5,339 research outputs found
The Optimal Single Copy Measurement for the Hidden Subgroup Problem
The optimization of measurements for the state distinction problem has
recently been applied to the theory of quantum algorithms with considerable
successes, including efficient new quantum algorithms for the non-abelian
hidden subgroup problem. Previous work has identified the optimal single copy
measurement for the hidden subgroup problem over abelian groups as well as for
the non-abelian problem in the setting where the subgroups are restricted to be
all conjugate to each other. Here we describe the optimal single copy
measurement for the hidden subgroup problem when all of the subgroups of the
group are given with equal a priori probability. The optimal measurement is
seen to be a hybrid of the two previously discovered single copy optimal
measurements for the hidden subgroup problem.Comment: 8 pages. Error in main proof fixe
Efficient Quantum Circuits for Schur and Clebsch-Gordan Transforms
The Schur basis on n d-dimensional quantum systems is a generalization of the
total angular momentum basis that is useful for exploiting symmetry under
permutations or collective unitary rotations. We present efficient (size
poly(n,d,log(1/\epsilon)) for accuracy \epsilon) quantum circuits for the Schur
transform, which is the change of basis between the computational and the Schur
bases. These circuits are based on efficient circuits for the Clebsch-Gordan
transformation. We also present an efficient circuit for a limited version of
the Schur transform in which one needs only to project onto different Schur
subspaces. This second circuit is based on a generalization of phase estimation
to any nonabelian finite group for which there exists a fast quantum Fourier
transform.Comment: 4 pages, 3 figure
Electronic states and Landau levels in graphene stacks
We analyze, within a minimal model that allows analytical calculations, the
electronic structure and Landau levels of graphene multi-layers with different
stacking orders. We find, among other results, that electrostatic effects can
induce a strongly divergent density of states in bi- and tri-layers,
reminiscent of one-dimensional systems. The density of states at the surface of
semi-infinite stacks, on the other hand, may vanish at low energies, or show a
band of surface states, depending on the stacking order
Interactions of Bacillus Mojavensis and Fusarium Verticillioides With a Benzoxazolinone (Boa) and Its Transformation Product, Apo
En:Journal of Chemical Ecology (2007, vol. 33, n. 10, p. 1885-1897)The benzoxazolinones, specifically benzoxazolin-2(3H)-one (BOA), are important transformation products of the benzoxazinones that can serve as allelochemicals providing resistance to maize from pathogenic bacteria, fungi, and insects. However, maize pathogens such as Fusarium verticillioides are capable of detoxifying the benzoxazolinones to 2-aminophenol (AP), which is converted to the less toxic N-(2-hydroxyphenyl) malonamic acid (HPMA) and 2-acetamidophenol (HPAA). As biocontrol strategies that utilize a species of endophytic bacterium, Bacillus mojavensis, are considered efficacious as a control of this Fusarium species, the in vitro transformation and effects of BOA on growth of this bacterium was examined relative to its interaction with strains of F. verticillioides. The results showed that a red pigment was produced and accumulated only on BOA-amended media when wild type and the progeny of genetic crosses of F. verticillioides are cultured in the presence of the bacterium. The pigment was identified as 2-amino-3H-phenoxazin-3-one (APO), which is a stable product. The results indicate that the bacterium interacts with the fungus preventing the usual transformation of AP to the nontoxic HPMA, resulting in the accumulation of higher amounts of APO than when the fungus is cultured alone. APO is highly toxic to F. verticillioides and other organisms. Thus, an enhanced biocontrol is suggested by this in vitro study.
=580 $aEn:Journal of Chemical Ecolog
The Stability of Quantum Concatenated Code Hamiltonians
Protecting quantum information from the detrimental effects of decoherence
and lack of precise quantum control is a central challenge that must be
overcome if a large robust quantum computer is to be constructed. The
traditional approach to achieving this is via active quantum error correction
using fault-tolerant techniques. An alternative to this approach is to engineer
strongly interacting many-body quantum systems that enact the quantum error
correction via the natural dynamics of these systems. Here we present a method
for achieving this based on the concept of concatenated quantum error
correcting codes. We define a class of Hamiltonians whose ground states are
concatenated quantum codes and whose energy landscape naturally causes quantum
error correction. We analyze these Hamiltonians for robustness and suggest
methods for implementing these highly unnatural Hamiltonians.Comment: 18 pages, small corrections and clarification
The Voluntary Adjustment of Railroad Obligations
Automatic memory management techniques eliminate many programming errors that are both hard to find and to correct. However, these techniques are not yet used in embedded systems with hard realtime applications. The reason is that current methods for automatic memory management have a number of drawbacks. The two major ones are: (1) not being able to always guarantee short real-time deadlines and (2) using large amounts of extra memory. Memory is usually a scarce resource in embedded applications. In this paper we present a new technique, Real-Time Reference Counting (RTRC) that overcomes the current problems and makes automatic memory management attractive also for hard real-time applications. The main contribution of RTRC is that often all memory can be used to store live objects. This should be compared to a memory overhead of about 500% for garbage collectors based on copying techniques and about 50% for garbage collectors based on mark-and-sweep techniques
How to hide a secret direction
We present a procedure to share a secret spatial direction in the absence of
a common reference frame using a multipartite quantum state. The procedure
guarantees that the parties can determine the direction if they perform joint
measurements on the state, but fail to do so if they restrict themselves to
local operations and classical communication (LOCC). We calculate the fidelity
for joint measurements, give bounds on the fidelity achievable by LOCC, and
prove that there is a non-vanishing gap between the two of them, even in the
limit of infinitely many copies. The robustness of the procedure under particle
loss is also studied. As a by-product we find bounds on the probability of
discriminating by LOCC between the invariant subspaces of total angular
momentum N/2 and N/2-1 in a system of N elementary spins.Comment: 4 pages, 1 figur
SAURON Observations of Disks in Spheroids
The panoramic integral-field spectrograph SAURON is currently being used to
map the stellar kinematics, gaseous kinematics, and stellar populations of a
large number of early-type galaxies and bulges. Here, we describe SAURON
observations of cold stellar disks embedded in spheroids (NGC3384, NGC4459,
NGC4526), we illustrate the kinematics and ionization state of large-scale
gaseous disks (NGC4278, NGC7742), and we show preliminary comparisons of SAURON
data with barred galaxy N-body simulations (NGC3623).Comment: 8 pages including 5 figures. To appear in Galaxies: The Third
Dimension, eds. M. Rosado, L. Binnette, & L. Arias (ASP: San Francisco
SAURON: An Innovative Look at Early-Type Galaxies
A summary of the SAURON project and its current status is presented. SAURON
is a panoramic integral-field spectrograph designed to study the stellar
kinematics, gaseous kinematics, and stellar populations of spheroids. Here, the
sample of galaxies and its properties are described. The instrument is detailed
and its capabilities illustrated through observational examples. These includes
results on the structure of central stellar disks, the kinematics and
ionization state of gaseous disks, and the stellar populations of galaxies with
decoupled cores.Comment: 10 pages, 6 figures. To appear in "The Dynamics, Structure & History
of Galaxies", eds. G. S. Da Costa & E. M. Sadler (San Francisco: ASP).
Version with full resolution images available at
http://www.strw.leidenuniv.nl/~dynamics/Instruments/Sauron/pub_list.htm
Exchange Interaction Between Three and Four Coupled Quantum Dots: Theory and Applications to Quantum Computing
Several prominent proposals have suggested that spins of localized electrons
could serve as quantum computer qubits. The exchange interaction has been
invoked as a means of implementing two qubit gates. In this paper, we analyze
the strength and form of the exchange interaction under relevant conditions. We
find that, when several spins are engaged in mutual interactions, the
quantitative strengths or even qualitative forms of the interactions can
change. It is shown that the changes can be dramatic within a Heitler-London
model. Hund-Mulliken calculations are also presented, and support the
qualititative conclusions from the Heitler-London model. The effects need to be
considered in spin-based quantum computer designs, either as a source of gate
error to be overcome or a new interaction to be exploited.Comment: 16 pages, 16 figures. v3: Added Hund-Mulliken calculations in 3-dots
case. A few small corrections. This version submitted to PR
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