27,841 research outputs found
GMOR-like relation in IR-conformal gauge theories
A generalization of the GMOR relation to the case of infrared-conformal gauge
theories is discussed. The starting point is the chiral Ward identity
connecting the isovector pseudoscalar susceptibility to the chiral condensate,
in a mass-deformed theory. A renormalization-group analysis shows that the
pseudoscalar susceptibility is not saturated by the lightest state, but a
contribution from the continuum part of the spectrum survives in the chiral
limit. The computation also shows how infrared-conformal gauge theories behave
differently, depending on whether the anomalous dimension of the chiral
condensate be smaller or larger than 1.Comment: 28 pages, 1 PDF figur
An analysis of mixed integer linear sets based on lattice point free convex sets
Split cuts are cutting planes for mixed integer programs whose validity is
derived from maximal lattice point free polyhedra of the form called split sets. The set obtained by adding all
split cuts is called the split closure, and the split closure is known to be a
polyhedron. A split set has max-facet-width equal to one in the sense that
. In this paper
we consider using general lattice point free rational polyhedra to derive valid
cuts for mixed integer linear sets. We say that lattice point free polyhedra
with max-facet-width equal to have width size . A split cut of width
size is then a valid inequality whose validity follows from a lattice point
free rational polyhedron of width size . The -th split closure is the set
obtained by adding all valid inequalities of width size at most . Our main
result is a sufficient condition for the addition of a family of rational
inequalities to result in a polyhedral relaxation. We then show that a
corollary is that the -th split closure is a polyhedron. Given this result,
a natural question is which width size is required to design a finite
cutting plane proof for the validity of an inequality. Specifically, for this
value , a finite cutting plane proof exists that uses lattice point free
rational polyhedra of width size at most , but no finite cutting plane
proof that only uses lattice point free rational polyhedra of width size
smaller than . We characterize based on the faces of the linear
relaxation
Exobiology on Mars
Descriptions of several instrument concepts that were generated during a workshop entitled, Exobiology Instrument Concepts for a Soviet Mars 94/94 Mission, held at NASA Ames Research Center in 1989 are presented. The objective was to define and describe instrument concepts for exobiology and related science that would be compatible with the mission types under discussion for the 1994 and 1996 Soviet Mars missions. Experiments that use existing technology were emphasized. The concepts discussed could also be used on U.S. missions that follow Mars Observer
Quantum Cloning of Binary Coherent States - Optimal Transformations and Practical Limits
The notions of qubits and coherent states correspond to different physical
systems and are described by specific formalisms. Qubits are associated with a
two-dimensional Hilbert space and can be illustrated on the Bloch sphere. In
contrast, the underlying Hilbert space of coherent states is
infinite-dimensional and the states are typically represented in phase space.
For the particular case of binary coherent state alphabets these otherwise
distinct formalisms can equally be applied. We capitalize this formal
connection to analyse the properties of optimally cloned binary coherent
states. Several practical and near-optimal cloning schemes are discussed and
the associated fidelities are compared to the performance of the optimal
cloner.Comment: 12 pages, 12 figure
Experimental test of strongly non-classical character of a noisy squeezed single-photon state
We experimentally verify the quantum non-Gaussian character of a
conditionally generated noisy squeezed single-photon state with positive Wigner
function. Employing an optimized witness based on probabilities of squeezed
vacuum and squeezed single-photon states we prove that the state cannot be
expressed as a mixture of Gaussian states. In our experiment, the non-Gaussian
state is generated by conditional subtraction of a single photon from squeezed
vacuum state. The state is probed with a homodyne detector and the witness is
determined by averaging a suitable pattern function over the measured homodyne
data. Our experimental results are in good agreement with a theoretical fit
obtained from a simple yet realistic model of the experimental setup.Comment: 10 pages, 8 figures, REVTeX
Experimental determination of the degree of quantum polarisation of continuous variable states
We demonstrate excitation-manifold resolved polarisation characterisation of
continuous-variable (CV) quantum states. In contrast to traditional
characterisation of polarisation that is based on the Stokes parameters, we
experimentally determine the Stokes vector of each excitation manifold
separately. Only for states with a given photon number does the methods
coincide. For states with an indeterminate photon number, for example Gaussian
states, the employed method gives a richer and more accurate description. We
apply the method both in theory and in experiment to some common states to
demonstrate its advantages.Comment: 5 page
Squeezed state purification with linear optics and feed forward
A scheme for optimal and deterministic linear optical purification of mixed
squeezed Gaussian states is proposed and experimentally demonstrated. The
scheme requires only linear optical elements and homodyne detectors, and allows
the balance between purification efficacy and squeezing degradation to be
controlled. One particular choice of parameters gave a ten-fold reduction of
the thermal noise with a corresponding squeezing degradation of only 11%. We
prove optimality of the protocol, and show that it can be used to enhance the
performance of quantum informational protocols such as dense coding and
entanglement generation.Comment: 4 pages, 3 figure
Continuous-wave spatial quantum correlations of light induced by multiple scattering
We present theoretical and experimental results on spatial quantum
correlations induced by multiple scattering of nonclassical light. A continuous
mode quantum theory is derived that enables determining the spatial quantum
correlation function from the fluctuations of the total transmittance and
reflectance. Utilizing frequency-resolved quantum noise measurements, we
observe that the strength of the spatial quantum correlation function can be
controlled by changing the quantum state of an incident bright squeezed-light
source. Our results are found to be in excellent agreement with the developed
theory and form a basis for future research on, e.g., quantum interference of
multiple quantum states in a multiple scattering medium.Comment: 8 pages, 6 figure
Band structure analysis of the conduction-band mass anisotropy in 6H and 4H SiC
The band structures of 6H and 4H SiC calculated by means of the FP-LMTO
method are used to determine the effective mass tensors for their
conduction-band minima. The results are shown to be consistent with recent
optically detected cyclotron resonance measurements and predict an unusual band
filling dependence for 6H-SiC.Comment: 5 pages including 4 postscript figures incorporated with epsfig figs.
available as part 2: sicfig.uu self-extracting file to appear in Phys. Rev.
B: Aug. 15 (Rapid Communications
- …