Krzysztof Sacha

Routes Towards Anderson-Like Localization of Bose-Einstein Condensates in Disordered Optical Lattices

We investigate, both experimentally and theoretically, possible routes towards Anderson-like localization of Bose-Einstein condensates in disordered potentials. The dependence of this quantum interference effect on the nonlinear interactions and the shape of the disorder potential is investigated. Experiments with an optical lattice and a superimposed disordered potential reveal the lack of Anderson localization. A theoretical analysis shows that this absence is due to the large length scale of the disorder potential as well as its screening by the nonlinear interactions. Further analysis shows that incommensurable superlattices should allow for the observation of the crossover from the nonlinear screening regime to the Anderson localized case within realistic experimental parameters.

How to strengthen or weaken the HRV dependence on heart rate — Description of the method and its perspectives

a Department of Cardiology, Regional Medical Center, Opole, Poland b Institute of Physics, Wroclaw University of Technology, Wroclaw, Poland c Instytut Fizyki imienia Mariana Smoluchowskiego and Mark Kac Complex Systems Research Center, Uniwersytet Jagiellonski, ulica Reymonta 4, PL-30-059 Krakow, Poland d 1. Medizinische Klinik und Deutsches Herzzentrum München der Technischen Universität München, Munich, Germany e Department of Cardiology-Intensive Therapy, University School of Medicine, Poznan, Poland f Institute of Physics, University of Zielona Gora, Zielona Gora, Poland

Modeling spontaneous breaking of time-translation symmetry

We show that an ultra-cold atomic cloud bouncing on an oscillating mirror can reveal spontaneous breaking of a discrete time translation symmetry. In many-body simulations we illustrate the process of the symmetry breaking that can be induced by atomic losses or by a measurement of particle positions. The results pave the way for understanding and realization of the time crystal idea where crystalline structures form in the time domain due to spontaneous breaking of continuous time translation symmetry.

Pathways to double ionization of atoms in strong fields

We discuss the final stages of double ionization of atoms in a strong linearly polarized laser field within a classical model. We propose that all trajectories leading to nonsequential double ionization pass close to a saddle in the phase space that we identify and characterize. The saddle lies in a two degree of freedom subspace of symmetrically escaping electrons. The distribution of a longitudinal momenta of ions as calculated within the subspace shows the double hump structure observed in experiments. Including a symmetric bending mode of the electrons allows us to reproduce the transverse ion momenta. We discuss also a path to sequential ionization and show that it does not lead to the observed momentum distributions.

Time crystals: a review

Time crystals are time-periodic self-organized structures postulated by Frank Wilczek in 2012. While the original concept was strongly criticized, it stimulated at the same time an intensive research leading to propositions and experimental verifications of discrete (or Floquet) time crystals-the structures that appear in the time domain due to spontaneous breaking of discrete time translation symmetry. The struggle to observe discrete time crystals is reviewed here together with propositions that generalize this concept introducing condensed matter like physics in the time domain. We shall also revisit the original Wilczeks idea and review strategies aimed at spontaneous breaking of continuous time translation symmetry.

Images of the dark soliton in a depleted condensate

The dark soliton created in a Bose–Einstein condensate becomes grey in the course of time evolution because its notch fills up with depleted atoms. This is the result of quantum mechanical calculations which describe the output of many experimental repetitions of creation of the stationary soliton, and its time evolution terminated by a destructive density measurement. However, such a description is not suitable to predict the outcome of a single realization of the experiment where two extreme scenarios and many combinations thereof are possible: one will see either (1) a displaced dark soliton without any atoms in the notch, but with a randomly displaced position, or (2) a grey soliton with a fixed position, but a random number of atoms filling its notch. In either case the average over many realizations will reproduce the mentioned quantum mechanical result. In this paper we use N-particle wavefunctions, which follow from the number-conserving Bogoliubov theory, to settle this issue.

How to select patients who will not benefit from ICD therapy by using heart rate and its variability

How to select patients who will not benefit from ICD therapy by using heart rate and its variability? Jerzy Sacha ⁎, Szymon Barabach , Gabriela Statkiewicz-Barabach , Krzysztof Sacha , Alexander Muller , Jaroslaw Piskorski , Petra Barthel , Georg Schmidt d,1 a Department of Cardiology, Regional Medical Center, Opole, Poland b Institute of Physics, Wroclaw University of Technology, Wroclaw, Poland c Instytut Fizyki imienia Mariana Smoluchowskiego and Mark Kac Complex Systems Research Center, Uniwersytet Jagiellonski, ulica Reymonta 4, PL-30-059 Krakow, Poland d 1. Medizinische Klinik und Deutsches Herzzentrum Munchen der Technischen Universitat Munchen, Munich, Germany e Department of Cardiology-Intensive Therapy, University School of Medicine, Poznan, Poland f Institute of Physics, University of Zielona Gora, Zielona Gora, Poland

Time-Resolved Quantum Dynamics of Double Ionization in Strong Laser Fields

Quantum calculations of a (1+1)-dimensional model for double ionization in strong laser fields are used to trace the time evolution from the ground state through ionization and rescattering to the two-electron escape. The subspace of symmetric escape, a prime characteristic of nonsequential double ionization, remains accessible by a judicious choice of 1D coordinates for the electrons. The time-resolved ionization fluxes show the onset of single and double ionization, the sequence of events during the pulse, and the influences of pulse duration and reveal the relative importance of sequential and nonsequential double ionization, even when ionization takes place during the same field cycle.

Depletion of the dark soliton: The anomalous mode of the Bogoliubov theory

Quantum depletion from an atomic quasi-one-dimensional Bose-Einstein condensate with a dark soliton is studied in a framework of the Bogoliubov theory. Depletion is dominated by an anomalous mode localized in a notch of the condensate wave function. Depletion in an anomalous mode requires a different treatment than depletion without anomalous modes. In particular, quantum depletion in the Bogoliubov vacuum of the anomalous mode is experimentally irrelevant. A dark soliton is initially prepared in a state with minimal depletion, which is not a stationary state of the Bogoliubov theory. The notch fills up with incoherent atoms depleted from the condensate. For realistic parameters the filling time can be as short as 10 ms.

Wannier threshold law for two-electron escape in the presence of an external electric field

We consider double ionization of atoms or ions by electron impact in the presence of a static electric field. As in Wanniers analysis of the analogous situation without external field the dynamics near threshold is dominated by a saddle. With a field the saddle lies in a subspace of symmetrically escaping electrons. Near threshold the classical cross-section scales with excess energy E like σ ~ Eα, where the exponent α can be determined from the stability of the saddle and does not depend on the field strength. For example, if the remaining ion has charge Z = 2, the exponent is 1.292, significantly different from the 1.056 without the field.