3,276 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
SuprimeCam Observation of Sporadic Meteors during Perseids 2004
We report the serendipitous findings of 13 faint meteors and 44 artificial
space objects by Subaru SuprimeCam imaging observations during 11-16 August
2004. The meteors, at about 100km altitude, and artificial satellites/debris in
orbit, at 500km altitude or higher, were clearly discriminated by their
apparent defocused image sizes. CCD photometry of the 13 meteors, including 1
Perseid, 1 Aquarid, and 11 sporadic meteors, was performed. We defined a peak
video-rate magnitude by comparing the integrated photon counts from the
brightest portion of the track traversed within 33ms to those from a 0-mag star
during the same time duration. This definition gives magnitudes in the range
4.0< V_{vr} <6.4 and 4.1< I_{vr}<5.9 for these 13 meteors. The corresponding
magnitude for virtual naked-eye observers could be somewhat fainter especially
for the V-band observation, in which the [OI] 5577 line lasting about 1 sec as
an afterglow could contribute to the integrated flux of the present 5-10 min
CCD exposures. Although the spatial resolution is insufficient to resolve the
source size of anything smaller than about 1 m, we developed a new estimate of
the collisionally excited column diameter of these meteors. A diameter as small
as a few mm was derived from their collisionally excited photon rates, meteor
speed, and the volume density of the oxygen atoms at the 100km altitude. The
actual column diameter of the radiating zone, however, could be as large as few
100m because the excited atoms travel that distance before they emit forbidden
lines in 0.7 sec of its average lifetime. Among the 44 artificial space
objects, we confirmed that 17 were cataloged satellites/space debris.Comment: 14 pages, 13 figures, 5 tables, submitted to PAS
Fermi arc in doped high-Tc cuprates
We propose a -density wave induced by the spin-orbit coupling in the CuO
plane. The spectral function of high-temperature superconductors in the under
doped and lightly doped regions is calculated in order to explain the Fermi arc
spectra observed recently by angle-resolved photoemission spectroscopy. We take
into account the tilting of CuO octahedra as well as the on-site
Coulombrepulsive interaction; the tilted octahedra induce the staggered
transfer integral between orbitals and Cu orbitals, and
bring about nontrivial effects of spin-orbit coupling for the electrons in
the CuO plane. The spectral weight shows a peak at around (,) for
light doping and extends around this point forming an arc as the carrier
density increases, where the spectra for light doping grow continuously to be
the spectra in the optimally doped region. This behavior significantly agrees
with that of the angle-resolved photoemissionspectroscopy spectra. Furthermore,
the spin-orbit term and staggered transfer effectively induce a flux state, a
pseudo-gap with time-reversal symmetry breaking. We have a nodal metallic state
in the light-doping case since the pseudogap has a symmetry.Comment: 5 pages, 7 figure
Off-diagonal Wave Function Monte Carlo Studies of Hubbard Model I
We propose a Monte Carlo method, which is a hybrid method of the quantum
Monte Carlo method and variational Monte Carlo theory, to study the Hubbard
model. The theory is based on the off-diagonal and the Gutzwiller type
correlation factors which are taken into account by a Monte Carlo algorithm. In
the 4x4 system our method is able to reproduce the exact results obtained by
the diagonalization. An application is given to investigate the half-filled
band case of two-dimensional square lattice. The energy is favorably compared
with quantum Monte Carlo data.Comment: 9 pages, 11 figure
Earliest detection of the optical afterglow of GRB 030329 and its variability
We report the earliest detection of an extremely bright optical afterglow of
the gamma-ray burst (GRB) 030329 using a 30cm-telescope at Tokyo Institute of
Technology (Tokyo, JAPAN). Our observation started 67 minutes after the burst,
and continued for succeeding two nights until the afterglow faded below the
sensitivity limit of the telescope (approximately 18 mag). Combining our data
with those reported in GCN Circulars, we find that the early afterglow light
curve of the first half day is described by a broken power-law (t^{- alpha})
function with indices alpha_{1} = 0.88 +/- 0.01 (0.047 < t < t_{b1} days),
alpha_{2} = 1.18 +/- 0.01 (t_{b1} < t < t_{b2} days), and alpha_{3} = 1.81 +/-
0.04 (t_{b2} < t < 1.2 days), where t_{b1} ~ 0.26 days and t_{b2} ~ 0.54 days,
respectively. The change of the power-law index at the first break at t ~ 0.26
days is consistent with that expected from a ``cooling-break'' when the cooling
frequency crossed the optical band. If the interpretation is correct, the decay
index before the cooling-break implies a uniform ISM environment.Comment: 13 pages, 1 table and 2 figures. Accepted to the Astrophysical
Journal Letter
Superconductivity, magnetic order, and quadrupolar order in the filled skutterudite system PrNdOsSb
Superconductivity, magnetic order, and quadrupolar order have been
investigated in the filled skutterudite system
PrNdOsSb as a function of composition in magnetic
fields up to 9 tesla and at temperatures between 50 mK and 10 K. Electrical
resistivity measurements indicate that the high field ordered phase (HFOP),
which has been identified with antiferroquadruoplar order, persists to
0.5. The superconducting critical temperature of PrOsSb
is depressed linearly with Nd concentration to 0.55, whereas the
Curie temperature of NdOsSb is depressed linearly with Pr
composition to () 0.45. In the superconducting region, the upper
critical field is depressed quadratically with in the range 0
0.3, exhibits a kink at 0.3, and then
decreases linearly with in the range 0.3 0.6. The
behavior of appears to be due to pair breaking caused by the
applied magnetic field and the exhange field associated with the polarization
of the Nd magnetic moments, in the superconducting state. From magnetic
susceptibility measurements, the correlations between the Nd moments in the
superconducting state appear to change from ferromagnetic in the range 0.3
0.6 to antiferromagnetic in the range 0
0.3. Specific heat measurements on a sample with 0.45
indicate that magnetic order occurs in the superconducting state, as is also
inferred from the depression of with .Comment: 7 pages, 7 figures, currently submitted to Phys. Rev.
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