1,113 research outputs found
Robust sub-shot-noise measurement via Rabi-Josephson oscillations in bimodal Bose-Einstein condensates
Mach-Zehnder atom interferometry requires hold-time phase-squeezing to attain
readout accuracy below the standard quantum limit. This increases its
sensitivity to phase-diffusion, restoring shot-noise scaling of the optimal
signal-to-noise ratio, , in the presence of interactions. The
contradiction between the preparations required for readout accuracy and
robustness to interactions, is removed by monitoring Rabi-Josephson
oscillations instead of relative-phase oscillations during signal acquisition.
Optimizing with a Gaussian squeezed input, we find that hold-time number
squeezing satisfies both demands and that sub-shot-noise scaling is retained
even for strong interactions.Comment: 6 pages, 4 figure
Directional `superradiant' collisions: bosonic amplification of atom pairs emitted from an elongated Bose-Einstein condensate
We study spontaneous directionality in the bosonic amplification of atom
pairs emitted from an elongated Bose-Einstein condensate (BEC), an effect
analogous to `superradiant' emission of atom-photon pairs. Using a simplified
model, we make analytic predictions regarding directional effects for both
atom-atom and atom-photon emission. These are confirmed by numerical mean-field
simulations, demonstrating the the feasibility of nearly perfect directional
emission along the condensate axis. The dependence of the emission angle on the
pump strength for atom-atom pairs is significantly different than for
atom-photon pairs
Thou Shalt is not You Will
In this paper we discuss some reasons why temporal logic might not be
suitable to model real life norms. To show this, we present a novel deontic
logic contrary-to-duty/derived permission paradox based on the interaction of
obligations, permissions and contrary-to-duty obligations. The paradox is
inspired by real life norms
Synthesis with rational environments
Synthesis is the automated construction of a system from its specification. The system has to satisfy its specification in all possible environments. The environment often consists of agents that have objectives of their own. Thus, it makes sense to soften the universal quantification on the behavior of the environment and take the objectives of its underlying agents into an account. Fisman et al. introduced rational synthesis: the problem of synthesis in the context of rational agents. The input to the problem consists of temporal logic formulas specifying the objectives of the system and the agents that constitute the environment, and a solution concept (e.g., Nash equilibrium). The output is a profile of strategies, for the system and the agents, such that the objective of the system is satisfied in the computation that is the outcome of the strategies, and the profile is stable according to the solution concept; that is, the agents that constitute the environment have no incentive to deviate from the strategies suggested to them. In this paper we continue to study rational synthesis. First, we suggest an alternative definition to rational synthesis, in which the agents are rational but not cooperative. We call such problem strong rational synthesis. In the strong rational synthesis setting, one cannot assume that the agents that constitute the environment take into account the strategies suggested to them. Accordingly, the output is a strategy for the system only, and the objective of the system has to be satisfied in all the compositions that are the outcome of a stable profile in which the system follows this strategy. We show that strong rational synthesis is 2ExpTime-complete, thus it is not more complex than traditional synthesis or rational synthesis. Second, we study a richer specification formalism, where the objectives of the system and the agents are not Boolean but quantitative. In this setting, the objective of the system and the agents is to maximize their outcome. The quantitative setting significantly extends the scope of rational synthesis, making the game-theoretic approach much more relevant. Finally, we enrich the setting to one that allows coalitions of agents that constitute the system or the environment
Diluted maximum-likelihood algorithm for quantum tomography
We propose a refined iterative likelihood-maximization algorithm for
reconstructing a quantum state from a set of tomographic measurements. The
algorithm is characterized by a very high convergence rate and features a
simple adaptive procedure that ensures likelihood increase in every iteration
and convergence to the maximum-likelihood state.
We apply the algorithm to homodyne tomography of optical states and quantum
tomography of entangled spin states of trapped ions and investigate its
convergence properties.Comment: v2: Convergence proof adde
Nonlinear adiabatic passage from fermion atoms to boson molecules
We study the dynamics of an adiabatic sweep through a Feshbach resonance in a
quantum gas of fermionic atoms. Analysis of the dynamical equations, supported
by mean-field and many-body numerical results, shows that the dependence of the
remaining atomic fraction on the sweep rate varies from
exponential Landau-Zener behavior for a single pair of particles to a power-law
dependence for large particle number . The power-law is linear, , when the initial molecular fraction is smaller than the 1/N
quantum fluctuations, and when it is larger.
Experimental data agree better with a linear dependence than with an
exponential Landau-Zener fit, indicating that many-body effects are significant
in the atom-molecule conversion process.Comment: 5 pages, 4 figure
Reconstruction of photon statistics using low performance photon counters
The output of a photodetector consists of a current pulse whose charge has
the statistical distribution of the actual photon numbers convolved with a
Bernoulli distribution. Photodetectors are characterized by a nonunit quantum
efficiency, i.e. not all the photons lead to a charge, and by a finite
resolution, i.e. a different number of detected photons leads to a
discriminable values of the charge only up to a maximum value. We present a
detailed comparison, based on Monte Carlo simulated experiments and real data,
among the performances of detectors with different upper limits of counting
capability. In our scheme the inversion of Bernoulli convolution is performed
by maximum-likelihood methods assisted by measurements taken at different
quantum efficiencies. We show that detectors that are only able to discriminate
between zero, one and more than one detected photons are generally enough to
provide a reliable reconstruction of the photon statistics for single-peaked
distributions, while detectors with higher resolution limits do not lead to
further improvements. In addition, we demonstrate that, for semiclassical
states, even on/off detectors are enough to provide a good reconstruction.
Finally, we show that a reliable reconstruction of multi-peaked distributions
requires either higher quantum efficiency or better capability in
discriminating high number of detected photons.Comment: 8 pages, 3 figure
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