arXiv subjects

Joanna Pietraszewicz

Publications and source records attributed to Joanna Pietraszewicz.

11 recordsLinked to original sources

arXiv2023

Electron Localization in Rydberg States

We discuss the possibility of localizing an electron in a highly excited Rydberg state. The second-order correlation of emitted photons is the tool for the determination of electron position. This second-order correlation of emitted radiation and, therefore, the correlation of operators describing the acceleration of the electron allows for a partial localization of the electron in its orbit. The correlation function is found by approximating the transition matrix elements by their values in the classical limit. It is shown that the second-order correlation, depending on two times, is a function of the time difference and is a periodic function of this argument with the period equal to the period of the corresponding classical motion. The function has sharp maxima corresponding to large electron acceleration in the vicinity of the ``perihelion.'' This allows the localization of the electron in its consecutive approach to the perihelion point.

quant-ph↗

arXiv2021

Wigner Function for Harmonic Oscillator and The Classical Limit

The Wigner function is a quantum analogue of the classical joined distribution of position and momentum. As such is should be a good tool to study quantum-classical correspondence. In this paper, the classical limit of the Wigner function is shown using the quantum harmonic oscillator as an example. The Wigner function is found exactly for all states. The semi-classical wavefunctions for highly excited states are used as the approach to the classical limit. Therefore, one can found the classical limit of the Wigner function for highly excited states and shown that it gives the classical microcanonical ensemble.

quant-ph↗

arXiv2020

Multifaceted phase ordering kinetics of an antiferromagnetic spin-1 condensate

We study phase domain coarsening in the long time limit after a quench of magnetic field in a quasi one-dimensional spin-1 antiferromagnetic condensate. We observe that the growth of correlation length obeys scaling laws predicted by the two different models of phase ordering kinetics, namely the binary mixture and vector field. We derive regimes of clear realization for both of them. We demonstrate appearance of atypical scaling laws, which emerge in intermediate regions.

cond-mat.quant-gas↗

arXiv2019

Quantum versus classical angular momentum

Angular momentum in classical and quantum mechanics is carried out beyond textbooks frames. We compare angular distribution of particle position with classical probabilistic approach. Addition of angular momenta is also discussed together with approximation to Clebsh-Gordan coefficients.

quant-ph↗

arXiv2019

A semiclassical field theory that is freed of the ultraviolet catastrophe

A more accurate semiclassical theory for ultracold gases is derived, in which the occupation of high energy modes is dynamically constrained to the Bose-Einstein distribution. This regularized version of the SGPE model preserves the proper nonlinear energy dependence of coupling to the thermal reservoir. As a result, inclusion of high energy modes above $k_BT$ does not cause a UV divergence. Instead, the reservoir becomes a constraint on the high energy tails which are included explicitly in the system. Millions of modes can be treated because computational cost scales slowly, like in other semiclassical methods. Implementations in 1d and 3d are presented, among them an accurate treatment of the famous case of the quadrupole mode (Jin et al, 1997), which had so far eluded satisfactory simulations with any field theory. Our study reveals that observed frequencies and damping of the thermal cloud depended on the experimental signal to noise ratio.

cond-mat.quant-gas↗

arXiv2019

Correlation evolution in dilute Bose-Einstein condensates after quantum quenches

The universal forms of quantum density and phase correlations after an interaction quench are found for dilute 1d, 2d, and 3d condensates. A Bogoliubov approach in a local density aproximation is used. We obtain compact expressions for the most visible effects. Our results show how loss of phase coherence and antibunching are built up after the quench by quantum fluctuations. We demonstrate further that the density correlations can be observed even with imaging resolution much worse than healing length. This indicates that the direct measurement of counterpropagating atom pairs in situ in a continuum system is realistic. The conditions in contemporary 1d experiments are especially favorable for the correlation wave observations.

cond-mat.quant-gas↗

arXiv2017

Mesoscopic density grains in the 1d interacting Bose gas from the exact Yang-Yang solution

Number fluctuations in a one-dimensional Bose gas consist of contributions from many smaller independent localized fluctuations, the density grains. We have derived a set of extended integral equations from the Yang-Yang solution for finite temperature that exactly determine all higher order moments of number fluctuations. These moments are closely related to the statistics of the localized (but not zero-range) density grains. We directly calculate the mean occupation of these fluctuations, and the variance, skewness, and kurtosis of their distribution across the whole parameter space of the gas. Findings include: Large mesoscopic density grains with a fat-tailed distribution in the thermal quasicondensate of the dilute gas and in the nonperturbative quantum turbulent regime; Regions of negative skewness and below-Gaussian kurtosis in a part of the fermionized gas, and an unexplained crossover region along $T\sim T_d/γ$; The existence of a peak in the density-density correlation function at finite interparticle spacing. We relate these density grain statistics to measurable behavior such as the statistics of coarse imaging bins, and finite-size scaling of number fluctuations. We propose how to experimentally test the relationship between thermodynamically independent density grains and density concentrations visible in single shot images.

cond-mat.quant-gas↗

arXiv2015

Classical field records of a quantum system: their internal consistency and accuracy

We determine the regime where the widespread classical field description for quantum Bose gases is quantitatively accurate in 1d, 2d, and 3d by a careful study of the ideal gas limit. Numerical benchmarking in 1d shows that the ideal gas results carry over unchanged into the weakly interacting gas. The optimum high energy cutoff is in general shown to depend strongly on the observable in question (e.g. energy, density fluctuations, phase coherence length, condensate fraction). This explains the wide spread of past results. A consistent classical field representation with less than 10% deviation in all typical observables can be given for systems at temperatures below 0.0064 degeneracy temperature in 1d, and 0.49 critical temperature in 3d. Surprisingly, this is not possible for the 2d ideal gas even at zero temperature because mean density, density fluctuations and energy cannot be simultaneously matched to the quantum results.

cond-mat.quant-gas↗

arXiv2013

Tunneling-Induced Restoration of the Degeneracy and the Time-Reversal Symmetry Breaking in Optical Lattices

We study the ground-state properties of bosons loaded into the $p$-band of a one dimensional optical lattice. We show that the phase diagram of the system is substantially affected by the anharmonicity of the lattice potential. In particular, for a certain range of tunneling strength, the full many-body ground state of the system becomes degenerate. In this region, an additional symmetry of the system, namely the parity of the occupation number of the chosen orbital, is spontaneously broken. The state with nonvanishing staggered angular momentum, which breaks the time-reversal symmetry, becomes the true ground state of the system.

cond-mat.quant-gas↗

arXiv2013

Spin dynamics of two bosons in an optical lattice site: a role of anharmonicity and anisotropy of the trapping potential

We study a spin dynamics of two magnetic Chromium atoms trapped in a single site of a deep optical lattice in a resonant magnetic field. Dipole-dipole interactions couple spin degrees of freedom of the two particles to their motion in the site. The motion is quantized, therefore a trap geometry combined with two-body contact s-wave interactions influence a spin dynamics through the energy spectrum of the two atom system. Anharmonicity and anisotropy of the site results in a `fine' structure of two body eigenenergies. The structure can be easily resolved by a weak magnetic dipole-dipole interactions. As an example we examine the effect of anharmonicity and anisotropy of the binding potential on the Einstein-de Haas effect. We show that the weak dipolar interactions provide a perfect tool for a precision spectroscopy of the energy spectrum of the interacting few particle system.

cond-mat.quant-gas↗

arXiv2011

Tunable dipolar resonances and Einstein-de Haas effect in a Rb-87 atoms condensate

We study a spinor condensate of Rb-87 atoms in F = 1 hyperfine state confined in an optical dipole trap. Putting initially all atoms in mF = 1 component we observe a significant transfer of atoms to other, initially empty Zeeman states exclusively due to dipolar forces. Because of conservation of a total angular momentum the atoms going to other Zeeman components acquire an orbital angular momentum and circulate around the center of the trap. This is a realization of Einstein-de Haas effect in a system of cold gases. We show that the transfer of atoms via dipolar interaction is possible only when the energies of the initial and the final sates are equal. This condition can be fulfilled utilizing a resonant external magnetic field, which tunes energies of involved states via the linear Zeeman effect. We found that there are many final states of different spatial density which can be tuned selectively to the initial state. We show a simple model explaining high selectivity and controllability of weak dipolar interactions in the condensate of Rb-87 atoms.

cond-mat.quant-gas↗