1,032 research outputs found
Driven Markovian Quantum Criticality
We identify a new universality class in one-dimensional driven open quantum
systems with a dark state. Salient features are the persistence of both the
microscopic non-equilibrium conditions as well as the quantum coherence of
dynamics close to criticality. This provides a non-equilibrium analogue of
quantum criticality, and is sharply distinct from more generic driven systems,
where both effective thermalization as well as asymptotic decoherence ensue,
paralleling classical dynamical criticality. We quantify universality by
computing the full set of independent critical exponents within a functional
renormalization group approach.Comment: 5+3 pages, 2 figures; published version with improved presentation of
result
Perturbative Field-Theoretical Renormalization Group Approach to Driven-Dissipative Bose-Einstein Criticality
The universal critical behavior of the driven-dissipative non-equilibrium
Bose-Einstein condensation transition is investigated employing the
field-theoretical renormalization group method. Such criticality may be
realized in broad ranges of driven open systems on the interface of quantum
optics and many-body physics, from exciton-polariton condensates to cold atomic
gases. The starting point is a noisy and dissipative Gross-Pitaevski equation
corresponding to a complex valued Landau-Ginzburg functional, which captures
the near critical non-equilibrium dynamics, and generalizes Model A for
classical relaxational dynamics with non-conserved order parameter. We confirm
and further develop the physical picture previously established by means of a
functional renormalization group study of this system. Complementing this
earlier numerical analysis, we analytically compute the static and dynamical
critical exponents at the condensation transition to lowest non-trivial order
in the dimensional epsilon expansion about the upper critical dimension d_c =
4, and establish the emergence of a novel universal scaling exponent associated
with the non-equilibrium drive. We also discuss the corresponding situation for
a conserved order parameter field, i.e., (sub-)diffusive Model B with complex
coefficients.Comment: 17 pages, 6 figures, to appear in Phys. Rev. X (2014
Vanishing density of states in weakly disordered Weyl semimetals
The Brillouin zone of the clean Weyl semimetal contains points at which the
density of states (DoS) vanishes. Previous work suggested that below a certain
critical concentration of impurities this features is preserved including in
the presence of disorder. This result got criticized for its neglect of rare
disorder fluctuations which might bind quantum states and hence generate a
finite DoS. We here show that in spite of their existence these states are so
fragile that their contribution effectively vanishes when averaged over
continuous disorder distributions. This means that the integrity of the nodal
points remains protected for weak disorder.Comment: 4 page
Attribution Required: Stack Overflow Code Snippets in GitHub Projects
Stack Overflow (SO) is the largest Q&A website for developers, providing a
huge amount of copyable code snippets. Using these snippets raises various
maintenance and legal issues. The SO license requires attribution, i.e.,
referencing the original question or answer, and requires derived work to adopt
a compatible license. While there is a heated debate on SO's license model for
code snippets and the required attribution, little is known about the extent to
which snippets are copied from SO without proper attribution. In this paper, we
present the research design and summarized results of an empirical study
analyzing attributed and unattributed usages of SO code snippets in GitHub
projects. On average, 3.22% of all analyzed repositories and 7.33% of the
popular ones contained a reference to SO. Further, we found that developers
rather refer to the whole thread on SO than to a specific answer. For Java, at
least two thirds of the copied snippets were not attributed.Comment: 3 pages, 1 figure, Proceedings of the 39th International Conference
on Software Engineering Companion (ICSE-C 2017), IEEE, 2017, pp. 161-16
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