1,850 research outputs found
Keldysh Field Theory for Driven Open Quantum Systems
Recent experimental developments in diverse areas - ranging from cold atomic
gases over light-driven semiconductors to microcavity arrays - move systems
into the focus, which are located on the interface of quantum optics, many-body
physics and statistical mechanics. They share in common that coherent and
driven-dissipative quantum dynamics occur on an equal footing, creating genuine
non-equilibrium scenarios without immediate counterpart in condensed matter.
This concerns both their non-thermal flux equilibrium states, as well as their
many-body time evolution. It is a challenge to theory to identify novel
instances of universal emergent macroscopic phenomena, which are tied
unambiguously and in an observable way to the microscopic drive conditions. In
this review, we discuss some recent results in this direction. Moreover, we
provide a systematic introduction to the open system Keldysh functional
integral approach, which is the proper technical tool to accomplish a merger of
quantum optics and many-body physics, and leverages the power of modern quantum
field theory to driven open quantum systems.Comment: 73 pages, 13 figure
Cell proliferation, cell shape, and microtubule and cellulose microfibril organization of tobacco BY-2 cells are not altered by exposure to near weightlessness in space
The microtubule cytoskeleton and the cell wall both play key roles in plant cell growth and division, determining the plant’s final stature. At near weightlessness, tubulin polymerizes into microtubules in vitro, but these microtubules do not self-organize in the ordered patterns observed at 1g. Likewise, at near weightlessness cortical microtubules in protoplasts have difficulty organizing into parallel arrays, which are required for proper plant cell elongation. However, intact plants do grow in space and therefore should have a normally functioning microtubule cytoskeleton. Since the main difference between protoplasts and plant cells in a tissue is the presence of a cell wall, we studied single, but walled, tobacco BY-2 suspension-cultured cells during an 8-day space-flight experiment on board of the Soyuz capsule and the International Space Station during the 12S mission (March–April 2006). We show that the cortical microtubule density, ordering and orientation in isolated walled plant cells are unaffected by near weightlessness, as are the orientation of the cellulose microfibrils, cell proliferation, and cell shape. Likely, tissue organization is not essential for the organization of these structures in space. When combined with the fact that many recovering protoplasts have an aberrant cortical microtubule cytoskeleton, the results suggest a role for the cell wall, or its production machinery, in structuring the microtubule cytoskeleto
Statistical periodicity in driven quantum systems: General formalism and application to noisy Floquet topological chains
Much recent experimental effort has focused on the realization of exotic
quantum states and dynamics predicted to occur in periodically driven systems.
But how robust are the sought-after features, such as Floquet topological
surface states, against unavoidable imperfections in the periodic driving? In
this work, we address this question in a broader context and study the dynamics
of quantum systems subject to noise with periodically recurring statistics. We
show that the stroboscopic time evolution of such systems is described by a
noise-averaged Floquet superoperator. The eigenvectors and -values of this
superoperator generalize the familiar concepts of Floquet states and
quasienergies and allow us to describe decoherence due to noise efficiently.
Applying the general formalism to the example of a noisy Floquet topological
chain, we re-derive and corroborate our recent findings on the noise-induced
decay of topologically protected end states. These results follow directly from
an expansion of the end state in eigenvectors of the Floquet superoperator.Comment: 13 pages, 5 figures. This is the final, published versio
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