21,416 research outputs found
Mass Volume Curves and Anomaly Ranking
This paper aims at formulating the issue of ranking multivariate unlabeled
observations depending on their degree of abnormality as an unsupervised
statistical learning task. In the 1-d situation, this problem is usually
tackled by means of tail estimation techniques: univariate observations are
viewed as all the more `abnormal' as they are located far in the tail(s) of the
underlying probability distribution. It would be desirable as well to dispose
of a scalar valued `scoring' function allowing for comparing the degree of
abnormality of multivariate observations. Here we formulate the issue of
scoring anomalies as a M-estimation problem by means of a novel functional
performance criterion, referred to as the Mass Volume curve (MV curve in
short), whose optimal elements are strictly increasing transforms of the
density almost everywhere on the support of the density. We first study the
statistical estimation of the MV curve of a given scoring function and we
provide a strategy to build confidence regions using a smoothed bootstrap
approach. Optimization of this functional criterion over the set of piecewise
constant scoring functions is next tackled. This boils down to estimating a
sequence of empirical minimum volume sets whose levels are chosen adaptively
from the data, so as to adjust to the variations of the optimal MV curve, while
controling the bias of its approximation by a stepwise curve. Generalization
bounds are then established for the difference in sup norm between the MV curve
of the empirical scoring function thus obtained and the optimal MV curve
A robust boson dispenser: Quantum state preparation in interacting many-particle systems
We present a technique to control the spatial state of a small cloud of
interacting particles at low temperatures with almost perfect fidelity using
spatial adiabatic passage. To achieve this, the resonant trap energies of the
system are engineered in such a way that a single, well-defined eigenstate
connects the initial and desired states and is isolated from the rest of the
spectrum. We apply this procedure to the task of separating a well-defined
number of particles from an initial cloud and show that it can be implemented
in radio-frequency traps using experimentally realistic parameters.Comment: 10 pages, 9 figure
Calibration of One-Class SVM for MV set estimation
A general approach for anomaly detection or novelty detection consists in
estimating high density regions or Minimum Volume (MV) sets. The One-Class
Support Vector Machine (OCSVM) is a state-of-the-art algorithm for estimating
such regions from high dimensional data. Yet it suffers from practical
limitations. When applied to a limited number of samples it can lead to poor
performance even when picking the best hyperparameters. Moreover the solution
of OCSVM is very sensitive to the selection of hyperparameters which makes it
hard to optimize in an unsupervised setting. We present a new approach to
estimate MV sets using the OCSVM with a different choice of the parameter
controlling the proportion of outliers. The solution function of the OCSVM is
learnt on a training set and the desired probability mass is obtained by
adjusting the offset on a test set to prevent overfitting. Models learnt on
different train/test splits are then aggregated to reduce the variance induced
by such random splits. Our approach makes it possible to tune the
hyperparameters automatically and obtain nested set estimates. Experimental
results show that our approach outperforms the standard OCSVM formulation while
suffering less from the curse of dimensionality than kernel density estimates.
Results on actual data sets are also presented.Comment: IEEE DSAA' 2015, Oct 2015, Paris, Franc
Twonniers: Interaction-induced effects on Bose-Hubbard parameters
We study the effects of the repulsive on-site interactions on the broadening
of the localized Wannier functions used for calculating the parameters to
describe ultracold atoms in optical lattices. For this, we replace the common
single-particle Wannier functions, which do not contain any information about
the interactions, by two-particle Wannier functions ("Twonniers") obtained from
an exact solution which takes the interactions into account. We then use these
interaction-dependent basis functions to calculate the Bose--Hubbard model
parameters, showing that they are substantially different both at low and high
lattice depths, from the ones calculated using single-particle Wannier
functions. Our results suggest that density effects are not negligible for many
parameter ranges and need to be taken into account in metrology experiments.Comment: 6 pages, 3 figure
Shaken not stirred: Creating exotic angular momentum states by shaking an optical lattice
We propose a method to create higher orbital states of ultracold atoms in the
Mott regime of an optical lattice. This is done by periodically modulating the
position of the trap minima (known as shaking) and controlling the interference
term of the lasers creating the lattice. These methods are combined with
techniques of shortcuts to adiabaticity. As an example of this, we show
specifically how to create an anti-ferromagnetic type ordering of angular
momentum states of atoms. The specific pulse sequences are designed using
Lewis-Riesenfeld invariants and a four-level model for each well. The results
are compared with numerical simulations of the full Schroedinger equation.Comment: 20 pages, 8 figure
XSIL: Extensible Scientific Interchange Language
We motivate and define the XSIL language as a flexible, hierarchical, extensible transport language for scientific data objects. The entire object may be represented in the file, or there may be metadata in the XSIL file, with a powerful, fault-tolerant linking mechanism to external data. The language is based on XML, and is designed not only for parsing and processing by machines, but also for presentation to humans through web browsers and web-database technology. There is a natural mapping between the elements of the XSIL language and the object model into which they are translated by the parser. As well as common objects (Parameter, Array, Time, Table), we have extended XSIL to include the IGWDFrame, used by gravitational-wave observatories
Transport of ultracold atoms between concentric traps via spatial adiabatic passage
Spatial adiabatic passage processes for ultracold atoms trapped in
tunnel-coupled cylindrically symmetric concentric potentials are investigated.
Specifically, we discuss the matter-wave analogue of the rapid adiabatic
passage (RAP) technique for a high fidelity and robust loading of a single atom
into a harmonic ring potential from a harmonic trap, and for its transport
between two concentric rings. We also consider a system of three concentric
rings and investigate the transport of a single atom between the innermost and
the outermost rings making use of the matter-wave analogue of the stimulated
Raman adiabatic passage (STIRAP) technique. We describe the RAP-like and
STIRAP-like dynamics by means of a two- and a three-state models, respectively,
obtaining good agreement with the numerical simulations of the corresponding
two-dimensional Schr\"odinger equation.Comment: 13 pages, 6 figure
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