Entanglement Trapping in Structured Environments

The entanglement dynamics of two independent qubits each embedded in a structured environment under conditions of inhibition of spontaneous emission is analyzed, showing entanglement trapping. We demonstrate that entanglement trapping can be used efficiently to prevent entanglement sudden death. For the case of realistic photonic band-gap materials, we show that high values of entanglement trapping can be achieved. This result is of both fundamental and applicative interest since it provides a physical situation where the entanglement can be preserved and manipulated, e.g. by Stark-shifting the qubit transition frequency outside and inside the gap.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Lett. on Friday 16 May 200

Association between frailty and main work during the LIFE: A cross-sectional analysis of the UK Biobank

Background: The role of main work during the life course in predicting frailty, a typical geriatric syndrome, is still largely unknown. Therefore, with this research, we aimed to investigate the potential association between the main work done during the life with frailty and pre-frailty among participants 60 years and older of the UK Biobank study. Methods: Frailty and pre-frailty presence were ascertained using a model including 5 indicators (weakness, slowness, weight loss, low physical activity, and exhaustion); the main employment status was ascertained using self-reported information. The association between frailty and main work was explored using an ordinal logistic regression model and reported as odds ratios (ORs) with their 95 % confidence intervals (CIs). Results: The final sample comprised a total of 50,447 individuals (mean age: 64.2 years, females: 50.2 %). Individuals with higher qualifications had a reduced risk of frailty (OR = 0.881, 95%CI = 0.83-0.95, p-value<0.001 for pre-frail and OR = 0.681, 95%CI = 0.63-0.73, p-value<0.001 for frail) compared to those with lower qualifications. Moreover, active participation in the workforce, compared to being inactive, emerged as a protective factor from frailty (OR = 0.753, 95%CI = 0.70-0.81, p-value<0.001). The categories of Associate Professional and Technical Occupations exhibited protective effects against both pre-frailty and frailty. Similarly, occupations categorized as Professional and Management demonstrated protective effects against pre-frailty and frailty when compared to Elementary Occupations. Additionally, engagement in Trades and Services occupations, as opposed to Elementary Occupations, appeared to be protective against frailty. Conclusions: In this large cross-sectional investigation based on the data of the UK Biobank we found that work during lifetime could be an important factor in determining frailty later in life

Tripartite entanglement dynamics in a system of strongly driven qubits

We study the dynamics of tripartite entanglement in a system of two strongly driven qubits individually coupled to a dissipative cavity. We aim at explanation of the previously noted entanglement revival between two qubits in this system. We show that the periods of entanglement loss correspond to the strong tripartite entanglement between the qubits and the cavity and the recovery has to do with an inverse process. We demonstrate that the overall process of qubit-qubit entanglement loss is due to the second order coupling to the external continuum which explains the exp[-g^2 t/2+g^2 k t^3/6+\cdot] for of the entanglement loss reported previously.Comment: 9 pages, 5 figure

Sudden death and sudden birth of entanglement in common structured reservoirs

We study the exact entanglement dynamics of two qubits in a common structured reservoir. We demonstrate that, for certain classes of entangled states, entanglement sudden death occurs, while for certain initially factorized states, entanglement sudden birth takes place. The backaction of the non-Markovian reservoir is responsible for revivals of entanglement after sudden death has occurred, and also for periods of disentanglement following entanglement sudden birth.Comment: 4 pages, 2 figure

Phenomenological memory-kernel master equations and time-dependent Markovian processes

Do phenomenological master equations with memory kernel always describe a non-Markovian quantum dynamics characterized by reverse flow of information? Is the integration over the past states of the system an unmistakable signature of non-Markovianity? We show by a counterexample that this is not always the case. We consider two commonly used phenomenological integro-differential master equations describing the dynamics of a spin 1/2 in a thermal bath. By using a recently introduced measure to quantify non-Markovianity [H.-P. Breuer, E.-M. Laine, and J. Piilo, Phys. Rev. Lett. 103, 210401 (2009)] we demonstrate that as far as the equations retain their physical sense, the key feature of non-Markovian behavior does not appear in the considered memory kernel master equations. Namely, there is no reverse flow of information from the environment to the open system. Therefore, the assumption that the integration over a memory kernel always leads to a non-Markovian dynamics turns out to be vulnerable to phenomenological approximations. Instead, the considered phenomenological equations are able to describe time-dependent and uni-directional information flow from the system to the reservoir associated to time-dependent Markovian processes.Comment: 5 pages, no figure

Limits in the characteristic function description of non-Lindblad-type open quantum systems

In this paper I investigate the usability of the characteristic functions for the description of the dynamics of open quantum systems focussing on non-Lindblad-type master equations. I consider, as an example, a non-Markovian generalized master equation containing a memory kernel which may lead to nonphysical time evolutions characterized by negative values of the density matrix diagonal elements [S.M. Barnett and S. Stenholm, Phys. Rev. A {\bf 64}, 033808 (2001)]. The main result of the paper is to demonstrate that there exist situations in which the symmetrically ordered characteristic function is perfectly well defined while the corresponding density matrix loses positivity. Therefore nonphysical situations may not show up in the characteristic function. As a consequence, the characteristic function cannot be considered an {\it alternative complete} description of the non-Lindblad dynamics.Comment: Revised version. 4 pages, 1 figur

Driven harmonic oscillator as a quantum simulator for open systems

We show theoretically how a driven harmonic oscillator can be used as a quantum simulator for non-Markovian damped harmonic oscillator. In the general framework, the results demonstrate the possibility to use a closed system as a simulator for open quantum systems. The quantum simulator is based on sets of controlled drives of the closed harmonic oscillator with appropriately tailored electric field pulses. The non-Markovian dynamics of the damped harmonic oscillator is obtained by using the information about the spectral density of the open system when averaging over the drives of the closed oscillator. We consider single trapped ions as a specific physical implementation of the simulator, and we show how the simulator approach reveals new physical insight into the open system dynamics, e.g. the characteristic quantum mechanical non-Markovian oscillatory behavior of the energy of the damped oscillator, usually obtained by the non-Lindblad-type master equation, can have a simple semiclassical interpretation.Comment: 10 pages, 4 figures. V2: Minor modifications and added 2 appendixes for more details about calculation

A preliminary study on cranio-facial characteristics associated with minor neurological dysfunctions (Mnds) in children with autism spectrum disorders (asd)

Background. Craniofacial anomalies and minor neurological dysfunction (MNDs) have been identified, in literature, as risk factors for neurodevelopmental disorders. They represent physical indicators of embryonic development suggesting a possible contributory role of complications during early, even pre-conceptional, phases of ontogeny in autism spectrum disorders (ASD). Limited research has been conducted about the co-occurrence of the two biomarkers in children with ASD. This study investigates the associative patterns of cranio-facial anomalies and MNDs in ASD children, and whether these neurodevelopmental markers correlate with intensity of ASD symptoms and overall functioning. Methods. Caucasian children with ASD (n = 33) were examined. Measures were based on five anthropometric cranio-facial indexes and a standardized and detailed neurological examination according to Touwen. Relationships between anthropometric z-scores, MNDs and participant characteristics (i.e., age, cognitive abilities, severity of autistic symptoms measured using the Childhood Autism Rating Scale (CARS) checklist) were assessed. Results. With respect to specific MNDs, significant positive correlations were found between Cephalic Index and Sensory deficits (p-value < 0.001), which did not correlate with CARS score. Importantly, CARS score was positively linked with Intercanthal Index (p-value < 0.001), and negatively associated with posture and muscle tone (p-value = 0.027) and Facial Index (p-value = 0.004). Conclusion. Our data show a link between a specific facial phenotype and anomalies in motor responses, suggesting early brain dysmaturation involving subcortical structures in cerebro-craniofacial development of autistic children. This research supports the concept of a “social brain functional morphology” in autism spectrum disorders