36,173 research outputs found
Calculation of laminar boundary layer-shock wave interaction on cooled walls by the method of integral relations
Calculation of laminar boundary layer shock wave interaction on cooled walls by method of integral relatio
Quantum state reconstruction with imperfect rotations on an inhomogeneously broadened ensemble of qubits
We present a method for performing quantum state reconstruction on qubits and
qubit registers in the presence of decoherence and inhomogeneous broadening.
The method assumes only rudimentary single qubit rotations as well as knowledge
of decoherence and loss mechanisms. We show that full state reconstruction is
possible even in the case where single qubit rotations may only be performed
imperfectly. Furthermore we show that for ensemble quantum computing proposals,
quantum state reconstruction is possible even if the ensemble experiences
inhomogeneous broadening and if only imperfect qubit manipulations are
available during state preparation and reconstruction.Comment: 6 pages, 5 figure
-kaon cross section in meson exchange model
We calculate the cross section for the dissociation of by kaons
within the framework of a meson exchange model including anomalous parity
interactions. Off-shell effects at the vertices were handled with QCD sum rule
estimates for the running coupling constants. The total -kaon cross
section was found to be mb for 4.1\leq\sqrt{s}\leq5 \GeV.Comment: 13 pages, 4 eps figure
Protected Rabi oscillation induced by natural interactions among physical qubits
For a system composed of nine qubits, we show that natural interactions among
the qubits induce the time evolution that can be regarded, at discrete times,
as the Rabi oscillation of a logical qubit. Neither fine tuning of the
parameters nor switching of the interactions is necessary. Although
straightforward application of quantum error correction fails, we propose a
protocol by which the logical Rabi oscillation is protected against all
single-qubit errors. The present method thus opens a simple and realistic way
of protecting the unitary time evolution against noise.Comment: In this revised manuscript, new sections V, VI, VII and new
appendices A, B, C have been added to give detailed discussions. 13 pages, 4
figure
Distance measures to compare real and ideal quantum processes
With growing success in experimental implementations it is critical to
identify a "gold standard" for quantum information processing, a single measure
of distance that can be used to compare and contrast different experiments. We
enumerate a set of criteria such a distance measure must satisfy to be both
experimentally and theoretically meaningful. We then assess a wide range of
possible measures against these criteria, before making a recommendation as to
the best measures to use in characterizing quantum information processing.Comment: 15 pages; this version in line with published versio
Error correction in ensemble registers for quantum repeaters and quantum computers
We propose to use a collective excitation blockade mechanism to identify
errors that occur due to disturbances of single atoms in ensemble quantum
registers where qubits are stored in the collective population of different
internal atomic states. A simple error correction procedure and a simple
decoherence-free encoding of ensemble qubits in the hyperfine states of alkali
atoms are presented.Comment: 4 pages, 2 figure
Entanglement of an impurity and conduction spins in the Kondo model
Based on Yosida's ground state of the single-impurity Kondo Hamiltonian, we
study three kinds of entanglement between an impurity and conduction electron
spins. First, it is shown that the impurity spin is maximally entangled with
all the conduction electrons. Second, a two-spin density matrix of the impurity
spin and one conduction electron spin is given by a Werner state. We find that
the impurity spin is not entangled with one conduction electron spin even
within the Kondo screening length , although there is the spin-spin
correlation between them. Third, we show the density matrix of two conduction
electron spins is nearly same to that of a free electron gas. The single
impurity does not change the entanglement structure of the conduction electrons
in contrast to the dramatic change in electrical resistance.Comment: 5 pages, 2 figures, accepted for publication in Physical Review
A study of the - coupled systems
We study the strangeness meson-baryon systems to obtain improved
and amplitudes and to look for a possible resonance formation by the
- coupled interaction. We obtain amplitudes for light vector
meson-baryon systems by implementing the -, -, - channel diagrams and
a contact interaction. The pseudoscalar meson-baryon interactions are obtained
by relying on the Weinberg-Tomozawa theorem. The transition amplitudes between
the systems consisting of pseudoscalars and vector mesons are calculated by
extending the Kroll-Ruderman term for pion photoproduction replacing the photon
by a vector meson. We fix the subtraction constants required to calculate the
loops by fitting our amplitudes to the data available for the isospin 0
and 1 -wave phase shifts. We provide the scattering lengths and the total
cross sections for the and systems obtained in our model, which
can be useful in future in-medium calculations. Our amplitudes do not
correspond to formation of any resonance in none of the isospin and spin
configurations.Comment: Published version, sent to avoid confusions recently noticed by
author
Quantum Kaleidoscopes and Bell's theorem
A quantum kaleidoscope is defined as a set of observables, or states,
consisting of many different subsets that provide closely related proofs of the
Bell-Kochen-Specker (BKS) and Bell nonlocality theorems. The kaleidoscopes
prove the BKS theorem through a simple parity argument, which also doubles as a
proof of Bell's nonlocality theorem if use is made of the right sort of
entanglement. Three closely related kaleidoscopes are introduced and discussed
in this paper: a 15-observable kaleidoscope, a 24-state kaleidoscope and a
60-state kaleidoscope. The close relationship of these kaleidoscopes to a
configuration of 12 points and 16 lines known as Reye's configuration is
pointed out. The "rotations" needed to make each kaleidoscope yield all its
apparitions are laid out. The 60-state kaleidoscope, whose underlying
geometrical structure is that of ten interlinked Reye's configurations
(together with their duals), possesses a total of 1120 apparitions that provide
proofs of the two Bell theorems. Some applications of these kaleidoscopes to
problems in quantum tomography and quantum state estimation are discussed.Comment: Two new references (No. 21 and 22) to related work have been adde
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