5,952 research outputs found
Computer analysis of Interplanetary Monitoring Platform /IMP/ spacecraft performance
Computer analysis of interplanetary monitoring platform spacecraft performanc
Crystalline droplets with emergent topological color-charge in many-body systems with sign-changing interactions
We introduce a novel type of self-bound droplet which carries an emergent
color charge. We consider a system of particles hopping on a lattice and
interacting via a commensurately sign-changing potential which is attractive at
a short range. The droplet formation is heralded by spontaneous crystallization
into topologically distinct domains. This endows each droplet with an emergent
color charge governing their mutual interactions: attractive for equal colors
and repulsive otherwise. The number of allowed colors is fixed only by the
discrete spatial symmetries of the sign-changing part of the interaction
potential. With increasing interaction range, the droplets become progressively
more mobile, with their color charge still being energetically protected,
allowing for nontrivial viscous dynamics of the interacting droplet plasmas
formed during cooling. Sign-changing potentials with a short-range attraction
appear quite naturally for light-mediated interactions and we concretely
propose a realization in state-of-the-art experiments with cold atoms in a
multimode optical cavity.Comment: version similar to published, including supplementary material
Emergent Quasicrystalline Symmetry in Light-Induced Quantum Phase Transitions
The discovery of quasicrystals with crystallographically forbidden rotational symmetries has changed the notion of the ordering in materials, yet little is known about the dynamical emergence of such exotic forms of order. Here we theoretically study a nonequilibrium cavity-QED setup realizing a zero-temperature quantum phase transition from a homogeneous Bose-Einstein condensate to a quasicrystalline phase via collective superradiant light scattering. Across the superradiant phase transition, collective light scattering creates a dynamical, quasicrystalline optical potential for the atoms. Remarkably, the quasicrystalline potential is " emergent" as its eightfold rotational symmetry is not present in the Hamiltonian of the system, rather appears solely in the low-energy states. For sufficiently strong two-body contact interactions between atoms, a quasicrystalline order is stabilized in the system, while for weakly interacting atoms the condensate is localized in one or few of the deepest minima of the quasicrystalline potential
Nonlinear Compton scattering in ultra-short laser pulses
A detailed analysis of the photon emission spectra of an electron scattered
by a laser pulse containing only very few cycles of the carrying
electromagnetic field is presented. The analysis is performed in the framework
of strong-field quantum electrodynamics, with the laser field taken into
account exactly in the calculations. We consider different emission regimes
depending on the laser intensity, placing special emphasis on the regime of
one-cycle beams and of high laser intensities, where the emission spectra
depend nonperturbatively on the laser intensity. In this regime we in
particular present an accurate stationary phase analysis of the integrals that
are shown to determine the computed emission spectra. The emission spectra show
significant differences with respect to those in a long pulsed or monochromatic
laser field: the emission lines obtained here are much broader and, more
important, no dressing of the electron mass is observed.Comment: 31 pages, 15 figure
Discrete Breathers in a Realistic Coarse-Grained Model of Proteins
We report the results of molecular dynamics simulations of an off-lattice
protein model featuring a physical force-field and amino-acid sequence. We show
that localized modes of nonlinear origin (discrete breathers) emerge naturally
as continuations of a subset of high-frequency normal modes residing at
specific sites dictated by the native fold. In the case of the small
-barrel structure that we consider, localization occurs on the turns
connecting the strands. At high energies, discrete breathers stabilize the
structure by concentrating energy on few sites, while their collapse marks the
onset of large-amplitude fluctuations of the protein. Furthermore, we show how
breathers develop as energy-accumulating centres following perturbations even
at distant locations, thus mediating efficient and irreversible energy
transfers. Remarkably, due to the presence of angular potentials, the breather
induces a local static distortion of the native fold. Altogether, the
combination of this two nonlinear effects may provide a ready means for
remotely controlling local conformational changes in proteins.Comment: Submitted to Physical Biolog
Cooling nonlinear lattices toward localisation
We describe the energy relaxation process produced by surface damping on
lattices of classical anharmonic oscillators. Spontaneous emergence of
localised vibrations dramatically slows down dissipation and gives rise to
quasi-stationary states where energy is trapped in the form of a gas of weakly
interacting discrete breathers. In one dimension (1D), strong enough on--site
coupling may yield stretched--exponential relaxation which is reminiscent of
glassy dynamics. We illustrate the mechanism generating localised structures
and discuss the crucial role of the boundary conditions. For two--dimensional
(2D) lattices, the existence of a gap in the breather spectrum causes the
localisation process to become activated. A statistical analysis of the
resulting quasi-stationary state through the distribution of breathers'
energies yield information on their effective interactions.Comment: 10 pages, 11 figure
Slow energy relaxation and localization in 1D lattices
We investigate the energy relaxation process produced by thermal baths at
zero temperature acting on the boundary atoms of chains of classical anharmonic
oscillators. Time-dependent perturbation theory allows us to obtain an explicit
solution of the harmonic problem: even in such a simple system nontrivial
features emerge from the interplay of the different decay rates of Fourier
modes. In particular, a crossover from an exponential to an inverse-square-root
law occurs on a time scale proportional to the system size . A further
crossover back to an exponential law is observed only at much longer times (of
the order ). In the nonlinear chain, the relaxation process is initially
equivalent to the harmonic case over a wide time span, as illustrated by
simulations of the Fermi-Pasta-Ulam model. The distinctive feature is
that the second crossover is not observed due to the spontaneous appearance of
breathers, i.e. space-localized time-periodic solutions, that keep a finite
residual energy in the lattice. We discuss the mechanism yielding such
solutions and also explain why it crucially depends on the boundary conditions.Comment: 16 pages, 6 figure
Macroscopic Superpositions of Phase States with Bose-Einstein Condensates
Quantum superpositions of macroscopically distinguishable states having
distinct phases can be created with a Bose-Einstein condensate trapped in a
periodic potential. The experimental signature is contained in the phase
distribution of the interference patterns obtained after releasing the traps.
Moreover, in the double well case, this distribution exhibits a dramatic
dependence on the parity of the total number of atoms. We finally show that,
for single well occupations up to a few hundred atoms, the macroscopic quantum
superposition can be robust enough against decoherence to be experimentally
revealable within current technology
Pair-production of charged Dirac particles on charged Nariai and ultracold black hole manifolds
Spontaneous loss of charge by charged black holes by means of pair-creation
of charged Dirac particles is considered. We provide three examples of exact
calculations for the spontaneous discharge process for 4D charged black holes
by considering the process on three special non-rotating de Sitter black hole
backgrounds, which allow to bring back the problem to a Kaluza-Klein reduction.
Both the zeta-function approach and the transmission coefficient approach are
taken into account. A comparison between the two methods is also provided, as
well as a comparison with WKB results. In the case of non-zero temperature of
the geometric background, we also discuss thermal effects on the discharge
process.Comment: 27 page
A Multi-path Interferometer with Ultracold Atoms Trapped in an Optical Lattice
We study an ultra-cold gas of bosons trapped in a one dimensional
-site optical lattice perturbed by a spatially dependent potential , where the unknown coupling strength is to be estimated. We find that
the measurement uncertainty is bounded by .
For a typical case of a linear potential, the sensitivity improves as ,
which is a result of multiple interferences between the sites -- an advantage
of multi-path interferometers over the two-mode setups. Next, we calculate the
estimation sensitivity for a specific measurement where, after the action of
the potential, the particles are released from the lattice and form an
interference pattern. If the parameter is estimated by a least-square fit of
the average density to the interference pattern, the sensitivity still scales
like for linear potentials and can be further improved by preparing a
properly correlated initial state in the lattice.Comment: 11 pages, 3 fugire
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