14,959 research outputs found
Normal form decomposition for Gaussian-to-Gaussian superoperators
In this paper we explore the set of linear maps sending the set of quantum
Gaussian states into itself. These maps are in general not positive, a feature
which can be exploited as a test to check whether a given quantum state belongs
to the convex hull of Gaussian states (if one of the considered maps sends it
into a non positive operator, the above state is certified not to belong to the
set). Generalizing a result known to be valid under the assumption of complete
positivity, we provide a characterization of these Gaussian-to-Gaussian (not
necessarily positive) superoperators in terms of their action on the
characteristic function of the inputs. For the special case of one-mode
mappings we also show that any Gaussian-to-Gaussian superoperator can be
expressed as a concatenation of a phase-space dilatation, followed by the
action of a completely positive Gaussian channel, possibly composed with a
transposition. While a similar decomposition is shown to fail in the multi-mode
scenario, we prove that it still holds at least under the further hypothesis of
homogeneous action on the covariance matrix
Quantum synchronization as a local signature of super- and subradiance
We study the relationship between the collective phenomena of super and
subradiance and spontaneous synchronization of quantum systems. To this aim we
revisit the case of two detuned qubits interacting through a pure dissipative
bosonic environment, which contains the minimal ingredients for our analysis.
By using the Liouville formalism, we are able to find analytically the ultimate
connection between these phenomena. We find that dynamical synchronization is
due to the presence of long standing coherence between the ground state of the
system and the subradiant state. We finally show that, under pure dissipation,
the emergence of spontaneous synchronization and of subradiant emission occur
on the same time scale. This reciprocity is broken in the presence of dephasing
noise.Comment: 12 pages, 6 figure
Entanglement control in hybrid optomechanical systems
We demonstrate the control of entanglement in a hybrid optomechanical system
comprising an optical cavity with a mechanical end-mirror and an intracavity
Bose-Einstein condensate (BEC). Pulsed laser light (tuned within realistic
experimental conditions) is shown to induce an almost sixfold increase of the
atom-mirror entanglement and to be responsible for interesting dynamics between
such mesoscopic systems. In order to assess the advantages offered by the
proposed control technique, we compare the time-dependent dynamics of the
system under constant pumping with the evolution due to the modulated laser
light.Comment: Published versio
Alien Registration- Palma, Harold B. (Hallowell, Kennebec County)
https://digitalmaine.com/alien_docs/16803/thumbnail.jp
Technology acceptance: Does the users accept the change of operating system of their smartphone?
The main objective of this study was to understand how the users accepts the change of their operating system. Objectives were defined, like clarifying each of the operating systems, understand the preference of consumers’ choice through a questionnaire and understand whether or not there is difficulty for users to change their operating system. Thus, a questionnaire was carried out to 204 participants aged between 16 and 72 years in the region of Lisbon. The main criteria were being over 12 years old and having a smartphone. Throughout the study, it was possible to understand that most people have a smartphone, that the satisfaction with the operating system they are currently using is quite high, that older consumers have more difficulty in changing operating system, and that product features are what most influences consumers to switch from an Android to an iOS or vice versa.info:eu-repo/semantics/acceptedVersio
Multi-sensor system using plastic optical fibers for intrinsically safe level measurements
A system for measuring liquid level in multiple tanks using optical fibe technology has been developed. Oil fiel service industry or any sector requiring liquid level measurements in flammabl atmospheres can be benefite from this intrinsically safe technology. The device used a single lens for the emitting and receiving fibe and it is based on amplitude variations as a function of the liquid distance and not in time of fligh or phase detection. Being the firs fiber-opti liquid level sensor with those characteristics for long ranges (>200 cm). A simple model to describe their behavior has been derived and tested on two prototypes. A Monte-Carlo method is used to fi the experimental data and obtain the model parameters. High accuracy between experimental data and fitte curve is obtained. The prototypes have a good linearity, better than 1.5% FS (full scale). Sensor heads are made of plastic optical fiber (POF) that are easy to handle, flexible and economical. They are excited by 650 nm lasers, housed in ST-connectors to obtain compact and rough prototypes. Optical multiplexing is used to increase the measuring safety area. Frequency division multiplexing is used to address each sensor head. A discussion about the influenc of tilts and aberrations is also included.Publicad
Simultaneous surface acoustic wave and surface plasmon resonance measurements: electrodeposition and biological interactions monitoring
We present results from an instrument combining surface acoustic wave (SAW)
propagation and surface plasmon resonance (SPR) measurements. The objective is
to use two independent methods, the former based on adsorbed mass change
measurements and the latter on surface dielectric properties variations, to
identify physical properties of protein layers, and more specifically their
water content. We display mass sensitivity calibration curves using
electrodeposition of copper leading to a sensitivity in liquid of 150
for the Love mode device used here, and the application to monitoring
biological processes. The extraction of protein layer thickness and protein to
water content ratio is also presented for S-layer proteins under investigation.
We obtain respectively 4.70.7 nm and 7515%.Comment: 13 pages, 4 figure
Berry phase for a spin 1/2 in a classical fluctuating field
The effect of fluctuations in the classical control parameters on the Berry
phase of a spin 1/2 interacting with a adiabatically cyclically varying
magnetic field is analyzed. It is explicitly shown that in the adiabatic limit
dephasing is due to fluctuations of the dynamical phase.Comment: 4 pages, 1 figure, published versio
Entangled states maximize the two qubit channel capacity for some Pauli channels with memory
We prove that a general upper bound on the maximal mutual information of
quantum channels is saturated in the case of Pauli channels with an arbitrary
degree of memory. For a subset of such channels we explicitly identify the
optimal signal states. We show analytically that for such a class of channels
entangled states are indeed optimal above a given memory threshold. It is
noteworthy that the resulting channel capacity is a non-differentiable function
of the memory parameter.Comment: 4 pages no figure
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