1,985 research outputs found
Out-of-equilibrium evolution of kinetically constrained many-body quantum systems under purely dissipative dynamics
We explore the relaxation dynamics of quantum many-body systems that undergo
purely dissipative dynamics through non-classical jump operators that can
establish quantum coherence. Our goal is to shed light on the differences in
the relaxation dynamics that arise in comparison to systems evolving via
classical rate equations. In particular, we focus on a scenario where both
quantum and classical dissipative evolution lead to a stationary state with the
same values of diagonal or "classical" observables. As a basis for illustrating
our ideas we use spin systems whose dynamics becomes correlated and complex due
to dynamical constraints, inspired by kinetically constrained models (KCMs) of
classical glasses. We show that in the quantum case the relaxation can be
orders of magnitude slower than the classical one due to the presence of
quantum coherences. Aspects of these idealized quantum KCMs become manifest in
a strongly interacting Rydberg gas under electromagnetically induced
transparency (EIT) conditions in an appropriate limit. Beyond revealing a link
between this Rydberg gas and the rather abstract dissipative KCMs of quantum
glassy systems, our study sheds light on the limitations of the use of
classical rate equations for capturing the non-equilibrium behavior of this
many-body system.Comment: 7 pages, 4 figure
On the stability of Hamiltonian relative equilibria with non-trivial isotropy
We consider Hamiltonian systems with symmetry, and relative equilibria with
isotropy subgroup of positive dimension. The stability of such relative
equilibria has been studied by Ortega and Ratiu and by Lerman and Singer. In
both papers the authors give sufficient conditions for stability which require
first determining a splitting of a subspace of the Lie algebra of the symmetry
group, with different splittings giving different criteria. In this note we
remove this splitting construction and so provide a more general and more
easily computed criterion for stability. The result is also extended to apply
to systems whose momentum map is not coadjoint equivariant
Dynamical phases and intermittency of the dissipative quantum Ising model
We employ the concept of a dynamical, activity order parameter to study the
Ising model in a transverse magnetic field coupled to a Markovian bath. For a
certain range of values of the spin-spin coupling, magnetic field and
dissipation rate, we identify a first order dynamical phase transition between
active and inactive {\em dynamical phases}. We demonstrate that dynamical
phase-coexistence becomes manifest in an intermittent behavior of the bath
quanta emission. Moreover, we establish the connection between the dynamical
order parameter that quantifies the activity, and the longitudinal
magnetization that serves as static order parameter. The system we consider can
be implemented in current experiments with Rydberg atoms and trapped ions
Facilitated spin models of dissipative quantum glasses
We introduce a class of dissipative quantum spin models with local
interactions and without quenched disorder that show glassy behaviour. These
models are the quantum analogs of the classical facilitated spin models. Just
like their classical counterparts, quantum facilitated models display complex
glassy dynamics despite the fact that their stationary state is essentially
trivial. In these systems, dynamical arrest is a consequence of kinetic
constraints and not of static ordering. These models display a quantum version
of dynamic heterogeneity: the dynamics towards relaxation is spatially
correlated despite the absence of static correlations. Associated dynamical
fluctuation phenomena such as decoupling of timescales is also observed.
Moreover, we find that close to the classical limit quantum fluctuations can
enhance glassiness, as recently reported for quantum liquids.Comment: 7 pages, 6 figure
Incident light orientation lets C4 monocotyledonous leaves make light work differently
Photosynthesis is an important driver of ecosystem sustainability in the face of climate change. Monocotyledonous crop species with C4 photosynthesis such as maize (Zea mays L; corn) and sugar cane are crucial for future food security and biofuel crop requirements, while C4 pasture grasses such as Paspalum are central to natural ecosystems. The global demand for corn will exceed that for wheat and rice by 2020, making it the world's most important crop. Light-driven photosynthesis supports plant biomass production, but plants have also evolved safety valve mechanisms that attenuate the absorption of potentially lethal levels of excess light. The array of survival responses that enables leaves to evade photoinhibition is complex and involves chloroplast and leaf movement as well as the molecular rearrangements that facilitate thermal energy dissipation. Here we report a novel morphological mechanism that allows C4 monocotyledonous leaves to regulate photosynthesis independently on each surface with respect to incident light allowing better adaptation to water deficits and light stress. We show that under abaxial illumination as occurs when monocotyledonous leaves curl in response to water stress the stomata close and photosynthetic metabolism shuts down on the adaxial surface of C4 leaves but these parameters increase in function to the abaxial surface. We discuss how this regulation confers a survival advantage to the C4 relative to C3 leaves which are unable to regulate their dorso-ventral functions in relation to light
Universal time-evolution of a Rydberg lattice gas with perfect blockade
We investigate the dynamics of a strongly interacting spin system that is
motivated by current experimental realizations of strongly interacting Rydberg
gases in lattices. In particular we are interested in the temporal evolution of
quantities such as the density of Rydberg atoms and density-density
correlations when the system is initialized in a fully polarized state without
Rydberg excitations. We show that in the thermodynamic limit the expectation
values of these observables converge at least logarithmically to universal
functions and outline a method to obtain these functions. We prove that a
finite one-dimensional system follows this universal behavior up to a given
time. The length of this universal time period depends on the actual system
size. This shows that already the study of small systems allows to make precise
predictions about the thermodynamic limit provided that the observation time is
sufficiently short. We discuss this for various observables and for systems
with different dimensions, interaction ranges and boundary conditions.Comment: 16 pages, 3 figure
Stability of relative equilibria with singular momentum values in simple mechanical systems
A method for testing -stability of relative equilibria in Hamiltonian
systems of the form "kinetic + potential energy" is presented. This method
extends the Reduced Energy-Momentum Method of Simo et al. to the case of
non-free group actions and singular momentum values. A normal form for the
symplectic matrix at a relative equilibrium is also obtained.Comment: Partially rewritten. Some mistakes fixed. Exposition improve
Interaction signatures and non-Gaussian photon states from a strongly driven atomic ensemble coupled to a nanophotonic waveguide
We study theoretically a laser-driven one-dimensional chain of atoms interfaced with the guided optical modes of a nanophotonic waveguide. The period of the chain and the orientation of the laser field can be chosen such that emission occurs predominantly into a single guided mode. We find that the fluorescence excitation line shape changes as the number of atoms is increased, eventually undergoing a splitting that provides evidence for the waveguide-mediated all-to-all interactions. Remarkably, in the regime of strong driving the light emitted into the waveguide is nonclassical with a significant negativity of the associated Wigner function. We show that both the emission properties and the non-Gaussian character of the light are robust against voids in the atom chain, enabling the experimental study of these effects with present-day technology. Our results offer a route towards novel types of fiber-coupled quantum light sources and an interesting perspective for probing the physics of interacting atomic ensembles through light
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