Why should we care about quantum discord?

Entanglement is a central feature of quantum theory. Mathematical properties and physical applications of pure state entanglement make it a template to study quantum correlations. However, an extension of entanglement measures to mixed states in terms of separability does not always correspond to all the operational aspects. Quantum discord measures allow an alternative way to extend the idea of quantum correlations to mixed states. In many cases these extensions are motivated by physical scenarios and quantum information protocols. In this chapter we discuss several settings involving correlated quantum systems, ranging from distributed gates to detectors testing quantum fields. In each setting we show how entanglement fails to capture the relevant features of the correlated system, and discuss the role of discord as a possible alternative.Comment: Written for "Lectures on general quantum correlations and their applications

Comments on black holes I: The possibility of complementarity

We comment on a recent paper of Almheiri, Marolf, Polchinski and Sully who argue against black hole complementarity based on the claim that an infalling observer 'burns' as he approaches the horizon. We show that in fact measurements made by an infalling observer outside the horizon are statistically identical for the cases of vacuum at the horizon and radiation emerging from a stretched horizon. This forces us to follow the dynamics all the way to the horizon, where we need to know the details of Planck scale physics. We note that in string theory the fuzzball structure of microstates does not give any place to 'continue through' this Planck regime. AMPS argue that interactions near the horizon preclude traditional complementarity. But the conjecture of 'fuzzball complementarity' works in the opposite way: the infalling quantum is absorbed by the fuzzball surface, and it is the resulting dynamics that is conjectured to admit a complementary description.Comment: 34 pages, 6 figures, v3: clarifications & references adde

Direct Binding of pRb/E2F-2 to GATA-1 Regulates Maturation and Terminal Cell Division during Erythropoiesis

Cell differentiation is often coupled with cell cycle arrest. Here, we show that direct binding of the erythroid transcription factor GATA-1 to the retinoblastoma protein and the pRb/E2F transcription factor complex is critical for red blood cell formation

Cystic fibrosis in Uruguay

We conducted clinical and genetic analyses of 52 cystic fibrosis (CF) patients in Uruguay, which is about half of the known affected individuals in the country. A relatively high proportion had a mild presentation, characterized by pancreatic sufficiency (28%), a strong pulmonary component (97%), and borderline sweat electrolyte measurements (25%). Mutational analysis of CF chromosomes demonstrated a relatively low incidence of the ΔF508 allele (40%) and a large number of other cystic fibrosis conductance regulator mutations, with an overall detection rate of about 71%. Fifteen different mutations were detected in our patients: ΔF508, G542X, R1162X, G85E, N1303K, R334W, R75Q, R74W, D1270N, W1282X, ΔI507, 2789+5G→A, R1066C, -816C/T, R553X, as well as RNA splicing variant IVS8-5T. This group of Uruguayan CF patients has some characteristics in common with other populations of similar origin (Hispanics), as well as some unique characteristics.link_to_OA_fulltex

Hawking versus Unruh effects, or the difficulty of slowly crossing a black hole horizon

When analyzing the perception of Hawking radiation by different observers, the Hawking effect becomes mixed with the Unruh effect. The separation of both effects is not always clear in the literature. Here we propose an inconsistency-free interpretation of what constitutes a Hawking effect and what an Unruh effect. An appropriate interpretation is important in order to elucidate what sort of effects a detector might experience depending on its trajectory and the state of the quantum field. Under simplifying assumptions we introduce an analytic formula that separates these two effects. Armed with the previous interpretation we argue that for a free-falling detector to cross the horizon without experiencing high-energy effects, it is necessary that the horizon crossing is not attempted at low velocities.Proyecto Nacional de Excelencia Mineco (FIS2014-54800-C2-1-P)6.063 JCR (2016) Q1, 3/29 Physics, Particles and FieldsUE