4,502 research outputs found
Tight Upper Bound Of The Maximum Speed Of Evolution Of A Quantum State
I report a tight upper bound of the maximum speed of evolution from one
quantum state to another with fidelity less than
or equal to an arbitrary but fixed value under the action of a time-independent
Hamiltonian. Since the bound is directly proportional to the average absolute
deviation from the median of the energy of the state , one may
interpret as a meaningful measure of the maximum information
processing capability of a system.Comment: 4 pages, 1 figure, minor changes with an additional reference added,
to appear in PR
Relation Between Quantum Speed Limits And Metrics On U(n)
Recently, Chau [Quant. Inform. & Comp. 11, 721 (2011)] found a family of
metrics and pseudo-metrics on -dimensional unitary operators that can be
interpreted as the minimum resources (given by certain tight quantum speed
limit bounds) needed to transform one unitary operator to another. This result
is closely related to the weighted -norm on . Here we
generalize this finding by showing that every weighted -norm on
with 1\le p \le \limitingp induces a metric and a
pseudo-metric on -dimensional unitary operators with quantum
information-theoretic meanings related to certain tight quantum speed limit
bounds. Besides, we investigate how far the correspondence between the
existence of metrics and pseudo-metrics of this type and the quantum speed
limits can go.Comment: minor amendments, 6 pages, to appear in J.Phys.
Exclusive Hadronic D Decays to eta' and eta
Hadronic decay modes and
are studied in the generalized
factorization approach. Form factors for transitions
are carefully evaluated by taking into account the wave function normalization
of the eta and eta'. The predicted branching ratios are generally in agreement
with experiment except for and
; the calculated decay rates for the first two decay modes
are too small by an order of magnitude. We show that the weak decays and followed by resonance-induced final-state
interactions (FSI), which are amenable technically, are able to enhance the
branching ratios of and dramatically
without affecting the agreement between theory and experiment for and . We argue that it is difficult to understand
the observed large decay rates of and
simultaneously; FSI, W-annihilation and the production of excess eta' from
gluons are not helpful in this regard. The large discrepancy between the
factorization hypothesis and experiment for the ratio of
and remains as an enigma.Comment: 15 pages, 1 figure, to appear in Phys. Rev. D. Form factors for D to
eta and eta' transitions are slightly change
Incorporating Inertia Into Multi-Agent Systems
We consider a model that demonstrates the crucial role of inertia and
stickiness in multi-agent systems, based on the Minority Game (MG). The inertia
of an agent is introduced into the game model by allowing agents to apply
hypothesis testing when choosing their best strategies, thereby reducing their
reactivity towards changes in the environment. We find by extensive numerical
simulations that our game shows a remarkable improvement of global cooperation
throughout the whole phase space. In other words, the maladaptation behavior
due to over-reaction of agents is removed. These agents are also shown to be
advantageous over the standard ones, which are sometimes too sensitive to
attain a fair success rate. We also calculate analytically the minimum amount
of inertia needed to achieve the above improvement. Our calculation is
consistent with the numerical simulation results. Finally, we review some
related works in the field that show similar behaviors and compare them to our
work.Comment: extensively revised, 8 pages, 10 figures in revtex
Key distillation from quantum channels using two-way communication protocols
We provide a general formalism to characterize the cryptographic properties
of quantum channels in the realistic scenario where the two honest parties
employ prepare and measure protocols and the known two-way communication
reconciliation techniques. We obtain a necessary and sufficient condition to
distill a secret key using this type of schemes for Pauli qubit channels and
generalized Pauli channels in higher dimension. Our results can be applied to
standard protocols such as BB84 or six-state, giving a critical error rate of
20% and 27.6%, respectively. We explore several possibilities to enlarge these
bounds, without any improvement. These results suggest that there may exist
weakly entangling channels useless for key distribution using prepare and
measure schemes.Comment: 21 page
Multiplpe Choice Minority Game With Different Publicly Known Histories
In the standard Minority Game, players use historical minority choices as the
sole public information to pick one out of the two alternatives. However,
publishing historical minority choices is not the only way to present global
system information to players when more than two alternatives are available.
Thus, it is instructive to study the dynamics and cooperative behaviors of this
extended game as a function of the global information provided. We numerically
find that although the system dynamics depends on the kind of public
information given to the players, the degree of cooperation follows the same
trend as that of the standard Minority Game. We also explain most of our
findings by the crowd-anticrowd theory.Comment: Extensively revised, to appear in New J Phys, 7 pages with 4 figure
Hadronic Charmed Meson Decays Involving Tensor Mesons
Charmed meson decays into a pseudoscalar meson P and a tensor meson T are
studied. The charm to tensor meson transition form factors are evaluated in the
Isgur-Scora-Grinstein-Wise (ISGW) quark model. It is shown that the
Cabibbo-allowed decay is dominated by the
W-annihilation contribution and has the largest branching ratio in
decays. We argue that the Cabibbo-suppressed mode
should be suppressed by one order of magnitude relative to . When the finite width effect of the tensor resonances is taken
into account, the decay rate of is generally enhanced by a factor of
. Except for , the predicted branching ratios
of decays are in general too small by one to two orders of magnitude
compared to experiment. However, it is very unlikely that the
transition form factors can be enhanced by a factor of within the
ISGW quark model to account for the discrepancy between theory and experiment.
As many of the current data are still preliminary and lack sufficient statistic
significance, more accurate measurements are needed to pin down the issue.Comment: 11 page
Quark Mass Hierarchies, Flavor Mixing and Maximal CP-Violation
Flavor mixing and the quark mass spectrum are intimately related. In view of
the observed strong hierarchy of the quark and lepton masses and of the flavor
mixing angles it is argued that the description of flavor mixing must take this
into account. One particular interesting way to describe the flavor mixing
emerges, which is particularly suited for models of quark mass matrices based
on flavor symmetries. We conclude that the unitarity triangle important for
physics should be close to or identical to a rectangular triangle.
violation is maximal in this sense.Comment: 21 latex page
Branching Ratio and CP Violation of B to pi pi Decays in Perturbative QCD Approach
We calculate the branching ratios and CP asymmetries for B^0 to pi^+pi^-, B^+
to pi^+pi^0 and B^0 to pi^0pi^0 decays, in a perturbative QCD approach. In this
approach, we calculate non-factorizable and annihilation type contributions, in
addition to the usual factorizable contributions. We found that the
annihilation diagram contributions are not very small as previous argument. Our
result is in agreement with the measured branching ratio of B to pi^+pi^- by
CLEO collaboration. With a non-negligible contribution from annihilation
diagrams and a large strong phase, we predict a large direct CP asymmetry in
B^0 to pi^+pi^-, and pi^0pi^0, which can be tested by the current running B
factories.Comment: Latex, 28 pages including 11 figures; added contents and figures,
corrected typo
Branching ratio and CP asymmetry of decays in the perturbative QCD approach
In this paper, we calculate the decay rate and CP asymmetry of the decay in perturbative QCD approach with Sudakov resummation. Since
none of the quarks in final states is the same as those of the initial
meson, this decay can occur only via annihilation diagrams in the standard
model. Besides the current-current operators, the contributions from the QCD
and electroweak penguin operators are also taken into account. We find that (a)
the branching ratio is about ; (b) the penguin diagrams
dominate the total contribution; and (c) the direct CP asymmetry is small in
size: no more than ; but the mixing-induced CP asymmetry can be as large
as ten percent testable in the near future LHC-b experiments.Comment: 12 pages, 4 figures included, RevTe
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