1,860 research outputs found
Relation between fundamental estimation limit and stability in linear quantum systems with imperfect measurement
From the noncommutative nature of quantum mechanics, estimation of canonical
observables and is essentially restricted in its
performance by the Heisenberg uncertainty relation, \mean{\Delta
\hat{q}^2}\mean{\Delta \hat{p}^2}\geq \hbar^2/4. This fundamental lower-bound
may become bigger when taking the structure and quality of a specific
measurement apparatus into account. In this paper, we consider a particle
subjected to a linear dynamics that is continuously monitored with efficiency
. It is then clarified that the above Heisenberg uncertainty
relation is replaced by \mean{\Delta \hat{q}^2}\mean{\Delta \hat{p}^2}\geq
\hbar^2/4\eta if the monitored system is unstable, while there exists a stable
quantum system for which the Heisenberg limit is reached.Comment: 4 page
Chiral Lagrangian and spectral sum rules for dense two-color QCD
We analytically study two-color QCD with an even number of flavors at high
baryon density. This theory is free from the fermion sign problem. Chiral
symmetry is broken spontaneously by the diquark condensate. Based on the
symmetry breaking pattern we construct the low-energy effective Lagrangian for
the Nambu-Goldstone bosons. We identify a new epsilon-regime at high baryon
density in which the quark mass dependence of the partition function can be
determined exactly. We also derive Leutwyler-Smilga-type spectral sum rules for
the complex eigenvalues of the Dirac operator in terms of the fermion gap. Our
results can in principle be tested in lattice QCD simulations.Comment: 24 pages, 1 table, no figur
Validation of CFD Codes for the Helicopter Wake in Ground Effect
When a helicopter takes off, lands, or makes hovering or taxiing flights in ground effect, its downwash
interferes with the ground. Encounters with such highly turbulent helicopter wakes have been blamed for two
fixed-wing aircraft crashes in the United Kingdom. Additional incidents including tents blown away are
reported in Japan. Due to these accidents, the Japan Aerospace Exploration Agency (JAXA) and the
University of Glasgow (UoG) are investigating the helicopter wake structure in ground effect, especially
during taxiing, by means of computational fluid dynamics (CFD). In this study, CFD codes of UoG and JAXA
are validated through comparing numerical results of each party and flight experiment data. As a result, it is
found that the CFD codes show qualitatively the same results each other and they are also close to the
experiment
Canonical-basis solution of the Hartree-Fock-Bogoliubov equation on three-dimensional Cartesian mesh
A method is presented to obtain the canonical-form solutions of the HFB
equation for atomic nuclei with zero-range interactions like the Skyrme force.
It is appropriate to describe pairing correlations in the continuum in
coordinate-space representations. An improved gradient method is used for
faster convergences under constraint of orthogonality between orbitals. To
prevent high-lying orbitals to shrink into a spatial point, a repulsive
momentum dependent force is introduced, which turns out to unveil the nature of
high-lying canonical-basis orbitals. The asymptotic properties at large radius
and the relation with quasiparticle states are discussed for the obtained
canonical basis.Comment: 23 pages including 17 figures, REVTeX4, revised version, scheduled to
appear in Phys. Rev. C, Vol.69, No.
Optical Identification of Close White Dwarf Binaries in the LISA Era
The Laser Interferometer Space Antenna (LISA) is expected to detect close
white dwarf binaries (CWDBs) through their gravitational radiation. Around 3000
binaries will be spectrally resolved at frequencies > 3 mHz, and their
positions on the sky will be determined to an accuracy ranging from a few tens
of arcminutes to a degree or more. Due to the small binary separation, the
optical light curves of >~ 30% of these CWDBs are expected to show eclipses,
giving a unique signature for identification in follow-up studies of the LISA
error boxes. While the precise optical location improves binary parameter
determination with LISA data, the optical light curve captures additional
physics of the binary, including the individual sizes of the stars in terms of
the orbital separation. To optically identify a substantial fraction of CWDBs
and thus localize them very accurately, a rapid monitoring campaign is
required, capable of imaging a square degree or more in a reasonable time, at
intervals of 10--100 seconds, to magnitudes between 20 and 25. While the
detectable fraction can be up to many tens of percent of the total resolved
LISA CWDBs, the exact fraction is uncertain due to unknowns related to the
white dwarf spatial distribution, and potentially interesting physics, such as
induced tidal heating of the WDs due to their small orbital separation.Comment: 4 pages, 2 figure
Efficient method for simulating quantum electron dynamics under the time dependent Kohn-Sham equation
A numerical scheme for solving the time-evolution of wave functions under the
time dependent Kohn-Sham equation has been developed. Since the effective
Hamiltonian depends on the wave functions, the wave functions and the effective
Hamiltonian should evolve consistently with each other. For this purpose, a
self-consistent loop is required at every time-step for solving the
time-evolution numerically, which is computationally expensive. However, in
this paper, we develop a different approach expressing a formal solution of the
TD-KS equation, and prove that it is possible to solve the TD-KS equation
efficiently and accurately by means of a simple numerical scheme without the
use of any self-consistent loops.Comment: 5 pages, 3 figures. Physical Review E, 2002, in pres
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