1,363 research outputs found
Entropy-power uncertainty relations : towards a tight inequality for all Gaussian pure states
We show that a proper expression of the uncertainty relation for a pair of
canonically-conjugate continuous variables relies on entropy power, a standard
notion in Shannon information theory for real-valued signals. The resulting
entropy-power uncertainty relation is equivalent to the entropic formulation of
the uncertainty relation due to Bialynicki-Birula and Mycielski, but can be
further extended to rotated variables. Hence, based on a reasonable assumption,
we give a partial proof of a tighter form of the entropy-power uncertainty
relation taking correlations into account and provide extensive numerical
evidence of its validity. Interestingly, it implies the generalized
(rotation-invariant) Schr\"odinger-Robertson uncertainty relation exactly as
the original entropy-power uncertainty relation implies Heisenberg relation. It
is saturated for all Gaussian pure states, in contrast with hitherto known
entropic formulations of the uncertainty principle.Comment: 15 pages, 5 figures, the new version includes the n-mode cas
G-Protein coupled receptor signalling in pluripotent stem cell-derived cardiovascular cells: Implications for disease modelling
Human pluripotent stem cell derivatives show promise as an in vitro platform to study a range of human cardiovascular diseases. A better understanding of the biology of stem cells and their cardiovascular derivatives will help to understand the strengths and limitations of this new model system. G-protein coupled receptors (GPCRs) are key regulators of stem cell maintenance and differentiation and have an important role in cardiovascular cell signaling. In this review, we will therefore describe the state of knowledge concerning the regulatory role of GPCRs in both the generation and function of pluripotent stem cell derived-cardiomyocytes, -endothelial, and -vascular smooth muscle cells. We will consider how far the in vitro disease models recapitulate authentic GPCR signaling and provide a useful basis for discovery of disease mechanisms or design of therapeutic strategies
Quantum thermodynamics in a multipartite setting: A resource theory of local Gaussian work extraction for multimode bosonic systems
Quantum thermodynamics can be cast as a resource theory by considering free
access to a heat bath, thereby viewing the Gibbs state at a fixed temperature
as a free state and hence any other state as a resource. Here, we consider a
multipartite scenario where several parties attempt at extracting work locally,
each having access to a local heat bath (possibly with a different
temperature), assisted with an energy-preserving global unitary. As a specific
model, we analyze a collection of harmonic oscillators or a multimode bosonic
system. Focusing on the Gaussian paradigm, we construct a reasonable resource
theory of local activity for a multimode bosonic system, where we identify as
free any state that is obtained from a product of thermal states (possibly at
different temperatures) acted upon by any linear-optics (passive Gaussian)
transformation. The associated free operations are then all linear-optics
transformations supplemented with tensoring and partial tracing. We show that
the local Gaussian extractable work (if each party applies a Gaussian unitary,
assisted with linear optics) is zero if and only if the covariance matrix of
the system is that of a free state. Further, we develop a resource theory of
local Gaussian extractable work, defined as the difference between the trace
and symplectic trace of the covariance matrix of the system. We prove that it
is a resource monotone that cannot increase under free operations. We also
provide examples illustrating the distillation of local activity and local
Gaussian extractable work.Comment: 22 pages, 5 figures, minor corrections to make it close to the
published version, updated list of reference
A tight uniform continuity bound for the Arimoto-R\'enyi conditional entropy and its extension to classical-quantum states
We prove a tight uniform continuity bound for Arimoto's version of the
conditional -R\'enyi entropy, for the range . This
definition of the conditional R\'enyi entropy is the most natural one among the
multiple forms which exist in the literature, since it satisfies two desirable
properties of a conditional entropy, namely, the fact that conditioning reduces
entropy, and that the associated reduction in uncertainty cannot exceed the
information gained by conditioning. Furthermore, it has found interesting
applications in various information theoretic tasks such as guessing with side
information and sequential decoding. This conditional entropy reduces to the
conditional Shannon entropy in the limit , and this in turn
allows us to recover the recently obtained tight uniform continuity bound for
the latter from our result. Finally, we apply our result to obtain a tight
uniform continuity bound for the conditional -R\'enyi entropy of a
classical-quantum state, for in the same range as above. This again
yields the corresponding known bound for the conditional entropy of the state
in the limit .Comment: 23 pages. Changes in v2: new references added and minor corrections
to existing reference
Complexity of Gaussian quantum optics with a limited number of non-linearities
It is well known in quantum optics that any process involving the preparation
of a multimode gaussian state, followed by a gaussian operation and gaussian
measurements, can be efficiently simulated by classical computers. Here, we
provide evidence that computing transition amplitudes of Gaussian processes
with a single-layer of non-linearities is hard for classical computers. To do
so, we show how an efficient algorithm to solve this problem could be used to
efficiently approximate outcome probabilities of a Gaussian boson sampling
experiment. We also extend this complexity result to the problem of computing
transition probabilities of Gaussian processes with two layers of
non-linearities, by developing a Hadamard test for continuous-variable systems
that may be of independent interest. Given recent experimental developments in
the implementation of photon-photon interactions, our results may inspire new
schemes showing quantum computational advantage or algorithmic applications of
non-linear quantum optical systems realizable in the near-term.Comment: 5 pages for the main file, 8 pages for the appendix, 3 figure
Two-boson quantum interference in time
The celebrated Hong-Ou-Mandel effect is the paradigm of two-particle quantum
interference. It has its roots in the symmetry of identical quantum particles,
as dictated by the Pauli principle. Two identical bosons impinging on a beam
splitter (of transmittance 1/2) cannot be detected in coincidence at both
output ports, as confirmed in numerous experiments with light or even matter.
Here, we establish that partial time reversal transforms the beamsplitter
linear coupling into amplification. We infer from this duality the existence of
an unsuspected two-boson interferometric effect in a quantum amplifier (of gain
2) and identify the underlying mechanism as timelike indistinguishability. This
fundamental mechanism is generic to any bosonic Bogoliubov transformation, so
we anticipate wide implications in quantum physics.Comment: 12 pages, 9 figure
Early death or retransplantation in adults after orthotopic liver transplantation: Can outcome be predicted?
Early, reliable outcome prediction after a liver transplant would help improve organ use by minimizing unnecessary retransplantations. At the same time, early intervention in those cases destined to fail may ameliorate the high morbidity and mortality associated with retransplantation. The purpose of this study was to analyze several parameters that have been identified in the past as being associated with patient and graft outcome, and to try to develop a model that would allow us to make predictions based on data available in the early postoperative period. A total of 148 patients were followed in a prospective, observational study. Graft failure was defined as patient death or retransplantation within 3 months of surgery. Preoperative variables studied included patient demographics, need for life support, presence of ascites, serum bilirubin, serum albumin, prothrombin time, serum creatinine, and the results of the cytotoxic crossmatch. During the first 5 postoperative days, standard measurements included serum transaminases, serum bilirubin, ketone body ratio, prothrombin time, factor V, and serum lactate. Oxygen consumption was measured shortly after surgery, once the patients had rewarmed to 36°C. There were 131 successful transplants (88.5%) and 17 failures (11.5%). Most of the variables studied were found to be associated with outcome (by univariate analysis) at different points in the early postoperative period. However, receiver operating characteristic curve analysis showed that the predictive ability of even the best parameter was not adequate to make decisions on individual patients. Multivariate analysis, using stepwise logistic regression, yielded a model with an overall accuracy of 92.7%. Again, receiver operating characteristic curve analysis suggested that this model did not achieve the discriminating power needed for routine clinical use. We are still not able to accurately predict outcome in the early posttransplant period. We must be very careful when evaluating parameters, or scoring systems, that are said to accomplish this. It is especially important in this era of cost containment, with its renewed pressures to guide therapy based on our perceived understanding of a patient’s future clinical course. © 1994 by Williams & Wilkins
Bosonic autonomous entanglement engines with weak bath coupling are impossible
Entanglement is a fundamental feature of quantum physics and a key resource
for quantum communication, computing and sensing. Entangled states are fragile
and maintaining coherence is a central challenge in quantum information
processing. Nevertheless, entanglement can be generated and stabilised through
dissipative processes. In fact, entanglement has been shown to exist in the
steady state of certain interacting quantum systems subject solely to
incoherent coupling to thermal baths. This has been demonstrated in a range of
bi- and multipartite settings using systems of finite dimension. Here we focus
on the steady state of infinite-dimensionsional bosonic systems. Specifically,
we consider any set of bosonic modes undergoing excitation-number-preserving
interactions of arbitrary strength and divided between an arbitrary number of
parties that each couple weakly to thermal baths at different temperatures. We
show that the steady state is always separable.Comment: 10 pages, 1 figur
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