Non-Hermitian Dynamics in the Quantum Zeno Limit

Measurement is one of the most counter-intuitive aspects of quantum physics. Frequent measurements of a quantum system lead to quantum Zeno dynamics where time evolution becomes confined to a subspace defined by the projections. However, weak measurement performed at a finite rate is also capable of locking the system into such a Zeno subspace in an unconventional way: by Raman-like transitions via virtual intermediate states outside this subspace, which are not forbidden. Here, we extend this concept into the realm of non-Hermitian dynamics by showing that the stochastic competition between measurement and a system's own dynamics can be described by a non-Hermitian Hamiltonian. We obtain an analytic solution for ultracold bosons in a lattice and show that a dark state of the tunnelling operator is a steady state in which the observable's fluctuations are zero and tunnelling is suppressed by destructive matter-wave interference. This opens a new venue of investigation beyond the canonical quantum Zeno dynamics and leads to a new paradigm of competition between global measurement backaction and short-range atomic dynamics.Comment: Accepted in Phys. Rev.

Model of light collimation by photonic crystal surface modes

We propose a quantitative model explaining the mechanism of light collimation by leaky surface modes that propagate on a corrugated surface around the output of a photonic crystal waveguide. The dispersion relation of these modes is determined for a number of surface terminations. Analytical results obtained on the basis of the model are compared to those of rigorous numerical simulations. Maximum collimation is shown to occur at frequency values corresponding to excitation of surface modes whose wave number retains a nonzero real part.Comment: 6 pages, 7 figures. Version 2: corrected sign of k_x' (sections 4-6, fig. 2), minor clarifications in section 2. Version 3: significant changes, including reformulation of the model using the theory of aperture antennas, as well as extended discussion of the accuracy of the mode

Free-streaming approximation in early dynamics of relativistic heavy-ion collisions

We investigate an approximation to early dynamics in relativistic heavy-ion collisions, where after formation the partons are free streaming and around the proper time of 1 fm/c undergo a sudden equilibration described in terms of the Landau matching condition. We discuss physical and formal aspects of this approach. In particular, we show that initial azimuthally asymmetric transverse flow develops for non-central collisions as a consequence of the sudden equilibration. Moreover, the energy-momentum tensor from the free-streaming stage matches very smoothly to the form used in the transverse hydrodynamics, whereas matching to isotropic hydrodynamics requires a more pronounced change in the energy-momentum tensor. After the hydrodynamic phase statistical hadronization is carried out with the help of THERMINATOR. The physical results for the transverse-momentum spectra, the elliptic-flow, and the Hanbury-Brown--Twiss correlation radii, including the ratio R_out/R_side as well as the dependence of the radii on the azimuthal angle (azHBT), are properly described within our approach. The agreement is equally good for a purely hydrodynamic evolution started at an early proper time of 0.25 fm/c, or for the free streaming started at that time, followed by the sudden equilibration at tau ~1 fm/c and then by perfect hydrodynamics. Thus, the inclusion of free streaming allows us to delay the start of hydrodynamics to more realistic times of the order of 1 fm/c.Comment: 10 pages, 12 figure

Pion transition form factor in the Regge approach and incomplete vector-meson dominance

The concept of incomplete vector-meson dominance and Regge models is applied to the transition form factor of the pion. First, we argue that variants of the chiral quark model fulfilling the chiral anomaly may violate the Terazawa-West unitarity bounds, as these bounds are based on unverified assumptions for the real parts of the amplitudes, precluding a possible presence of polynomial terms. A direct consequence is that the transition form factor need not necessarily vanish at large values of the photon virtuality. Moreover, in the range of the BaBar experiment, the Terazawa-West bound is an order of magnitude above the data, thus is of formal rather than practical interest. Then we demonstrate how the experimental data may be properly explained with incomplete vector-meson dominance in a simple model with one state, as well as in more sophisticated Regge models. Generalizations of the simple Regge model along the lines of Dominguez result in a proper description of the data, where one may adjust the parameters in such a way that the Terazawa-West bound is satisfied or violated. We also impose the experimental constraint from the Z -> pi0 gamma decay. Finally, we point out that the photon momentum asymmetry parameter may noticeably influence the precision analysis.Comment: 11 pages, 7 figure

Single-freeze-out model for ultra relativistic heavy-ion collisions at sNN=2.76\sqrt{s_{\rm NN}}=2.76 TeV and the LHC proton puzzle

The single-freeze-out model with parametrized hypersurface and flow geometry is employed to analyze the transverse-momentum spectra of hadrons produced in the Pb+Pb collisions at the collision energy of {$\sqrt{s_{\rm NN}}=2.76$ TeV} at the CERN Large Hadron Collider (LHC). With the notable exception for protons and antiprotons, we find a very good agreement between the model results and the data for the measured hadron species. The additional analysis of the HBT radii of pions helps us to select, from several different types of freeze-out studied in this work, the most realistic form of the freeze-out hypersurface. We find that discrepancy ratio between the model and experiment for the proton/antiproton spectra depends on $p_T$, dropping from 2 in the soft region to 1 around $p_T=1.5$ GeV.Comment: 9 pages, 10 figure

Phase Transition in Sexual Reproduction and Biological Evolution

Using Monte Carlo model of biological evolution we have discovered that populations can switch between two different strategies of their genomes' evolution; Darwinian purifying selection and complementing the haplotypes. The first one is exploited in the large panmictic populations while the second one in the small highly inbred populations. The choice depends on the crossover frequency. There is a power law relation between the critical value of crossover frequency and the size of panmictic population. Under the constant inbreeding this critical value of crossover does not depend on the population size and has a character of phase transition. Close to this value sympatric speciation is observed.Comment: 13 pages, 8 figure

High intensity study of THz detectors based on field effect transistors

Terahertz power dependence of the photoresponse of field effect transistors, operating at frequencies from 0.1 to 3 THz for incident radiation power density up to 100 kW/cm^2 was studied for Si metal-oxide-semiconductor field-effect transistors and InGaAs high electron mobility transistors. The photoresponse increased linearly with increasing radiation power up to kW/cm^2 range. The saturation of the photoresponse was observed for all investigated field effect transistors for intensities above several kW/cm^2. The observed signal saturation is explained by drain photocurrent saturation similar to saturation in direct currents output characteristics. The theoretical model of terahertz field effect transistor photoresponse at high intensity was developed. The model explains quantitatively experimental data both in linear and nonlinear (saturation) range. Our results show that dynamic range of field effect transistors is very high and can extend over more than six orderd of magnitudes of power densities (from 0.5 mW/cm^2 to 5 kW/cm^2)

Rapidity-dependent chemical potentials in a statistical approach

We present a single-freeze-out model with thermal and geometric parameters dependent on the position within the fireball and use it to describe the rapidity and transverse-momentum spectra of pions, kaons, protons, and antiprotons measured at RHIC at 200 GeV} by BRAHMS. THERMINATOR is used to perform the necessary simulation, which includes all resonance decays. The result of the fit to the data is the expected growth of the baryon and strange chemical potentials with the spatial rapidity\alpha_\parallel. The value of the baryon chemical potential at \alpha_\parallel ~ 3 is about 200 MeV, i.e. lies in the range of the highest SPS energies. The chosen geometry of the fireball has a decreasing transverse size as the magnitude of \alpha_\parallel is increased, which also corresponds to decreasing transverse flow. The strange chemical potential obtained from the fit to the K+/K- ratio is such that the local strangeness density in the fireball is compatible with zero. The resulting rapidity spectra of net protons are described qualitatively within the statistical approach. As a result of our study, the knowledge of the ``topography'' of the fireball is acquired, allowing for other analyses and predictions.Comment: 6 pages, tals at SQM 200

Learning curve or experience-related outcome : what really matters in paediatric laparoscopic pyeloplasty

Introduction: The process of improving one's skills over time is called a “learning curve”. This term has attracted great attention during the last decades, especially in relation to laparoscopic techniques. Aim: To assess the outcome of paediatric laparoscopic pyeloplasty (LP). Material and methods: Retrospective analysis of the consecutive LPs. The inclusion criteria: (1) children aged < 18 years, (2) transperitoneal approach, and (3) the same operating paediatric urologist (RC). Patients with a history of any procedure on the upper urinary tract were excluded. Any surgical reintervention during follow-up was defined as a failure. The outcomes of LPs performed before 2012 (G1) were compared to those conducted between 2012 and 2016 (G2). Fisher's exact test was used for statistical analysis. Results: Ninety patients met the inclusion criteria, and a total of 95 LPs were performed. The mean operation time was 155 min, and the mean hospitalisation period was 2.4 days. In G1, 19 patients underwent Anderson-Hynes LP, 16 had Fenger non-dismembered LP and two underwent vascular hitch. In G2, 54, 2 and 2 patients underwent these procedures, respectively. The overall success rate was 91.5%. There were six failures in G1 and three in G2 (p = 0.147). Of the Anderson-Hynes LPs, 1/19 in G1 and 3/58 in G2 required reintervention (p = 1). For Fenger LPs, this was 4/16 and 0/2, respectively (p = 1). Only one patient required reoperation after vascular hitch. Conclusions: The surgeons' learning curve reflects their experience with regard to the entire therapeutic process, but not exclusively their manual skills