In: Physical Review E, 2013, vol. 87, no. 2, p. 023305
We investigate the possibility to assist the numerically ill-posed calculation of spectral properties of interacting quantum systems in thermal equilibrium by extending the imaginary-time simulation to a finite Schwinger-Keldysh contour. The effect of this extension is tested within the standard maximum entropy approach to analytic continuation. We find that the inclusion of real-time data...
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In: Physical Review Letters, 2012, vol. 109, no. 22, p. 226401
We present a fully self-consistent combined GW and dynamical mean field (DMFT) study of the extended two-dimensional Hubbard model. The inclusion of the local dynamical vertex stemming from the DMFT self-energy and polarization is shown to cure the known problems of self-consistent GW. We calculate momentum-resolved spectral functions, two-particle polarizations, and electron-loss spectra, as...
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In: Computer Physics Communications, 2013, vol. 184, no. 4, p. 1280–1286
Strongly correlated quantum impurity problems appear in a wide variety of contexts ranging from nanoscience and surface physics to material science and the theory of strongly correlated lattice models, where they appear as auxiliary systems within dynamical mean-field theory. Accurate and unbiased solutions must usually be obtained numerically, and continuous-time quantum Monte Carlo algorithms,...
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In: Physical Review A - Atomic, molecular and optical physics, 2012, vol. 85, no. 1, p. 013822
We present a theoretical technique for solving the quantum transport problem of a few photons through a one-dimensional, strongly nonlinear waveguide. We specifically consider the situation where the evolution of the optical field is governed by the quantum nonlinear Schrödinger equation. Although this kind of nonlinearity is quite general, we focus on a realistic implementation involving cold...
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In: Physical Review Letters, 2012, vol. 108, no. 8, p. 080404
We study the influence of geometry of quantum systems underlying space of states on its quantum many-body dynamics. We observe an interplay between dynamical and topological ingredients of quantum nonequilibrium dynamics revealed by the geometrical structure of the quantum space of states. As a primary example we use the anisotropic XY ring in a transverse magnetic field with an additional...
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In: EPL - Europhysics Letters, 2011, vol. 94, no. 5, p. 54006
We theoretically study the transmission of few-photon quantum fields through a strongly nonlinear optical medium. We develop a general approach to investigate nonequilibrium quantum transport of bosonic fields through a finite-size nonlinear medium and apply it to a recently demonstrated experimental system where cold atoms are loaded in a hollow-core optical fiber. We show that when the...
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In: Physical Review B, 2010, vol. 81, no. 1, p. 012303
We study the dynamical response of a system to a sudden change of the tuning parameter λ starting (or ending) at the quantum critical point. In particular, we analyze the scaling of the excitation probability, number of excited quasiparticles, heat and entropy with the quench amplitude, and the system size. We extend the analysis to quenches with arbitrary power law dependence on time of the...
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In: Physical Review A, 2009, vol. 80, p. 033604
We investigate theoretically the evolution of the two-point density correlation function of a low-dimensional ultracold Bose gas after release from a tight transverse confinement. In the course of expansion thermal and quantum fluctuations present in the trapped systems transform into density fluctuations. For the case of free ballistic expansion relevant to current experiments, we present simple...
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In: Applied Radiation and Isotopes, 2008, vol. 66, no. 6-7, p. 737-741
After the nuclear reactor accident of Chernobyl, the “Integrated Measurement and Information System (IMIS) for Monitoring the Environmental Radioactivity and Detecting Emissions from Nuclear Plants was implemented in Germany. IMIS is a nationwide comprehensive measuring system which permanently monitors the radioactivity in all important environment media in the whole federal territory. At...
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In: Physical Review B, 2004, vol. 69, p. 115327
On the basis of energy calculations we investigate the competition between quantum-liquid and electron-solid phases in the Landau levels n = 1, 2, and 3 as a function of their partial filling factor ̅ν̅. Whereas the quantum-liquid phases are stable only in the vicinity of quantized values of ν̅= 1/(2s + 1), an electron solid in the form of a triangular lattice of clusters with...
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