3,777 research outputs found
Design of Robust Radar Detectors Through Random Perturbation of the Target Signature
The paper addresses the problem of designing radar detectors more robust than Kelly's detector to possible mismatches of the assumed target signature, but with no performance degradation under matched conditions. The idea is to model the received signal under the signal-plus-noise hypothesis by adding a random component, parameterized via a design covariance matrix, that makes the hypothesis more plausible in presence of mismatches. Moreover, an unknown power of such component, to be estimated from the observables, can lead to no performance loss, under matched conditions. Derivation of the (one-step) GLRT is provided for two choices of the design matrix, obtaining detectors with different complexity and behavior. A third parametric detector is also obtained by an ad-hoc generalization of one of such GLRTs. The analysis shows that the proposed approach can cover a range of different robustness levels that is not achievable by state-of-the-art with the same performance of Kelly's detector under matched conditions
A universal setup for active control of a single-photon detector
The influence of bright light on a single-photon detector has been described
in a number of recent publications. The impact on quantum key distribution
(QKD) is important, and several hacking experiments have been tailored to fully
control single-photon detectors. Special attention has been given to avoid
introducing further errors into a QKD system. We describe the design and
technical details of an apparatus which allows to attack a
quantum-cryptographic connection. This device is capable of controlling
free-space and fiber-based systems and of minimizing unwanted clicks in the
system. With different control diagrams, we are able to achieve a different
level of control. The control was initially targeted to the systems using BB84
protocol, with polarization encoding and basis switching using beamsplitters,
but could be extended to other types of systems. We further outline how to
characterize the quality of active control of single-photon detectors.Comment: 10 pages, 10 figure
Theory of CW lidar aerosol backscatter measurements and development of a 2.1 microns solid-state pulsed laser radar for aerosol backscatter profiling
The performance and calibration of a focused, continuous wave, coherent detection CO2 lidar operated for the measurement of atmospheric backscatter coefficient, B(m), was examined. This instrument functions by transmitting infrared (10 micron) light into the atmosphere and collecting the light which is scattered in the rearward direction. Two distinct modes of operation were considered. In volume mode, the scattered light energy from many aerosols is detected simultaneously, whereas in the single particle mode (SPM), the scattered light energy from a single aerosol is detected. The analysis considered possible sources of error for each of these two cases, and also considered the conditions where each technique would have superior performance. The analysis showed that, within reasonable assumptions, the value of B(m) could be accurately measured by either the VM or the SPM method. The understanding of the theory developed during the analysis was also applied to a pulsed CO2 lidar. Preliminary results of field testing of a solid state 2 micron lidar using a CW oscillator is included
Integrated Photonic Sensing
Loss is a critical roadblock to achieving photonic quantum-enhanced
technologies. We explore a modular platform for implementing integrated
photonics experiments and consider the effects of loss at different stages of
these experiments, including state preparation, manipulation and measurement.
We frame our discussion mainly in the context of quantum sensing and focus
particularly on the use of loss-tolerant Holland-Burnett states for optical
phase estimation. In particular, we discuss spontaneous four-wave mixing in
standard birefringent fibre as a source of pure, heralded single photons and
present methods of optimising such sources. We also outline a route to
programmable circuits which allow the control of photonic interactions even in
the presence of fabrication imperfections and describe a ratiometric
characterisation method for beam splitters which allows the characterisation of
complex circuits without the need for full process tomography. Finally, we
present a framework for performing state tomography on heralded states using
lossy measurement devices. This is motivated by a calculation of the effects of
fabrication imperfections on precision measurement using Holland-Burnett
states.Comment: 19 pages, 7 figure
Parametric infrared tunable laser system
A parametric tunable infrared laser system was built to serve as transmitter for the remote detection and density measurement of pollutant, poisonous, or trace gases in the atmosphere. The system operates with a YAG:Nd laser oscillator amplifier chain which pumps a parametric tunable frequency converter. The completed system produced pulse energies of up to 30 mJ. The output is tunable from 1.5 to 3.6 micrometers at linewidths of 0.2-0.5 /cm (FWHM), although the limits of the tuning range and the narrower line crystals presently in the parametric converter by samples of the higher quality already demonstrated is expected to improve the system performance further
Conditional control of the quantum states of remote atomic memories for quantum networking
Quantum networks hold the promise for revolutionary advances in information
processing with quantum resources distributed over remote locations via
quantum-repeater architectures. Quantum networks are composed of nodes for
storing and processing quantum states, and of channels for transmitting states
between them. The scalability of such networks relies critically on the ability
to perform conditional operations on states stored in separated quantum
memories. Here we report the first implementation of such conditional control
of two atomic memories, located in distinct apparatuses, which results in a
28-fold increase of the probability of simultaneously obtaining a pair of
single photons, relative to the case without conditional control. As a first
application, we demonstrate a high degree of indistinguishability for remotely
generated single photons by the observation of destructive interference of
their wavepackets. Our results demonstrate experimentally a basic principle for
enabling scalable quantum networks, with applications as well to linear optics
quantum computation.Comment: 10 pages, 8 figures; Minor corrections. References updated. Published
at Nature Physics 2, Advanced Online Publication of 10/29 (2006
Novel sources of near- and mid-infrared femtosecond pulses for applications in gas sensing, pulse shaping and material processing
In this thesis the design, construction process and the performance of two femtosecond
optical parametric oscillators and one second–harmonic generation femtosecond
pulse shaper is described. One oscillator was applied to gas sensing
while potential applications of other devices are outlined.
ATi:sapphire oscillator was used to pump a periodically–poled lithium niobate–
based optical parametric oscillator. This signal–resonant device was configured
to produce broadband idler pulses tunable in the range of 2.7–3.4 μm. This wavelength
coverage was matched to the ν3 optical absorption band of methane, and
Fourier–transform spectroscopy of a CH4:N2 mixture was implemented by employing
a mid–IR silica photonic bandgap fibre simultaneously as a gas cell and
an optical waveguide. Methane sensing below a 1% concentration was demonstrated
and the main limiting factors were identified and improvements suggested.
Another optical parametric oscillator was demonstrated which was pumped
by a commercial Yb:fibre master oscillator/power amplifier system and was based
on a periodically–poled lithium niobate crystal. The signal was tunable between
1.42–1.57 μm and was intended as a source for a subsequent project for waveguide
writing in silicon. The oscillator was a novel long–cavity device operating
at 15 MHz. The 130 nJ pump pulse energies allowed for 21 nJ signal pulses at
a pump power of 2 W. The performance of the oscillator was characterised via
temporal and spectral measurements and the next steps of its development are
outlined.
Finally a pulse shaper based on second harmonic generation in a grating–
engineered periodically–poled lithium niobate crystal was demonstrated. Pulses
from a 1.53 μm femtosecond Er:fibre laser were compressed and then used as the
input to the shaper. The performance of the shaper was tested by performing
cross–correlation frequency–resolved optical gating measurements on the output
second harmonic pulses and this confirmed the successful creation of multiple
pulses and other tailored shapes including square and chirped pulses, agreeing
well with theoretical calculations
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