35,984 research outputs found
Prediction of airfoil stall using Navier-Stokes equations in streamline coordinates
A Navier-Stokes procedure to calculate the flow about an airfoil at incidence was developed. The parabolized equations are solved in the streamline coordinates generated for an arbitrary airfoil shape using conformal mapping. A modified k-epsilon turbulence model is applied in the entire domain, but the eddy viscosity in the laminar region is suppressed artificially to simulate the region correctly. The procedure was applied to airfoils at various angles of attack, and the results are quite satisfactory for both laminar and turbulent flows. It is shown that the present choice of the coordinate system reduces the error due to numerical diffusion, and that the lift is accurately predicted for a wide range of incidence
Quantum cryptography based on qutrit Bell inequalities
We present a cryptographic protocol based upon entangled qutrit pairs. We analyze the scheme under a symmetric incoherent attack and plot the region for which the protocol is secure and compare this with the region of violations of certain Bell inequalities
Kinematic approach to off-diagonal geometric phases of nondegenerate and degenerate mixed states
Off-diagonal geometric phases have been developed in order to provide
information of the geometry of paths that connect noninterfering quantal
states. We propose a kinematic approach to off-diagonal geometric phases for
pure and mixed states. We further extend the mixed state concept proposed in
[Phys. Rev. Lett. {\bf 90}, 050403 (2003)] to degenerate density operators. The
first and second order off-diagonal geometric phases are analyzed for unitarily
evolving pairs of pseudopure states.Comment: New section IV, new figure, journal ref adde
Sufficiency Criterion for the Validity of the Adiabatic Approximation
We examine the quantitative condition which has been widely used as a
criterion for the adiabatic approximation but was recently found insufficient.
Our results indicate that the usual quantitative condition is sufficient for a
special class of quantum mechanical systems. For general systems, it may not be
sufficient, but it along with additional conditions is sufficient. The usual
quantitative condition and the additional conditions constitute a general
criterion for the validity of the adiabatic approximation, which is applicable
to all dimensional quantum systems. Moreover, we illustrate the use of the
general quantitative criterion in some physical models.Comment: 9 pages, no figure,appearing in PRL98(2007)15040
Realizations of the -Heisenberg and -Virasoro Algebras
We give field theoretic realizations of both the -Heisenberg and the
-Virasoro algebra. In particular, we obtain the operator product expansions
among the current and the energy momentum tensor obtained using the Sugawara
construction.Comment: 9 page
Kinematic approach to the mixed state geometric phase in nonunitary evolution
A kinematic approach to the geometric phase for mixed quantal states in
nonunitary evolution is proposed. This phase is manifestly gauge invariant and
can be experimentally tested in interferometry. It leads to well-known results
when the evolution is unitary.Comment: Minor changes; journal reference adde
Geometric phase in open systems: beyond the Markov approximation and weak coupling limit
Beyond the quantum Markov approximation and the weak coupling limit, we
present a general theory to calculate the geometric phase for open systems with
and without conserved energy. As an example, the geometric phase for a
two-level system coupling both dephasingly and dissipatively to its environment
is calculated. Comparison with the results from quantum trajectory analysis is
presented and discussed
Graphical Nonbinary Quantum Error-Correcting Codes
In this paper, based on the nonbinary graph state, we present a systematic
way of constructing good non-binary quantum codes, both additive and
nonadditive, for systems with integer dimensions. With the help of computer
search, which results in many interesting codes including some nonadditive
codes meeting the Singleton bounds, we are able to construct explicitly four
families of optimal codes, namely, , ,
and for any odd dimension and a family of nonadditive code
for arbitrary . In the case of composite numbers as
dimensions, we also construct a family of stabilizer codes for odd , whose coding subspace is {\em not} of a dimension
that is a power of the dimension of the physical subsystem.Comment: 12 pages, 5 figures (pdf
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