5,900 research outputs found
Quantum information reclaiming after amplitude damping
We investigate the quantum information reclaim from the environment after
amplitude damping has occurred. In particular we address the question of
optimal measurement on the environment to perform the best possible correction
on two and three dimensional quantum systems. Depending on the dimension we
show that the entanglement fidelity (the measure quantifying the correction
performance) is or is not the same for all possible measurements and uncover
the optimal measurement leading to the maximum entanglement fidelity
Universal Programmable Quantum Circuit Schemes to Emulate an Operator
Unlike fixed designs, programmable circuit designs support an infinite number
of operators. The functionality of a programmable circuit can be altered by
simply changing the angle values of the rotation gates in the circuit. Here, we
present a new quantum circuit design technique resulting in two general
programmable circuit schemes. The circuit schemes can be used to simulate any
given operator by setting the angle values in the circuit. This provides a
fixed circuit design whose angles are determined from the elements of the given
matrix-which can be non-unitary-in an efficient way. We also give both the
classical and quantum complexity analysis for these circuits and show that the
circuits require a few classical computations. They have almost the same
quantum complexities as non-general circuits. Since the presented circuit
designs are independent from the matrix decomposition techniques and the global
optimization processes used to find quantum circuits for a given operator, high
accuracy simulations can be done for the unitary propagators of molecular
Hamiltonians on quantum computers. As an example, we show how to build the
circuit design for the hydrogen molecule.Comment: combined with former arXiv:1207.174
Trends in stratospheric minor constituents
Photochemical models predict that increasing source gas concentrations are also expected to lead to changes in the concentrations of both catalytically active radical species (such as NO2, ClO, and OH) and inactive reservoir species (such as HNO3, HCl, and H2O). For simplicity, we will refer to all these as trace species. Those species that are expected to have increasing concentration levels are investigated. Additionally, the trace species concentration levels are monitored for unexpected changes on the basis of the measure increase in source gases. Carrying out these investigations is difficult due to the limited data base of measurements of stratospheric trace species. In situ measurements are made only infrequently, and there are few satelliteborne measurements, most over a time space insufficient for trend determination. Instead, ground-based measurements of column content must be used for many species, and interpretation is complicated by contributions from the troposphere or mesosphere or both. In this chapter, we examine existing measurements as published or tabulated
State-space distribution and dynamical flow for closed and open quantum systems
We present a general formalism for studying the effects of dynamical
heterogeneity in open quantum systems. We develop this formalism in the state
space of density operators, on which ensembles of quantum states can be
conveniently represented by probability distributions. We describe how this
representation reduces ambiguity in the definition of quantum ensembles by
providing the ability to explicitly separate classical and quantum sources of
probabilistic uncertainty. We then derive explicit equations of motion for
state space distributions of both open and closed quantum systems and
demonstrate that resulting dynamics take a fluid mechanical form analogous to a
classical probability fluid on Hamiltonian phase space, thus enabling a
straightforward quantum generalization of Liouville's theorem. We illustrate
the utility of our formalism by analyzing the dynamics of an open two-level
system using the state-space formalism that are shown to be consistent with the
derived analytical results
Mixing Times in Quantum Walks on Two-Dimensional Grids
Mixing properties of discrete-time quantum walks on two-dimensional grids
with torus-like boundary conditions are analyzed, focusing on their connection
to the complexity of the corresponding abstract search algorithm. In
particular, an exact expression for the stationary distribution of the coherent
walk over odd-sided lattices is obtained after solving the eigenproblem for the
evolution operator for this particular graph. The limiting distribution and
mixing time of a quantum walk with a coin operator modified as in the abstract
search algorithm are obtained numerically. On the basis of these results, the
relation between the mixing time of the modified walk and the running time of
the corresponding abstract search algorithm is discussed.Comment: 11 page
Liquid-like behaviour of gold nanowire bridges
A combination of Focused Ion Beam (FIB) and Reactive Ion Etch (RIE) was used to fabricate free standing gold nanowire bridges with radii of 30 nm and below. These were subjected to point loading to failure at their mid-points using an Atomic Force Microscope (AFM), providing strength and deformation data. The results demonstrate a dimensionally dependent transition from conventional solid metallic properties to liquid-like behaviour including the unexpected reformation of a fractured bridge. The work reveals mechanical and materials properties of nanowires which could have significant impact on nanofabrication processes and nanotechnology devices such as Nano Electro Mechanical Systems (NEMS)
The Formal Dynamism of Categories: Stops vs. Fricatives, Primitivity vs. Simplicity
Minimalist Phonology (MP; Pöchtrager 2006) constructs its theory based on the phonological epistemological principle (Kaye 2001) and exposes the arbitrary nature of standard Government Phonology (sGP) and strict-CV (sCV), particularly with reference to their confusion of melody and structure.
For Pöchtrager, these are crucially different, concluding that place of articulation is melodic (expressed with elements), while manner of articulation is structural. In this model, the heads (xN and xO) can license and incorporate the length of the other into their own interpretation, that is xN influences xO projections as well as its own and vice versa. This dynamism is an aspect of the whole framework and this paper in particular will show that stops and fricatives evidence a plasticity of category and that, although fricatives are simpler in structure, stops are the more primitive of the two.
This will be achieved phonologically through simply unifying the environment of application of the licensing forces within Pöchtrager's otherwise sound onset structure. In doing so, we automatically make several predictions about language acquisition and typology and show how lenition in Qiang (Sino-Tibetan) can be more elegantly explained
Single-qubit unitary gates by graph scattering
We consider the effects of plane-wave states scattering off finite graphs, as
an approach to implementing single-qubit unitary operations within the
continuous-time quantum walk framework of universal quantum computation. Four
semi-infinite tails are attached at arbitrary points of a given graph,
representing the input and output registers of a single qubit. For a range of
momentum eigenstates, we enumerate all of the graphs with up to vertices
for which the scattering implements a single-qubit gate. As increases, the
number of new unitary operations increases exponentially, and for the
majority correspond to rotations about axes distributed roughly uniformly
across the Bloch sphere. Rotations by both rational and irrational multiples of
are found.Comment: 8 pages, 7 figure
Initial carbon, nitrogen, and phosphorus fluxes following ponderosa pine restoration treatments
Southwestern ponderosa pine forests were dramatically altered by fire regime disruption that accompanied Euro-American settlement in the 1800s. Major changes include increased tree density, diminished herbaceous cover, and a shift from a frequent lowintensity fire regime to a stand-replacing fire regime. Ecological restoration via thinning and prescribed burning is being widely applied to return forests to the pre-settlement condition, but the effects of restoration on ecosystem function are unknown. We measured carbon (C), nitrogen (N), and phosphorus (P) fluxes during the first two years after the implementation of a replicated field experiment comparing thinning and composite (thinning, forest floor fuel reduction, and prescribed burning) restoration treatments to untreated controls in a ponderosa pine forest in northern Arizona, USA. Total net primary productivity (260 g Cm22yr21) was similar among treatments because a 3050(percent) decrease in pine foliage and fine-root production in restored ecosystems was balanced by greater wood, coarse root, and herbaceous production. Herbaceous plants accounted for ,20(percent) of total plant C, N, and P uptake in the controls but from 25(percent) to 70(percent) in restored plots. Total plant N uptake was ;3 g Nm22yr21 in all treatments, but net N mineralization was just one-half and twothirds of this value in the control and composite restoration, respectively. Element flux rates in controls generally declined more in a drought year than rates in restoration treatments. In this ponderosa pine forest, ecological restoration that emulated pre-settlement stand structure and fire characteristics had a small effect on plant C, N, and P fluxes at the whole ecosystem level because lower pine foliage and fine-root fluxes in treated plots (compared to controls) were approximately balanced by higher fluxes in wood and herbaceous plants
Simulation of Classical Thermal States on a Quantum Computer: A Transfer Matrix Approach
We present a hybrid quantum-classical algorithm to simulate thermal states of
a classical Hamiltonians on a quantum computer. Our scheme employs a sequence
of locally controlled rotations, building up the desired state by adding qubits
one at a time. We identify a class of classical models for which our method is
efficient and avoids potential exponential overheads encountered by Grover-like
or quantum Metropolis schemes. Our algorithm also gives an exponential
advantage for 2D Ising models with magnetic field on a square lattice, compared
with the previously known Zalka's algorithm.Comment: 5 pages, 3 figures; (new in version 2: added new figure, title
changed, rearranged paragraphs
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