Dynamic formation of Rydberg aggregates at off-resonant excitation

The dynamics of a cloud of ultra-cold two-level atoms is studied at off-resonant laser driving to a Rydberg state. We find that resonant excitation channels lead to strongly peaked spatial correlations associated with the buildup of asymmetric excitation structures. These aggregates can extend over the entire ensemble volume, but are in general not localized relative to the system boundaries. The characteristic distances between neighboring excitations depend on the laser detuning and on the interaction potential. These properties lead to characteristic features in the spatial excitation density, the Mandel $Q$ parameter, and the total number of excitations. As an application an implementation of the three-atom CSWAP or Fredkin gate with Rydberg atoms is discussed. The gate not only exploits the Rydberg blockade, but also utilizes the special features of an asymmetric geometric arrangement of the three atoms. We show that continuous-wave off-resonant laser driving is sufficient to create the required spatial arrangement of atoms out of a homogeneous cloud.Comment: 8 pages, 7 figure

Universal time-evolution of a Rydberg lattice gas with perfect blockade

We investigate the dynamics of a strongly interacting spin system that is motivated by current experimental realizations of strongly interacting Rydberg gases in lattices. In particular we are interested in the temporal evolution of quantities such as the density of Rydberg atoms and density-density correlations when the system is initialized in a fully polarized state without Rydberg excitations. We show that in the thermodynamic limit the expectation values of these observables converge at least logarithmically to universal functions and outline a method to obtain these functions. We prove that a finite one-dimensional system follows this universal behavior up to a given time. The length of this universal time period depends on the actual system size. This shows that already the study of small systems allows to make precise predictions about the thermodynamic limit provided that the observation time is sufficiently short. We discuss this for various observables and for systems with different dimensions, interaction ranges and boundary conditions.Comment: 16 pages, 3 figure

Acoustically driven ferromagnetic resonance

Surface acoustic waves (SAW) in the GHz frequency range are exploited for the all-elastic excitation and detection of ferromagnetic resonance (FMR) in a ferromagnetic/ferroelectric (nickel/lithium niobate) hybrid device. We measure the SAW magneto-transmission at room temperature as a function of frequency, external magnetic field magnitude, and orientation. Our data are well described by a modified Landau-Lifshitz-Gilbert approach, in which a virtual, strain-induced tickle field drives the magnetization precession. This causes a distinct magnetic field orientation dependence of elastically driven FMR that we observe in both model and experiment.Comment: 4 page

Interferometric phase detection at x-ray energies via Fano resonance control

Modern x-ray light sources promise access to structure and dynamics of matter in largely unexplored spectral regions. However, the desired information is encoded in the light intensity and phase, whereas detectors register only the intensity. This phase problem is ubiquitous in crystallography and imaging, and impedes the exploration of quantum effects at x-ray energies. Here, we demonstrate phase-sensitive measurements characterizing the quantum state of a nuclear two-level system at hard x-ray energies. The nuclei are initially prepared in a superposition state. Subsequently, the relative phase of this superposition is interferometrically reconstructed from the emitted x-rays. Our results form a first step towards x-ray quantum state tomography, and provide new avenues for structure determination and precision metrology via x-ray Fano interference.Comment: 5 pages, 3 figures, plus supplementary informatio

Si-compatible candidates for high-K dielectrics with the Pbnm perovskite structure

We analyze both experimentally (where possible) and theoretically from first-principles the dielectric tensor components and crystal structure of five classes of Pbnm perovskites. All of these materials are believed to be stable on silicon and are therefore promising candidates for high-K dielectrics. We also analyze the structure of these materials with various simple models, decompose the lattice contribution to the dielectric tensor into force constant matrix eigenmode contributions, explore a peculiar correlation between structural and dielectric anisotropies in these compounds and give phonon frequencies and infrared activities of those modes that are infrared-active. We find that CaZrO_3, SrZrO_3, LaHoO_3, and LaYO_3 are among the most promising candidates for high-K dielectrics among the compounds we considered.Comment: 17 pages, 9 figures, 4 tables. Supplementary information: http://link.aps.org/supplemental/10.1103/PhysRevB.82.064101 or http://www.physics.rutgers.edu/~sinisa/highk/supp.pd

Enhanced electrical and magnetic properties in La0.7Sr0.3MnO3 thin films deposited on CaTiO3-buffered silicon substrates

We investigate the suitability of an epitaxial CaTiO3 buffer layer deposited onto (100) Si by reactive molecular-beam epitaxy (MBE) for the epitaxial integration of the colossal magnetoresistive material La0.7Sr0.3MnO3 with silicon. The magnetic and electrical properties of La0.7Sr0.3MnO3 films deposited by MBE on CaTiO3-buffered silicon (CaTiO3/Si) are compared with those deposited on SrTiO3-buffered silicon (SrTiO3/Si). In addition to possessing a higher Curie temperature and a higher metal-to-insulator transition temperature, the electrical resistivity and 1/f noise level at 300 K are reduced by a factor of two in the heterostructure with the CaTiO3 buffer layer. These results are relevant to device applications of La0.7Sr0.3MnO3 thin films on silicon substrates

Optical band gap of BiFeO3 grown by molecular-beam epitaxy

BiFeO3 thin films have been deposited on (001) SrTiO3 substrates by adsorption-controlled reactive molecular-beam epitaxy. For a given bismuth overpressure and oxygen activity, single-phase BiFeO3 films can be grown over a range of deposition temperatures in accordance with thermodynamic calculations. Four-circle x-ray diffraction reveals phase-pure, epitaxial films with w rocking curve full width at half maximum values as narrow as 29 arc sec (0.008°). Multiple-angle spectroscopic ellipsometry reveals a direct optical band gap at 2.74 eV for stoichiometric as well as 5% bismuth-deficient single-phase BiFeO3 films

COVID-19: treatment strategies of German-speaking pediatric rheumatologists Results of an online survey

Zusammenfassung Hintergrund Zuverlässige Daten zu Verlauf und Therapie von COVID-19 („corona virus disease 2019“) bei Kindern mit rheumatischen Erkrankungen unter Immunsuppression fehlen. Ziel der Arbeit Abbildung individueller Strategien der Mitglieder der Gesellschaft für Kinder- und Jugendrheumatologie (GKJR) im Umgang mit COVID-19. Methodik Mittels Online-Umfrage wurden im Mai 2020 das Meinungsbild der GKJR-Mitglieder zum Umgang mit DMARDs („disease-modifying anti-rheumatic drugs“) bei COVID-19-Erkrankung sowie die Bereitschaft zum Einsatz spezieller Therapieansätze bei Patienten mit unterschiedlicher Schwere von COVID-19 erhoben. Ergebnisse Es nahmen 71 Kollegen (27,3 % aller befragten ärztlichen Mitglieder) an der Umfrage teil; davon hatten 28,2 % bereits Patienten mit COVID-19 betreut. Über 95 % der Teilnehmer lehnten eine präventive Anpassung der antirheumatischen Therapie im Rahmen der SARS-CoV-2-Pandemie ab. Bei ambulanten Patienten unter Immunsuppression mit nachgewiesener COVID-19-Erkrankung würden mehr als 50 % der Teilnehmer folgende Therapien aussetzen: intravenöse hoch dosierte Steroide, Cyclophosphamid, Anti-CD20-Antikörper, sowie eine BAFF-, CTLA-4-, TNF-α-Blockade. Hingegen würden nichtsteroidale Antiphlogistika, Hydroxychloroquin (HCQ), orale Steroide, Mycophenolat, IL-1-Blockade sowie Immunglobuline (Ig) von >70 % der Kollegen weiter fortgeführt. Bei stationären Patienten mit COVID-19 würden insgesamt 74,6 % der Kollegen eine COVID-19-gerichtete Therapie erwägen. Bei stabilem Verlauf unter O 2 -Therapie (Stufe I) würden am häufigsten HCQ (18,3 %), Azithromycin (16,9 %) und Ig (9,9 %) in Betracht gezogen. Bei drohendem (Stufe II) bzw. manifestem Zytokinsturm (Stufe III) würden am häufigsten Anakinra (40,8 % bei Stufe II bzw. 46,5 % bei Stufe III), Tocilizumab (26,8 % bzw. 40,8 %), Steroide (25,4 % bzw. 33,8 %) und Remdesivir (29,6 % bzw. 38,0 %) eingesetzt. Von vielen Kollegen wurde betont, dass die Therapiestrategie individuell und der klinischen Situation entsprechend angepasst werden soll. Diskussion Die Ergebnisse der Online-Umfrage sind vor dem Hintergrund einer aktuell in Deutschland niedrigen Prävalenz von COVID-19 zu sehen und spiegeln somit theoretische Überlegungen der Befragten wider. Da Kinder derzeit nicht im Fokus von prospektiven COVID-19-Studien stehen, scheint der kontinuierliche und kritische kollegiale Fachaustausch bei Therapieentscheidungen umso wichtiger zu sein