9,603 research outputs found
An analytical decomposition protocol for optimal implementation of two-qubit entangling gates
This paper addresses the question how to implement a desired two-qubit gate U
using a given tunable two-qubit entangling interaction H_int. We present a
general method which is based on the K_1 A K_2 decomposition of unitary
matrices in SU(4) to calculate analytically the smallest number of two-qubit
gates U_int [based on H_int] and single-qubit rotations, and the explicit
sequence of these operations that are required to implement U. We illustrate
our protocol by calculating the implementation of (1) the transformation from
standard basis to Bell basis, (2) the CNOT gate, and (3) the quantum Fourier
transform for two kinds of interaction - Heisenberg exchange interaction and
quantum inductive coupling - and discuss the relevance of our results for
solid-state qubits.Comment: 16 pages, published versio
Fourier spectra from exoplanets with polar caps and ocean glint
The weak orbital-phase dependent reflection signal of an exoplanet contains
information on the planet surface, such as the distribution of continents and
oceans on terrestrial planets. This light curve is usually studied in the time
domain, but because the signal from a stationary surface is (quasi)periodic,
analysis of the Fourier series may provide an alternative, complementary
approach.
We study Fourier spectra from reflected light curves for geometrically simple
configurations. Depending on its atmospheric properties, a rotating planet in
the habitable zone could have circular polar ice caps. Tidally locked planets,
on the other hand, may have symmetric circular oceans facing the star. These
cases are interesting because the high-albedo contrast at the sharp edges of
the ice-sheets and the glint from the host star in the ocean may produce
recognizable light curves with orbital periodicity, which could also be
interpreted in the Fourier domain.
We derive a simple general expression for the Fourier coefficients of a
quasiperiodic light curve in terms of the albedo map of a Lambertian planet
surface. Analytic expressions for light curves and their spectra are calculated
for idealized situations, and dependence of spectral peaks on the key
parameters inclination, obliquity, and cap size is studied.Comment: 15 pages, 2 tables, 13 figure
Muon localization site in U(Pt,Pd)3
The angular and temperature (10-250 K) variation of the Knight shift of
single-crystalline U(Pt0.95Pd0.05)3 has been measured in transverse field
(B=0.6 T) mSR experiments. By analysing the temperature variation of the Knight
shift with a modified Curie-Weiss expression the muon localization site in this
hexagonal material is determined at (0,0,0).Comment: 12 pages (including 4 figures); postscript file; Proc. 8th Int. Conf.
on Muon Spin Rotation, Relaxation and Resonance (Aug.30-Sept.3, Les
Diablerets); 2nd version with minor correction
Resistivity of non-Fermi liquid U2Pt2In under pressure
Non-Fermi liquid behaviour in single-crystalline U2Pt2In has been studied by
means of resistivity experiments (I||c) under hydrostatic pressure (P<1.5 GPa).
At ambient pressure the resistivity rho(T) follows a power law rho~T^alpha with
alpha~0.5. Upon applying pressure alpha increases. For P>1 GPa a minimum
develops in rho(T). A study of the field dependence of the minimum confirms its
magnetic origin. The ratio c/a is proposed as the effective control parameter,
rather than the unit cell volume.Comment: 5 pages (incl. 2 figures), submitted to SCES'99, Nagan
Tweede fase BIOVEEM gestart!
We zijn veel meer gericht op vernieuwing van onderdelen van het veehouderijbedrijf en het oplossen van door veehouders ervaren knelpunte
Evolutionary accessibility of mutational pathways
Functional effects of different mutations are known to combine to the total
effect in highly nontrivial ways. For the trait under evolutionary selection
(`fitness'), measured values over all possible combinations of a set of
mutations yield a fitness landscape that determines which mutational states can
be reached from a given initial genotype. Understanding the accessibility
properties of fitness landscapes is conceptually important in answering
questions about the predictability and repeatability of evolutionary
adaptation. Here we theoretically investigate accessibility of the globally
optimal state on a wide variety of model landscapes, including landscapes with
tunable ruggedness as well as neutral `holey' landscapes. We define a
mutational pathway to be accessible if it contains the minimal number of
mutations required to reach the target genotype, and if fitness increases in
each mutational step. Under this definition accessibility is high, in the sense
that at least one accessible pathwayexists with a substantial probability that
approaches unity as the dimensionality of the fitness landscape (set by the
number of mutational loci) becomes large. At the same time the number of
alternative accessible pathways grows without bound. We test the model
predictions against an empirical 8-locus fitness landscape obtained for the
filamentous fungus \textit{Aspergillus niger}. By analyzing subgraphs of the
full landscape containing different subsets of mutations, we are able to probe
the mutational distance scale in the empirical data. The predicted effect of
high accessibility is supported by the empirical data and very robust, which we
argue to reflect the generic topology of sequence spaces.Comment: 16 pages, 4 figures; supplementary material available on reques
XT: a bundle of program transformation tools : system description
{sc xt bundles existing and newly developed program transformation libraries and tools into an open framework that supports component-based development of program transformations. We discuss the roles of {sc xt's constituents in the development process of program transformation tools, as well as some experiences with building program transformation systems with {sc xt. <pr
- …