152,147 research outputs found
Controlled generation of field squeezing with cold atomic clouds coupled to a superconducting transmission line resonator
We propose an efficient method for controlled generation of field squeezing
with cold atomic clouds trapped close to a superconducting transmission line
resonator. It is shown that, based on the coherent strong magnetic coupling
between the collective atomic spins and microwave fields in the transmission
line resonator, two-mode or single mode field squeezed states can be generated
through coherent control on the dynamics of the system. The degree of squeezing
and preparing time can be directly controlled through tuning the external
classical fields. This protocol may offer a promising platform for implementing
scalable on-chip quantum information processing with continuous variables.Comment: accepted by Phys. Rev.
Method for classifying multiqubit states via the rank of the coefficient matrix and its application to four-qubit states
We construct coefficient matrices of size 2^l by 2^{n-l} associated with pure
n-qubit states and prove the invariance of the ranks of the coefficient
matrices under stochastic local operations and classical communication (SLOCC).
The ranks give rise to a simple way of partitioning pure n-qubit states into
inequivalent families and distinguishing degenerate families from one another
under SLOCC. Moreover, the classification scheme via the ranks of coefficient
matrices can be combined with other schemes to build a more refined
classification scheme. To exemplify we classify the nine families of four
qubits introduced by Verstraete et al. [Phys. Rev. A 65, 052112 (2002)] further
into inequivalent subfamilies via the ranks of coefficient matrices, and as a
result, we find 28 genuinely entangled families and all the degenerate classes
can be distinguished up to permutations of the four qubits. We also discuss the
completeness of the classification of four qubits into nine families
Digital evolution in time-dependent fitness landscapes
We study the response of populations of digital organisms that adapt to a time-varying (periodic) fitness landscape of two oscillating peaks. We corroborate in general predictions from quasi-species theory in dynamic landscapes, such as adaptation to the average fitness landscape at small periods (high frequency) and quasistatic adaptation at large periods (low frequency). We also observe adaptive phase shifts (time tags between a change in the fitness landscape and art adaptive change in the population) that indicate a low-pass filter effect, in agreement with existing theory,. Finally, we witness long-term adaptation to fluctuating environments not anticipated in previous theoretical work
Efficient Learning for Undirected Topic Models
Replicated Softmax model, a well-known undirected topic model, is powerful in
extracting semantic representations of documents. Traditional learning
strategies such as Contrastive Divergence are very inefficient. This paper
provides a novel estimator to speed up the learning based on Noise Contrastive
Estimate, extended for documents of variant lengths and weighted inputs.
Experiments on two benchmarks show that the new estimator achieves great
learning efficiency and high accuracy on document retrieval and classification.Comment: Accepted by ACL-IJCNLP 2015 short paper. 6 page
Anisotropy and interaction effects of strongly strained SrIrO3 thin films
Magneto-transport properties of SrIrO thin films epitaxially grown on
SrTiO, using reactive RF sputtering, are investigated. A large anisotropy
between the in-plane and the out-of-plane resistivities is found, as well as a
signature of the substrate cubic to tetragonal transition. Both observations
result from the structural distortion associated to the epitaxial strain. The
low-temperature and field dependences of the Hall number are interpreted as due
to the contribution of Coulomb interactions to weak localization, evidencing
the strong correlations in this material. The introduction of a contribution
from magnetic scatters, in the analysis of magnetoconductance in the weakly
localized regime, is proposed as an alternative to an anomalously large
temperature dependence of the Land\'{e} coefficient
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