1,390,102 research outputs found
Quantum state transfer for multi-input linear quantum systems
Effective state transfer is one of the most important problems in quantum
information processing. Typically, a quantum information device is composed of
many subsystems with multi-input ports. In this paper, we develop a general
theory describing the condition for perfect state transfer from the multi-input
ports to the internal system components, for general passive linear quantum
systems. The key notion used is the zero of the transfer function matrix.
Application to entanglement generation and distribution in a quantum network is
also discussed.Comment: 6 pages, 3 figures. A preliminary condensed version of this work will
appear in Proceedings of the 55th IEEE Conference on Decision and Contro
Informative and misinformative interactions in a school of fish
It is generally accepted that, when moving in groups, animals process
information to coordinate their motion. Recent studies have begun to apply
rigorous methods based on Information Theory to quantify such distributed
computation. Following this perspective, we use transfer entropy to quantify
dynamic information flows locally in space and time across a school of fish
during directional changes around a circular tank, i.e. U-turns. This analysis
reveals peaks in information flows during collective U-turns and identifies two
different flows: an informative flow (positive transfer entropy) based on fish
that have already turned about fish that are turning, and a misinformative flow
(negative transfer entropy) based on fish that have not turned yet about fish
that are turning. We also reveal that the information flows are related to
relative position and alignment between fish, and identify spatial patterns of
information and misinformation cascades. This study offers several
methodological contributions and we expect further application of these
methodologies to reveal intricacies of self-organisation in other animal groups
and active matter in general
Causal order as a resource for quantum communication
In theories of communication, it is usually presumed that the involved
parties perform actions in a fixed causal order. However, practical and
fundamental reasons can induce uncertainties in the causal order. Here we show
that a maximal uncertainty in the causal order forbids asymptotic quantum
communication, while still enabling the noisy transfer of classical
information. Therefore causal order, like shared entanglement, is an additional
resource for communication. The result is formulated within an asymptotic
setting for processes with no fixed causal order, which sets a basis for a
quantum information theory in general quantum causal structures.Comment: 5 pages, 1 figur
Follow the fugitive: an application of the method of images to open dynamical systems
Borrowing and extending the method of images we introduce a theoretical
framework that greatly simplifies analytical and numerical investigations of
the escape rate in open dynamical systems. As an example, we explicitly derive
the exact size- and position-dependent escape rate in a Markov case for holes
of finite size. Moreover, a general relation between the transfer operators of
closed and corresponding open systems, together with the generating function of
the probability of return to the hole is derived. This relation is then used to
compute the small hole asymptotic behavior, in terms of readily calculable
quantities. As an example we derive logarithmic corrections in the second order
term. Being valid for Markov systems, our framework can find application in
information theory, network theory, quantum Weyl law and via Ulam's method can
be used as an approximation method in more general dynamical systems.Comment: 9 pages, 1 figur
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