663 research outputs found
Efficient Algorithms for Universal Quantum Simulation
A universal quantum simulator would enable efficient simulation of quantum
dynamics by implementing quantum-simulation algorithms on a quantum computer.
Specifically the quantum simulator would efficiently generate qubit-string
states that closely approximate physical states obtained from a broad class of
dynamical evolutions. I provide an overview of theoretical research into
universal quantum simulators and the strategies for minimizing computational
space and time costs. Applications to simulating many-body quantum simulation
and solving linear equations are discussed
Universal simulation of Hamiltonian dynamics for qudits
What interactions are sufficient to simulate arbitrary quantum dynamics in a
composite quantum system? Dodd et al. (quant-ph/0106064) provided a partial
solution to this problem in the form of an efficient algorithm to simulate any
desired two-body Hamiltonian evolution using any fixed two-body entangling
N-qubit Hamiltonian, and local unitaries. We extend this result to the case
where the component systems have D dimensions. As a consequence we explain how
universal quantum computation can be performed with any fixed two-body
entangling N-qudit Hamiltonian, and local unitaries.Comment: 13 pages, an error in the "Pauli-Euclid-Gottesman Lemma" fixed, main
results unchange
Aerial Survey Estimates of Abundance of the Eastern Chukchi Sea Stock of Beluga Whales (Delphinapterus leucas) in 2012
The eastern Chukchi Sea (ECS) stock of beluga whales is one of three stocks in western Alaska that are co-managed by the National Marine Fisheries Service and the Alaska Beluga Whale Committee. Abundance of this stock was estimated as 3710 in 1991 from incomplete data. Analysis of data from satellite-linked time-depth recorders (SDRs) attached to belugas in summer concentration areas of the ECS and Beaufort Sea (BS) stocks provided an overview of beluga distribution and movements and allowed the identification of an area (140Ë W to 157Ë W in the BS) and a time period (19 July â 20 August) in which the distributions of the two stocks do not overlap. Aerial survey data were collected by the Aerial Surveys of Arctic Marine Mammals (ASAMM) project in that region and time period in 2012. We used those data in a line transect analysis that estimated there were 5547 (CV = 0.22) surface-visible belugas in the study area. Data from SDRs were used to develop correction factors to account for animals that were missed because they were either outside of the study area or diving too deep to be seen, resulting in a total abundance estimate of 20 752 (CV = 0.70). The average annual Alaska Native subsistence harvest from the ECS stock (57) is about 0.3% of the population estimate. Without data collected by the ASAMM project and from satellite-linked tags, this analysis would not have been possible. Additional surveys and tagging of ECS belugas are warranted.Le stock de bĂ©lugas de lâest de la mer des Tchouktches (EMT) figure parmi les trois stocks de lâouest de lâAlaska Ă ĂȘtre gĂ©rĂ©s conjointement par le National Marine Fisheries Service et lâAlaska Beluga Whale Committee. Ă partir de donnĂ©es incomplĂštes, lâabondance de ce stock a Ă©tĂ© estimĂ©e Ă 3 710 en 1991. Lâanalyse des donnĂ©es recueillies Ă lâaide dâenregistreurs de profondeur temporelle satellitaires (SDR) fixĂ©s aux bĂ©lugas dans les zones de concentration estivales de lâEMT et de la mer de Beaufort (MB) a permis dâobtenir un aperçu de la rĂ©partition et du dĂ©placement des bĂ©lugas ainsi que de cerner une zone (de 140Ë O Ă 157Ë O dans la MB) et une pĂ©riode (du 19 juillet au 20 aoĂ»t) pour lesquelles la rĂ©partition des deux stocks ne se chevauchent pas. Le projet Aerial Surveys of Arctic Marine Mammals (ASAMM) a permis de recueillir des donnĂ©es Ă partir de levĂ©s aĂ©riens pour la rĂ©gion et la pĂ©riode concernĂ©es en 2012. GrĂące Ă une analyse de lignes interceptĂ©es, ces donnĂ©es ont permis dâestimer quâil y avait 5 547 (CV = 0,22) bĂ©lugas visibles Ă la surface dans la zone Ă lâĂ©tude. Les donnĂ©es en provenance de SDR ont servi Ă mettre au point des facteurs de correction pour tenir compte des bĂ©lugas qui nâont pas Ă©tĂ© captĂ©s, soit parce quâils se trouvaient en dehors de la zone visĂ©e par lâĂ©tude, soit parce quâils plongeaient trop loin pour ĂȘtre vus, ce qui sâest traduit par une estimation totale dâabondance de 20 752 (CV = 0,70) bĂ©lugas. La prise de subsistance annuelle moyenne de stock (57) par les Autochtones de lâAlaska dans lâEMT correspond Ă environ Ă 0,3 % de lâestimation de la population. Cette analyse nâaurait pu ĂȘtre possible sans les donnĂ©es prĂ©levĂ©es par le projet ASAMM et les SDR. Dâautres levĂ©s et lâĂ©tiquetage des bĂ©lugas de lâEMT sâimposent
Universal quantum computation and simulation using any entangling Hamiltonian and local unitaries
What interactions are sufficient to simulate arbitrary quantum dynamics in a
composite quantum system? We provide an efficient algorithm to simulate any
desired two-body Hamiltonian evolution using any fixed two-body entangling
n-qubit Hamiltonian and local unitaries. It follows that universal quantum
computation can be performed using any entangling interaction and local unitary
operations.Comment: Added references to NMR refocusing and to earlier work by Leung et al
and Jones and Knil
Protecting Quantum Information with Entanglement and Noisy Optical Modes
We incorporate active and passive quantum error-correcting techniques to
protect a set of optical information modes of a continuous-variable quantum
information system. Our method uses ancilla modes, entangled modes, and gauge
modes (modes in a mixed state) to help correct errors on a set of information
modes. A linear-optical encoding circuit consisting of offline squeezers,
passive optical devices, feedforward control, conditional modulation, and
homodyne measurements performs the encoding. The result is that we extend the
entanglement-assisted operator stabilizer formalism for discrete variables to
continuous-variable quantum information processing.Comment: 7 pages, 1 figur
Mechanistic investigation of Rh(i)-catalysed asymmetric SuzukiâMiyaura coupling with racemic allyl halides
Understanding how catalytic asymmetric reactions with racemic starting materials can operate would enable new enantioselective cross-coupling reactions that give chiral products. Here we propose a catalytic cycle for the highly enantioselective Rh(I)-catalysed SuzukiâMiyaura coupling of boronic acids and racemic allyl halides. Natural abundance 13C kinetic isotope effects provide quantitative information about the transition-state structures of two key elementary steps in the catalytic cycle, transmetallation and oxidative addition. Experiments with configurationally stable, deuterium-labelled substrates revealed that oxidative addition can happen via syn- or anti-pathways, which control diastereoselectivity. Density functional theory calculations attribute the extremely high enantioselectivity to reductive elimination from a common Rh complex formed from both allyl halide enantiomers. Our conclusions are supported by analysis of the reaction kinetics. These insights into the sequence of bond-forming steps and their transition-state structures will contribute to our understanding of asymmetric Rhâallyl chemistry and enable the discovery and application of asymmetric reactions with racemic substrates
NMR quantum computation with indirectly coupled gates
An NMR realization of a two-qubit quantum gate which processes quantum
information indirectly via couplings to a spectator qubit is presented in the
context of the Deutsch-Jozsa algorithm. This enables a successful comprehensive
NMR implementation of the Deutsch-Jozsa algorithm for functions with three
argument bits and demonstrates a technique essential for multi-qubit quantum
computation.Comment: 9 pages, 2 figures. 10 additional figures illustrating output spectr
Predicting knee osteoarthritis
Treatment options for osteoarthritis (OA) beyond pain relief or total knee replacement are very limited. Because of this, attention has shifted to identifying which factors increase the risk of OA in vulnerable populations in order to be able to give recommendations to delay disease onset or to slow disease progression. The gold standard is then to use principles of risk management, first to provide subject-specific estimates of risk and then to find ways of reducing that risk. Population studies of OA risk based on statistical associations do not provide such individually tailored information. Here we argue that mechanistic models of cartilage tissue maintenance and damage coupled to statistical models incorporating model uncertainty, united within the framework of structural reliability analysis, provide an avenue for bridging the disciplines of epidemiology, cell biology, genetics and biomechanics. Such models promise subject-specific OA risk assessment and personalized strategies for mitigating or even avoiding OA. We illustrate the proposed approach with a simple model of cartilage extracellular matrix synthesis and loss regulated by daily physical activity
On the relationship between continuous- and discrete-time quantum walk
Quantum walk is one of the main tools for quantum algorithms. Defined by
analogy to classical random walk, a quantum walk is a time-homogeneous quantum
process on a graph. Both random and quantum walks can be defined either in
continuous or discrete time. But whereas a continuous-time random walk can be
obtained as the limit of a sequence of discrete-time random walks, the two
types of quantum walk appear fundamentally different, owing to the need for
extra degrees of freedom in the discrete-time case.
In this article, I describe a precise correspondence between continuous- and
discrete-time quantum walks on arbitrary graphs. Using this correspondence, I
show that continuous-time quantum walk can be obtained as an appropriate limit
of discrete-time quantum walks. The correspondence also leads to a new
technique for simulating Hamiltonian dynamics, giving efficient simulations
even in cases where the Hamiltonian is not sparse. The complexity of the
simulation is linear in the total evolution time, an improvement over
simulations based on high-order approximations of the Lie product formula. As
applications, I describe a continuous-time quantum walk algorithm for element
distinctness and show how to optimally simulate continuous-time query
algorithms of a certain form in the conventional quantum query model. Finally,
I discuss limitations of the method for simulating Hamiltonians with negative
matrix elements, and present two problems that motivate attempting to
circumvent these limitations.Comment: 22 pages. v2: improved presentation, new section on Hamiltonian
oracles; v3: published version, with improved analysis of phase estimatio
On Quantum Control via Encoded Dynamical Decoupling
I revisit the ideas underlying dynamical decoupling methods within the
framework of quantum information processing, and examine their potential for
direct implementations in terms of encoded rather than physical degrees of
freedom. The usefulness of encoded decoupling schemes as a tool for engineering
both closed- and open-system encoded evolutions is investigated based on simple
examples.Comment: 12 pages, no figures; REVTeX style. This note collects various
theoretical considerations complementing/motivated by the experimental
demonstration of encoded control by Fortunato et a
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