Phase-Driving Hole Spin Qubits.

The spin-orbit interaction in spin qubits enables spin-flip transitions, resulting in Rabi oscillations when an external microwave field is resonant with the qubit frequency. Here, we introduce an alternative driving mechanism mediated by the strong spin-orbit interactions in hole spin qubits, where a far-detuned oscillating field couples to the qubit phase. Phase-driving at radio frequencies, orders of magnitude slower than the microwave qubit frequency, induces highly nontrivial spin dynamics, violating the Rabi resonance condition. By using a qubit integrated in a silicon fin field-effect transistor, we demonstrate a controllable suppression of resonant Rabi oscillations and their revivals at tunable sidebands. These sidebands enable alternative qubit control schemes using global fields and local far-detuned pulses, facilitating the design of dense large-scale qubit architectures with local qubit addressability. Phase-driving also decouples Rabi oscillations from noise, an effect due to a gapped Floquet spectrum and can enable Floquet engineering high-fidelity gates in future quantum processors.

Edge-State Wave Functions from Momentum-Conserving Tunneling Spectroscopy.

We perform momentum-conserving tunneling spectroscopy using a GaAs cleaved-edge overgrowth quantum wire to investigate adjacent quantum Hall edge states. We use the lowest five wire modes with their distinct wave functions to probe each edge state and apply magnetic fields to modify the wave functions and their overlap. This reveals an intricate and rich tunneling conductance fan structure which is succinctly different for each of the wire modes. We self-consistently solve the Poisson-Schrödinger equations to simulate the spectroscopy, reproducing the striking fans in great detail, thus, confirming the calculations. Further, the model predicts hybridization between wire states and Landau levels, which is also confirmed experimentally. This establishes momentum-conserving tunneling spectroscopy as a powerful technique to probe edge state wave functions.

Closed-Form Weak Localization Magnetoconductivity in Quantum Wells with Arbitrary Rashba and Dresselhaus Spin-Orbit Interactions.

We derive a closed-form expression for the weak localization (WL) corrections to the magnetoconductivity of a 2D electron system with arbitrary Rashba α and Dresselhaus ß (linear) and ß_{3} (cubic) spin-orbit interaction couplings, in a perpendicular magnetic field geometry. In a system of reference with an in-plane z[over ^] axis chosen as the high spin-symmetry direction at α=ß, we formulate a new algorithm to calculate the three independent contributions that lead to WL. The antilocalization is counterbalanced by the term associated with the spin relaxation along z[over ^], dependent only on α-ß. The other term is generated by two identical scattering modes characterized by spin-relaxation rates which are explicit functions of the orientation of the scattered momentum. Excellent agreement is found with data from GaAs quantum wells, where, in particular, our theory correctly captures the shift of the minima of the WL curves as a function of α/ß. This suggests that the anisotropy of the effective spin-relaxation rates is fundamental to understanding the effect of the spin-orbit coupling in transport.

Blurring the Boundaries Between Topological and Nontopological Phenomena in Dots.

We investigate the electronic and transport properties of topological and nontopological InAs_{0.85}Bi_{0.15} quantum dots (QDs) described by a ∼30 meV gapped Bernevig-Hughes-Zhang (BHZ) model with cylindrical confinement, i.e., "BHZ dots." Via modified Bessel functions, we analytically show that nontopological dots quite unexpectedly have discrete helical edge states, i.e., Kramers pairs with spin-angular-momentum locking similar to topological dots. These unusual nontopological edge states are geometrically protected due to confinement for a wide range of parameters and remarkably contrast with the bulk-edge correspondence in topological insulators, as no bulk topological invariant guarantees their existence. Moreover, for a conduction window with four edge states, we find that the two-terminal conductance G versus the QD radius R and the gate V_{g} controlling its levels shows a double peak at 2e^{2}/h for both topological and trivial BHZ QDs. This is in stark contrast to conductance measurements in 2D quantum spin Hall and trivial insulators. All of these results were also found in HgTe QDs. Bi-based BHZ dots should also prove important as hosts to room temperature edge spin qubits.

Persistent Skyrmion Lattice of Noninteracting Electrons with Spin-Orbit Coupling.

A persistent spin helix (PSH) is a robust helical spin-density pattern arising in disordered 2D electron gases with Rashba α and Dresselhaus ß spin-orbit (SO) tuned couplings, i.e., α=±ß. Here, we investigate the emergence of a persistent Skyrmion lattice (PSL) resulting from the coherent superposition of PSHs along orthogonal directions-crossed PSHs-in wells with two occupied subbands ν=1, 2. For realistic GaAs wells, we show that the Rashba α_{ν} and Dresselhaus ß_{ν} couplings can be simultaneously tuned to equal strengths but opposite signs, e.g., α_{1}=ß_{1} and α_{2}=-ß_{2}. In this regime, and away from band anticrossings, our noninteracting electron gas sustains a topologically nontrivial Skyrmion-lattice spin-density excitation, which inherits the robustness against spin-independent disorder and interactions from its underlying crossed PSHs. We find that the spin relaxation rate due to the interband SO coupling is comparable to that of the cubic Dresselhaus term as a mechanism of the PSL decay. Near anticrossings, the interband-induced spin mixing leads to unusual spin textures along the energy contours beyond those of the Rahsba-Dresselhaus bands. Our PSL opens up the unique possibility of observing topological phenomena, e.g., topological and Skyrmion Hall effects, in ordinary GaAs wells with noninteracting electrons.

Many-body effects on the rho(xx) ringlike structures in two-subband wells.

The longitudinal resistivity rho(xx) of two-dimensional electron gases formed in wells with two subbands displays ringlike structures when plotted in a density-magnetic-field diagram, due to the crossings of spin-split Landau levels (LLs) from distinct subbands. Using spin density functional theory and linear response, we investigate the shape and spin polarization of these structures as a function of temperature and magnetic-field tilt angle. We find that (i) some of the rings "break" at sufficiently low temperatures due to a quantum Hall ferromagnetic phase transition, thus exhibiting a high degree of spin polarization (approximately 50%) within, consistent with the NMR data of Zhang et al. [Phys. Rev. Lett. 98, 246802 (2007)], and (ii) for increasing tilting angles the interplay between the anticrossings due to inter-LL couplings and the exchange-correlation effects leads to a collapse of the rings at some critical angle theta(c), in agreement with the data of Guo et al. [Phys. Rev. B 78, 233305 (2008)].

Spin-orbit interaction in symmetric wells with two subbands.

We investigate the spin-orbit (SO) interaction in two-dimensional electron gases in quantum wells with two subbands. From the 8x8 Kane model, we derive a new intersubband-induced SO term which resembles the functional form of the Rashba SO but is nonzero even in symmetric structures. This follows from the distinct parity of the confined states (even or odd) which obliterates the need for asymmetric potentials. We self-consistently calculate the new SO coupling strength for realistic wells and find it comparable to the usual Rashba constant. Our new SO term gives rise to a nonzero ballistic spin-Hall conductivity, which changes sign as a function of the Fermi energy (epsilonF) and can induce an unusual Zitterbewegung with cycloidal trajectories without magnetic fields.

Hysteretic resistance spikes in quantum hall ferromagnets without domains.

We use spin-density-functional theory to study recently reported hysteretic magnetoresistance rho(xx) spikes in Mn-based 2D electron gases [Phys. Rev. Lett. 89, 266802 (2002)10.1103/PhysRevLett.89.266802]. We find hysteresis loops in our calculated Landau fan diagrams and total energies signaling quantum Hall ferromagnet phase transitions. Spin-dependent exchange-correlation effects are crucial to stabilize the relevant magnetic phases arising from distinct symmetry-broken excited- and ground-state solutions of the Kohn-Sham equations. Besides hysteretic spikes in rho(xx), we predict hysteretic dips in the Hall resistance rho(xy). Our theory, without domain walls, satisfactorily explains the recent data.

Nonballistic spin-field-effect transistor.

We propose a spin-field-effect transistor based on spin-orbit coupling of both the Rashba and the Dresselhaus types. Different from earlier proposals, spin transport through our device is tolerant against spin-independent scattering processes. Hence the requirement of strictly ballistic transport can be relaxed. This follows from a unique interplay between the Dresselhaus and the Rashba coupling; these can be tuned to have equal strengths, leading to k-independent eigenspinors even in two dimensions. We discuss two-dimensional devices as well as quantum wires. In the latter, our setup presents strictly parabolic dispersions which avoids complications from anticrossings of different bands.

Rashba spin-orbit interaction and shot noise for spin-polarized and entangled electrons.

We study shot noise for spin-polarized currents and entangled electron pairs in a four-probe (beam-splitter) geometry with a local Rashba spin-orbit (s-o) interaction in the incoming leads. Within the scattering formalism we find that shot noise exhibits Rashba-induced oscillations with continuous bunching and antibunching. We show that entangled states and triplet states can be identified via their Rashba phase in noise measurements. For two-channel leads, we find an additional spin rotation due to s-o induced interband coupling which enhances spin control. We show that the s-o interaction deter-mines the Fano factor, which provides a direct way to measure the Rashba coupling constant via noise.

Infección nosocomial, vigilancia y control de la infección en Neonatología / Nosocomial infection, surveillance and control in Neonatology infection

La infección nosocomial representa un desafío creciente en neonatología, dado que cada vez se atienden niños con mayor grado de inmadurez y se utilizan procedimientos tecnológicos que constituyen una puerta de entrada potencial a los microorganismos. Partiendo de la revisión y análisis de los datos existentes en la Unidad de Neonatología del Hospital Virgen del Camino, así como de los aspectos epidemiológicos diferenciales en la edad perinatal, se detallan las actuaciones a realizar para la prevención, diagnóstico y control de la infección nosocomial en neonatología. (AU)

[Children with limb reductions in a population of 25,193 malformed newborns: the recognized causes. ECEMC. The Spanish Collaborative Study of Congenital Malformations]. / Niños con reducción de extremidades en una población de 25.193 recién nacidos malformados: causas reconocidas. ECEMC. Estudio Colaborativo Español de Malformaciones Congénitas.

OBJECTIVE: The purposes of this study were to analyze the causes of limb reduction deficiencies based on a clinical-epidemiological approach and to study the causes by clinical presentation. PATIENTS AND METHODS: We have used the data from the Spanish Collaborative Study of Congenital Malformations (ECEMC) during the period from 1976 to 1996, which corresponded to more than 1,300,000 births. Among these, we identified 851 liver-born and 40 stillborn infants with limb reduction defects. RESULTS: We could identify the cause in 177 (19.87%) of the 891 cases with limb reduction defects. In the analysis by clinical presentation, in 52.19% of the cases the limb deficiencies were the only defect present in the children (isolated), 30.75% presented multiple congenital anomaly patterns, and 17.06% were syndromes. The most frequent etiology was the genetic one. CONCLUSIONS: First, most of infants with limb deficiencies have unknown cause and these defects are most frequently isolated malformations. On the other hand, the results of this analysis permitted the following considerations in relation to the guidance for the diagnosis of infants with limb reduction defects. If the child presents with multiple congenital anomalies (multiply malformed infant) a chromosomal analysis should be performed and it should be determined if the infant was prenatally exposed to a teratogenic agent. If these two aspects are normal, we should clinically analyze if the infant could have a known syndrome. In addition, since in our data 10.32% of isolated cases were due to autosomal dominant genes, a detailed clinical analysis of close relatives should be done to determine if some of them present mild limb deficiencies in order to provide an adequate information to the family.

Primary midline developmental field. II. Clinical/epidemiological analysis of alteration of laterality (normal body symmetry and asymmetry).

Lubinsky [Am J Med Genet 3:23-28, 1987] has suggested that the properties of the midline involve early determinative informational processes and are related to the midline's position and definition of the body's plane of symmetry. Opitz [Am J Med Genet 21:175-176, 1985, BD: OAS XXIX(1):3-37 1993] has pointed out that the laterality sequences represent a midline developmental field complex. Thus, bilateral left-sidedness (with asplenia) and bilateral right-sidedness (with asplenia) have been considered laterality sequences or syndromes if cause is known. Using the malformed infants registered by the Spanish Collaborative Study of Congenital Malformations (ECEMC), we performed a clinical/epidemiological analysis of the relationship between midline defects and alteration of normal body asymmetry and symmetry. The results support the assumption that both conditions could be consequence of disturbances in the midline primary developmental field.

Severe spondylocostal dysostosis associated with other congenital anomalies: a clinical/epidemiologic analysis and description of ten cases from the Spanish registry.

We describe 10 cases born to nondiabetic mothers who presented with severe spondylocostal dysostosis (SCD) associated with other anomalies, identified among 20,526 malformed liveborn infants from the Spanish Collaborative Study of Congenital Malformations (ECEMC). We analyze the associated malformations in the 10 cases with severe SCD, as well as in all cases with less severe SCD among children with MCA patterns of unknown cause. Cases with SCD were preferentially associated with caudal dysgenesis, diaphragmatic hernia, and central nervous system anomalies.

Short rib-polydactyly syndrome (SRPS) with anencephaly and other central nervous system anomalies: a new type of SRPS or a more severe expression of a known SRPS entity?

We describe two patients with short rib-polydactyly syndrome (SRPS) from two unrelated Spanish families. These patients present clinical and radiological characteristics that overlap those of the different established types of SRPS. In addition, one patient had anencephaly and the other patient had severe brain abnormalities with a family history of an older sister with anencephaly, and a brother diagnosed with SRPS. This second family is interesting in that the two affected brothers present with different clinical and radiological findings; for example, one had ovoid tibiae and the other did not. This particular family shows that intrafamiliar variation is also observed within SRPS. It remains unsettled whether these cases might be considered a new type of SRPS or a variant of an established entity or whether the differences between the SRPS represent variability or heterogeneity. Molecular studies may answer this question in the near future.

[Trisomy 9p. Apropos of 2 cases]. / Trisomía 9p. A propósito de dos observaciones.

Two cases of trisomy 9p are presented. The different cytogenetic mechanism given in these cases shows us that with independence of it, it exists a triplication of the half distal short arm of chromosome 9 which gives specificity to these phenotypic features. It might be a possible meiotic origin of the chromosomic rearrangement on both translocations, the formation of satellited chromosomes and isochromosomes of the short arm on chromosome 9 and the consequently wrong segregation of each one of them. The non-existence of chromosomic material with activity in the transcription, confers to both situations the category of a pure trisomy 9p. The prenatal diagnosis through amniocentesis might be useful, even in the so called "de novo" cases, in order to avoid the repetition of this kind of structural aberration or some others that could appear due to fragility of certain chromosomic regions.

[Camptomelic dysplasia associated with true hermaphroditism]. / Displasia campomélica asociada a hermafroditismo vero.

Authors present a new case of campomelic dysplasia associated to true hermaphroditism. Clinical and radiological findings are described. Ethiopatogenical factors are widely discussed, and special correlation between campomelic dysplasia and sexual reverse, is noted, according to new concepts on H-Y antigen. Differential diagnosis with neonatal chondrodystrophies associated with respiratory distress and congenital incurved extremities are also reviewed.

[Myocardial infarction in relation to perinatal hypoxia]. / Infarto de miocardio en relación con hipoxia perinatal.

Six newborn infants with myocardial infarction are presented. All of them had a history of perinatal hypoxemia and their natal weights were below 2,500 g. All infants developed cardiogenic "shock" during and required assisted ventilation. Autopsy confirmed the diagnosis in five of the six infants. Other autopsy findings were intracranial bleeding (three cases) and pulmonary atelectasis (two cases). Authors review pathophysiology of this clinical picture and point out its possible influence in the origin of neonatal shock.