arXiv subjects

Attila Czirjak

Publications and source records attributed to Attila Czirjak.

7 recordsLinked to original sources

arXiv2025

Low-energy proton impact dynamics on hydrocarbons: Dependence on kinetic energy and incident site

The dynamics of low-energy proton collisions with hydrocarbon with hydrocarbon molecules are investigated using real-time time-dependent density functional theory. Through systematic variation of proton kinetic energy and impact site on the molecular surface, the resulting scattering, proton capture, and bond dissociation pathways are analyzed. The simulations reveal a strong dependence of reaction outcomes on both incident energy and collision geometry, with the interplay between electronic and nuclear degrees of freedom highlighted as governing molecular fragmentation and reaction mechanisms.

physics.chem-ph↗

arXiv2012

Oscillations in Quantum Entanglement During Rescattering

We study the time evolution of quantum entanglement between an electron and its parent ion during the rescattering due to a strong few-cycle laser pulse. Based on a simple one-dimensional model, we compute the Neumann entropy during the process for several values of the carrier-envelope phase. The local maxima of the oscillations in the Neumann entropy coincide with the zero crossings of the electric field of the laser pulse. We employ the Wigner function to qualitatively explain the quantum dynamics of rescattering in the phase space.

quant-ph↗

arXiv2011

Time dependence of quantum entanglement in the collision of two particles

We follow the emergence of quantum entanglement in a scattering event between two initially uncorrelated distinguishable quantum particles interacting via a delta potential. We calculate the time dependence of the Neumann entropy of the one-particle reduced density matrix. By using the exact propagator for the delta potential, we derive an approximate analytic formula for the asymptotic form of the two-particle wave function which is sufficiently accurate to account for the entanglement features of the system.

quant-ph↗

arXiv2009

Exact density oscillations in the Tonks-Girardeau gas and their optical detection

We construct the exact time dependent density profile for a superposition of the ground and singly excited states of a harmonically trapped one dimensional Bose-Einstein condensate in the limit of strongly interacting particles, the Tonks-Girardeau gas. Results of an off resonant light scattering experiment probing the system could allow to determine the number of particles contained in the gas, as well as the coefficients of the superposition.

quant-ph↗

arXiv2002

Decoherence of molecular wave packets in an anharmonic potential

The time evolution of anharmonic molecular wave packets is investigated under the influence of the environment consisting of harmonic oscillators. These oscillators represent photon or phonon modes and assumed to be in thermal equilibrium. Our model explicitly incorporates the fact that in the case of a nonequidistant spectrum the rates of the environment induced transitions are different for each transition. The nonunitary time evolution is visualized by the aid of the Wigner function related to the vibrational state of the molecule. The time scale of decoherence is much shorter than that of dissipation, and gives rise to states which are mixtures of localized states along the phase space orbit of the corresponding classical particle. This behavior is to a large extent independent of the coupling strength, the temperature of the environment and also of the initial state.

quant-ph↗

arXiv2001

Preparation of decoherence-free, subradiant states in a cavity

The cause of decoherence in a quantum system can be traced back to the interaction with the environment. As it has been pointed out first by Dicke, in a system of N two-level atoms where each of the atoms is individually dipole coupled to the environment, there are collective, subradiant states, that have no dipole coupling to photon modes, and therefore they are expected to decay slower. This property also implies that these type of states, which form an N-1 dimensional subspace of the atomic subsytem, also decohere slower. We propose a scheme which will create such states. First the two-level atoms are placed in a strongly detuned cavity and one of the atoms, called the control atom is excited. The time evolution of the coupled atom-cavity system leads to an appropriately entangled state of the atoms. By applying subsequent laser pulses at a well defined time instant, it is possible to drive the atomic state into the subradiant, i. e., decoherence free subspace. Up to a certain average number of the photons, the result is independent of the state of the cavity. The analysis of the conditions shows that this scheme is feasible with present day techniques achieved in atom cavity interaction experiments.

quant-ph↗

arXiv2001

Rapid and slow decoherence in conjunction with dissipation in a system of two-level atoms

We investigate the time evolution of a superposition of macroscopically distinct quantum states in a system of two-level atoms interacting with a thermal environment of photon modes. We show that the atomic coherent states are robust against decoherence, therefore we call their superpositions atomic Schrödinger cat states. The initial fast regime of the time evolution is associated with the process of decoherence, and it is directed towards the statistical mixture of the constituent coherent states of the original state for most of the initial conditions. However, certain superpositions, called symmetric, exhibit exceptionally slow decoherence. By introducing a new measure, we generalize the usual decoherence scheme regarding the evolution of the state to account also for the symmetric case. To stress the fact that the environment preserves symmetric superpositions much longer than the other ones,we present Wigner function images of the decoherence of a suitably oriented four component cat state.

quant-ph↗