5,570 research outputs found
Superspace formulation of general massive gauge theories and geometric interpretation of mass-dependent BRST symmetries
A superspace formulation is proposed for the osp(1,2)-covariant Lagrangian
quantization of general massive gauge theories. The superalgebra os0(1,2) is
considered as subalgebra of sl(1,2); the latter may be considered as the
algebra of generators of the conformal group in a superspace with two
anticommuting coordinates. The mass-dependent (anti)BRST symmetries of proper
solutions of the quantum master equations in the osp(1,2)-covariant formalism
are realized in that superspace as invariance under translations combined with
mass-dependent special conformal transformations. The Sp(2) symmetry - in
particular the ghost number conservation - and the "new ghost number"
conservation are realized as invariance under symplectic rotations and
dilatations, respectively. The transformations of the gauge fields - and of the
full set of necessarily required (anti)ghost and auxiliary fields - under the
superalgebra sl(1,2) are determined both for irreducible and first-stage
reducible theories with closed gauge algebra.Comment: 35 pages, AMSTEX, precision of reference
Final state interaction contribution to the response of confined relativistic particles
We report studies of the response of a massless particle confined by a
potential. At large momentum transfer q it exhibits \tilde{y} or equivalently
Nachtmann \xi scaling, and acquires a constant width independent of q. This
width has a contribution from the final state interactions of the struck
particle, which persists in the q->\infty limit. The width of the response
predicted using plane wave impulse approximation is smaller because of the
neglect of final state interactions in that approximation. However, the exact
response may be obtained by folding the approximate response with a function
representing final state interaction effects. We also study the response
obtained from the momentum distribution assuming that the particle is on the
energy shell both before and after being struck. Quantitative results are
presented for the special case of a linear confining potential. In this case
the response predicted with the on-shell approximation has correct values for
the total strength, mean energy and width, however its shape is wrong.Comment: 11 pages, 3 figures, submitted to Phys. Rev.
Unsupervised classification and areal measurement of land and water coastal features on the Texas coast
Multispectral scanner (MSS) digital data from ERTS-1 was used to delineate coastal land, vegetative, and water features in two portions of the Texas Coastal Zone. Data (Scene ID's 1037-16244 and 1037-16251) acquired on August 29, 1972, were analyzed on NASA Johnson Space Center systems through the use of two clustering algorithms. Seventeen to 30 spectrally homogeneous classes were so defined. Many classes were identified as being pure features such as water masses, salt marsh, beaches, pine, hardwoods, and exposed soil or construction materials. Most classes were identified to be mixtures of the pure class types. Using an objective technique for measuring the percentage of wetland along salt marsh boundaries, an analysis was made of the accuracy of areal measurement of salt marshes. Accuracies ranged from 89 to 99 percent. Aircraft photography was used as the basis for determining the true areal size of salt marshes in the study sites
The Counterpart Principle of Analogical Support by Structural Similarity
We propose and investigate an Analogy Principle in the context of Unary Inductive Logic based on a notion of support by structural similarity which is often employed to motivate scientific conjectures
High efficiency tomographic reconstruction of quantum states by quantum nondemolition measurements
We propose a high efficiency tomographic scheme to reconstruct an unknown
quantum state of the qubits by using a series of quantum nondemolition (QND)
measurements. The proposed QND measurements of the qubits are implemented by
probing the the stationary transmissions of the dispersively-coupled resonator.
It is shown that only one kind of QND measurements is sufficient to determine
all the diagonal elements of the density matrix of the detected quantum state.
The remaining non-diagonal elements of the density matrix can be determined by
other spectral measurements by beforehand transferring them to the diagonal
locations using a series of unitary operations. Compared with the pervious
tomographic reconstructions based on the usual destructively projective (DP)
measurements (wherein one kind of such measurements could only determine one
diagonal element of the density matrix), the present approach exhibits
significantly high efficiency for N-qubit (N > 1). Specifically, our generic
proposal is demonstrated by the experimental circuit-quantumelectrodynamics
(circuit-QED) systems with a few Josephson charge qubits.Comment: 9pages,4figure
Quantum Machines
We discuss quantum information processing machines. We start with single
purpose machines that either redistribute quantum information or identify
quantum states. We then move on to machines that can perform a number of
functions, with the function they perform being determined by a program, which
is itself a quantum state. Examples of both deterministic and probabilistic
programmable machines are given, and we conclude with a discussion of the
utility of quantum programs.Comment: To appear in Contemporary Physic
Phase estimation for thermal Gaussian states
We give the optimal bounds on the phase-estimation precision for mixed
Gaussian states in the single-copy and many-copy regimes. Specifically, we
focus on displaced thermal and squeezed thermal states. We find that while for
displaced thermal states an increase in temperature reduces the estimation
fidelity, for squeezed thermal states a larger temperature can enhance the
estimation fidelity. The many-copy optimal bounds are compared with the minimum
variance achieved by three important single-shot measurement strategies. We
show that the single-copy canonical phase measurement does not always attain
the optimal bounds in the many-copy scenario. Adaptive homodyning schemes do
attain the bounds for displaced thermal states, but for squeezed states they
yield fidelities that are insensitive to temperature variations and are,
therefore, sub-optimal. Finally, we find that heterodyne measurements perform
very poorly for pure states but can attain the optimal bounds for sufficiently
mixed states. We apply our results to investigate the influence of losses in an
optical metrology experiment. In the presence of losses squeezed states cease
to provide Heisenberg limited precision and their performance is close to that
of coherent states with the same mean photon number.Comment: typos correcte
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