1,269 research outputs found
Adiabatic quantum search algorithm for structured problems
The study of quantum computation has been motivated by the hope of finding
efficient quantum algorithms for solving classically hard problems. In this
context, quantum algorithms by local adiabatic evolution have been shown to
solve an unstructured search problem with a quadratic speed-up over a classical
search, just as Grover's algorithm. In this paper, we study how the structure
of the search problem may be exploited to further improve the efficiency of
these quantum adiabatic algorithms. We show that by nesting a partial search
over a reduced set of variables into a global search, it is possible to devise
quantum adiabatic algorithms with a complexity that, although still
exponential, grows with a reduced order in the problem size.Comment: 7 pages, 0 figur
Searching for the QCD Axion with Gravitational Microlensing
The phase transition responsible for axion dark matter production can create
large amplitude isocurvature perturbations which collapse into dense objects
known as axion miniclusters. We use microlensing data from the EROS survey, and
from recent observations with the Subaru Hyper Suprime Cam to place constraints
on the minicluster scenario. We compute the microlensing event rate for
miniclusters treating them as spatially extended objects with an extended mass
function. Using the published bounds on the number of microlensing events we
bound the fraction of DM collapsed into miniclusters, . For an
axion with temperature dependent mass consistent with the QCD axion we find
, which represents the first
observational constraint on the minicluster fraction. We forecast that a
high-efficiency observation of ten nights with Subaru would be sufficient to
constrain over the entire QCD axion mass range. We
make various approximations to derive these constraints and dedicated analyses
by the observing teams of EROS and Subaru are necessary to confirm our results.
If accurate theoretical predictions for can be made in future then
microlensing can be used to exclude, or discover, the QCD axion. Further
details of our computations are presented in a companion paper.Comment: 5 pages, 4 figures, v2 contains an improved description of our
modeling of miniclusters and lensing with revised limits, matches version
accepted in PR
Information transmission via entangled quantum states in Gaussian channels with memory
Gaussian quantum channels have recently attracted a growing interest, since
they may lead to a tractable approach to the generally hard problem of
evaluating quantum channel capacities. However, the analysis performed so far
has always been restricted to memoryless channels. Here, we consider the case
of a bosonic Gaussian channel with memory, and show that the classical capacity
can be significantly enhanced by employing entangled input symbols instead of
product symbols.Comment: 13 pages, 5 figures, Workshop on Quantum entanglement in physical and
information sciences, Pisa, December 14-18, 200
Quantum circuit implementation of the Hamiltonian versions of Grover's algorithm
We analyze three different quantum search algorithms, the traditional
Grover's algorithm, its continuous-time analogue by Hamiltonian evolution, and
finally the quantum search by local adiabatic evolution. We show that they are
closely related algorithms in the sense that they all perform a rotation, at a
constant angular velocity, from a uniform superposition of all states to the
solution state. This make it possible to implement the last two algorithms by
Hamiltonian evolution on a conventional quantum circuit, while keeping the
quadratic speedup of Grover's original algorithm.Comment: 5 pages, 3 figure
Sedimentation of active colloidal suspensions
In this paper, we investigate experimentally the non-equilibrium steady state
of an active colloidal suspension under gravity field. The active particles are
made of chemically powered colloids, showing self propulsion in the presence of
an added fuel, here hydrogen peroxide. The active suspension is studied in a
dedicated microfluidic device, made of permeable gel microstructures. Both the
microdynamics of individual colloids and the global stationary state of the
suspension under gravity - density profiles, number fluctuations - are measured
with optical microscopy. This allows to connect the sedimentation length to the
individual self-propelled dynamics, suggesting that in the present dilute
regime the active colloids behave as 'hot' particles. Our work is a first step
in the experimental exploration of the out-of-equilibrium properties of
artificial active systems.Comment: 4 pages, 4 figure
Time-dependent Internal DFT formalism and Kohn-Sham scheme
We generalize to the time-dependent case the stationary Internal DFT /
Kohn-Sham formalism presented in Ref. [14]. We prove that, in the
time-dependent case, the internal properties of a self-bound system (as an
atomic nuclei) are all defined by the internal one-body density and the initial
state. We set-up a time-dependent Internal Kohn-Sham scheme as a practical way
to compute the internal density. The main difference with the traditional DFT /
Kohn-Sham formalism is the inclusion of the center-of-mass correlations in the
functional.Comment: 13 pages. To be published in Phys. Rev.
Simulating quantum correlations as a distributed sampling problem
It is known that quantum correlations exhibited by a maximally entangled
qubit pair can be simulated with the help of shared randomness, supplemented
with additional resources, such as communication, post-selection or non-local
boxes. For instance, in the case of projective measurements, it is possible to
solve this problem with protocols using one bit of communication or making one
use of a non-local box. We show that this problem reduces to a distributed
sampling problem. We give a new method to obtain samples from a biased
distribution, starting with shared random variables following a uniform
distribution, and use it to build distributed sampling protocols. This approach
allows us to derive, in a simpler and unified way, many existing protocols for
projective measurements, and extend them to positive operator value
measurements. Moreover, this approach naturally leads to a local hidden
variable model for Werner states.Comment: 13 pages, 2 figure
Review of The Papered Wall: The History, Patterns and Techniques of Wallpaper by Lesley Hoskins
Translation from French to English by Pamela J. Warner of Jérémie Cerman\u27s book review of:
Lesley Hoskins, ed. The Papered Wall: The History, Patterns and Techniques of Wallpaper, 2nd ed. London and New York: Thames & Hudson, 2005. 272 pp., 216 color pls., 153 b/w ills., bibliog., gloss., index. Paper, $34.95, £19.95
Simulation of bipartite qudit correlations
We present a protocol to simulate the quantum correlations of an arbitrary
bipartite state, when the parties perform a measurement according to two
traceless binary observables. We show that bits of classical
communication is enough on average, where is the dimension of both systems.
To obtain this result, we use the sampling approach for simulating the quantum
correlations. We discuss how to use this method in the case of qudits.Comment: 7 page
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