20,753 research outputs found
Unbounded sequence of observers exhibiting Einstein-Podolsky-Rosen steering
A sequential steering scenario is investigated, where multiple Bobs aim at
demonstrating steering using successively the same half of an entangled quantum
state. With isotropic entangled states of local dimension , the number of
Bobs that can steer Alice is found to be , thus
leading to an arbitrary large number of successive instances of steering with
independently chosen and unbiased inputs. This scaling is achieved when
considering a general class of measurements along orthonormal bases, as well as
complete sets of mutually unbiased bases. Finally, we show that similar results
can be obtained in an anonymous sequential scenario, where none of the Bobs
know their position in the sequence.Comment: 7 pages, 4 figure
The practice of going helps children to stop:The importance of context monitoring in inhibitory control
How do we stop ourselves during ongoing action? Recent work implies that stopping per se is easy given sufficient monitoring of contextual cues signaling the need to change action. We test key implications of this idea for improving inhibitory control. Seven- to 9-year old children practiced stopping an ongoing action, or monitoring for cues that signaled the need to go again. Both groups subsequently showed better response inhibition in a Stop-Signal task than active controls, and practice monitoring yielded a dose-response relationship. When monitoring practice was optimized to occur while children engaged in responding, the greatest benefits were observed – even greater than from practicing stopping itself. These findings demonstrate the importance of monitoring processes in developing response inhibition, and suggest promising new directions for interventions
Depinning of disordered bosonic chains
We consider one-dimensional bosonic chains with a repulsive boson-boson
interaction that decays exponentially on large length-scales. This model
describes transport of Cooper-pairs in a Josepshon junction array, or transport
of magnetic flux quanta in quantum-phase-slip ladders, i.e. arrays of
superconducting wires in a ladder-configuration that allow for the coherent
tunnelling of flux quanta. In the low-frequency, long wave-length regime these
chains can be mapped to an effective model of a one-dimensional elastic field
in a disordered potential. The onset of transport in these systems, when biased
by external voltage, is described by the standard depinning theory of elastic
media in disordered pinning potentials. We numerically study the regimes that
are of relevance for quantum-phase-slip ladders. These are (i) very short
chains and (ii) the regime of weak disorder. For chains shorter than the
typical pinning length, i.e., the Larkin length, the chains reach a saturation
regime where the depinning voltage does not depend on the decay length of the
repulsive interaction. In the regime of weak disorder we find an emergent
correlation length-scale that depends on the disorder strength. For arrays
shorter than this length the onset of transport is similar to the clean arrays,
i.e., is due to the penetration of solitons into the array. We discuss the
depinning scenarios for longer arrays in this regime.Comment: 11 pages, 6 figure
Defining a bulk-edge correspondence for non-Hermitian Hamiltonians via singular-value decomposition
We address the breakdown of the bulk-boundary correspondence observed in
non-Hermitian systems, where open and periodic systems can have distinct phase
diagrams. The correspondence can be completely restored by considering the
Hamiltonian's singular value decomposition instead of its eigendecomposition.
This leads to a natural topological description in terms of a flattened
singular decomposition. This description is equivalent to the usual approach
for Hermitian systems and coincides with a recent proposal for the
classification of non-Hermitian systems. We generalize the notion of the
entanglement spectrum to non-Hermitian systems, and show that the edge physics
is indeed completely captured by the periodic bulk Hamiltonian. We exemplify
our approach by considering the chiral non-Hermitian Su-Schrieffer-Heger and
Chern insulator models. Our work advocates a different perspective on
topological non-Hermitian Hamiltonians, paving the way to a better
understanding of their entanglement structure.Comment: 6+5 pages, 8 figure
Investigating dynamic dependence using copulae
A general methodology for time series modelling is developed which works down from distributional
properties to implied structural models including the standard regression relationship. This
general to specific approach is important since it can avoid spurious assumptions such as linearity
in the form of the dynamic relationship between variables. It is based on splitting the multivariate
distribution of a time series into two parts: (i) the marginal unconditional distribution, (ii) the
serial dependence encompassed in a general function , the copula. General properties of the class of
copula functions that fulfill the necessary requirements for Markov chain construction are exposed.
Special cases for the gaussian copula with AR(p) dependence structure and for archimedean copulae
are presented. We also develop copula based dynamic dependency measures — auto-concordance
in place of autocorrelation. Finally, we provide empirical applications using financial returns and
transactions based forex data. Our model encompasses the AR(p) model and allows non-linearity.
Moreover, we introduce non-linear time dependence functions that generalize the autocorrelation
function
- …