9,056 research outputs found
Non-stationary coherent quantum many-body dynamics through dissipation
The assumption that quantum systems relax to a stationary state in the
long-time limit underpins statistical physics and much of our intuitive
understanding of scientific phenomena. For isolated systems this follows from
the eigenstate thermalization hypothesis. When an environment is present the
expectation is that all of phase space is explored, eventually leading to
stationarity. Notable exceptions are decoherence-free subspaces that have
important implications for quantum technologies and have so far only been
studied for systems with a few degrees of freedom. Here we identify simple and
generic conditions for dissipation to prevent a quantum many-body system from
ever reaching a stationary state. We go beyond dissipative quantum state
engineering approaches towards controllable long-time non-stationarity
typically associated with macroscopic complex systems. This coherent and
oscillatory evolution constitutes a dissipative version of a quantum
time-crystal. We discuss the possibility of engineering such complex dynamics
with fermionic ultracold atoms in optical lattices.Comment: Main text in MS Word (10 pages, 4 figures) and Supplementary material
in TeX (10 pages, 2 figures). Main text PDF embedded in TeX. Version as
accepted by Nature Communication
Uncovering the wider structure of extreme right communities spanning popular online networks
AbstractRecent years have seen increased interest in the online presence of extreme right groups. Although originally composed of dedicated websites, the online extreme right milieu now spans multiple networks, including popular social media platforms such as Twitter, Facebook and YouTube. Ideally therefore, any contemporary analysis of online extreme right activity requires the consideration of multiple data sources, rather than being restricted to a single platform.We investigate the potential for Twitter to act as one possible gateway to communities within the wider online network of the extreme right, given its facility for the dissemination of content. A strategy for representing heterogeneous network data with a single homogeneous network for the purpose of community detection is presented, where these inherently dynamic communities are tracked over time. We use this strategy to discover and analyze persistent English and German language extreme right communities.Authored by Derek O’Callaghan, Derek Greene, Maura Conway, Joe Carthy and Padraig Cunningham
- …