849 research outputs found
Optimal Reachability in Divergent Weighted Timed Games
Weighted timed games are played by two players on a timed automaton equipped
with weights: one player wants to minimise the accumulated weight while
reaching a target, while the other has an opposite objective. Used in a
reactive synthesis perspective, this quantitative extension of timed games
allows one to measure the quality of controllers. Weighted timed games are
notoriously difficult and quickly undecidable, even when restricted to
non-negative weights. Decidability results exist for subclasses of one-clock
games, and for a subclass with non-negative weights defined by a semantical
restriction on the weights of cycles. In this work, we introduce the class of
divergent weighted timed games as a generalisation of this semantical
restriction to arbitrary weights. We show how to compute their optimal value,
yielding the first decidable class of weighted timed games with negative
weights and an arbitrary number of clocks. In addition, we prove that
divergence can be decided in polynomial space. Last, we prove that for untimed
games, this restriction yields a class of games for which the value can be
computed in polynomial time
Density modulations in an elongated Bose-Einstein condensate released from a disordered potential
We observe large density modulations in time-of-flight images of elongated
Bose-Einstein condensates, initially confined in a harmonic trap and in the
presence of weak disorder. The development of these modulations during the
time-of-flight and their dependence with the disorder are investigated. We
render an account of this effect using numerical and analytical calculations.
We conclude that the observed large density modulations originate from the weak
initial density modulations induced by the disorder, and not from initial phase
fluctuations (thermal or quantum).Comment: Published version; 4+ pages; 4 figure
Efficient engineering of multi-atom entanglement through single-photon detections
We propose an efficient scheme to engineer multi-atom entanglement by
detecting cavity decay through single-photon detectors. In the special case of
two atoms, this scheme is much more efficient than previous probabilistic
schemes, and insensitive to randomness in the atom's position. More generally,
the scheme can be used to prepare arbitrary superpositions of multi-atom Dicke
states without the requirements of high-efficiency detection and separate
addressing of different atoms.Comment: 5 pages, 2 figure
The Complexity of Codiagnosability for Discrete Event and Timed Systems
In this paper we study the fault codiagnosis problem for discrete event
systems given by finite automata (FA) and timed systems given by timed automata
(TA). We provide a uniform characterization of codiagnosability for FA and TA
which extends the necessary and sufficient condition that characterizes
diagnosability. We also settle the complexity of the codiagnosability problems
both for FA and TA and show that codiagnosability is PSPACE-complete in both
cases. For FA this improves on the previously known bound (EXPTIME) and for TA
it is a new result. Finally we address the codiagnosis problem for TA under
bounded resources and show it is 2EXPTIME-complete.Comment: 24 pages
Anisotropic 2D diffusive expansion of ultra-cold atoms in a disordered potential
We study the horizontal expansion of vertically confined ultra-cold atoms in
the presence of disorder. Vertical confinement allows us to realize a situation
with a few coupled harmonic oscillator quantum states. The disordered potential
is created by an optical speckle at an angle of 30{\deg} with respect to the
horizontal plane, resulting in an effective anisotropy of the correlation
lengths of a factor of 2 in that plane. We observe diffusion leading to
non-Gaussian density profiles. Diffusion coefficients, extracted from the
experimental results, show anisotropy and strong energy dependence, in
agreement with numerical calculations
Localization of a matter wave packet in a disordered potential
We theoretically study the Anderson localization of a matter wave packet in a
one-dimensional disordered potential. We develop an analytical model which
includes the initial phase-space density of the matter wave and the spectral
broadening induced by the disorder. Our approach predicts a behavior of the
localized density profile significantly more complex than a simple exponential
decay. These results are confirmed by large-scale and long-time numerical
calculations. They shed new light on recent experiments with ultracold atoms
and may impact their analysis
CONCUR Test-Of-Time Award 2020 Announcement
This short article announces the recipients of the CONCUR Test-of-Time Award 2020
Real-Time Synthesis is Hard!
We study the reactive synthesis problem (RS) for specifications given in
Metric Interval Temporal Logic (MITL). RS is known to be undecidable in a very
general setting, but on infinite words only; and only the very restrictive BRRS
subcase is known to be decidable (see D'Souza et al. and Bouyer et al.). In
this paper, we precise the decidability border of MITL synthesis. We show RS is
undecidable on finite words too, and present a landscape of restrictions (both
on the logic and on the possible controllers) that are still undecidable. On
the positive side, we revisit BRRS and introduce an efficient on-the-fly
algorithm to solve it
Phases and relativity in atomic gravimetry
The phase observable measured by an atomic gravimeter built up on stimulated
Raman transitions is discussed in a fully relativistic context. It is written
in terms of laser phases which are invariant under relativistic gauge
transformations. The dephasing is the sum of light and atomic contributions
which are connected to one another through their interplay with conservation
laws at the interaction vertices. In the case of a closed geometry, a compact
form of the dephasing is written in terms of a Legendre transform of the laser
phases. These general expressions are illustrated by discussing two techniques
used for compensating the Doppler shift, one corresponding to chirped
frequencies and the other one to ramped variations.Comment: 7 pages, 1 figur
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