Search results for "angle"

Orbital character variation of the Fermi surface and doping dependent changes of the dimensionality inBaFe2−xCoxAs2from angle-resolved photoemission …

2010

From a combination of high resolution angle-resolved photoemission spectroscopy and density functional calculations, we derive information on the dimensionality and the orbital character of the electronic states of ${\text{BaFe}}_{2\ensuremath{-}x}{\text{Co}}_{x}{\text{As}}_{2}$. Upon increasing Co doping, the electronic states in the vicinity of the Fermi level take on increasingly three-dimensional character. Both the orbital variation with ${k}_{z}$ and the more three-dimensional nature of the doped compounds have important consequences for the nesting conditions and thus possibly also for the appearance of antiferromagnetic and superconducting phases.

Spin-echo entanglement protection from random telegraph noise

2014

We analyze local spin-echo procedures to protect entanglement between two non-interacting qubits, each subject to pure-dephasing random telegraph noise. For superconducting qubits this simple model captures characteristic features of the effect of bistable impurities coupled to the device. An analytic expression for the entanglement dynamics is reported. Peculiar features related to the non-Gaussian nature of the noise already observed in the single qubit dynamics also occur in the entanglement dynamics for proper values of the ratio $g=v/\gamma$, between the qubit-impurity coupling strength and the switching rate of the random telegraph process, and of the separation between the pulses $\D…

Hydrodynamic Equations of Anisotropic, Polarized, Turbulent Superfluids

2009

Changes in the trajectory of the radio jet in 0735+178?

2001

We present multi-epoch 8.4 and 43 GHz Very Long Baseline Array images of the BL Lac object 0735+178. The images confirm the presence of a twisted jet with two sharp apparent bends of 90$^{\circ}$ within two milliarcseconds of the core, resembling a helix in projection. The observed twisted geometry could be the result of precession of the jet inlet, but is more likely produced by pressure gradients in the external medium through which the jet propagates. Quasi-stationary components are observed at the locations of the 90$^{\circ}$ bends, possibly produced by differential Doppler boosting. Identification of components across epochs, since the earliest VLBI observations of this source in 1979…

THE ACCELERATING JET OF 3C 279

2012

Analysis of the proper motions of the subparsec scale jet of the quasar 3C 279 at 15 GHz with the Very Long Baseline Array shows significant accelerations in four of nine superluminal features. Analysis of these motions is combined with the analysis of flux density light curves to constrain values of Lorentz factor and viewing angle (and their derivatives) for each component. The data for each of these components are consistent with significant changes to the Lorentz factor, viewing angle, and azimuthal angle, suggesting jet bending with changes in speed. We see that for these observed components Lorentz factors are in the range Γ = 10-41, viewing angles are in the range = 0.°1-5.°0, and in…

Geometric efficiency for a parallel-surface source and detector system with at least one axisymmetric surface

2007

Abstract An exact and numerically friendly method is given to calculate the geometric efficiency G of a planar radiation source and cosine detector system. Either the source or the detector, but not necessarily both, must have axial symmetry. For two non-coaxial disks the results are in exact agreement with a recent generalization of Ruby's formula for G. Detailed formulas and sample numerical results are given for a disk combined with rectangles and triangles. A disk and a general polygon can be solved by dividing the polygon into triangles. The method can also be applied to electrical inductance calculations and a solution recently given for the inductance of circular and elliptic loops c…

Teleportation of atomic states via position measurements

2007

We present a scheme for conditionally teleporting an unknown atomic state in cavity QED, which requires two atoms and one cavity mode. The translational degrees of freedom of the atoms are taken into account using the optical Stern-Gerlach model. We show that successful teleportation with probability 1/2 can be achieved through local measurements of the cavity photon number and atomic positions. Neither direct projection onto highly entangled states nor holonomous interaction-time constraints are required.

Theoretical analysis of a realistic atom-chip quantum gate

2006

9 pages, 5 color figures; International audience; We present a detailed, realistic analysis of the implementation of a proposal for a quantum phase gate based on atomic vibrational states, specializing it to neutral rubidium atoms on atom chips. We show how to create a double-well potential with static currents on the atom chips, using for all relevant parameters values that are achieved with present technology. The potential barrier between the two wells can be modified by varying the currents in order to realize a quantum phase gate for qubit states encoded in the atomic external degree of freedom. The gate performance is analyzed through numerical simulations; the operation time is ~10 m…

Entanglement and heat capacity in a two-atom Bose–Hubbard model

2012

Abstract We show that a two-atom Bose–Hubbard model exhibits three different phases in the behavior of thermal entanglement in its parameter space. These phases are demonstrated to be traceable back to the existence of level crossings in the ground state of the same system. Significant similarities between the behaviors of thermal entanglement and heat capacity in the parameter space are brought to light thus allowing to interpret the occurrence and the meaning of all these three phases.

On Interchangeability of Probe-Object Roles in Quantum-Quantum Interaction-Free Measurement

2019

In this paper we examine Interaction-free measurement (IFM) where both the probe and the object are quantum particles. We argue that in this case the description of the measurement procedure must by symmetrical with respect to interchange of the roles of probe and object. A thought experiment is being suggested that helps to determine what does and what doesn't happen to the state of the particles in such a setup. It seems that unlike the case of classical object, here the state of both the probe and the object must change. A possible explanation of this might be that the probe and the object form an entangled pair as a result of non-interaction.