arXiv subjects

Kazimierz Rzazewski

Publications and source records attributed to Kazimierz Rzazewski.

26 records · Page 2Linked to original sources

arXiv2004

Correlations in atomic systems: Diagnosing coherent superpositions

While investigating quantum correlations in atomic systems, we note that single measurements contain information about these correlations. Using a simple model of measurement -- analogous to the one used in quantum optics -- we show how to extract higher order correlation functions from individual "phtotographs" of the atomic sample. As a possible application we apply the method to detect a subtle phase coherence in mesoscopic superpostitions.

cond-mat.soft↗

arXiv2004

Ground state of two-component degenerate fermionic gases

We analyze the ground state of the two--component gas of trapped ultracold fermionic atoms. We neglect the forces between atoms in the same hyperfine state (the same component). For the case when the forces between distinguishable atoms (i.e., atoms in different hyperfine states) are repulsive (positive mutual scattering length), we find the existence of critical interaction strength above which one atomic fraction expels the other from the center of the trap. When atoms from different components attract each other (negative mutual scattering length) the ground state of the system dramatically changes its structure for strong enough attraction -- the Cooper pairs built of atoms in different hyperfine states appear.

cond-mat.soft↗

arXiv2003

Temperature dependent Bogoliubov approximation in the classical fields approach to weakly interacting Bose gas

A classical fields approximation to the finite temperature microcanonical thermodynamics of weakly interacting Bose gas is applied to the idealized case of atoms confined in a box with periodic boundary conditions. We analyze in some detail the microcanonical temperature in the model. We also analyze the spectral properties of classical amplitudes of the plane waves -- the eigenmodes of the time averaged one--particle density matrix. Looking at the zero momentum component -- the order parameter of the condensate, we obtain the nonperturbative results for the chemical potential. Analogous analysis of the other modes yields nonperturbative temperature dependent Bogoliubov frequencies and their damping rates. Damping rates are linear functions of momenta in the phonon range and show more complex behavior for the particle sector. Where available, we make comparison with the analytic estimates of these quantities.

cond-mat↗

arXiv2002

Dynamics of optically generated vortices in a one-component ultracold fermionic gases

We show that the phase imprinting method is capable of generating vortices in a one-component gas of neutral fermionic atoms at zero and finite temperatures. We find qualitative differences in dynamics of vortices in comparision with the case of Bose-Einstein condensate. The results of the imprinting strongly depend on the geometry of the trap, e.g., in asymmetric traps no single vortex state exists. The observations could be considered as a signature of Cooper-pair based superfluidity in a Fermi gas.

cond-mat↗

arXiv2002

Spontaneous emission of atoms via collisions of Bose-Einstein condensates

The widely used Gross-Pitaevskii equation treats only coherent aspects of the evolution of a Bose-Einstein condensate. However, inevitably some atoms scatter out of the condensate. We have developed a method, based on the field theory formulation, describing the dynamics of incoherent processes which are due to elastic collisions. We can therefore treat processes of spontaneous emission of atoms into the empty modes, as opposed to stimulated processes, which require non-zero initial occupation. In this article we study two counter-propagating plane waves of atoms, calculating the full dynamics of mode occupation, as well as the statistics of scattered atoms. The more realistic case of Gaussian wavepackets is also analyzed.

cond-mat↗

arXiv1999

Quantum Anti-Zeno Effect

We demonstrate that near threshold decay processes may be accelerated by repeated measurements. Examples include near threshold photodetachment of an electron from a negative ion, and spontaneous emission in a cavity close to the cutoff frequency, or in a photon band gap material.

quant-ph↗

arXiv1998

Superradiant Laser: First-Order Phase Transition and Non-stationary Regime

We solve the superradiant laser model in two limiting cases. First the stationary low-pumping regime is considered where a first-order phase transition in the semiclassical solution occurs. This discontinuity is smeared out in the quantum regime. Second, we solve the model in the non-stationary regime where we find a temporally periodic solution. For a certain parameter range well separated pulses may occur.

quant-ph↗

arXiv1996

Multielectron dissociative ionization of molecules by intense laser radiation

We solve the hydrodynamic-ballistic equations of motion for a one-dimensional time-dependent Thomas-Fermi model of Cl_2 exposed to an intense subpicosecond laser field, and observe simultaneous multielectron ionization and molecular dissociation. The fragment kinetic energy defect with respect to the simple Coulomb explosion picture is found to originate in ejected-electron screening of the escaping fragments; its magnitude agrees with that observed in recent experiments.

physics.atom-ph↗