904 research outputs found
Superbunching and Nonclassicality as new Hallmarks of Superradiance
Superradiance, i.e., spontaneous emission of coherent radiation by an
ensemble of identical two-level atoms in collective states introduced by Dicke
in 1954, is one of the enigmatic problems of quantum optics. The startling gist
is that even though the atoms have no dipole moment they radiate with increased
intensity in particular directions. Following the advances in our understanding
of superradiant emission by atoms in entangled states we examine the
quantum statistical properties of superradiance. Such investigations require
the system to have at least two excitations as one needs to explore the
photon-photon correlations of the radiation emitted by such states. We present
specifically results for the spatially resolved photon-photon correlations of
systems prepared in doubly excited states and give conditions when the
atomic system emits nonclassial light. Equally, we derive the conditions for
the occurrence of bunching and even of superbunching, a rare phenomenon
otherwise known only from nonclassical states of light like the squeezed
vacuum. We finally investigate the photon-photon cross correlations of the
spontaneously scattered light and highlight the nonclassicalty of such
correlations.Comment: 14 pages, 7 picture
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The Texas Spoofing Test Battery: Toward a Standard for Evaluating GPS Signal Authentication Techniques
A battery of recorded spoofing scenarios has been compiled
for evaluating civil Global Positioning System (GPS) signal
authentication techniques. The battery can be considered
the data component of an evolving standard meant to
define the notion of spoof resistance for commercial GPS
receivers. The setup used to record the scenarios is described.
A detailed description of each scenario reveals
readily detectable anomalies that spoofing detectors could target to improve GPS securityAerospace Engineering and Engineering Mechanic
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A Testbed for Developing and Evaluating GNSS Signal Authentication Techniques
An experimental testbed has been created for developing
and evaluating Global Navigation Satellite System (GNSS)
signal authentication techniques. The testbed advances the state
of the art in GNSS signal authentication by subjecting candidate
techniques to the strongest publicly-acknowledged GNSS spoofing
attacks. The testbed consists of a real-time phase-coherent GNSS
signal simulator that acts as spoofer, a real-time softwaredefined
GNSS receiver that plays the role of defender, and
post-processing versions of both the spoofer and defender. Two
recently-proposed authentication techniques are analytically and
experimentally evaluated: (1) a defense based on anomalous
received power in a GNSS band, and (2) a cryptographic
defense against estimation-and-replay-type spoofing attacks. The
evaluation reveals weaknesses in both techniques; nonetheless,
both significantly complicate a successful GNSS spoofing attackAerospace Engineering and Engineering Mechanic
Generation of N00N-like interferences with two thermal light sources
Measuring the th-order intensity correlation function of light emitted by
two statistically independent thermal light sources may display N00N-like
interferences of arbitrary order . We show that via a particular
choice of detector positions one can isolate -photon quantum paths where
either all photons are emitted from the same source or photons are
collectively emitted by both sources. The latter superposition displays
N00N-like oscillations with which may serve, e.g., in astronomy, for
imaging two distant thermal sources with -fold increased resolution. We
also discuss slightly modified detection schemes improving the visibility of
the N00N-like interference pattern and present measurements verifying the
theoretical predictions.Comment: 9 pages, 6 figure
Generating Greenberger-Horne-Zeilinger states using multiport splitters
Symmetric multiport splitters are versatile tools in optical quantum
information processing. They can be used for studying multiparticle scattering,
studying distinguishability and mixedness, and also for the generation of
multipartite entangled quantum states. Here, we show that N-photon N-mode
Greenberger-Horne-Zeilinger (GHZ) states can be generated using symmetric
multiport beam splitters. Varying the input states' internal degrees of freedom
and post-selecting onto certain photon-number distributions allows the
probabilistic generation of GHZ states with arbitrary photon numbers. We
present two novel schemes, one for odd and one for even numbers of photons, to
generate GHZ states using symmetric multiport splitters and compare them to a
strategy utilizing a 2N-port network as well as the standard post-selection
method
Experimental entanglement generation using multiport beam splitters
Multi-photon entanglement plays a central role in optical quantum
technologies. One way to entangle two photons is to prepare them in orthogonal
internal states, for example, in two polarisations, and then send them through
a balanced beam splitter. Post-selecting on the cases where there is one photon
in each output port results in a maximally entangled state. This idea can be
extended to schemes for the post-selected generation of larger entangled
states. Typically, switching between different types of entangled states
require different arrangements of beam splitters and so a new experimental
setup. Here, we demonstrate a simple and versatile scheme to generate different
types of genuine tripartite entangled states with only one experimental setup.
We send three photons through a three-port splitter and vary their internal
states before post-selecting on certain output distributions. This results in
the generation of tripartite W, G and GHZ states. We obtain fidelities of up to
with regard to the respective ideal states, confirming a
successful generation of genuine tripartite entanglement
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