76,061 research outputs found
Mixed Qubit Cannot Be Universally Broadcast
We show that there does not exist any universal quantum cloning machine that
can broadcast an arbitrary mixed qubit with a constant fidelity. Based on this
result, we investigate the dependent quantum cloner in the sense that some
parameter of the input qubit is regarded as
constant in the fidelity. For the case of constant , we establish the
optimal symmetric dependent cloner with a fidelity 1/2. It is also
shown that the optimal quantum cloning machine for pure qubits is also
optimal for mixed qubits, when is the unique parameter in the
fidelity. For general broadcasting of mixed qubits, the situation is
very different.Comment: 5 pages, Revte
Galaxy formation with cold gas accretion and evolving stellar initial mass function
The evolution of the galaxy stellar mass function is especially useful to
test the current model of galaxy formation. Observational data have revealed a
few inconsistencies with predictions from the model. For
example, most massive galaxies have already been observed at very high
redshifts, and they have experienced only mild evolution since then. In
conflict with this, semi-analytical models of galaxy formation predict an
insufficient number of massive galaxies at high redshift and a rapid evolution
between redshift 1 and 0 . In addition, there is a strong correlation between
star formation rate and stellar mass for star-forming galaxies, which can be
roughly reproduced with the model, but with a normalization that is too low at
high redshift. Furthermore, the stellar mass density obtained from the integral
of the cosmic star formation history is higher than the measured one by a
factor of 2. In this paper, we study these issues using a semi-analytical model
that includes: 1) cold gas accretion in massive halos at high redshift; 2)
tidal stripping of stellar mass from satellite galaxies; and 3) an evolving
stellar initial mass function (bottom-light) with a higher gas recycle
fraction. Our results show that the combined effects from 1) and 2) can predict
sufficiently massive galaxies at high redshifts and reproduce their mild
evolution at low redshift, While the combined effects of 1) and 3) can
reproduce the correlation between star formation rate and stellar mass for
star-forming galaxies across wide range of redshifts. A bottom-light/top-heavy
stellar IMF could partly resolve the conflict between the stellar mass density
and cosmic star formation history.Comment: 9 pages, 7 figures. Accepted for publication in Ap
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Photoacoustic Imaging for Noninvasive Periodontal Probing Depth Measurements.
The periodontal probe is the gold standard tool for periodontal examinations, including probing depth measurements, but is limited by systematic and random errors. Here, we used photoacoustic ultrasound for high-spatial resolution imaging of probing depths. Specific contrast from dental pockets was achieved with food-grade cuttlefish ink as a contrast medium. Here, 39 porcine teeth (12 teeth with artificially deeper pockets) were treated with the contrast agent, and the probing depths were measured with novel photoacoustic imaging and a Williams periodontal probe. There were statistically significant differences between the 2 measurement approaches for distal, lingual, and buccal sites but not mesial. Bland-Altman analysis revealed that all bias values were < ±0.25 mm, and the coefficients of variation for 5 replicates were <11%. The photoacoustic imaging approach also offered 0.01-mm precision and could cover the entire pocket, as opposed to the probe-based approach, which is limited to only a few sites. This report is the first to use photoacoustic imaging for probing depth measurements with potential implications to the dental field, including tools for automated dental examinations or noninvasive examinations
The I^G J^{PC}=1^- 1^{-+} Tetraquark States
We study the tetraquark states with I^G J^{PC}=1^- 1^{-+} in the QCD sum
rule. After exhausting all possible flavor structures, we analyses both the SVZ
and finite energy sum rules. Both approaches lead to a mass around 1.6 GeV for
the state with the quark contents q q q_bar q_bar, and around 2.0 GeV for the
state with the quark contents q s q_bar s_bar. The flavor structure 3_bar *
6_bar + 6 * 3 is preferred. Our analysis strongly indicates that both pi1(1600)
and pi1(2015) are also compatible with the exotic tetraquark interpretation,
which are sometimes labeled as candidates of the 1^{-+} hybrid mesons. Moreover
one of their dominant decay modes is a pair of axial-vector and pseudoscalar
mesons such as b1(1235) pi, which is sometimes considered as the characteristic
decay mode of the hybrid mesons.Comment: 18 pages, 14 figures, revised version to appear in Phys. Rev.
Geometric interpretation for A-fidelity and its relation with Bures fidelity
A geometric interpretation for the A-fidelity between two states of a qubit
system is presented, which leads to an upper bound of the Bures fidelity. The
metrics defined based on the A-fidelity are studied by numerical method. An
alternative generalization of the A-fidelity, which has the same geometric
picture, to a -state quantum system is also discussed.Comment: 4 pages, 1 figure. Phys. Rev.
Mechanics of Tunable Helices and Geometric Frustration in Biomimetic Seashells
Helical structures are ubiquitous in nature and engineering, ranging from DNA
molecules to plant tendrils, from sea snail shells to nanoribbons. While the
helical shapes in natural and engineered systems often exhibit nearly uniform
radius and pitch, helical shell structures with changing radius and pitch, such
as seashells and some plant tendrils, adds to the variety of this family of
aesthetic beauty. Here we develop a comprehensive theoretical framework for
tunable helical morphologies, and report the first biomimetic seashell-like
structure resulting from mechanics of geometric frustration. In previous
studies, the total potential energy is everywhere minimized when the system
achieves equilibrium. In this work, however, the local energy minimization
cannot be realized because of the geometric incompatibility, and hence the
whole system deforms into a shape with a global energy minimum whereby the
energy in each segment may not necessarily be locally optimized. This novel
approach can be applied to develop materials and devices of tunable geometries
with a range of applications in nano/biotechnology
Casimir effect of an ideal Bose gas trapped in a generic power-law potential
The Casimir effect of an ideal Bose gas trapped in a generic power-law
potential and confined between two slabs with Dirichlet, Neumann, and periodic
boundary conditions is investigated systematically, based on the grand
potential of the ideal Bose gas, the Casimir potential and force are
calculated. The scaling function is obtained and discussed. The special cases
of free and harmonic potentials are also discussed. It is found that when T<Tc
(where Tc is the critical temperature of Bose-Einstein condensation), the
Casimir force is a power-law decay function; when T>Tc, the Casimir force is an
exponential decay function; and when T>>Tc, the Casimir force vanishes.Comment: 5 pages, 1 figur
Exotic Tetraquark ud bar[s] bar[s] of J^P=0^+ in the QCD Sum Rule
We study a QCD sum rule analysis for an exotic tetraquark ud bar[s] bar[s] of
J^P=0^+ and I = 1. We construct q q bar[q] bar[q] currents in a local product
form and find that there are five independent currents for this channel. Due to
high dimensional nature of the current, it is not easy to form a good sum rule
when using a single current. This means that we do not find any sum rule window
to extract reliable results, due to the insufficient convergence of the OPE and
to the exceptional important role of QCD continuum. Then we examine sum rules
by using currents of linear combinations of two currents among the independent
ones. We find two reasonable cases that predict a mass of the tetraquark around
1.5 GeV.Comment: 15 pages, 8 figures, revised versio
Light Scalar Tetraquark Mesons in the QCD Sum Rule
We study the lowest-lying scalar mesons in the QCD sum rule by considering
them as tetraquark states. We find that there are five independent currents for
each state with a certain flavor structure. By forming linear combinations, we
find that some mixed currents give reliable QCD sum rules. Among various
tetraquark currents, we consider those which are constructed by the diquarks
having anti-symmetric and symmetric flavor structures. That the results of the
QCD sum rule derived from the two types of currents are similar suggests that
the tetraquark states can have a large mixing between different flavor
structures.Comment: 18 pages, 5 figures; reference added, minor corrections; version to
appear in Phys.Rev.
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