15 research outputs found
Polarization tagging of two-photon double ionization by elliptically polarized XUV pulses
We explore the influence of elliptical polarization on the (non)sequential two-photon double ionization of atomic helium with ultrashort extreme ultraviolet (XUV) light fields using time-dependent full ab initio simulations. The energy and angular distributions of photoelectrons are found to be strongly dependent on the ellipticity. The correlation minimum in the joint angular distribution becomes more prominently visible with increasing ellipticity. In a pump-probe sequence of two subsequent XUV pulses with varying ellipticities, polarization tagging allows us to discriminate between sequential and nonsequential photoionization. This clear separation demonstrates the potential of elliptically polarized XUV fields for improved control of electronic emission processes.This work was supported by the WWTF through Project No. MA14-002, and the FWF through Projects No. FWF-SFB041-VICOM, No. FWF-SFB049-NEXTlite, and No. FWF-W1243-Solids4Fun, as well as the IMPRS-APS. J.F. acknowledges support by the Spanish MINECO through a RamĂłn y Cajal grant and the âMarĂa de Maeztuâ program for Units of Excellence in R&D (MDM-2014-0377
Diffractive paths for weak localization in quantum billiards
We study the weak localization effect in quantum transport through a clean
ballistic cavity with regular classical dynamics. We address the question which
paths account for the suppression of conductance through a system where
disorder and chaos are absent. By exploiting both quantum and semiclassical
methods, we unambiguously identify paths that are diffractively backscattered
into the cavity (when approaching the lead mouths from the cavity interior) to
play a key role. Diffractive scattering couples transmitted and reflected paths
and is thus essential to reproduce the weak-localization peak in reflection and
the corresponding anti-peak in transmission. A comparison of semiclassical
calculations featuring these diffractive paths yields good agreement with full
quantum calculations and experimental data. Our theory provides system-specific
predictions for the quantum regime of few open lead modes and can be expected
to be relevant also for mixed as well as chaotic systems.Comment: 5 pages, 3 figures, final version with extended discussion and added
reference
Tuning canonical typicality by quantum chaos
One key issue of the foundation of statistical mechanics is the emergence of
equilibrium ensembles in isolated and closed quantum systems. Recently, it was
predicted that in the thermodynamic () limit the
canonical density matrix emerges for small subsystems from almost all pure
states of large quantum many-body systems. This notion of "canonical
typicality" is assumed to originate from the entanglement between subsystem and
environment and the resulting intrinsic quantum complexity of the many-body
state. We show that quantum chaos plays a crucial role in the emergence of
canonical typicality for large but finite quantum systems. We demonstrate that
the degree of canonical typicality can be quantitatively controlled and tuned
by the degree of quantum chaoticity present in the many-body system.Comment: 10 pages, 10 figure
Antimicrobial effect of selected lactic acid bacteria against microorganisms with decarboxylase activity
The main purpose of this study was to evaluate the antimicrobial activity of twenty-one bacteriocinogenic lactic acid bacteria (12 strains of Lactococcus lactis subsp. lactis, 4 strains of Lactobacillus gasseri, 3 strains of Lb. helveticus and 2 strains of Lb. acidophilus, LAB) against 28 Staphylococcus and 33 Enterococcus strains able to produce tyramine, putrescine, 2-phenylethylamine and cadaverine. The antimicrobial activity of cell-free supernatants (CFS) from tested LAB was examined by an agar-well diffusion assay. Nine out of twenty-one strains (33%) showed the inhibitory effect on tested enterococci and staphylococci, namely 9 strains of Lactococcus lactis subsp. lactis. The diameters of inhibition zones ranged between 7 mm and 14 mm. The biggest diameter of 14 mm inhibition was obtained with the CFS's from strains CCDM 670 and CCDM 731 on Enterococcus sp. E16 and E28. The cell-free supernatants from Lactococcus lactis subsp. lactis CCDM 71 and from Lactococcus lactis subsp. lactis CCDM 731 displayed the broadest antibacterial activity (52% inhibition of all tested strains). On the other hand, the cell-free supernatants from the screened Lactobacillus strains did not show any inhibitory effect on the tested Staphylococcus and Enterococcus strains. Nowadays, the great attention is given to the antibacterial substances produced by lactic acid bacteria. With the ability to produce a variety of metabolites displaying inhibitory effect, the LAB have great potential in biopreservation of food. © 2017 Potravinarstvo Slovak Journal of Food Sciences
Wave chaos as signature for depletion of a Bose-Einstein condensate
We study the expansion of repulsively interacting Bose-Einstein condensates
(BECs) in shallow one-dimensional potentials. We show for these systems that
the onset of wave chaos in the Gross-Pitaevskii equation (GPE), i.e. the onset
of exponential separation in Hilbert space of two nearby condensate wave
functions, can be used as indication for the onset of depletion of the BEC and
the occupation of excited modes within a many-body description. Comparison
between the multiconfigurational time-dependent Hartree for bosons (MCTDHB)
method and the GPE reveals a close correspondence between the many-body effect
of depletion and the mean-field effect of wave chaos for a wide range of
single-particle external potentials. In the regime of wave chaos the GPE fails
to account for the fine-scale quantum fluctuations because many-body effects
beyond the validity of the GPE are non-negligible. Surprisingly, despite the
failure of the GPE to account for the depletion, coarse grained expectation
values of the single-particle density such as the overall width of the atomic
cloud agree very well with the many-body simulations. The time dependent
depletion of the condensate could be investigated experimentally, e.g., via
decay of coherence of the expanding atom cloud.Comment: 12 pages, 10 figure
Transport through open quantum dots: making semiclassics quantitative
We investigate electron transport through clean open quantum dots (quantum
billiards). We present a semiclassical theory that allows to accurately
reproduce quantum transport calculations. Quantitative agreement is reached for
individual energy and magnetic field dependent elements of the scattering
matrix. Two key ingredients are essential: (i) inclusion of pseudo-paths which
have the topology of linked classical paths resulting from diffraction in
addition to classical paths and (ii) a high-level approximation to diffractive
scattering. Within this framework of the pseudo-path semiclassical
approximation (PSCA), typical shortcomings of semiclassical theories such as
violation of the anti-correlation between reflection and transmission and the
overestimation of conductance fluctuations are overcome. Beyond its predictive
capabilities the PSCA provides deeper insights into the quantum-to-classical
crossover.Comment: 20 pages, 19 figure
Theory of Subcycle Linear Momentum Transfer in Strong-Field Tunneling Ionization
Interaction of a strong laser pulse with matter transfers not only energy but also linear momentum of the photons. Recent experimental advances have made it possible to detect the small amount of linear momentum delivered to the photoelectrons in strong-field ionization of atoms. We present numerical simulations as well as an analytical description of the subcycle phase (or time) resolved momentum transfer to an atom accessible by an attoclock protocol. We show that the light-field-induced momentum transfer is remarkably sensitive to properties of the ultrashort laser pulse such as its carrier-envelope phase and ellipticity. Moreover, we show that the subcycle-resolved linear momentum transfer can provide novel insights into the interplay between nonadiabatic and nondipole effects in strong-field ionization. This work paves the way towards the investigation of the so-far unexplored time-resolved nondipole nonadiabatic tunneling dynamics. © 2020 authors