1,985 research outputs found
Spin-Orbit Qubits of Rare-Earth-Metal Ions in Axially Symmetric Crystal Fields
Contrary to the well known spin qubits, rare-earth qubits are characterized
by a strong influence of crystal field due to large spin-orbit coupling. At low
temperature and in the presence of resonance microwaves, it is the magnetic
moment of the crystal-field ground-state which nutates (for several s) and
the Rabi frequency is anisotropic. Here, we present a study of the
variations of with the magnitude and direction of the
static magnetic field for the odd Er isotope in a single
crystal CaWO:Er. The hyperfine interactions split the
curve into eight different curves which are fitted
numerically and described analytically. These "spin-orbit qubits" should allow
detailed studies of decoherence mechanisms which become relevant at high
temperature and open new ways for qubit addressing using properly oriented
magnetic fields
Evaluation of superalloy heavy-duty grinding based on multivariate tests
The quality and economy of grinding depend on proper selection of grinding conditions for the materials to be ground. In order to evaluate the effect of heavy-duty grinding, a new performance index, which includes specific material removal rate, size accuracy, and grinding forces, was proposed. Robust design of experiment, including orthogonal arrays, the signal-to-noise ratio (SNR) method, and analysis of variance (ANOVA) for multivariate data, was employed to estimate the effect of uniform experimental design and to optimize grinding parameters. Empirical models of grinding force were investigated for finite element analysis of new fixture design. These empirical models, based on robust design of experiments and multiple regression methodology, have been confirmed through further verification experiments. Correlation coefficients from 0.87 to 0.96 were achieved
Minimal unitary representation of SU(2,2) and its deformations as massless conformal fields and their supersymmetric extensions
We study the minimal unitary representation (minrep) of SO(4,2) over an
Hilbert space of functions of three variables, obtained by quantizing its
quasiconformal action on a five dimensional space. The minrep of SO(4,2), which
coincides with the minrep of SU(2,2) similarly constructed, corresponds to a
massless conformal scalar in four spacetime dimensions. There exists a
one-parameter family of deformations of the minrep of SU(2,2). For positive
(negative) integer values of the deformation parameter \zeta one obtains
positive energy unitary irreducible representations corresponding to massless
conformal fields transforming in (0,\zeta/2) ((-\zeta/2,0)) representation of
the SL(2,C) subgroup. We construct the supersymmetric extensions of the minrep
of SU(2,2) and its deformations to those of SU(2,2|N). The minimal unitary
supermultiplet of SU(2,2|4), in the undeformed case, simply corresponds to the
massless N=4 Yang-Mills supermultiplet in four dimensions. For each given
non-zero integer value of \zeta, one obtains a unique supermultiplet of
massless conformal fields of higher spin. For SU(2,2|4) these supermultiplets
are simply the doubleton supermultiplets studied in arXiv:hep-th/9806042.Comment: Revised with an extended introduction and additional references.
Typos corrected. 49 pages; Latex fil
Simulations of magnetic and magnetoelastic properties of Tb2Ti2O7 in paramagnetic phase
Magnetic and magnetoelastic properties of terbium titanate pyrochlore in
paramagnetic phase are simulated. The magnetic field and temperature
dependences of magnetization and forced magnetostriction in Tb2Ti2O7 single
crystals and polycrystalline samples are calculated in the framework of
exchange charge model of crystal field theory and a mean field approximation.
The set of electron-deformation coupling constants has been determined.
Variations of elastic constants with temperature and applied magnetic field are
discussed. Additional strong softening of the crystal lattice at liquid helium
temperatures in the magnetic field directed along the rhombic symmetry axis is
predicted.Comment: 13 pages, 4 figures, 2 table
One-Parameter Squeezed Gaussian States of Time-Dependent Harmonic Oscillator and Selection Rule for Vacuum States
By using the invariant method we find one-parameter squeezed Gaussian states
for both time-independent and time-dependent oscillators. The squeezing
parameter is expressed in terms of energy expectation value for
time-independent case and represents the degree of mixing positive and negative
frequency solutions for time-dependent case. A {\it minimum uncertainty
proposal} is advanced to select uniquely vacuum states at each moment of time.
We show that the Gaussian states with minimum uncertainty coincide with the
true vacuum state for time-independent oscillator and the Bunch-Davies vacuum
for a massive scalar field in a de Sitter spacetime.Comment: 13 Pages, ReVTeX, no figure
Decoherence window and electron-nuclear cross-relaxation in the molecular magnet V 15
Rabi oscillations in the V_15 Single Molecule Magnet (SMM) embedded in the
surfactant DODA have been studied at different microwave powers. An intense
damping peak is observed when the Rabi frequency Omega_R falls in the vicinity
of the Larmor frequency of protons w_N, while the damping time t_R of
oscillations reaches values 10 times shorter than the phase coherence time t_2
measured at the same temperature. The experiments are interpreted by the N-spin
model showing that t_R is directly associated with the decoherence via
electronic/nuclear spin cross-relaxation in the rotating reference frame. It is
shown that this decoherence is accompanied with energy dissipation in the range
of the Rabi frequencies w_N - sigma_e < Omega_R < w_N, where sigma_e is the
mean super-hyperfine field (in frequency units) induced by protons at SMMs.
Weaker damping without dissipation takes place outside this dissipation window.
Simple local field estimations suggest that this rapid cross-relaxation in
resonant microwave field observed for the first time in SMMV_15 should take
place in other SMMs like Fe_8 and Mn_12 containing protons, too
Supersymmetry of a Nonstationary Pauli Equation
The supersymmetry of the electron in both the nonstationary magnetic and
electric fields in a two-dimensional case is studied. The supercharges which
are the integrals of motion and their algebra are established. Using the
obtained algebra the solutions of nonstationary Pauli equation are generated.Comment: 12 pages, Late
Parity doubling in particle physics
Parity doubling in excited hadrons is reviewed. Parity degeneracy in hadrons
was first experimentally observed 40 years ago. Recently new experimental data
on light mesons caused much excitement and renewed interest to the phenomenon,
which still remains to be enigmatic. The present retrospective review is an
attempt to trace the history of parity doubling phenomenon, thus providing a
kind of introduction to the subject. We begin with early approaches of 1960s
(Regge theory and dynamical symmetries) and end up with the latest trends
(manifestations of broader degeneracies and AdS/QCD). We show the evolution of
various ideas about parity doubling. The experimental evidence for this
phenomenon is scrutinized in the non-strange sector. Some experiments of 1960s
devoted to the search for missing non-strange bosons are re-examined and it is
argued that results of these experiments are encouraging from the modern
perspective.Comment: Version to appear in Int. J. Mod. Phys. A, 63 pages, 9 figure
Time-Dependent Invariants for Dirac Equation and Newton-Wigner Position Operator
For Dirac equation, operator-invariants containing explicit time-dependence
in parallel to known time-dependent invariants of nonrelativistic Schr\"odinger
equation are introduced and discussed. As an example, a free Dirac particle is
considered and new invariants are constructed for it. The integral of motion,
which is initial Newton-Wigner position operator, is obtained explicitly for a
free Dirac particle. For such particle with kick modeled by delta-function of
time, the time-depending integral, which has physical meaning of initial
momentum, is found.Comment: LATEX,21 pages,submitted to Physica Script
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