husimi-Temperlay model). In particular, we formulate this problem in light of the Langevin equation and investigate study the effects of various types of noises. We study characteristics of the probability of stationary state of a finite system and find that there exist two types of regions in the ordered state: the saturated region in which the maximum of the distribution locates at the maximum value of the Ising variable (±1) and the transient region in which the maximum of the distribution locates at a nonsaturated value. We introduce an additional type of noise that represents fluctuation due to direct coupling to the thermal bath. Finally we also study the finite-size effects on the dynamical aspect by studying the mean first-passage times.