7,447,831 research outputs found
Robust and fragile Werner states in the collective dephasing
We investigate the concurrence and Bell violation of the standard Werner
state or Werner-like states in the presence of collective dephasing. It is
shown that the standard Werner state and certain kinds of Werner-like states
are robust against the collective dephasing, and some kinds of Werner-like
states is fragile and becomes completely disentangled in a finite-time. The
threshold time of complete disentanglement of the fragile Werner-like states is
given. The influence of external driving field on the finite-time
disentanglement of the standard Werner state or Werner-like states is
discussed. Furthermore, we present a simple method to control the stationary
state entanglement and Bell violation of two qubits. Finally, we show that the
theoretical calculations of fidelity based on the initial Werner state
assumption well agree with previous experimental results.Comment: 7 pages, 6 figures, 1 table, RevTex4, Accepted by EPJ
Geometric Phase in Entangled Bipartite Systems
The geometric phase (GP) for bipartite systems in transverse external
magnetic fields is investigated in this paper. Two different situations have
been studied. We first consider two non-interacting particles. The results show
that because of entanglement, the geometric phase is very different from that
of the non-entangled case. When the initial state is a Werner state, the
geometric phase is, in general, zero and moreover the singularity of the
geometric phase may appear with a proper evolution time. We next study the
geometric phase when intra-couplings appear and choose Werner states as the
initial states to entail this discussion. The results show that unlike our
first case, the absolute value of the GP is not zero, and attains its maximum
when the rescaled coupling constant is less than 1. The effect of
inhomogeneity of the magnetic field is also discussed.Comment: 5 pages and to be published in Euro. Phys. J.
Masses and couplings of vector mesons from the pion electromagnetic, weak, and \pi\gamma transition form factors
We analyse the pion electromagnetic, charged-current, and
transition form factors at timelike momentum transfers ,
GeV, using a dispersion approach. We discuss in detail the propagator
matrix of the photon-vector-meson system and define certain reduced amplitudes,
or vertex functions, describing the coupling of this system to final states. We
then apply the derived analytic expressions to the analysis of the recent
, , and data. We find the reduced amplitudes for the coupling of the
photon and vector mesons to two pseudoscalars to be constant, independent of
, in the range considered, indicating a "freezing" of the amplitudes for
GeV. The fit to the form factor data leads to the following values of
the Breit-Wigner resonance masses m_{\rho^-}=775.3\pm 0.8 MeV,
m_{\rho^0}=773.7\pm 0.6 MeV and m_\omega=782.43\pm 0.05 MeV, where the errors
are only statistical.Comment: revtex, 23 page
Accurate spectroscopy of Sr atoms
We report the frequency measurement with an accuracy in the 100 kHz range of
several optical transitions of atomic Sr : at 689 nm, at 688 nm and at 679 nm. Measurements are performed with
a frequency chain based on a femtosecond laser referenced to primary frequency
standards. They allowed the indirect determination with a 70 kHz uncertainty of
the frequency of the doubly forbidden 5s^2^1S_0- 5s5p^3P_0 transition of
Sr at 698 nm and in a second step its direct observation. Frequency
measurements are performed for Sr and Sr, allowing the
determination of , and isotope shifts, as well as the
hyperfine constants.Comment: 12 pages, 16 figure
Determining the Stau Trilinear Coupling A_tau in Supersymmetric Higgs Decays
The measurement of the trilinear couplings A in the part of the Lagrangian
which breaks supersymmetry softly will be a difficult experimental task. In
this report the heavy Higgs decays H,A -> stau_1 stau_2 to stau pairs are
investigated for measuring the stau trilinear coupling A_tau. Based on detailed
simulations of signal and backgrounds for a specific reference point in future
high luminosity e+e- linear collider experiments, it is concluded that the
parameter $_tau can be determined with a precision at the 10% level in the
region of moderate to large tan(beta).Comment: 13 page
Probing dense and hot matter with low-mass dileptons and photons
Results on low-mass dileptons, covering the very broad energy range from the
BEVALAC up to SPS are reviewed. The emphasis is on the open questions raised by
the intriguing results obtained so far and the prospects for addressing them in
the near future with the second generation of experiments, in particular HADES,
NA60 and PHENIX.Comment: 6 pages, 8 figures, Proceedings of Hard Probes 2004 Conference,
Ericeira, November 4-10, 2004. Caption of Figure 2 corrected. To be published
in Eur. Phys. J. C. The orginal version is available at www.springerlink.co
Measurement of the LT-asymmetry in \pi^0 electroproduction at the energy of the \Delta (1232) resonance
The reaction p(e,e'p)pi^0 has been studied at Q^2=0.2 (GeV/c)^2 in the region
of W=1232 MeV. From measurements left and right of q, cross section asymmetries
\rho_LT have been obtained in forward kinematics \rho_LT(\theta_\pi^0=20deg) =
(-11.68 +/- 2.36_stat +/- 2.36_sys)$ and backward kinematics
\rho_LT(\theta_\pi^0=160deg) =(12.18 +/- 0.27_stat +/- 0.82_sys). Multipole
ratios \Re(S_1+^* M_1+)/|M_1+|^2 and \Re(S_0+^* M_1+)/|M_1+|^2 were determined
in the framework of the MAID2003 model. The results are in agreement with older
data. The unusally strong negative \Re(S_0+^* M_1+)/|M_1+|^2 required to bring
also the result of Kalleicher et al. in accordance with the rest of the data is
almost excluded.Comment: 7 pages, 7 figures, 4 tables. Changed content. Accepted for
publication in EPJ
Transport of a quantum degenerate heteronuclear Bose-Fermi mixture in a harmonic trap
We report on the transport of mixed quantum degenerate gases of bosonic 87Rb
and fermionic 40K in a harmonic potential provided by a modified QUIC trap. The
samples are transported over a distance of 6 mm to the geometric center of the
anti-Helmholtz coils of the QUIC trap. This transport mechanism was implemented
by a small modification of the QUIC trap and is free of losses and heating. It
allows all experiments using QUIC traps to use the highly homogeneous magnetic
fields that can be created in the center of a QUIC trap and improves the
optical access to the atoms, e.g., for experiments with optical lattices. This
mechanism may be cascaded to cover even larger distances for applications with
quantum degenerate samples.Comment: 7 pages, 8 figure
Integrable spin-boson interaction in the Tavis-Cummings model from a generic boundary twist
We construct models describing interaction between a spin and a single
bosonic mode using a quantum inverse scattering procedure. The boundary
conditions are generically twisted by generic matrices with both diagonal and
off-diagonal entries. The exact solution is obtained by mapping the transfer
matrix of the spin-boson system to an auxiliary problem of a spin- coupled
to the spin- with general twist of the boundary condition. The corresponding
auxiliary transfer matrix is diagonalized by a variation of the method of
-matrices of Baxter. The exact solution of our problem is obtained applying
certain large- limit to , transforming it into the bosonic algebra.Comment: 6 pages, revtex; 1 figure. To be published in EPJ
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