552 research outputs found
New method for the time calibration of an interferometric radio antenna array
Digital radio antenna arrays, like LOPES (LOFAR PrototypE Station), detect
high-energy cosmic rays via the radio emission from atmospheric extensive air
showers. LOPES is an array of dipole antennas placed within and triggered by
the KASCADE-Grande experiment on site of the Karlsruhe Institute of Technology,
Germany. The antennas are digitally combined to build a radio interferometer by
forming a beam into the air shower arrival direction which allows measurements
even at low signal-to-noise ratios in individual antennas. This technique
requires a precise time calibration. A combination of several calibration steps
is used to achieve the necessary timing accuracy of about 1 ns. The group
delays of the setup are measured, the frequency dependence of these delays
(dispersion) is corrected in the subsequent data analysis, and variations of
the delays with time are monitored. We use a transmitting reference antenna, a
beacon, which continuously emits sine waves at known frequencies. Variations of
the relative delays between the antennas can be detected and corrected for at
each recorded event by measuring the phases at the beacon frequencies.Comment: 9 pages, 9 figures, 1 table, pre-print of article published in
Nuclear Inst. and Methods in Physics Research, A, available at:
http://www.sciencedirect.com/science/article/B6TJM-4Y9CF4B-4/2/37bfcb899a0f387d9875a5a0729593a
Radio detection of cosmic ray air showers with lopes
Cosmic ray air showers are high energetic particles coming from the Universe toward the\ud
Earth every second. It is well known that they generate electromagnetic waves in the Earth\ud
atmosphere detectable on the ground. LOPES is an interferometric array of simple dipole radio 2 Radio detection of cosmic ray air showers with LOPES 309\ud
antennas designed to measure radio signals initiated by cosmic air showers. It is working in\ud
coincidence with the particle detector array KASCADE-Grande at Karlsruhe Institute of Technology (KIT), campus North, from where receives the well-reconstructed shower observables. Determination of the emission mechanism is an important issue for LOPES, and here polarization measurements can play an important role. For first hints towards the verification of the radio emission mechanism, a comparison between measured data and an analytical approach is elaborated.MIURINAFMSHEANCSEntre outra
Test Particle in a Quantum Gas
A master equation with a Lindblad structure is derived, which describes the
interaction of a test particle with a macroscopic system and is expressed in
terms of the operator valued dynamic structure factor of the system. In the
case of a free Fermi or Bose gas the result is evaluated in the Brownian limit,
thus obtaining a single generator master equation for the description of
quantum Brownian motion in which the correction due to quantum statistics is
explicitly calculated. The friction coefficients for Boltzmann and Bose or
Fermi statistics are compared.Comment: 9 pages, revtex, no figure
Quantum to Classical Transition from the Cosmic Background Radiation
We have revisited the Ghirardi-Rimini-Weber-Pearle (GRWP) approach for
continuous dynamical evolution of the state vector for a macroscopic object.
Our main concern is to recover the decoupling of the state vector dynamics for
the center-of-mass (CM) and internal motion, as in the GRWP model, but within
the framework of the standard cosmology. In this connection we have taken the
opposite direction of the GRWP argument, that the cosmic background radiation
(CBR) has originated from a fundamental stochastic hitting process. We assume
the CBR as a clue of the Big Bang, playing a main role in the decoupling of the
state vector dynamics of the CM and internal motion. In our model, instead of
describing a continuous spontaneous localization (CSL) of a system of massive
particles as proposed by Ghirardi, Pearle and Rimini, the It\^{o} stochastic
equation accounts for the intervention of the CBR on the system of particles.
Essentially, this approach leads to a pre-master equation for both the CBR and
particles degrees of freedom. The violation of the principle of energy
conservation characteristic of the CSL model is avoided as well as the
additional assumption on the size of the GRWP's localization width necessary to
reach the decoupling between the collective and internal motions. Moreover,
realistic estimation for the decoherence time, exhibiting an interesting
dependence on the CBR temperature, is obtained. From the formula for the
decoherence time it is possible to analyze the transition from micro to macro
dynamics in both the early hot Universe and the nowadays cold one. The entropy
of the system under decoherence is analyzed and the emergent `pointer basis' is
discussed. In spite of not having imposed a privileged basis, in our model the
position still emerges as the preferred observable as in the CSL model.Comment: 14 pages, no figure. To appear in Phys. Rev.
Symplectic evolution of Wigner functions in markovian open systems
The Wigner function is known to evolve classically under the exclusive action
of a quadratic hamiltonian. If the system does interact with the environment
through Lindblad operators that are linear functions of position and momentum,
we show that the general evolution is the convolution of the classically
evolving Wigner function with a phase space gaussian that broadens in time. We
analyze the three generic cases of elliptic, hyperbolic and parabolic
Hamiltonians. The Wigner function always becomes positive in a definite time,
which is shortest in the hyperbolic case. We also derive an exact formula for
the evolving linear entropy as the average of a narrowing gaussian taken over a
probability distribution that depends only on the initial state. This leads to
a long time asymptotic formula for the growth of linear entropy.Comment: this new version treats the dissipative cas
Stochastic Collapse and Decoherence of a Non-Dissipative Forced Harmonic Oscillator
Careful monitoring of harmonically bound (or as a limiting case, free) masses
is the basis of current and future gravitational wave detectors, and of
nanomechanical devices designed to access the quantum regime. We analyze the
effects of stochastic localization models for state vector reduction, and of
related models for environmental decoherence, on such systems, focusing our
analysis on the non-dissipative forced harmonic oscillator, and its free mass
limit. We derive an explicit formula for the time evolution of the expectation
of a general operator in the presence of stochastic reduction or
environmentally induced decoherence, for both the non-dissipative harmonic
oscillator and the free mass. In the case of the oscillator, we also give a
formula for the time evolution of the matrix element of the stochastic
expectation density matrix between general coherent states. We show that the
stochastic expectation of the variance of a Hermitian operator in any
unraveling of the stochastic process is bounded by the variance computed from
the stochastic expectation of the density matrix, and we develop a formal
perturbation theory for calculating expectation values of operators within any
unraveling. Applying our results to current gravitational wave interferometer
detectors and nanomechanical systems, we conclude that the deviations from
quantum mechanics predicted by the continuous spontaneous localization (CSL)
model of state vector reduction are at least five orders of magnitude below the
relevant standard quantum limits for these experiments. The proposed LISA
gravitational wave detector will be two orders of magnitude away from the
capability of observing an effect.Comment: TeX; 34 page
Intrinsic Decoherence Dynamics in Smooth Hamiltonian Systems: Quantum-classical Correspondence
A direct classical analog of the quantum dynamics of intrinsic decoherence in
Hamiltonian systems, characterized by the time dependence of the linear entropy
of the reduced density operator, is introduced. The similarities and
differences between the classical and quantum decoherence dynamics of an
initial quantum state are exposed using both analytical and computational
results. In particular, the classicality of early-time intrinsic decoherence
dynamics is explored analytically using a second-order perturbative treatment,
and an interesting connection between decoherence rates and the stability
nature of classical trajectories is revealed in a simple approximate classical
theory of intrinsic decoherence dynamics. The results offer new insights into
decoherence, dynamics of quantum entanglement, and quantum chaos.Comment: 12 pages, 7 figures, to appear in Physical Review
Amplitude calibration of a digital radio antenna array for measuring cosmic ray air showers
Radio pulses are emitted during the development of air showers, where air
showers are generated by ultra-high energy cosmic rays entering the Earth's
atmosphere. These nanosecond short pulses are presently investigated by various
experiments for the purpose of using them as a new detection technique for
cosmic particles. For an array of 30 digital radio antennas (LOPES experiment)
an absolute amplitude calibration of the radio antennas including the full
electronic chain of the data acquisition system is performed, in order to
estimate absolute values of the electric field strength for these short radio
pulses. This is mandatory, because the measured radio signals in the MHz
frequency range have to be compared with theoretical estimates and with
predictions from Monte Carlo simulations to reconstruct features of the primary
cosmic particle. A commercial reference radio emitter is used to estimate
frequency dependent correction factors for each single antenna of the radio
antenna array. The expected received power is related to the power recorded by
the full electronic chain. Systematic uncertainties due to different
environmental conditions and the described calibration procedure are of order
20%.Comment: Article accepted by Nuclear Instruments and Methods in Physics
Research, A (NIM A
Master-equations for the study of decoherence
Different structures of master-equation used for the description of
decoherence of a microsystem interacting through collisions with a surrounding
environment are considered and compared. These results are connected to the
general expression of the generator of a quantum dynamical semigroup in
presence of translation invariance recently found by Holevo.Comment: 10 pages, latex, no figures, to appear in Int. J. Theor. Phy
- …