9,242 research outputs found
Entanglement, BEC, and superfluid-like behavior of two-mode photon systems
A system of two interacting photon modes, without constraints on the photon
number, in the presence of a Kerr nonlinearity, exhibits BEC if the transfer
amplitude is greater than the mode frequency. A symmetry-breaking field (SBF)
can be introduced by taking into account a classical electron current. The
ground state, in the limit of small nonlinearity, becomes a squeezed state, and
thus the modes become entangled. The smaller is the SBF, the greater is
entanglement. Superfluid-like behavior is observed in the study of entanglement
growth from an initial coherent state, since in the short-time range the growth
does not depend on the SBF amplitude, and on the initial state amplitude. On
the other hand, the latter is the only parameter which determines entanglement
in the absence of the SBF
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
Quantum correlation dynamics in photosynthetic processes assisted by molecular vibrations
During the long course of evolution, nature has learnt how to exploit quantum
effects. In fact, recent experiments reveal the existence of quantum processes
whose coherence extends over unexpectedly long time and space ranges. In
particular, photosynthetic processes in light-harvesting complexes display a
typical oscillatory dynamics ascribed to quantum coherence. Here, we consider
the simple model where a dimer made of two chromophores is strongly coupled
with a quasi-resonant vibrational mode. We observe the occurrence of wide
oscillations of genuine quantum correlations, between electronic excitations
and the environment, represented by vibrational bosonic modes. Such a quantum
dynamics has been unveiled through the calculation of the negativity of
entanglement and the discord, indicators widely used in quantum information for
quantifying the resources needed to realize quantum technologies. We also
discuss the possibility of approximating additional weakly-coupled off-resonant
vibrational modes, simulating the disturbances induced by the rest of the
environment, by a single vibrational mode.
Within this approximation, one can show that the off-resonant bath behaves
like a classical source of noise
Power calculation for gravitational radiation: oversimplification and the importance of time scale
A simplified formula for gravitational-radiation power is examined. It is
shown to give completely erroneous answers in three situations, making it
useless even for rough estimates. It is emphasized that short timescales, as
well as fast speeds, make classical approximations to relativistic calculations
untenable.Comment: Three pages, no figures, accepted for publication in Astronomische
Nachrichte
Orthogonal measurements are {\it almost} sufficient for quantum discord of two qubits
The common use in literature of orthogonal measurements in obtaining quantum
discord for two-qubit states is discussed and compared with more general
measurements. We prove the optimality of orthogonal measurements for rank 2
states. While for rank 3 and 4 mixed states they are not optimal, we present
strong numerical evidence showing that they give the correct quantum discord up
to minimal corrections. Based on the connection, through purification with an
ancilla, between discord and entanglement of formation (EoF), we give a tight
upper bound for the EoF of a mixed state of rank 2, given by an
optimal decomposition of 2 elements. We also provide an alternative way to
compute the quantum discord for two qubits based on the Bloch vectors of the
state.Comment: EPL 96, 40005 (2011
Integrated geophysical surveys to assess the structural conditions of a karstic cave of archaeological importance
An integrated geophysical survey using both the electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) methods was undertaken over a cave of great archaeological interest in southern Italy. The survey was performed to assess the stability of the carbonate rock roof of the cave. A geophysical survey was preferred to boreholes and geotechnical tests, in order to avoid the risk of mass movements. The interpretation of integrated data from ERT and GPR resulted in an evaluation of some of the electromagnetic (EM) characteristics (such as the EM wave velocity) and the detection of discontinuities (fractures) in the carbonate rock. It is well known that rock fractures constitute a serious problem in cave maintenance, and progressive cracking within the bed rock is considered to be one of the main causes of collapse. An analysis of the back-scattered energy was also required for the GPR data interpretation. Cracks within the bedrock were detected to a depth of about 2 m by using GPR, which allowed for the identification of the loosened zone around the cave
Comparison of the ERA5 Wave Forecasting Dataset against Buoy Record
Appropriate design of marine structures, such as offshore facilities and harbours, requires a detailed estimation of synthetic wave parameters. Inaccuracies and unreliability of wave data have implications in many aspects of marine engineering, such as structural strength, cost, and design. In this paper, a critical analysis of the most common data acquisition methods is made, focusing on in-situ instrumentation and numerical models. Considering the Pantelleria island as case study, records of a proprietary wave buoy and the ERA5 dataset of ECMWF (European Centre for Medium-Range Weather Forecasts) have been compared. This paper first highlights the methods and challenges of offshore experimental campaigns for wave monitoring and eventually presents a critical and quantitative comparison of the two approaches (experimental versus numerical), highlighting their respective advantages and disadvantages
SBV regularity for Hamilton-Jacobi equations in
In this paper we study the regularity of viscosity solutions to the following
Hamilton-Jacobi equations In particular, under the
assumption that the Hamiltonian is uniformly convex, we
prove that and belong to the class .Comment: 15 page
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