3,439 research outputs found
Independent sets of maximum weight in apple-free graphs
We present the first polynomial-time algorithm to solve the maximum weight independent set problem for apple-free graphs, which is a common generalization of several important classes where the problem can be solved efficiently, such as claw-free graphs, chordal graphs, and cographs. Our solution is based on a combination of two algorithmic techniques (modular decomposition and decomposition by clique separators) and a deep combinatorial analysis of the structure of apple-free graphs. Our algorithm is robust in the sense that it does not require the input graph G to be apple-free; the algorithm either finds an independent set of maximum weight in G or reports that G is not apple-free
Efficient discrete-time simulations of continuous-time quantum query algorithms
The continuous-time query model is a variant of the discrete query model in
which queries can be interleaved with known operations (called "driving
operations") continuously in time. Interesting algorithms have been discovered
in this model, such as an algorithm for evaluating nand trees more efficiently
than any classical algorithm. Subsequent work has shown that there also exists
an efficient algorithm for nand trees in the discrete query model; however,
there is no efficient conversion known for continuous-time query algorithms for
arbitrary problems.
We show that any quantum algorithm in the continuous-time query model whose
total query time is T can be simulated by a quantum algorithm in the discrete
query model that makes O[T log(T) / log(log(T))] queries. This is the first
upper bound that is independent of the driving operations (i.e., it holds even
if the norm of the driving Hamiltonian is very large). A corollary is that any
lower bound of T queries for a problem in the discrete-time query model
immediately carries over to a lower bound of \Omega[T log(log(T))/log (T)] in
the continuous-time query model.Comment: 12 pages, 6 fig
Interface bonding of a ferromagnetic/semiconductor junction : a photoemission study of Fe/ZnSe(001)
We have probed the interface of a ferromagnetic/semiconductor (FM/SC)
heterojunction by a combined high resolution photoemission spectroscopy and
x-ray photoelectron diffraction study. Fe/ZnSe(001) is considered as an example
of a very low reactivity interface system and it expected to constitute large
Tunnel Magnetoresistance devices. We focus on the interface atomic environment,
on the microscopic processes of the interface formation and on the iron
valence-band. We show that the Fe contact with ZnSe induces a chemical
conversion of the ZnSe outermost atomic layers. The main driving force that
induces this rearrangement is the requirement for a stable Fe-Se bonding at the
interface and a Se monolayer that floats at the Fe growth front. The released
Zn atoms are incorporated in substitution in the Fe lattice position. This
formation process is independent of the ZnSe surface termination (Zn or Se).
The Fe valence-band evolution indicates that the d-states at the Fermi level
show up even at submonolayer Fe coverage but that the Fe bulk character is only
recovered above 10 monolayers. Indeed, the Fe 1-band states,
theoretically predicted to dominate the tunneling conductance of Fe/ZnSe/Fe
junctions, are strongly modified at the FM/SC interface.Comment: 23 pages, 5 figures, submitted to Physical review
Resonant tunneling magnetoresistance in epitaxial metal-semiconductor heterostructures
We report on resonant tunneling magnetoresistance via localized states
through a ZnSe semiconducting barrier which can reverse the sign of the
effective spin polarization of tunneling electrons. Experiments performed on
Fe/ZnSe/Fe planar junctions have shown that positive, negative or even its
sign-reversible magnetoresistance can be obtained, depending on the bias
voltage, the energy of localized states in the ZnSe barrier and spatial
symmetry. The averaging of conduction over all localized states in a junction
under resonant condition is strongly detrimental to the magnetoresistance
Statistical Assertions for Validating Patterns and Finding Bugs in Quantum Programs
In support of the growing interest in quantum computing experimentation,
programmers need new tools to write quantum algorithms as program code.
Compared to debugging classical programs, debugging quantum programs is
difficult because programmers have limited ability to probe the internal states
of quantum programs; those states are difficult to interpret even when
observations exist; and programmers do not yet have guidelines for what to
check for when building quantum programs. In this work, we present quantum
program assertions based on statistical tests on classical observations. These
allow programmers to decide if a quantum program state matches its expected
value in one of classical, superposition, or entangled types of states. We
extend an existing quantum programming language with the ability to specify
quantum assertions, which our tool then checks in a quantum program simulator.
We use these assertions to debug three benchmark quantum programs in factoring,
search, and chemistry. We share what types of bugs are possible, and lay out a
strategy for using quantum programming patterns to place assertions and prevent
bugs.Comment: In The 46th Annual International Symposium on Computer Architecture
(ISCA '19). arXiv admin note: text overlap with arXiv:1811.0544
Configurations of business model themes and strategies in small firms: a qualitative comparative analysis
Firms' strategies and business model themes (BMTs) entail choices that create a configuration of interdependent elements that ultimately affect a firm's performance. So far, extant studies on BMTs (i.e. novelty, efficiency, complementarity and lock-in) have neglected an explorative analysis of how configurations of BMTs and the choices of a firm's strategy (namely, the source of the competitive advantage and the market scope) are associated with a firm's performance in small and medium enterprises (SMEs). We address this limitation by analysing a sample of 96 small firms using a configurational approach. We identified four equifinal configurations leading to high performance and five equifinal configurations associated with low performance. Overall, our results suggest that in small firms, it is essential to combine a differentiation strategy with either consistent pairs of BMTs or the search for new avenues of value creation and capture, while featuring too many BMTs might be detrimental to their growth. Our study contributes to the scholarly debate about the relationship between business models and strategy
Approximating Fractional Time Quantum Evolution
An algorithm is presented for approximating arbitrary powers of a black box
unitary operation, , where is a real number, and
is a black box implementing an unknown unitary. The complexity of
this algorithm is calculated in terms of the number of calls to the black box,
the errors in the approximation, and a certain `gap' parameter. For general
and large , one should apply a total of times followed by our procedure for approximating the fractional
power . An example is also given where for
large integers this method is more efficient than direct application of
copies of . Further applications and related algorithms are also
discussed.Comment: 13 pages, 2 figure
- …