21,351 research outputs found
The Importance of Lawyers in Judge Barksdale\u27s Writings
It is my honor to contribute a piece to this wonderful collection commemorating Judge Barksdale\u27s extraordinary career on the bench. It was truly a privilege to clerk for the Judge and it is no less so to have the opportunity to write a bit about his impact on the law
An MDL approach to the climate segmentation problem
This paper proposes an information theory approach to estimate the number of
changepoints and their locations in a climatic time series. A model is
introduced that has an unknown number of changepoints and allows for series
autocorrelations, periodic dynamics, and a mean shift at each changepoint time.
An objective function gauging the number of changepoints and their locations,
based on a minimum description length (MDL) information criterion, is derived.
A genetic algorithm is then developed to optimize the objective function. The
methods are applied in the analysis of a century of monthly temperatures from
Tuscaloosa, Alabama.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS289 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Quantum Correlations in Nonlocal BosonSampling
Determination of the quantum nature of correlations between two spatially
separated systems plays a crucial role in quantum information science. Of
particular interest is the questions of if and how these correlations enable
quantum information protocols to be more powerful. Here, we report on a
distributed quantum computation protocol in which the input and output quantum
states are considered to be classically correlated in quantum informatics.
Nevertheless, we show that the correlations between the outcomes of the
measurements on the output state cannot be efficiently simulated using
classical algorithms. Crucially, at the same time, local measurement outcomes
can be efficiently simulated on classical computers. We show that the only
known classicality criterion violated by the input and output states in our
protocol is the one used in quantum optics, namely, phase-space
nonclassicality. As a result, we argue that the global phase-space
nonclassicality inherent within the output state of our protocol represents
true quantum correlations.Comment: 5 pages, 1 figure, comments are very welcome
Quantum Correlations and Global Coherence in Distributed Quantum Computing
Deviations from classical physics when distant quantum systems become
correlated are interesting both fundamentally and operationally. There exist
situations where the correlations enable collaborative tasks that are
impossible within the classical formalism. Here, we consider the efficiency of
quantum computation protocols compared to classical ones as a benchmark for
separating quantum and classical resources and argue that the computational
advantage of collaborative quantum protocols in the discrete variable domain
implies the nonclassicality of correlations. By analysing a toy model, it turns
out that this argument implies the existence of quantum correlations distinct
from entanglement and discord. We characterize such quantum correlations in
terms of the net global coherence resources inherent within quantum states and
show that entanglement and discord can be understood as special cases of our
general framework. Finally, we provide an operational interpretation of such
correlations as those allowing two distant parties to increase their respective
local quantum computational resources only using locally incoherent operations
and classical communication.Comment: Minor modifications and correction
Effective slip boundary conditions for flows over nanoscale chemical heterogeneities
We study slip boundary conditions for simple fluids at surfaces with
nanoscale chemical heterogeneities. Using a perturbative approach, we examine
the flow of a Newtonian fluid far from a surface described by a heterogeneous
Navier slip boundary condition. In the far-field, we obtain expressions for an
effective slip boundary condition in certain limiting cases. These expressions
are compared to numerical solutions which show they work well when applied in
the appropriate limits. The implications for experimental measurements and for
the design of surfaces that exhibit large slip lengths are discussed.Comment: 14 pages, 3 figure
What can quantum optics say about computational complexity theory?
Considering the problem of sampling from the output photon-counting
probability distribution of a linear-optical network for input Gaussian states,
we obtain results that are of interest from both quantum theory and the
computational complexity theory point of view. We derive a general formula for
calculating the output probabilities, and by considering input thermal states,
we show that the output probabilities are proportional to permanents of
positive-semidefinite Hermitian matrices. It is believed that approximating
permanents of complex matrices in general is a #P-hard problem. However, we
show that these permanents can be approximated with an algorithm in BPP^NP
complexity class, as there exists an efficient classical algorithm for sampling
from the output probability distribution. We further consider input
squeezed-vacuum states and discuss the complexity of sampling from the
probability distribution at the output.Comment: 5 pages, 1 figur
Adaptive Phase Measurements in Linear Optical Quantum Computation
Photon counting induces an effective nonlinear optical phase shift on certain
states derived by linear optics from single photons. Although this no
nlinearity is nondeterministic, it is sufficient in principle to allow scalable
linear optics quantum computation (LOQC). The most obvious way to encode a
qubit optically is as a superposition of the vacuum and a single photon in one
mode -- so-called "single-rail" logic. Until now this approach was thought to
be prohibitively expensive (in resources) compared to "dual-rail" logic where a
qubit is stored by a photon across two modes. Here we attack this problem with
real-time feedback control, which can realize a quantum-limited phase
measurement on a single mode, as has been recently demonstrated experimentally.
We show that with this added measurement resource, the resource requirements
for single-rail LOQC are not substantially different from those of dual-rail
LOQC. In particular, with adaptive phase measurements an arbitrary qubit state
can be prepared deterministically
Quantum Sampling Problems, BosonSampling and Quantum Supremacy
There is a large body of evidence for the potential of greater computational
power using information carriers that are quantum mechanical over those
governed by the laws of classical mechanics. But the question of the exact
nature of the power contributed by quantum mechanics remains only partially
answered. Furthermore, there exists doubt over the practicality of achieving a
large enough quantum computation that definitively demonstrates quantum
supremacy. Recently the study of computational problems that produce samples
from probability distributions has added to both our understanding of the power
of quantum algorithms and lowered the requirements for demonstration of fast
quantum algorithms. The proposed quantum sampling problems do not require a
quantum computer capable of universal operations and also permit physically
realistic errors in their operation. This is an encouraging step towards an
experimental demonstration of quantum algorithmic supremacy. In this paper, we
will review sampling problems and the arguments that have been used to deduce
when sampling problems are hard for classical computers to simulate. Two
classes of quantum sampling problems that demonstrate the supremacy of quantum
algorithms are BosonSampling and IQP Sampling. We will present the details of
these classes and recent experimental progress towards demonstrating quantum
supremacy in BosonSampling.Comment: Survey paper first submitted for publication in October 2016. 10
pages, 4 figures, 1 tabl
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