608 research outputs found
Quantum information and physics: Some future directions
I consider some promising future directions for quantum information theory that could influence the development of 21st century physics. Advances in the theory of the distinguishability of superoperators may lead to new strategies for improving the precision of quantum-limited measurements. A better grasp of the properties of multi-partite quantum entanglement may lead to deeper understanding of strongly-coupled dynamics in quantum many-body systems, quantum field theory, and quantum gravity
The evaluation of failure detection and isolation algorithms for restructurable control
Three failure detection and identification techniques were compared to determine their usefulness in detecting and isolating failures in an aircraft flight control system; excluding sensor and flight control computer failures. The algorithms considered were the detection filter, the Generalized Likelihood Ratio test and the Orthogonal Series Generalized Likelihood Ratio test. A modification to the basic detection filter is also considered which uses secondary filtering of the residuals to produce unidirectional failure signals. The algorithms were evaluated by testing their ability to detect and isolate control surface failures in a nonlinear simulation of a C-130 aircraft. It was found that failures of some aircraft controls are difficult to distinguish because they have a similar effect on the dynamics of the vehicle. Quantitative measures for evaluating the distinguishability of failures are considered. A system monitoring strategy for implementing the failure detection and identification techniques was considered. This strategy identified the mix of direct measurement of failures versus the computation of failure necessary for implementation of the technology in an aircraft system
An Event-Based Approach to Distributed Diagnosis of Continuous Systems
Distributed fault diagnosis solutions are becoming necessary due to the complexity of modern engineering systems, and the advent of smart sensors and computing elements. This paper presents a novel event-based approach for distributed diagnosis of abrupt parametric faults in continuous systems, based on a qualitative abstraction of measurement deviations from the nominal behavior. We systematically derive dynamic fault signatures expressed as event-based fault models. We develop a distributed diagnoser design algorithm that uses these models for designing local event-based diagnosers based on global diagnosability analysis. The local diagnosers each generate globally correct diagnosis results locally, without a centralized coordinator, and by communicating a minimal number of measurements between themselves. The proposed approach is applied to a multi-tank system, and results demonstrate a marked improvement in scalability compared to a centralized approach
Quantum computing and the entanglement frontier - Rapporteur talk at the 25th Solvay Conference
Quantum information science explores the frontier of highly complex quantum states,
the "entanglement frontier". This study is motivated by the observation (widely believed
but unproven) that classical systems cannot simulate highly entangled quantum systems
efficiently, and we hope to hasten the day when well controlled quantum systems can
perform tasks surpassing what can be done in the classical world. One way to achieve
such "quantum supremacy" would be to run an algorithm on a quantum computer which
solves a problem with a super-polynomial speedup relative to classical computers, but
there may be other ways that can be achieved sooner, such as simulating exotic quantum
states of strongly correlated matter. To operate a large scale quantum computer reliably
we will need to overcome the debilitating effects of decoherence, which might be done
using "standard" quantum hardware protected by quantum error-correcting codes, or by
exploiting the nonabelian quantum statistics of anyons realized in solid state systems,
or by combining both methods. Only by challenging the entanglement frontier will we
learn whether Nature provides extravagant resources far beyond what the classical world
would allow
Detection of abrupt changes in dynamic systems
Some of the basic ideas associated with the detection of abrupt changes in dynamic systems are presented. Multiple filter-based techniques and residual-based method and the multiple model and generalized likelihood ratio methods are considered. Issues such as the effect of unknown onset time on algorithm complexity and structure and robustness to model uncertainty are discussed
Improving Distributed Diagnosis Through Structural Model Decomposition
Complex engineering systems require efficient fault diagnosis methodologies, but centralized approaches do not scale well, and this motivates the development of distributed solutions. This work presents an event-based approach for distributed diagnosis of abrupt parametric faults in continuous systems, by using the structural model decomposition capabilities provided by Possible Conflicts. We develop a distributed diagnosis algorithm that uses residuals computed by extending Possible Conflicts to build local event-based diagnosers based on global diagnosability analysis. The proposed approach is applied to a multitank system, and results demonstrate an improvement in the design of local diagnosers. Since local diagnosers use only a subset of the residuals, and use subsystem models to compute residuals (instead of the global system model), the local diagnosers are more efficient than previously developed distributed approaches
Generalized multi-photon quantum interference
Non-classical interference of photons lies at the heart of optical quantum
information processing. This effect is exploited in universal quantum gates as
well as in purpose-built quantum computers that solve the BosonSampling
problem. Although non-classical interference is often associated with perfectly
indistinguishable photons this only represents the degenerate case, hard to
achieve under realistic experimental conditions. Here we exploit tunable
distinguishability to reveal the full spectrum of multi-photon non-classical
interference. This we investigate in theory and experiment by controlling the
delay times of three photons injected into an integrated interferometric
network. We derive the entire coincidence landscape and identify transition
matrix immanants as ideally suited functions to describe the generalized case
of input photons with arbitrary distinguishability. We introduce a compact
description by utilizing a natural basis which decouples the input state from
the interferometric network, thereby providing a useful tool for even larger
photon numbers
Boosting Linear-Optical Bell Measurement Success Probability with Pre-Detection Squeezing and Imperfect Photon-Number-Resolving Detectors
Linear optical realizations of Bell state measurement (BSM) on two
single-photon qubits succeed with probability no higher than .
However pre-detection quadrature squeezing, i.e., quantum noise limited phase
sensitive amplification, in the usual linear-optical BSM circuit, can yield
. The ability to achieve has been found to be
critical in resource-efficient realizations of linear optical quantum computing
and all-photonic quantum repeaters. Yet, the aforesaid value of is
not known to be the maximum achievable using squeezing, thereby leaving it open
whether close-to- efficient BSM might be achievable using squeezing as a
resource. In this paper, we report new insights on why squeezing-enhanced BSM
achieves . Using this, we show that the previously-reported at single-mode squeezing strength ---for unambiguous
state discrimination (USD) of all four Bell states---is an experimentally
unachievable point result, which drops to with the slightest
change in . We however show that squeezing-induced boosting of with
USD operation is still possible over a continuous range of , with an
experimentally achievable maximum occurring at , achieving . Finally, deviating from USD operation, we explore a
trade-space between , the probability with which the BSM circuit declares
a "success", versus the probability of error , the probability of an input
Bell state being erroneously identified given the circuit declares a success.
Since quantum error correction could correct for some , this tradeoff
may enable better quantum repeater designs by potentially increasing the
entanglement generation rates with exceeding what is possible with
traditionally-studied USD operation of BSMs.Comment: 13 pages, 10 figure
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