177,357 research outputs found
Producing high fidelity single photons with optimal brightness via waveguided parametric down-conversion
Parametric down-conversion (PDC) offers the possibility to control the
fabrication of non-Gaussian states such as Fock states. However, in
conventional PDC sources energy and momentum conservation introduce strict
frequency and photon number correlations, which impact the fidelity of the
prepared state. In our work we optimize the preparation of single-photon Fock
states from the emission of waveguided PDC via spectral filtering. We study the
effect of correlations via photon number resolving detection and quantum
interference. Our measurements show how the reduction of mixedness due to
filtering can be evaluated. Interfering the prepared photon with a coherent
state we establish an experimentally measured fidelity of the produced target
state of 78%.Comment: 15 pages, 10 Figures, published versio
Experimental generation of multi-photon Fock states
We experimentally demonstrate the generation of multi-photon Fock states with
up to three photons in well-defined spatial-temporal modes synchronized with a
classical clock. The states are characterized using quantum optical homodyne
tomography to ensure mode selectivity. The three-photon Fock states are
probabilistically generated by pulsed spontaneous parametric down conversion at
a rate of one per second, enabling complete characterization in 12 hours.Comment: 9 pages, 5 figure
Heralding two- and four-photon path entanglement on chip
Generating quantum entanglement is not only an important scientific endeavor,
but will be essential to realizing quantum-enhanced technologies, in
particular, quantum-enhanced measurements with precision beyond classical
limits. We investigate the heralded generation of multiphoton entanglement for
quantum metrology using a reconfigurable integrated waveguide device in which
projective measurement of auxiliary photons heralds the generation of
path-entangled states. We use four and six-photon inputs, to analyze the
heralding process of two- and four-photon NOON states-a superposition of N
photons in two paths, capable of enabling phase supersensitive measurements at
the Heisenberg limit. Realistic devices will include imperfections; as part of
the heralded state preparation, we demonstrate phase superresolution within our
chip with a state that is more robust to photon loss
Multiband Spectrum Access: Great Promises for Future Cognitive Radio Networks
Cognitive radio has been widely considered as one of the prominent solutions
to tackle the spectrum scarcity. While the majority of existing research has
focused on single-band cognitive radio, multiband cognitive radio represents
great promises towards implementing efficient cognitive networks compared to
single-based networks. Multiband cognitive radio networks (MB-CRNs) are
expected to significantly enhance the network's throughput and provide better
channel maintenance by reducing handoff frequency. Nevertheless, the wideband
front-end and the multiband spectrum access impose a number of challenges yet
to overcome. This paper provides an in-depth analysis on the recent
advancements in multiband spectrum sensing techniques, their limitations, and
possible future directions to improve them. We study cooperative communications
for MB-CRNs to tackle a fundamental limit on diversity and sampling. We also
investigate several limits and tradeoffs of various design parameters for
MB-CRNs. In addition, we explore the key MB-CRNs performance metrics that
differ from the conventional metrics used for single-band based networks.Comment: 22 pages, 13 figures; published in the Proceedings of the IEEE
Journal, Special Issue on Future Radio Spectrum Access, March 201
Low-complexity medium access control protocols for QoS support in third-generation radio access networks
One approach to maximizing the efficiency of
medium access control (MAC) on the uplink in a future wideband
code-division multiple-access (WCDMA)-based third-generation
radio access network, and hence maximize spectral efficiency,
is to employ a low-complexity distributed scheduling control
approach. The maximization of spectral efficiency in third-generation
radio access networks is complicated by the need to
provide bandwidth-on-demand to diverse services characterized
by diverse quality of service (QoS) requirements in an interference
limited environment. However, the ability to exploit the full
potential of resource allocation algorithms in third-generation
radio access networks has been limited by the absence of a metric
that captures the two-dimensional radio resource requirement,
in terms of power and bandwidth, in the third-generation radio
access network environment, where different users may have
different signal-to-interference ratio requirements. This paper
presents a novel resource metric as a solution to this fundamental
problem. Also, a novel deadline-driven backoff procedure has
been presented as the backoff scheme of the proposed distributed
scheduling MAC protocols to enable the efficient support of
services with QoS imposed delay constraints without the need
for centralized scheduling. The main conclusion is that low-complexity
distributed scheduling control strategies using overload
avoidance/overload detection can be designed using the proposed
resource metric to give near optimal performance and thus maintain
a high spectral efficiency in third-generation radio access
networks and that importantly overload detection is superior to
overload avoidance
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