3,149 research outputs found
Measurement of an integral of a classical field with a single quantum particle
A method for measuring an integral of a classical field via local interaction
of a single quantum particle in a superposition of 2^N states is presented. The
method is as efficient as a quantum method with N qubits passing through the
field one at a time and it is exponentially better than any known classical
method that uses N bits passing through the field one at a time. A related
method for searching a string with a quantum particle is proposed.Comment: 3 page
Thermo-magnetic history effects in the vortex state of YNi_2B_2C superconductor
The nature of five-quadrant magnetic isotherms for is different from that for
in a single crystal of YNi2B2C, pointing towards an anisotropic behaviour of
the flux line lattice (FLL). For, a well defined peak effect (PE) and second
magnetization peak (SMP) can be observed and the loop is open prior to the PE.
However, for, the loop is closed and one can observe only the PE. We have
investigated the history dependence of magnetization hysteresis data for by
recording minor hysteresis loops. The observed history dependence in across
different anomalous regions are rationalized on the basis of
su-perheating/supercooling of the vortex matter across the first-order-like
phase transition and possible additional effects due to annealing of the
disordered vortex bundles to the underlying equilibrium state.Comment: 4 pages, 4 figure
Comparison of Gravitational Wave Detector Network Sky Localization Approximations
Gravitational waves emitted during compact binary coalescences are a
promising source for gravitational-wave detector networks. The accuracy with
which the location of the source on the sky can be inferred from gravitational
wave data is a limiting factor for several potential scientific goals of
gravitational-wave astronomy, including multi-messenger observations. Various
methods have been used to estimate the ability of a proposed network to
localize sources. Here we compare two techniques for predicting the uncertainty
of sky localization -- timing triangulation and the Fisher information matrix
approximations -- with Bayesian inference on the full, coherent data set. We
find that timing triangulation alone tends to over-estimate the uncertainty in
sky localization by a median factor of for a set of signals from
non-spinning compact object binaries ranging up to a total mass of , and the over-estimation increases with the mass of the system. We
find that average predictions can be brought to better agreement by the
inclusion of phase consistency information in timing-triangulation techniques.
However, even after corrections, these techniques can yield significantly
different results to the full analysis on specific mock signals. Thus, while
the approximate techniques may be useful in providing rapid, large scale
estimates of network localization capability, the fully coherent Bayesian
analysis gives more robust results for individual signals, particularly in the
presence of detector noise.Comment: 11 pages, 7 Figure
Energy and Efficiency of Adiabatic Quantum Search Algorithms
We present the results of a detailed analysis of a general, unstructured
adiabatic quantum search of a data base of items. In particular we examine
the effects on the computation time of adding energy to the system. We find
that by increasing the lowest eigenvalue of the time dependent Hamiltonian {\it
temporarily} to a maximum of , it is possible to do the
calculation in constant time. This leads us to derive the general theorem which
provides the adiabatic analogue of the bound of conventional quantum
searches. The result suggests that the action associated with the oracle term
in the time dependent Hamiltonian is a direct measure of the resources required
by the adiabatic quantum search.Comment: 6 pages, Revtex, 1 figure. Theorem modified, references and comments
added, sections introduced, typos corrected. Version to appear in J. Phys.
Implementation of quantum search algorithm using classical Fourier optics
We report on an experiment on Grover's quantum search algorithm showing that
{\em classical waves} can search a -item database as efficiently as quantum
mechanics can. The transverse beam profile of a short laser pulse is processed
iteratively as the pulse bounces back and forth between two mirrors. We
directly observe the sought item being found in iterations, in
the form of a growing intensity peak on this profile. Although the lack of
quantum entanglement limits the {\em size} of our database, our results show
that entanglement is neither necessary for the algorithm itself, nor for its
efficiency.Comment: 4 pages, 3 figures; minor revisions plus extra referenc
Nested quantum search and NP-complete problems
A quantum algorithm is known that solves an unstructured search problem in a
number of iterations of order , where is the dimension of the
search space, whereas any classical algorithm necessarily scales as . It
is shown here that an improved quantum search algorithm can be devised that
exploits the structure of a tree search problem by nesting this standard search
algorithm. The number of iterations required to find the solution of an average
instance of a constraint satisfaction problem scales as , with
a constant depending on the nesting depth and the problem
considered. When applying a single nesting level to a problem with constraints
of size 2 such as the graph coloring problem, this constant is
estimated to be around 0.62 for average instances of maximum difficulty. This
corresponds to a square-root speedup over a classical nested search algorithm,
of which our presented algorithm is the quantum counterpart.Comment: 18 pages RevTeX, 3 Postscript figure
Quantum phase retrieval of a Rydberg wave packet using a half-cycle pulse
A terahertz half-cycle pulse was used to retrieve information stored as
quantum phase in an -state Rydberg atom data register. The register was
prepared as a wave packet with one state phase-reversed from the others (the
"marked bit"). A half-cycle pulse then drove a significant portion of the
electron probability into the flipped state via multimode interference.Comment: accepted by PR
Note and Comment
Deeds Delivered Conditionally to the Grantee - Generally courts have shown a commendable disposition to get away from the formalism, which in the past played such a large part in determination of questions of delivery. While the actual tradition of the instrument to the grantee or to someone on his behalf, on the one hand, or its retention in the hands of the maker, on the other, is still very important evidentially, such facts are not by any means controlling. Thus it is entirely possible for a deed to be delivered though it never has been out of the grantor\u27s hands; likewise a deed may be undelivered though in the hands of the grantee by the voluntary act of the grantor. See the discussion by Professor Tiffany ir I7 MCHc. L. Rv. 1o4, et seq., citing many cases. This result has come from the growing appreciation by the courts that delivery after all is simply the manifestation of the grantor\u27s intent that, as to him, the instrument is a completed legal act. This intent is normally shown by a handing over of the deed to the grantee or to someone- for him, but there are other ways of showing such intent. A deed in the hands of the grantor prima fade has been delivered; if in the hands of the grantor, prima facie, it has not been delivered
HKT Geometry and Fake Five Dimensional Supergravity
Recent results on the relation between hyper-Kahler geometry with torsion and
solutions admitting Killing spinors in minimal de sitter supergravity are
extended to more general supergravity models with vector multiplets.Comment: 14 pages, latex. Minor typos corrected, references adde
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