1,417 research outputs found
Gates for the Kane Quantum Computer in the Presence of Dephasing
In this paper we investigate the effect of dephasing on proposed quantum
gates for the solid-state Kane quantum computing architecture. Using a simple
model of the decoherence, we find that the typical error in a CNOT gate is . We also compute the fidelities of Z, X, Swap, and Controlled Z
operations under a variety of dephasing rates. We show that these numerical
results are comparable with the error threshold required for fault tolerant
quantum computation.Comment: 9 pages, 9 figure
Decays of the Meson to a -Wave Charmonium State or
The semileptonic decays,
, and the two-body
nonleptonic decays, , (here and
denote and respectively, and
indicates a meson) were computed. All of the form factors appearing in the
relevant weak-current matrix elements with as its initial state and a
-wave charmonium state as its final state for the decays were precisely
formulated in terms of two independent overlapping-integrations of the
wave-functions of and the -wave charmonium and with proper kinematics
factors being `accompanied'. We found that the decays are quite sizable, so
they may be accessible in Run-II at Tevatron and in the foreseen future at LHC,
particularly, when BTeV and LHCB, the special detectors for B-physics, are
borne in mind. In addition, we also pointed out that the decays may potentially be used as a fresh window to look for the
charmonium state, and the cascade decays,
() with one of the radiative decays
being followed accordingly, may affect
the observations of meson through the decays () substantially.Comment: 24 pages, 3 figures, the replacement for improving the presentation
and adding reference
The meson annihilation to leptons and inclusive light hadrons
The annihilation of the meson to leptons and inclusive light hadrons is
analyzed in the framework of nonrelativistic QCD (NRQCD) factorization. We find
that the decay mode, which escapes from the helicity suppression, contributes a
sizable fraction width. According to the analysis, the branching ratio due to
the contribution from the color-singlet component of the meson can be of
order (10^{-2}). We also estimate the contributions from the color-octet
components. With the velocity scaling rule of NRQCD, we find that the
color-octet contributions are sizable too, especially, in certain phase space
of the annihilation they are greater than (or comparative to) the color-singlet
component. A few observables relevant to the spectrum of charged lepton are
suggested, that may be used as measurements on the color-octet and
color-singlet components in the future experiments. A typical long
distance contribution in the annihilation is estimated too.Comment: 26 pages, 5 figures (6 eps-files), submitted to Phys. Rev.
Comment on "Grover search with pairs of trapped ions"
In this Comment on Feng's paper [Phys. Rev. A 63, 052308 (2001)], we show that Grover's algorithm may be performed exactly using the gate set given, provided that small changes are made to the gate sequence. An analytic expression for the probability of success of Grover's algorithm for any unitary operator U instead of Hadamard gate is presented
Molecular-level interplays during co-pyrolysis of cellulose and thermoplastics
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Non-covalent catalytic and inhibitory interactions between cellulose and lignin during whole biomass fast pyrolysis
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Non-Markovian reduced dynamics and entanglement evolution of two coupled spins in a quantum spin environment
The exact quantum dynamics of the reduced density matrix of two coupled spin
qubits in a quantum Heisenberg XY spin star environment in the thermodynamic
limit at arbitrarily finite temperatures is obtained using a novel operator
technique. In this approach, the transformed Hamiltonian becomes effectively
Jaynes-Cumming like and thus the analysis is also relevant to cavity quantum
electrodynamics. This special operator technique is mathematically simple and
physically clear, and allows us to treat systems and environments that could
all be strongly coupled mutually and internally. To study their entanglement
evolution, the concurrence of the reduced density matrix of the two coupled
central spins is also obtained exactly. It is shown that the dynamics of the
entanglement depends on the initial state of the system and the coupling
strength between the two coupled central spins, the thermal temperature of the
spin environment and the interaction between the constituents of the spin
environment. We also investigate the effect of detuning which in our model can
be controlled by the strength of a locally applied external magnetic field. It
is found that the detuning has a significant effect on the entanglement
generation between the two spin qubits.Comment: 9 pages (two-coulumn), 6 figures. To appear in Phys. Rev.
Biclustering random matrix partitions with an application to classification of forensic body fluids
Classification of unlabeled data is usually achieved by supervised learning
from labeled samples. Although there exist many sophisticated supervised
machine learning methods that can predict the missing labels with a high level
of accuracy, they often lack the required transparency in situations where it
is important to provide interpretable results and meaningful measures of
confidence. Body fluid classification of forensic casework data is the case in
point. We develop a new Biclustering Dirichlet Process (BDP), with a
three-level hierarchy of clustering, and a model-based approach to
classification which adapts to block structure in the data matrix. As the class
labels of some observations are missing, the number of rows in the data matrix
for each class is unknown. The BDP handles this and extends existing
biclustering methods by simultaneously biclustering multiple matrices each
having a randomly variable number of rows. We demonstrate our method by
applying it to the motivating problem, which is the classification of body
fluids based on mRNA profiles taken from crime scenes. The analyses of
casework-like data show that our method is interpretable and produces
well-calibrated posterior probabilities. Our model can be more generally
applied to other types of data with a similar structure to the forensic data.Comment: 45 pages, 10 figure
Charge Transport in a Quantum Electromechanical System
We describe a quantum electromechanical system(QEMS) comprising a single
quantum dot harmonically bound between two electrodes and facilitating a
tunneling current between them. An example of such a system is a fullerene
molecule between two metal electrodes [Park et al., Nature, 407, 57 (2000)].
The description is based on a quantum master equation for the density operator
of the electronic and vibrational degrees of freedom and thus incorporates the
dynamics of both diagonal (population) and off diagonal (coherence) terms. We
derive coupled equations of motion for the electron occupation number of the
dot and the vibrational degrees of freedom, including damping of the vibration
and thermo-mechanical noise. This dynamical description is related to
observable features of the system including the stationary current as a
function of bias voltage.Comment: To appear in Phys. Rev. B., 13 pages, single colum
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