21,050 research outputs found
Electron-Phonon Interactions for Optical Phonon Modes in Few-Layer Graphene
We present a first-principles study of the electron-phonon (e-ph)
interactions and their contributions to the linewidths for the optical phonon
modes at and K in one to three-layer graphene. It is found that due to
the interlayer coupling and the stacking geometry, the high-frequency optical
phonon modes in few-layer graphene couple with different valence and conduction
bands, giving rise to different e-ph interaction strengths for these modes.
Some of the multilayer optical modes derived from the - mode of
monolayer graphene exhibit slightly higher frequencies and much reduced
linewidths. In addition, the linewidths of K- related modes in
multilayers depend on the stacking pattern and decrease with increasing layer
numbers.Comment: 6 pages,5 figures, submitted to PR
Dynamic aperture studies during collisions in the LHC
The dynamic aperture during collisions in the LHC is mainly determined by the beam-beam interactions and by multipole errors of the high gradient quadrupoles in the interaction regions. The computer code JJIP has been modified to accommodate the LHC lattice configuration and parameters and is employed in this study. Simulations over a range of machine parameters are carried out, and results of preliminary investigation are presented
Preparation of Dicke States in an Ion Chain
We have investigated theoretically and experimentally a method for preparing
Dicke states in trapped atomic ions. We consider a linear chain of ion
qubits that is prepared in a particular Fock state of motion, . The
phonons are removed by applying a laser pulse globally to the qubits, and
converting the motional excitation to flipped spins. The global nature of
this pulse ensures that the flipped spins are shared by all the target ions
in a state that is a close approximation to the Dicke state \D{N}{m}. We
calculate numerically the fidelity limits of the protocol and find small
deviations from the ideal state for and . We have demonstrated
the basic features of this protocol by preparing the state \D{2}{1} in two
Mg target ions trapped simultaneously with an Al
ancillary ion.Comment: 5 pages, 2 figure
Towards experimental entanglement connection with atomic ensembles in the single excitation regime
We present a protocol for performing entanglement connection between pairs of
atomic ensembles in the single excitation regime. Two pairs are prepared in an
asynchronous fashion and then connected via a Bell measurement. The resulting
state of the two remaining ensembles is mapped to photonic modes and a reduced
density matrix is then reconstructed. Our observations confirm for the first
time the creation of coherence between atomic systems that never interacted, a
first step towards entanglement connection, a critical requirement for quantum
networking and long distance quantum communications
Direct measurement of decoherence for entanglement between a photon and stored atomic excitation
Violations of a Bell inequality are reported for an experiment where one of
two entangled qubits is stored in a collective atomic memory for a user-defined
time delay. The atomic qubit is found to preserve the violation of a Bell
inequality for storage times up to 21 microseconds, 700 times longer than the
duration of the excitation pulse that creates the entanglement. To address the
question of the security of entanglement-based cryptography implemented with
this system, an investigation of the Bell violation as a function of the
cross-correlation between the generated nonclassical fields is reported, with
saturation of the violation close to the maximum value allowed by quantum
mechanics.Comment: 4 pages, 3 figures. Minor changes. Published versio
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