1,108 research outputs found
Simulating Z_2 topological insulators with cold atoms in a one-dimensional optical lattice
We propose an experimental scheme to simulate and detect the properties of
time-reversal invariant topological insulators, using cold atoms trapped in
one-dimensional bichromatic optical lattices. This system is described by a
one-dimensional Aubry-Andre model with an additional SU(2) gauge structure,
which captures the essential properties of a two-dimensional Z2 topological
insulator. We demonstrate that topologically protected edge states, with
opposite spin orientations, can be pumped across the lattice by sweeping a
laser phase adiabatically. This process constitutes an elegant way to transfer
topologically protected quantum states in a highly controllable environment. We
discuss how density measurements could provide clear signatures of the
topological phases emanating from our one-dimensional system.Comment: 5 pages +, 3 figures, to appear in Physical Review
Probing Half-odd Topological Number with Cold Atoms in a Non-Abelian Optical Lattice
We propose an experimental scheme to probe the contribution of a single Dirac
cone to the Hall conductivity as half-odd topological number sequence. In our
scheme, the quantum anomalous Hall effect as in graphene is simulated with cold
atoms trapped in an optical lattice and subjected to a laser-induced
non-Abelian gauge field. By tuning the laser intensity to change the gauge
flux, the energies of the four Dirac points in the first Brillouin zone are
shifted with each other and the contribution of the single Dirac cone to the
total atomic Hall conductivity is manifested. We also show such manifestation
can be experimentally probed with atomic density profile measurements.Comment: 5 pages, 3 figure
Generating entanglement of photon-number states with coherent light via cross-Kerr nonlinearity
We propose a scheme for generating entangled states of light fields. This
scheme only requires the cross-Kerr nonlinear interaction between coherent
light-beams, followed by a homodyne detection. Therefore, this scheme is within
the reach of current technology. We study in detail the generation of the
entangled states between two modes, and that among three modes. In addition to
the Bell states between two modes and the W states among three modes, we find
plentiful new kinds of entangled states. Finally, the scheme can be extend to
generate the entangled states among more than three modes.Comment: 2 figure
Kinematics of the Broad-line Region of 3C 273 from a Ten-year Reverberation Mapping Campaign
Despite many decades of study, the kinematics of the broad-line region of
3C~273 are still poorly understood. We report a new, high signal-to-noise,
reverberation mapping campaign carried out from November 2008 to March 2018
that allows the determination of time lags between emission lines and the
variable continuum with high precision. The time lag of variations in H
relative to those of the 5100 Angstrom continuum is days
in the rest frame, which agrees very well with the Paschen- region
measured by the GRAVITY at The Very Large Telescope Interferometer. The time
lag of the H emission line is found to be nearly the same as for
H. The lag of the Fe II emission is days, longer
by a factor of 2 than that of the Balmer lines. The velocity-resolved lag
measurements of the H line show a complex structure which can be
possibly explained by a rotation-dominated disk with some inflowing radial
velocity in the H-emitting region. Taking the virial factor of , we derive a BH mass of and an accretion rate of from the
H line. The decomposition of its images yields a host stellar mass
of , and a ratio of in agreement with the Magorrian relation. In the near
future, it is expected to compare the geometrically-thick BLR discovered by the
GRAVITY in 3C 273 with its spatially-resolved torus in order to understand the
potential connection between the BLR and the torus.Comment: 17 pages, 12 figures, 6 tables, accepted for publication in The
Astrophysical Journa
Scaling of critical connectivity of mobile ad hoc communication networks
In this paper, critical global connectivity of mobile ad hoc communication
networks (MAHCN) is investigated. We model the two-dimensional plane on which
nodes move randomly with a triangular lattice. Demanding the best communication
of the network, we account the global connectivity as a function of
occupancy of sites in the lattice by mobile nodes. Critical phenomena
of the connectivity for different transmission ranges are revealed by
numerical simulations, and these results fit well to the analysis based on the
assumption of homogeneous mixing . Scaling behavior of the connectivity is
found as , where , is
the length unit of the triangular lattice and is the scaling index in
the universal function . The model serves as a sort of site percolation
on dynamic complex networks relative to geometric distance. Moreover, near each
critical corresponding to certain transmission range , there
exists a cut-off degree below which the clustering coefficient of such
self-organized networks keeps a constant while the averaged nearest neighbor
degree exhibits a unique linear variation with the degree k, which may be
useful to the designation of real MAHCN.Comment: 6 pages, 6 figure
Strong quantum fluctuation of vortices in the new superconductor
By using transport and magnetic measurement, the upper critical field
and the irreversibility line has been determined. A
big separation between and has been found showing the
existence of a quantum vortex liquid state induced by quantum fluctuation of
vortices in the new superconductor . Further investigation on the
magnetic relaxation shows that both the quantum tunneling and the thermally
activated flux creep weakly depends on temperature. But when the melting field
is approached, a drastic rising of the relaxation rate is observed.
This may imply that the melting of the vortex matter at a finite temperature is
also induced by the quantum fluctuation of vortices.Comment: 4 pages, 4 figure
Detecting unambiguously non-Abelian geometric phases with trapped ions
We propose for the first time an experimentally feasible scheme to disclose
the noncommutative effects induced by a light-induced non-Abelian gauge
structure with trapped ions. Under an appropriate configuration, a true
non-Abelian gauge potential naturally arises in connection with the geometric
phase associated with two degenerated dark states in a four-state atomic system
interacting with three pulsed laser fields. We show that the population in
atomic state at the end of a composed path formed by two closed loops and
in the parameter space can be significantly different from the composed
counter-ordered path. This population difference is directly induced by the
noncommutative feature of non-Abelian geometric phases and can be detected
unambiguously with current technology.Comment: 6 page
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