1,549 research outputs found
Dark pair coherent states of the motion of a trapped ion
We propose a scheme for generating vibrational pair coherent states of the
motion of an ion in a two-dimensional trap. In our scheme, the trapped ion is
excited bichromatically by three laser beams along different directions in the
X-Y plane of the ion trap. We show that if the initial vibrational state is
given by a two-mode Fock state, the final steady state, indicated by the
extinction of the fluorescence emitted by the ion, is a pure state. The
motional state of the ion in the equilibrium realizes that of the
highly-correlated pair coherent state.Comment: 14 pages, 3 figure
Decoherence and robustness of parity-dependent entanglement in the dynamics of a trapped ion
We study the entanglement between the 2D vibrational motion and two ground
state hyperfine levels of a trapped ion, Under particular conditions this
entanglement depends on the parity of the total initial vibrational quanta. We
study the robustness of this quantum coherence effect with respect to the
presence of non-dissipative sources of decoherence, and of an imperfect initial
state preparation.Comment: 13 pages, 5 figure
GeV Emission from TeV Blazars and Intergalactic Magnetic Fields
Several high-frequency peaked BL Lac objects such as Mrk 501 are strong TeV
emitters. However, a significant fraction of the TeV gamma rays emitted are
likely to be absorbed in interactions with the diffuse IR background, yielding
electron-positron pairs. Hence, the observed TeV spectrum must be steeper than
the intrinsic one. Using the recently derived intrinsic -ray spectrum
of Mrk 501 during its 1997 high state, we study the inverse-Compton scattering
of cosmic microwave photons by the resulting electron-positron pairs, which
implies the existence of a hitherto undiscovered GeV emission. The typical
duration of the GeV emission is determined by the flaring activity time and the
energy-dependent magnetic deflection time. We numerically calculate the
scattered photon spectrum for different intergalactic magnetic field (IGMF)
strengths, and find a spectral turnover and flare duration at GeV energies
which are dependent on the field strength. We also estimate the scattered
photon flux in the quiescent state of Mrk 501. The GeV flux levels predicted
are consistent with existing EGRET upper limits, and should be detectable above
the synchrotron -- self Compton (SSC) component with the {\em Gamma-Ray Large
Area Space Telescope} ({\em GLAST}) for IGMFs G, as
expected in voids. Such detections would provide constraints on the strength of
weak IGMFs.Comment: ApJL in press, expanded version with one extra figur
The early high-energy afterglow emission from Short GRBs
We calculate the high energy afterglow emission from short Gamma-Ray Bursts
(SGRBs) in the external shock model. There are two possible components
contributing to the high energy afterglow: the electron synchrotron emission
and the synchrotron self-Compton (SSC) emission. We find that for typical
parameter values of SGRBs, the early high-energy afterglow emission in 10
MeV-10 GeV is dominated by the synchrotron emission. For a burst occurring at
redshift z =0.1, the high-energy emission can be detectable by Fermi LAT if the
blast wave has an energy E>=10^51 ergs and the fraction of energy in electrons
is \epsilon_e>=0.1 . This provides a possible explanation for the high energy
tail of SGRB 081024B.Comment: 5 pages, 5 figures. This is a slightly expanded version of the paper
that will appear in Science in China Series
Nonlinear Decoherence in Quantum State Preparation of a Trapped Ion
We present a nonlinear decoherence model which models decoherence effect
caused by various decohereing sources in a quantum system through a nonlinear
coupling between the system and its environment, and apply it to investigating
decoherence in nonclassical motional states of a single trapped ion. We obtain
an exactly analytic solution of the model and find very good agreement with
experimental results for the population decay rate of a single trapped ion
observed in the NIST experiments by Meekhof and coworkers (D. M. Meekhof, {\it
et al.}, Phys. Rev. Lett. {\bf 76}, 1796 (1996)).Comment: 5 pages, Revte
Quantum mechanical counterpart of nonlinear optics
Raman-type laser excitation of a trapped atom allows one to realize the
quantum mechanical counterpart of phenomena of nonlinear optics, such as
Kerr-type nonlinearities, parametric amplification, and multi-mode mixing.
Additionally, huge nonlinearities emerge from the interference of the atomic
wave function with the laser waves. They lead to a partitioning of the phase
space accompanied by a significantly different action of the time evolution in
neighboring phase-space zones. For example, a nonlinearly modified coherent
"displacement" of the motional quantum state may induce strong amplitude
squeezing and quantum interferences.Comment: 6 pages, 4 figures, to be published in Phys. Rev. A 55 (June
Proposal for measurment of harmonic oscillator Berry phase in ion traps
We propose a scheme for measuring the Berry phase in the vibrational degree
of freedom of a trapped ion. Starting from the ion in a vibrational coherent
state we show how to reverse the sign of the coherent state amplitude by using
a purely geometric phase. This can then be detected through the internal
degrees of freedom of the ion. Our method can be applied to preparation of
Schr\"odinger cat states.Comment: Replaced with revised versio
Next to leading order spin-orbit effects in the motion of inspiralling compact binaries
Using effective field theory (EFT) techniques we calculate the
next-to-leading order (NLO) spin-orbit contributions to the gravitational
potential of inspiralling compact binaries. We use the covariant spin
supplementarity condition (SSC), and explicitly prove the equivalence with
previous results by Faye et al. in arXiv:gr-qc/0605139. We also show that the
direct application of the Newton-Wigner SSC at the level of the action leads to
the correct dynamics using a canonical (Dirac) algebra. This paper then
completes the calculation of the necessary spin dynamics within the EFT
formalism that will be used in a separate paper to compute the spin
contributions to the energy flux and phase evolution to NLO.Comment: 25 pages, 4 figures, revtex4. v2: minor changes, refs. added. To
appear in Class. Quant. Gra
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