arXiv subjects

J. Pietraszewicz

Publications and source records attributed to J. Pietraszewicz.

5 recordsLinked to original sources

arXiv2019

Classical limit of entangled states of two angular momenta

We consider a system of two particles, each with large angular momentum $j$, in the singlet state. The probabilities of finding projections of the angular momenta on selected axes are determined. The generalized Bell inequalities involve these probabilities and we study them using statistical methods. We show that most of Bells inequalities cannot be violated, or are violated only marginally, in the limit $j\to \infinity$. The precision required to confirm a violation appears to be difficult to achieve. In practice, the quantum system, in spite of being entangled, becomes indistinguishable from its classical counterpart.

quant-ph↗

arXiv2018

Complex wave fields in the interacting one-dimensional Bose gas

We study the temperature regimes of the 1d interacting gas to determine when the matter wave (c-field) theory is, in fact, correct and usable. The judgment is made by investigating the level of discrepancy in many observables at once in comparison to the exact Yang-Yang theory. We also determine what cutoff maximizes the accuracy of such an approach. Results are given in terms of a bound on accuracy, as well as an optimal cutoff prescription. For a wide range of temperatures the optimal cutoff is independent of density or interaction strength and so its temperature dependent form is suitable for many cloud shapes and, possibly, basis choices. However, this best global choice is higher in energy than most prior determinations. The high value is needed to obtain the correct kinetic energy, but does not detrimentally affect other observables.

cond-mat.quant-gas↗

arXiv2018

Classical fields in the one-dimensional Bose gas: applicability and determination of the optimal cutoff

To finalize information about the accuracy of the classical field approach for the 1d Bose gas, the lowest temperature quasicondensate was studied by comparing the extended Bogoliubov model of Mora and Castin, to its classical field analogue. The parameters for which the physics is well described by matter waves are now presented for all 1d regimes, and concurrently, the optimal cutoff that best matches all observables together is also provided. This cutoff rises strongly with density when the chemical potential is higher than the thermal energy to account for kinetic energy. As a consequence, clouds that reach this coldest quantum fluctuating regime are better described using a trap basis than plane waves. This contrasts with higher temperature clouds for which the basis choice is less important. In passing, estimates for chemical potential, density fluctuations, kinetic and interaction energy in the low temperature quasicondensate are obtained up to several leading terms.

cond-mat.quant-gas↗

arXiv2017

Continuum of classical-field ensembles from canonical to grand canonical and the onset of their equivalence

The canonical and grand-canonical ensembles are two usual marginal cases for ultracold Bose gases, but real collections of experimental runs commonly have intermediate properties. Here we study the continuum of intermediate cases, and look into the appearance of ensemble equivalence as interaction rises for mesoscopic 1d systems. We demonstrate how at sufficient interaction strength the distributions of condensate and excited atoms become practically identical regardless of the ensemble used. Importantly, we find that features that are fragile in the ideal gas and appear only in a strict canonical ensemble can become robust in all ensembles when interactions become strong. As evidence, the steep cliff in the distribution of the number of excited atoms is preserved. To make this study, a straightforward approach for generating canonical and intermediate classical field ensembles using a modified stochastic Gross-Pitaevskii equation (SGPE) is developed.

cond-mat.quant-gas↗

arXiv2012

Two component Bose-Hubbard model with higher angular momentum states

We study a Bose-Hubbard Hamiltonian of ultracold two component gas of spinor Chromium atoms. Dipolar interactions of magnetic moments while tuned resonantly by ultralow magnetic field can lead to spin flipping. Due to approximate axial symmetry of individual lattice site, total angular momentum is conserved. Therefore, all changes of the spin are accompanied by the appearance of the angular orbital momentum. This way excited Wannier states with non vanishing angular orbital momentum can be created. Resonant dipolar coupling of the two component Bose gas introduces additional degree of control of the system, and leads to a variety of different stable phases. The phase diagram for small number of particles is discussed.

cond-mat.quant-gas↗