1,334 research outputs found
Hawking-Unruh effect and the entanglement of two-mode squeezed states in Riemannian spacetime
We consider the system of free scalar field, which is assumed to be a
two-mode squeezed state from an inertial point of view. This setting allows the
use of entanglement measure for continuous variables, which can be applied to
discuss free and bound entanglement from the point of view from non-inertial
observer.Comment: Phys. Lett. A, accepted for publicatio
Quantum Graphical Models and Belief Propagation
Belief Propagation algorithms acting on Graphical Models of classical
probability distributions, such as Markov Networks, Factor Graphs and Bayesian
Networks, are amongst the most powerful known methods for deriving
probabilistic inferences amongst large numbers of random variables. This paper
presents a generalization of these concepts and methods to the quantum case,
based on the idea that quantum theory can be thought of as a noncommutative,
operator-valued, generalization of classical probability theory. Some novel
characterizations of quantum conditional independence are derived, and
definitions of Quantum n-Bifactor Networks, Markov Networks, Factor Graphs and
Bayesian Networks are proposed. The structure of Quantum Markov Networks is
investigated and some partial characterization results are obtained, along the
lines of the Hammersely-Clifford theorem. A Quantum Belief Propagation
algorithm is presented and is shown to converge on 1-Bifactor Networks and
Markov Networks when the underlying graph is a tree. The use of Quantum Belief
Propagation as a heuristic algorithm in cases where it is not known to converge
is discussed. Applications to decoding quantum error correcting codes and to
the simulation of many-body quantum systems are described.Comment: 58 pages, 9 figure
Strong subadditivity inequality for quantum entropies and four-particle entanglement
Strong subadditivity inequality for a three-particle composite system is an
important inequality in quantum information theory which can be studied via a
four-particle entangled state. We use two three-level atoms in
configuration interacting with a two-mode cavity and the Raman adiabatic
passage technique for the production of the four-particle entangled state.
Using this four-particle entanglement, we study for the first time various
aspects of the strong subadditivity inequality.Comment: 5 pages, 3 figures, RevTeX4, submitted to PR
Experimentally realizable characterizations of continuous variable Gaussian states
Measures of entanglement, fidelity and purity are basic yardsticks in quantum
information processing. We propose how to implement these measures using linear
devices and homodyne detectors for continuous variable Gaussian states. In
particular, the test of entanglement becomes simple with some prior knowledge
which is relevant to current experiments.Comment: 4 pages, This paper supersedes quant-ph/020315
Nonadditive entropy for random quantum spin-S chains
We investigate the scaling of Tsallis entropy in disordered quantum spin-S
chains. We show that an extensive scaling occurs for specific values of the
entropic index. Those values depend only on the magnitude S of the spins, being
directly related with the effective central charge associated with the model.Comment: 5 pages, 7 figures. v3: Minor corrections and references updated.
Published versio
Identification of physical activity and sedentary behaviour dimensions that predict mortality risk in older adults: Development of a machine learning model in the Whitehall II accelerometer sub-study and external validation in the CoLaus study.
Identification of new physical activity (PA) and sedentary behaviour (SB) features relevant for health at older age is important to diversify PA targets in guidelines, as older adults rarely adhere to current recommendations focusing on total duration. We aimed to identify accelerometer-derived dimensions of movement behaviours that predict mortality risk in older populations.
We used data on 21 accelerometer-derived features of daily movement behaviours in 3991 participants of the UK-based Whitehall II accelerometer sub-study (25.8% women, 60-83 years, follow-up: 2012-2013 to 2021, mean = 8.3 years). A machine-learning procedure was used to identify core PA and SB features predicting mortality risk and derive a composite score. We estimated the added predictive value of the score compared to traditional sociodemographic, behavioural, and health-related risk factors. External validation in the Switzerland-based CoLaus study (N = 1329, 56.7% women, 60-86 years, follow-up: 2014-2017 to 2021, mean = 3.8 years) was conducted.
In total, 11 features related to overall activity level, intensity distribution, bouts duration, frequency, and total duration of PA and SB, were identified as predictors of mortality in older adults and included in a composite score. Both in the derivation and validation cohorts, the score was associated with mortality (hazard ratio = 1.10 (95% confidence interval = 1.05-1.15) and 1.18 (1.10-1.26), respectively) and improved the predictive value of a model including traditional risk factors (increase in C-index = 0.007 (0.002-0.014) and 0.029 (0.002-0.055), respectively).
The identified accelerometer-derived PA and SB features, beyond the currently recommended total duration, might be useful for screening of older adults at higher mortality risk and for diversifying PA and SB targets in older populations whose adherence to current guidelines is low.
National Institute on Aging; UK Medical Research Council; British Heart Foundation; Wellcome Trust; French National Research Agency; GlaxoSmithKline; Lausanne Faculty of Biology and Medicine; Swiss National Science Foundation
Immunological status of bladder cancer patients based on urine leukocyte composition at radical cystectomy
Altres ajuts: Roche donationBackground: Bladder cancer (BC) is the ninth most common malignancy worldwide, with high rates of recurrence. The use of urine leukocyte composition at the time of radical cystectomy (RC) as a marker for the study of patients' immunological status and to predict the recurrence of muscle-invasive bladder cancer (MIBC) has received little attention. Methods: Urine and matched peripheral blood samples were collected from 24 MIBC patients at the time of RC. Leukocyte composition and expression of PD-L1 and PD-1 in each subpopulation were determined by flow cytometry. Results: All MIBC patients had leukocytes in urine. There were different proportions of leukocyte subpopulations. The expression of PD-L1 and PD-1 on each subpopulation differed between patients. Neoadjuvant chemotherapy (NAC), smoking status, and the affectation of lymph nodes influenced urine composition. We observed a link between leukocytes in urine and blood circulation. Recurrent patients without NAC and with no affectation of lymph nodes had a higher proportion of lymphocytes, macrophages, and PD-L1+ neutrophils in urine than non-recurrent patients. Conclusions: Urine leukocyte composition may be a useful tool for analyzing the immunological status of MIBC patients. Urine cellular composition allowed us to identify a new subgroup of LN− patients with a higher risk of recurrence
Entangling power and operator entanglement in qudit systems
We establish the entangling power of a unitary operator on a general
finite-dimensional bipartite quantum system with and without ancillas, and give
relations between the entangling power based on the von Neumann entropy and the
entangling power based on the linear entropy. Significantly, we demonstrate
that the entangling power of a general controlled unitary operator acting on
two equal-dimensional qudits is proportional to the corresponding operator
entanglement if linear entropy is adopted as the quantity representing the
degree of entanglement. We discuss the entangling power and operator
entanglement of three representative quantum gates on qudits: the SUM, double
SUM, and SWAP gates.Comment: 8 pages, 1 figure. Version 3: Figure was improved and the MS was a
bit shortene
Long-range quantum discord in critical spin systems
We show that quantum correlations as quantified by quantum discord can
characterize quantum phase transitions by exhibiting nontrivial long-range
decay as a function of distance in spin systems. This is rather different from
the behavior of pairwise entanglement, which is typically short-ranged even in
critical systems. In particular, we find a clear change in the decay rate of
quantum discord as the system crosses a quantum critical point. We illustrate
this phenomenon for first-order, second-order, and infinite-order quantum phase
transitions, indicating that pairwise quantum discord is an appealing quantum
correlation function for condensed matter systems
Entanglement capability of self-inverse Hamiltonian evolution
We determine the entanglement capability of self-inverse Hamiltonian
evolution, which reduces to the known result for Ising Hamiltonian, and
identify optimal input states for yielding the maximal entanglement rate. We
introduce the concept of the operator entanglement rate, and find that the
maximal operator entanglement rate gives a lower bound on the entanglement
capability of a general Hamiltonian.Comment: 4 pages, no figures. Version 3: small change
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