9,217 research outputs found
Robust quantum repeater with atomic ensembles and single-photon sources
We present a quantum repeater protocol using atomic ensembles, linear optics
and single-photon sources. Two local 'polarization' entangled states of atomic
ensembles and are generated by absorbing a single photon emitted by an
on-demand single-photon sources, based on which high-fidelity local
entanglement between four ensembles can be established efficiently through
Bell-state measurement. Entanglement in basic links and entanglement connection
between links are carried out by the use of two-photon interference. In
addition to being robust against phase fluctuations in the quantum channels,
this scheme may speed up quantum communication with higher fidelity by about 2
orders of magnitude for 1280 km compared with the partial read (PR) protocol
(Sangouard {\it et al.}, Phys. Rev. A {\bf77}, 062301 (2008)) which may
generate entanglement most quickly among the previous schemes with the same
ingredients.Comment: 5 pages 4 figure
Large-field CO(1--0) observations toward the Galactic historical supernova remnants: a large cavity around Tycho's supernova remnant
The investigation of the interaction between the supernova remnants (SNRs)
and interstellar gas is not only necessary to improve our knowledge of SNRs,
but also to understand the nature of the progenitor systems. As a part of the
Milky Way Imaging Scroll Painting CO line survey (MWISP), we study the
interstellar gas surrounding the Galactic historical SNRs, using the PMO
13.7-meter telescope. In this work, we present large-field
(32) and high-sensitivity CO(1-0) molecular line
observations toward Tycho's SNR. The CO observations reveal, from the outside
in, large molecular clouds, stream-like structures, and an inner rim around
Tycho's SNR. We derived the basic properties (column density, mass, and
kinematics) of these objects based on the CO observations. The large molecular
clouds individually show an arc toward the remnant center, outlining a large
cavity with radii of 0.30.6 (or 13 pc 27
pc at a distance of 2.5 kpc) around the remnant. The CO line broadenings and
asymmetries detected in the surrounding clouds, the observed expansion of the
cavity, in concert with enhanced CO(2-1)/(1-0) intensity ratio detected
in previous studies, suggest the interaction of the large cavity with a wind in
the region. After excluding the scenario of a large bubble produced by bright
massive stars, we suggest that the large cavity could be explained by accretion
wind from the progenitor system of Tycho's supernova. Nevertheless, the
possibility of the random distribution of a large cavity around Tycho's SNR
cannot be ruled out thus far. Further observations are needed to confirm the
physical association of the large cavity with Tycho's SNR.Comment: 15 pages, 9 figures, updated according to the A&A proo
Van der Waals phase transition in the framework of holography
Phase structure of the quintessence Reissner-Nordstr\"{o}m-AdS black hole is
probed with the nonlocal observables such as holographic entanglement entropy
and two point correlation function. Our result shows that, as the case of the
thermal entropy, both the observables exhibit the similar Van der Waals-like
phase transition. To reinforce the conclusion, we further check the equal area
law for the first order phase transition and critical exponent of the heat
capacity for the second order phase transition. We also discuss the effect of
the state parameter on the phase structure of the nonlocal observables.Comment: 16 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1511.0038
Holographic Van der Waals-like phase transition in the Gauss-Bonnet gravity
The Van der Waals-like phase transition is observed in temperature-thermal
entropy plane in spherically symmetric charged Gauss-Bonnet-AdS black hole
background. In terms of AdS/CFT, the non-local observables such as holographic
entanglement entropy, Wilson loop, and two point correlation function of very
heavy operators in the field theory dual to spherically symmetric charged
Gauss-Bonnet-AdS black hole have been investigated. All of them exhibit the Van
der Waals-like phase transition for a fixed charge parameter or Gauss-Bonnet
parameter in such gravity background. Further, with choosing various values of
charge or Gauss-Bonnet parameter, the equal area law and the critical exponent
of the heat capacity are found to be consistent with phase structures in
temperature-thermal entropy plane.Comment: Some statements about the analogy between the black hole phase
transition in plane and Van der Waals-like phase transition in
plane are added. This is the published versio
Phase transition of holographic entanglement entropy in massive gravity
The phase structure of holographic entanglement entropy is studied in massive
gravity for the quantum systems with finite and infinite volumes, which in the
bulk is dual to calculate the minimal surface area for a black hole and black
brane respectively. In the entanglement entropytemperature plane, we find
for both the black hole and black brane there is a Van der Waals-like phase
transition as the case in thermal entropytemperature plane. That is, there
is a first order phase transition for the small charge and a second order phase
transition at the critical charge. For the first order phase transition, the
equal area law is checked and for the second order phase transition, the
critical exponent of the heat capacity is obtained. All the results show that
the phase structure of holographic entanglement entropy is the same as that of
thermal entropy regardless of the volume of the spacetime on the boundary.Comment: 15 pages, many figures, some statments are adde
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