16,263 research outputs found
Electronic ripple indicator
Electronic circuit for monitoring excessive ripple voltage on dc power lines senses voltage variations from few millivolts to maximum of 10 volts rms. Instrument is used wherever power supply fluctuations might endanger system operations or damage equipment. Device is inexpensive and easily packaged in small chassis
Thermal resistance measurement techniques study program Final report
Thermal resistance measurement technique development for transistor
A Unified and Generalized Approach to Quantum Error Correction
We present a unified approach to quantum error correction, called operator
quantum error correction. This scheme relies on a generalized notion of
noiseless subsystems that is not restricted to the commutant of the interaction
algebra. We arrive at the unified approach, which incorporates the known
techniques -- i.e. the standard error correction model, the method of
decoherence-free subspaces, and the noiseless subsystem method -- as special
cases, by combining active error correction with this generalized noiseless
subsystem method. Moreover, we demonstrate that the quantum error correction
condition from the standard model is a necessary condition for all known
methods of quantum error correction.Comment: 5 page
Cosmological Models with Shear and Rotation
Cosmological models involving shear and rotation are considered, first in the
General Relat ivistic and then in the Newtonian framework with the aim of
investigating singularities in them by using numerical and analytical
techniques. The dynamics of these rotating models ar e studied. It is shown
that singularities are unavoidable in such models and that the centr ifugal
force arising due to rotation can never overcome the gravitational and shearing
forc e over a length of time.Comment: 17 pages, 6 figures Journal Ref: J. Astrophys. Astr. (1999) 20, 79-8
On rigidly rotating perfect fluid cylinders
The gravitational field of a rigidly rotating perfect fluid cylinder with
gamma- law equation of state is found analytically. The solution has two
parameters and is physically realistic for gamma in the interval (1.41,2].
Closed timelike curves always appear at large distances.Comment: 10 pages, Revtex (galley
Generalization of Quantum Error Correction via the Heisenberg Picture
We show that the theory of operator quantum error correction can be naturally
generalized by allowing constraints not only on states but also on observables.
The resulting theory describes the correction of algebras of observables (and
may therefore suitably be called ``operator algebra quantum error
correction''). In particular, the approach provides a framework for the
correction of hybrid quantum-classical information and it does not require the
state to be entirely in one of the corresponding subspaces or subsystems. We
discuss applications to quantum teleportation and to the study of information
flows in quantum interactions.Comment: 5 pages, preprint versio
Interpretations of the NuTeV
We summarize theoretical explanations of the three discrepancy
between measured by NuTeV and predicted by the Standard Model
global fit. Possible new physics explanations ({\it e.g.} an unmized ) are
not compelling. The discrepancy would be reduced by a positive momentum
asymmetry in the strange sea; present experimental estimates of are
unreliable or incomplete. Upgrading the NuTeV analysis to NLO would alleviate
concerns that the discrepancy is a QCD effect.Comment: (proceedings for the NuFact'02 Workshop); reference and footnote
added, following the NuTeV proceeding
A method to find quantum noiseless subsystems
We develop a structure theory for decoherence-free subspaces and noiseless
subsystems that applies to arbitrary (not necessarily unital) quantum
operations. The theory can be alternatively phrased in terms of the
superoperator perspective, or the algebraic noise commutant formalism. As an
application, we propose a method for finding all such subspaces and subsystems
for arbitrary quantum operations. We suggest that this work brings the
fundamental passive technique for error correction in quantum computing an
important step closer to practical realization.Comment: 5 pages, to appear in Physical Review Letter
The structure of preserved information in quantum processes
We introduce a general operational characterization of information-preserving
structures (IPS) -- encompassing noiseless subsystems, decoherence-free
subspaces, pointer bases, and error-correcting codes -- by demonstrating that
they are isometric to fixed points of unital quantum processes. Using this, we
show that every IPS is a matrix algebra. We further establish a structure
theorem for the fixed states and observables of an arbitrary process, which
unifies the Schrodinger and Heisenberg pictures, places restrictions on
physically allowed kinds of information, and provides an efficient algorithm
for finding all noiseless and unitarily noiseless subsystems of the process
- …