332 research outputs found
Human brain distinctiveness based on EEG spectral coherence connectivity
The use of EEG biometrics, for the purpose of automatic people recognition,
has received increasing attention in the recent years. Most of current analysis
rely on the extraction of features characterizing the activity of single brain
regions, like power-spectrum estimates, thus neglecting possible temporal
dependencies between the generated EEG signals. However, important
physiological information can be extracted from the way different brain regions
are functionally coupled. In this study, we propose a novel approach that fuses
spectral coherencebased connectivity between different brain regions as a
possibly viable biometric feature. The proposed approach is tested on a large
dataset of subjects (N=108) during eyes-closed (EC) and eyes-open (EO) resting
state conditions. The obtained recognition performances show that using brain
connectivity leads to higher distinctiveness with respect to power-spectrum
measurements, in both the experimental conditions. Notably, a 100% recognition
accuracy is obtained in EC and EO when integrating functional connectivity
between regions in the frontal lobe, while a lower 97.41% is obtained in EC
(96.26% in EO) when fusing power spectrum information from centro-parietal
regions. Taken together, these results suggest that functional connectivity
patterns represent effective features for improving EEG-based biometric
systems.Comment: Key words: EEG, Resting state, Biometrics, Spectral coherence, Match
score fusio
A strongly interacting gas of two-electron fermions at an orbital Feshbach resonance
We report on the experimental observation of a strongly interacting gas of
ultracold two-electron fermions with orbital degree of freedom and magnetically
tunable interactions. This realization has been enabled by the demonstration of
a novel kind of Feshbach resonance occurring in the scattering of two 173Yb
atoms in different nuclear and electronic states. The strongly interacting
regime at resonance is evidenced by the observation of anisotropic hydrodynamic
expansion of the two-orbital Fermi gas. These results pave the way towards the
realization of new quantum states of matter with strongly correlated fermions
with orbital degree of freedom.Comment: 5 pages, 4 figure
The inverse problem for the Gross - Pitaevskii equation
Two different methods are proposed for the generation of wide classes of
exact solutions to the stationary Gross - Pitaevskii equation (GPE). The first
method, suggested by the work by Kondrat'ev and Miller (1966), applies to
one-dimensional (1D) GPE. It is based on the similarity between the GPE and the
integrable Gardner equation, all solutions of the latter equation (both
stationary and nonstationary ones) generating exact solutions to the GPE, with
the potential function proportional to the corresponding solutions. The second
method is based on the "inverse problem" for the GPE, i.e. construction of a
potential function which provides a desirable solution to the equation.
Systematic results are presented for 1D and 2D cases. Both methods are
illustrated by a variety of localized solutions, including solitary vortices,
for both attractive and repulsive nonlinearity in the GPE. The stability of the
1D solutions is tested by direct simulations of the time-dependent GPE
Coherent Manipulation of Orbital Feshbach Molecules of Two-Electron Atoms
Ultracold molecules have experienced increasing attention in recent years.
Compared to ultracold atoms, they possess several unique properties that make
them perfect candidates for the implementation of new quantum-technological
applications in several fields, from quantum simulation to quantum sensing and
metrology. In particular, ultracold molecules of two-electron atoms (such as
strontium or ytterbium) also inherit the peculiar properties of these atomic
species, above all the possibility to access metastable electronic states via
direct excitation on optical clock transitions with ultimate sensitivity and
accuracy. In this paper we report on the production and coherent manipulation
of molecular bound states of two fermionic Yb atoms in different
electronic (orbital) states S and P in proximity of a
scattering resonance involving atoms in different spin and electronic states,
called orbital Feshbach resonance. We demonstrate that orbital molecules can be
coherently photoassociated starting from a gas of ground-state atoms in a
three-dimensional optical lattices by observing several photoassociation and
photodissociation cycles. We also show the possibility to coherently control
the molecular internal state by using Raman-assisted transfer to swap the
nuclear spin of one of the atoms forming the molecule, thus demonstrating a
powerful manipulation and detection tool of these molecular bound states.
Finally, by exploiting this peculiar detection technique we provide first
information on the lifetime of the molecular states in a many-body setting,
paving the way towards future investigations of strongly interacting Fermi
gases in a still unexplored regime.Comment: 11 pages, 8 figure
Condensate fraction of cold gases in non-uniform external potential
Exact calculation of the condensate fraction in multi-dimensional
inhomogeneous interacting Bose systems which do not possess continuous
symmetries is a difficult computational problem. We have developed an iterative
procedure which allows to calculate the condensate fraction as well as the
corresponding eigenfunction of the one-body density matrix. We successfully
validate this procedure in diffusion Monte Carlo simulations of a Bose gas in
an optical lattice at zero temperature. We also discuss relation between
different criteria used for testing coherence in cold Bose systems, such as
fraction of particles that are superfluid, condensed or are in the
zero-momentum state.Comment: 4 pages, 2 figure
Synthetic dimensions and spin-orbit coupling with an optical clock transition
We demonstrate a novel way of synthesizing spin-orbit interactions in
ultracold quantum gases, based on a single-photon optical clock transition
coupling two long-lived electronic states of two-electron Yb atoms. By
mapping the electronic states onto effective sites along a synthetic
"electronic" dimension, we have engineered synthetic fermionic ladders with
tunable magnetic fluxes. We have detected the spin-orbit coupling with
fiber-link-enhanced clock spectroscopy and directly measured the emergence of
chiral edge currents, probing them as a function of the magnetic field flux.
These results open new directions for the investigation of topological states
of matter with ultracold atomic gases.Comment: Minor changes with respect to v1 (we have corrected some typos, fixed
the use of some mathematical symbols, added one reference
Learning feedback control strategies for quantum metrology
We consider the problem of frequency estimation for a single bosonic field
evolving under a squeezing Hamiltonian and continuously monitored via homodyne
detection. In particular, we exploit reinforcement learning techniques to
devise feedback control strategies achieving increased estimation precision. We
show that the feedback control determined by the neural network greatly
surpasses in the long time limit the performances of both the "no-control" and
the "standard open-loop control" strategies, that we considered as benchmarks.
We indeed observe how the devised strategy is able to optimize the nontrivial
estimation problem by preparing a large fraction of trajectories corresponding
to more sensitive quantum conditional states.Comment: 11 pages, 8 figure
Density of states in an optical speckle potential
We study the single particle density of states of a one-dimensional speckle
potential, which is correlated and non-Gaussian. We consider both the repulsive
and the attractive cases. The system is controlled by a single dimensionless
parameter determined by the mass of the particle, the correlation length and
the average intensity of the field. Depending on the value of this parameter,
the system exhibits different regimes, characterized by the localization
properties of the eigenfunctions. We calculate the corresponding density of
states using the statistical properties of the speckle potential. We find good
agreement with the results of numerical simulations.Comment: 11 pages, 11 figures, revtex
Dissipative Transport of a Bose-Einstein Condensate
We investigate the effects of impurities, either correlated disorder or a
single Gaussian defect, on the collective dipole motion of a Bose-Einstein
condensate of Li in an optical trap. We find that this motion is damped at
a rate dependent on the impurity strength, condensate center-of-mass velocity,
and interatomic interactions. Damping in the Thomas-Fermi regime depends
universally on the disordered potential strength scaled to the condensate
chemical potential and the condensate velocity scaled to the peak speed of
sound. The damping rate is comparatively small in the weakly interacting
regime, and the damping in this case is accompanied by strong condensate
fragmentation. \textit{In situ} and time-of-flight images of the atomic cloud
provide evidence that this fragmentation is driven by dark soliton formation.Comment: 14 pages, 20 figure
State-dependent interactions in ultracold 174Yb probed by optical clock spectroscopy
We report on the measurement of the scattering properties of ultracold
Yb bosons in a three-dimensional (3D) optical lattice. Site occupancy
in an atomic Mott insulator is resolved with high-precision spectroscopy on an
ultranarrow optical clock transition. Scattering lengths and loss rate
coefficients for Yb atoms in different collisional channels involving
the ground state S and the metastable P are derived. These
studies set important constraints for future experimental studies of
two-electron atoms for quantum-technological applications.Comment: 14 pages, 6 figure
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