Dicke superradiance as a nondestructive probe for optical lattices

Wir entwickeln eine neue, umfassende Methode zur zerstörungsfreien Messung ultrakalter Atome in optischen Gittern, die auf den spezifischen Eigenschaften von Dicke-Superradianz basiert. Insbesondere schlagen wir ein Pump-Probe-Schema vor, in dem ein einzelnes Photon von einem Ensemble von Atomen in einem optischen Gitter zunächst kollektiv und kohärent absorbiert, dann für eine variable Zeitspanne gespeichert, und schließlich kollektiv reemittiert wird. Im Falle unbeweglicher Atome erwartet man gerichtete, superradiante Emission aufgrund der Kohärenz des atomaren Dicke-Zustands, der durch die kollektive Absorption des Photons erzeugt wird. Dementgegen betrachten wir jedoch bewegliche Atome in einem optischen Gitter, die wir durch die zwei am häufigsten betrachteten Modellsysteme beschreiben -- das Bose-Hubbard-Modell und das Fermi-Hubbard-Modell. Im Allgemeinen beeinträchtigt die Gitterdynamik die räumliche Phasenkohärenz des Dicke-Zustands, wodurch wiederum die superradianten Emissionseigenschaften verändert werden. Umgekehrt können über die Messung der Emissionseigenschaften Rückschlüsse auf den Quantenzustand der Atome im optischen Gitter gezogen werden. Im Hauptteil der vorliegenden Dissertation untersuchen wir detailliert die Emissionseigenschaften für verschiedene Anfangszustände des Gitters und diskutieren ob diese mit der vorgestellten Messmethode unterschieden werden können. Dabei zeigen wir, dass im Falle von bosonischen Atomen zwischen angeregten Zuständen und dem superfluiden Grundzustand differenziert werden kann, während bei Fermionen der Mott-Néel-Zustand vom metallischen Grundzustand unterschieden werden kann. Ferner ist das Pump-Probe-Schema prädestiniert zur Erforschung von Nichtgleichgewichts-Phänomenen, wie z.B. Quanten-Phasenübergängen. Deshalb untersuchen wir, inwiefern ein adiabatischer Phasenübergang von einem Mott-Isolator zur superfluiden bzw. metallischen Phase von einem abrupten (d.h. nichtadiabatischen) Übergang unterschieden werden kann. Im Gegensatz zu fast allen gängigen Messmethoden, wie z.B. Time-of-Flight-Messungen oder In-situ-Abbildungen, kann die vorgestellte Messmethode als zerstörungsfrei angesehen werden, da die kohärente Interaktion mit einem einzelnen Photon nicht die Phasenkohärenz des Zustands des Gitters zerstört. Zuletzt untersuchen wir eine abgewandelte Messmethode, die klassische Laserfelder anstatt einzelner Photonen einsetzt, und zeigen, dass diese vergleichbare Eigenschaften aufweist, während sie womöglich einfacher experimentell umzusetzen ist. Außerdem geben wir weitere Anregungen zur experimentellen Realisierung.We develop a new, comprehensive method to nondestructively probe ultracold atoms in optical lattices, utilizing the unique features of Dicke superradiance. In particular, we propose a pump-and-probe scheme, in which a single photon is collectively and coherently absorbed, then stored for a variable period of time, and later collectively re-emitted by an ensemble of atoms in an optical lattice. For an immovable collection of atoms, directed superradiant re-emission is predicted due to the coherence of the atomic Dicke state, which is created by the collective absorption of the photon. In contrast, we consider moving atoms in an optical lattice, modeled via the two most commonly studied lattice models -- the Bose-Hubbard model and the Fermi-Hubbard model. In general, these lattice dynamics impair the spatial phase coherence of the Dicke state, which in turn modifies the superradiant emission characteristics. Conversely, measuring the emission characteristics allows to obtain information about the quantum state of the atoms in the optical lattice. As a main part of this Thesis, we study in detail the emission characteristics for different initial lattice states and discuss whether they can be distinguished using the suggested probing scheme. We find that it is possible to differentiate between excited states and the superfluid ground state in the case of bosonic atoms, while the Mott-Néel state can be distinguished from the metallic ground state in the case of fermions. Furthermore, the pump-and-probe scheme is predestined to investigate nonequilibrium phenomena, such as quantum phase transitions. Thus, we explore whether an adiabatic phase transition from the Mott insulator phase to the superfluid or metallic phase, respectively, can be distinguished from a sudden quench. As opposed to almost all commonly used detection techniques, such as time-of-flight measurements or in situ imaging, the proposed probing scheme can be considered nondestructive, as the coherent interaction with a single photon does not destroy the phase coherence of the optical lattice state. Finally, we study a modified probing scheme employing classical laser fields instead of single-photon absorption and emission, demonstrating that it reproduces the features of the single-photon probe, while it is probably easier to implement experimentally. We give further suggestions on experimental realization

Entangling photons via the double quantum Zeno effect

We propose a scheme for entangling two photons via the quantum Zeno effect, which describes the inhibition of quantum evolution by frequent measurements and is based on the difference between summing amplitudes and probabilities. For a given error probability $P_{\rm error}$, our scheme requires that the one-photon loss rate $\xi_{1\gamma}$ and the two-photon absorption rate $\xi_{2\gamma}$ in some medium satisfy $\xi_{1\gamma}/\xi_{2\gamma}=2P_{\rm error}^2/\pi^2$, which is significantly improved in comparison to previous approaches. Again based on the quantum Zeno effect, as well as coherent excitations, we present a possibility to fulfill this requirement in an otherwise linear optics set-up.Comment: 4 pages RevTeX, 2 figure

On the feasibility of a nuclear exciton laser

Nuclear excitons known from M\"ossbauer spectroscopy describe coherent excitations of a large number of nuclei -- analogous to Dicke states (or Dicke super-radiance) in quantum optics. In this paper, we study the possibility of constructing a laser based on these coherent excitations. In contrast to the free electron laser (in its usual design), such a device would be based on stimulated emission and thus might offer certain advantages, e.g., regarding energy-momentum accuracy. Unfortunately, inserting realistic parameters, the window of operability is probably not open (yet) to present-day technology -- but our design should be feasible in the UV regime, for example.Comment: 7 pages RevTeX, 4 figure

International Consensus Statement on Allergy and Rhinology: Allergic Rhinitis

Critical examination of the quality and validity of available allergic rhinitis (AR) literature is necessary to improve understanding and to appropriately translate this knowledge to clinical care of the AR patient. To evaluate the existing AR literature, international multidisciplinary experts with an interest in AR have produced the International Consensus statement on Allergy and Rhinology: Allergic Rhinitis (ICAR:AR). Using previously described methodology, specific topics were developed relating to AR. Each topic was assigned a literature review, evidence-based review (EBR), or evidence-based review with recommendations (EBRR) format as dictated by available evidence and purpose within the ICAR:AR document. Following iterative reviews of each topic, the ICAR:AR document was synthesized and reviewed by all authors for consensus. The ICAR:AR document addresses over 100 individual topics related to AR, including diagnosis, pathophysiology, epidemiology, disease burden, risk factors for the development of AR, allergy testing modalities, treatment, and other conditions/comorbidities associated with AR. This critical review of the AR literature has identified several strengths; providers can be confident that treatment decisions are supported by rigorous studies. However, there are also substantial gaps in the AR literature. These knowledge gaps should be viewed as opportunities for improvement, as often the things that we teach and the medicine that we practice are not based on the best quality evidence. This document aims to highlight the strengths and weaknesses of the AR literature to identify areas for future AR research and improved understandin