26,870 research outputs found
Efficient single-photon-assisted entanglement concentration for partially entangled photon pairs
We present two realistic entanglement concentration protocols (ECPs) for pure
partially entangled photons. A partially entangled photon pair can be
concentrated to a maximally entangled pair with only an ancillary single photon
in a certain probability, while the conventional ones require two copies of
partially entangled pairs at least. Our first protocol is implemented with
linear optics and the second one is implemented with cross-Kerr nonlinearities.
Compared with other ECPs, they do not need to know the accurate coefficients of
the initial state. With linear optics, it is feasible with current experiment.
With cross-Kerr nonlinearities, it does not require the sophisticated
single-photon detectors and can be repeated to get a higher success
probability. Moreover, the second protocol can get the higher entanglement
transformation efficiency and it maybe the most economical one by far.
Meanwhile, both of protocols are more suitable for multi-photon system
concentration, because they need less operations and classical communications.
All these advantages make two protocols be useful in current long-distance
quantum communications
Differential measurement of atmospheric refraction with a telescope with double fields of view
For the sake of complete theoretical research of atmospheric refraction, the
atmospheric refraction under the condition of lower angles of elevation is
still worthy to be analyzed and explored. In some engineering applications, the
objects with larger zenith distance must be observed sometimes. Carrying out
observational research of the atmospheric refraction at lower angles of
elevation has an important significance. It has been considered difficult to
measure the atmospheric refraction at lower angles of elevation. A new idea for
determining atmospheric refraction by utilizing differential measurement with
double fields of view is proposed. Taking the observational principle of
HIPPARCOS satellite as a reference, a schematic prototype with double fields of
view was developed. In August of 2013, experimental observations were carried
out and the atmospheric refractions at lower angles of elevation can be
obtained by the schematic prototype. The measured value of the atmospheric
refraction at the zenith distance of 78.8 degree is , and the
feasibility of differential measurement of atmospheric refraction with double
fields of view was justified. The limitations of the schematic prototype such
as inadequate ability of gathering light, lack of accurate meteorological data
recording and lower automatic level of observation and data processing were
also pointed out, which need to be improved in subsequent work.Comment: 10 pages, 6 figure
Loss Rank Mining: A General Hard Example Mining Method for Real-time Detectors
Modern object detectors usually suffer from low accuracy issues, as
foregrounds always drown in tons of backgrounds and become hard examples during
training. Compared with those proposal-based ones, real-time detectors are in
far more serious trouble since they renounce the use of region-proposing stage
which is used to filter a majority of backgrounds for achieving real-time
rates. Though foregrounds as hard examples are in urgent need of being mined
from tons of backgrounds, a considerable number of state-of-the-art real-time
detectors, like YOLO series, have yet to profit from existing hard example
mining methods, as using these methods need detectors fit series of
prerequisites. In this paper, we propose a general hard example mining method
named Loss Rank Mining (LRM) to fill the gap. LRM is a general method for
real-time detectors, as it utilizes the final feature map which exists in all
real-time detectors to mine hard examples. By using LRM, some elements
representing easy examples in final feature map are filtered and detectors are
forced to concentrate on hard examples during training. Extensive experiments
validate the effectiveness of our method. With our method, the improvements of
YOLOv2 detector on auto-driving related dataset KITTI and more general dataset
PASCAL VOC are over 5% and 2% mAP, respectively. In addition, LRM is the first
hard example mining strategy which could fit YOLOv2 perfectly and make it
better applied in series of real scenarios where both real-time rates and
accurate detection are strongly demanded.Comment: 8 pages, 6 figure
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