3,184 research outputs found
Leader neurons in leaky integrate and fire neural network simulations
Several experimental studies show the existence of leader neurons in
population bursts of 2D living neural networks. A leader neuron is, basically,
a neuron which fires at the beginning of a burst (respectively network spike)
more often that we expect by looking at its whole mean neural activity. This
means that leader neurons have some burst triggering power beyond a simple
statistical effect. In this study, we characterize these leader neuron
properties. This naturally leads us to simulate neural 2D networks. To build
our simulations, we choose the leaky integrate and fire (lIF) neuron model. Our
lIF model has got stable leader neurons in the burst population that we
simulate. These leader neurons are excitatory neurons and have a low membrane
potential firing threshold. Except for these two first properties, the
conditions required for a neuron to be a leader neuron are difficult to
identify and seem to depend on several parameters involved in the simulations
themself. However, a detailed linear analysis shows a trend of the properties
required for a neuron to be a leader neuron. Our main finding is: A leader
neuron sends a signal to many excitatory neurons as well as to a few inhibitory
neurons and a leader neuron receives only a few signals from other excitatory
neurons. Our linear analysis exhibits five essential properties for leader
neurons with relative importance. This means that considering a given neural
network with a fixed mean number of connections per neuron, our analysis gives
us a way of predicting which neuron can be a good leader neuron and which
cannot. Our prediction formula gives us a good statistical prediction even if,
considering a single given neuron, the success rate does not reach hundred
percent.Comment: 25 pages, 13 figures, 2 table
The speed of quantum information and the preferred frame: analysis of experimental data
The results of EPR experiments performed in Geneva are analyzed in the frame
of the cosmic microwave background radiation, generally considered as a good
candidate for playing the role of preferred frame. We set a lower bound for the
speed of quantum information in this frame at 1.5 x 10^4 c.Comment: 9 pages including 3 figure
Fast and User-friendly Quantum Key Distribution
Some guidelines for the comparison of different quantum key distribution
experiments are proposed. An improved 'plug & play' interferometric system
allowing fast key exchange is then introduced. Self-alignment and compensation
of birefringence remain. Original electronics implementing the BB84 protocol
and allowing user-friendly operation is presented. Key creation with 0.1 photon
per pulse at a rate of 486 Hz with a 5.4% QBER - corresponding to a net rate of
210Hz - over a 23 Km installed cable was performed.Comment: 21 pages, 6 figures, added referenc
Tunable Up-Conversion Photon Detector
We introduce a simple approach for a tunable up-conversion detector. This
scheme is relevant for both single photon detection or anywhere where low light
levels at telecom wavelengths need to be detected with a high degree of
temporal resolution or where high count rates are desired. A system combining a
periodically poled Lithium niobate waveguide for the nonlinear wavelength
conversion and a low jitter Silicon avalanche photodiode are used in
conjunction with a tunable pump source. We report more than a ten-fold increase
in the detectable bandwidth using this tuning scheme.Comment: 3 pages, 3 figures, Accepted for publication in AP
Intrinsically stable light source at telecom wavelengths
We present a highly stable light source at telecom wavelengths, based on a
short erbium doped fiber. The high stability arises from the high inversion of
the Er3+ion population. This source is developed to work as a stable reference
in radiometric applications and is useful in any application where high
stability and/or a large bandwidth are necessary. The achieved long-term
stability is 10 ppm
Long-distance Bell-type tests using energy-time entangled photons
Long-distance Bell-type experiments are presented. The different experimental
challenges and their solutions in order to maintain the strong quantum
correlations between energy-time entangled photons over more than 10 km are
reported and the results analyzed from the point of view of tests of
fundamental physics as well as from the more applied side of quantum
communication, specially quantum key distribution. Tests using more than one
analyzer on each side are also presented.Comment: 22 pages including 7 figures and 5 table
A high-speed multi-protocol quantum key distribution transmitter based on a dual-drive modulator
We propose a novel source based on a dual-drive modulator that is adaptable
and allows Alice to choose between various practical quantum key distribution
(QKD) protocols depending on what receiver she is communicating with.
Experimental results show that the proposed transmitter is suitable for
implementation of the Bennett and Brassard 1984 (BB84), coherent one-way (COW)
and differential phase shift (DPS) protocols with stable and low quantum bit
error rate. This could become a useful component in network QKD, where
multi-protocol capability is highly desirable.Comment: 15 pages, 7 figure
Practical fast gate rate InGaAs/InP single-photon avalanche photodiodes
We present a practical and easy-to-implement method for high-speed near
infrared single-photon detection based on InGaAs/InP single-photon avalanche
photodiodes (SPADs), combining aspects of both sine gating and
self-differencing techniques. At a gating frequency of 921 MHz and temperature
of -30 C we achieve: a detection efficiency of 9.3 %, a dark count
probability of 2.8 ns, while the afterpulse probability
is 1.6 ns, with a 10 ns "count-off time" setting. In
principle, the maximum count rate of the SPAD can approach 100 MHz, which can
significantly improve the performance for diverse applications.Comment: 3 pages and a few lines, 5 figures, 1 table. Accepted by Applied
Physics Letter
Quantum random number generation on a mobile phone
Quantum random number generators (QRNGs) can significantly improve the
security of cryptographic protocols, by ensuring that generated keys cannot be
predicted. However, the cost, size, and power requirements of current QRNGs has
prevented them from becoming widespread. In the meantime, the quality of the
cameras integrated in mobile telephones has improved significantly, so that now
they are sensitive to light at the few-photon level. We demonstrate how these
can be used to generate random numbers of a quantum origin
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