5,672 research outputs found
Detecting quantum speedup in closed and open systems
We construct a general measure for detecting the quantum speedup in both
closed and open systems. The speed measure is based on the changing rate of the
position of quantum states on a manifold with appropriate monotone Riemannian
metrics. Any increase in speed is a clear signature of dynamical speedup. To
clarify the mechanisms for quantum speedup, we first introduce the concept of
longitudinal and transverse types of speedup: the former stems from the time
evolution process itself with fixed initial conditions, while the latter is a
result of adjusting initial conditions. We then apply the proposed measure to
several typical closed and open quantum systems, illustrating that quantum
coherence (or entanglement) and the memory effect of the environment together
can become resources for longitudinally or transversely accelerating dynamical
evolution under specific conditions and assumptions.Comment: 7 pages, 4 figures; Accepted for publication in New Journal of
Physic
Temperature dependence of cross sections for meson-meson nonresonant reactions in hadronic matter
We study unpolarized cross sections for the endothermic nonresonant
reactions: pion pion to rho rho for I=2, KK to K*K* for I=1, KK* to K*K* for
I=1, pion K to rho K* for I=3/2, pion K* to rho K* for I=3/2, rho K to rho K*
for I=3/2, and pion K* to rho K for I=3/2, which take place in hadronic matter.
We provide a potential that is given by perturbative QCD with loop corrections
at short distances, becomes a distance-independent and temperature-dependent
value at long distances, and has a spin-spin interaction with relativistic
modifications. The Schrodinger equation with the potential yields
temperature-dependent meson masses and mesonic quark-antiquark relative-motion
wave functions. In the first Born approximation with the quark-interchange
mechanism, the temperature dependence of the potential, meson masses and wave
functions brings about temperature dependence of unpolarized cross sections for
the seven nonresonant reactions. Noticeably, rapid changes of pion and K radii
cause an increase in peak cross sections while the temperature approaches the
critical temperature. Parametrizations of the numerical cross sections are
given for their future applications in heavy ion collisions.Comment: 24 pages, 8 figure
Relation between quark-antiquark potential and quark-antiquark free energy in hadronic matter
In the high-temperature quark-gluon plasma and its subsequent hadronic matter
created in a high-energy nucleus-nucleus collision, the quark-antiquark
potential depends on the temperature. The temperature-dependent potential is
expected to be derived from the free energy obtained in lattice gauge theory
calculations. This requires one to study the relation between the
quark-antiquark potential and the quark-antiquark free energy. When the
system's temperature is above the critical temperature, the potential of a
heavy quark and a heavy antiquark almost equals the free energy, but the
potential of a light quark and a light antiquark, of a heavy quark and a light
antiquark and of a light quark and a heavy antiquark is substantially larger
than the free energy. When the system's temperature is below the critical
temperature, the quark-antiquark free energy can be taken as the
quark-antiquark potential. This allows one to apply the quark-antiquark free
energy to study hadron properties and hadron-hadron reactions in hadronic
matter.Comment: 11 page
Quantum-speed-limit time for multiqubit open systems
Quantum-speed-limit (QSL) time captures the intrinsic minimal time interval
for a quantum system evolving from an initial state to a target state. In
single qubit open systems, it was found that the memory (non-Markovian) effect
of environment plays an essential role in shortening QSL time or, say,
increasing the capacity for potential speedup. In this paper, we investigate
the QSL time for multiqubit open systems. We find that for a certain class of
states the memory effect still acts as the indispensable requirement for
cutting the QSL time down, while for another class of states this takes place
even when the environment is of no memory. In particular, when the initial
state is in product state |111...1>, there exists a sudden transition from no
capacity for potential speedup to potential speedup in a memoryless
environment. In addition, we also display evidence for the subtle connection
between QSL time and entanglement that weak entanglement may shorten QSL time
even more.Comment: 5pages, 3 figure
Folding membrane proteins by deep transfer learning
Computational elucidation of membrane protein (MP) structures is challenging
partially due to lack of sufficient solved structures for homology modeling.
Here we describe a high-throughput deep transfer learning method that first
predicts MP contacts by learning from non-membrane proteins (non-MPs) and then
predicting three-dimensional structure models using the predicted contacts as
distance restraints. Tested on 510 non-redundant MPs, our method has contact
prediction accuracy at least 0.18 better than existing methods, predicts
correct folds for 218 MPs (TMscore at least 0.6), and generates
three-dimensional models with RMSD less than 4 Angstrom and 5 Angstrom for 57
and 108 MPs, respectively. A rigorous blind test in the continuous automated
model evaluation (CAMEO) project shows that our method predicted
high-resolution three-dimensional models for two recent test MPs of 210
residues with RMSD close to 2 Angstrom. We estimated that our method could
predict correct folds for between 1,345 and 1,871 reviewed human multi-pass MPs
including a few hundred new folds, which shall facilitate the discovery of
drugs targeting at membrane proteins
Temperature-dependent cross sections for charmonium dissociation in collisions with kaons and eta mesons in hadronic matter
We study kaon-charmonium and eta-charmonium dissociation reactions. The
K-charmonium dissociation and the eta-charmonium dissociation include 27
reactions. Cross sections for the reactions are calculated in the Born
approximation, in the quark-interchange mechanism and with a
temperature-dependent quark potential. The temperature dependence of peak cross
sections of endothermic reactions is linked to the temperature dependence of
quark-antiquark relative-motion wave functions, meson masses and the quark
potential. Although the eta meson and kaon have similar masses, the energy and
temperature dependence of the eta-charmonium dissociation cross sections are
quite different from those of the K-charmonium dissociation cross sections.
Using the eta-charmonium and pion-charmonium dissociation cross sections, we
calculate the ratio of the corresponding dissociation rates in hadronic matter
and we find that such rates are comparable at low J/psi momenta.Comment: 54 pages, 29 figures, 6 table
Non-Markovian effect on remote state preparation
Memory effect of non-Markovian dynamics in open quantum systems is often
believed to be beneficial for quantum information processing. In this work, we
employ an experimentally controllable two-photon open system, with one photon
experiencing a dephasing environment and the other being free from noise, to
show that non-Markovian effect may also have a negative impact on quantum tasks
such as remote state preparation: For a certain period of controlled time
interval, stronger non-Markovian effect yields lower fidelity of remote state
preparation, as opposed to the common wisdom that more information leads to
better performance. As a comparison, a positive non-Markovian effect on the RSP
fidelity with another typical non-Markovian noise is analyzed. Consequently,
the observed dual character of non-Markovian effect will be of great importance
in the field of open systems engineering.Comment: 7 pages, 5 figure
Cross sections for inelastic meson-meson scattering via quark-antiquark annihilation
We study inelastic meson-meson scattering that is governed by quark-antiquark
annihilation and creation involving a quark and an antiquark annihilating into
a gluon, and subsequently the gluon creating another quark-antiquark pair. The
resultant hadronic reactions include for I=1: pion + pion to rho + rho, kaon +
antikaon to kaon* + antikaon*, kaon + antikaon* to kaon* + antikaon*, kaon* +
antikaon to kaon* + antikaon*, as well as pion + pion to kaon + antikaon, pion
+ rho to kaon + antikaon*, pion + rho to kaon* + antikaon, and kaon + antikaon
to rho + rho. In each reaction, one or two Feynman diagrams are involved in the
Born approximation. We derive formulas for the unpolarized cross section, the
transition amplitude, and the transition potential for quark-antiquark
annihilation and creation. The unpolarized cross sections for the reactions are
calculated at six temperatures, and prominent temperature dependence is found.
It is due to differences among mesonic temperature dependence in hadronic
matter.Comment: 53 pages, 13 figure
Necessary and sufficient criterion for k-separability of N-qubit noisy GHZ states
A Multipartite entangled state has many different kinds of entanglement
specified by the number of partitions. The most essential example of
multipartite entanglement is the entanglement of multi-qubit
Greenberger-Horne-Zeilinger (GHZ) state in white noise. We explicitly construct
the entanglement witnesses for these states with stabilizer generators of the
GHZ states. For a qubit GHZ state in white noise, we demonstrate the
necessary and sufficient criterion of separability when it is divided into
parties with for arbitrary and . The criterion covers more
than a half of all kinds of partial entanglement for -qubit GHZ states in
white noise. For the rest of multipartite entanglement problems, we present a
method to obtain the sufficient conditions of separability. As an application,
we consider qubit GHZ state as a codeword of the degenerate quantum code
passing through depolarizing channel. We find that the output state is neither
genuinely entangled nor fully separable when the quantum channel capacity
reduces from positive to zero.Comment: 10 pages, 1 figur
Early thermalization of quark-gluon matter with the elastic scattering of ggq and ggqbar
Elastic gluon-gluon-quark (gluon-gluon-antiquark) scattering is studied in
perturbative QCD with 123 Feynman diagrams at the tree level. Individually
squared amplitudes and interference terms of the Feynman diagrams are derived.
With the elastic gluon-gluon-quark scattering and the elastic
gluon-gluon-antiquark scattering transport equations are established. In the
thermalization process of initially created quark-gluon matter, this matter is
governed by elastic 2-to-2 scattering and elastic 3-to-3 scattering. Solutions
of the transport equations show that initially created quark-gluon matter takes
early thermalization, i.e., thermal states are established rapidly. Different
thermalization times of gluon matter and quark matter are obtained.Comment: 31 pages, 8 figure
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