Die Sprossende Hauswurz (Sempervivum globiferum L. subsp. globiferum) in Mitteldeutschland

Dieser Beitrag dokumentiert das Vorkommen von Sempervivum globiferum subsp. globiferum in Mitteldeutschland (Sachsen, Sachsen-Anhalt und Thüringen) und versucht, Schlussfolgerungen aus dem vorliegenden Verbreitungsmuster zu ziehen. In Mitteldeutschland finden sich neben dem häufig angepflanzten Sempervivum tectorum auch traditionelle Anpflanzungen von Sempervivum globiferum, insbesondere auf Mauern und Toranlagen alter Gehöfte in den Ortskernen. Auffällige Häufungen der Verwendung von S. globiferum anstelle von S. tectorum oder der gemeinsamen Verwendung auf Mauern und Torpfeilern wurden in den Dörfern der Täler der Elster von Sachsen, Sachsen-Anhalt und Thüringen, der Unstrut bis zum Südharz und im Gebiet der Ilm in Thüringen festgestellt. Tatsächlich gibt es eine gute Übereinstimmung zwischen den Nachweisen von S. globiferum auf Mauerkronen und Torpfeilern und Nachweisen früher friedlicher Kontakte von aus dem Osten zugewanderten Volksgruppen (wohl vorwiegend Slawen) mit germanischen Volksgruppen. Verwilderungen von S. globiferum findet man nie im Tiefland links der Elbe. Dagegen können sich in montanen Bereichen nach Verwilderungen sehr stabile Populationen an Felsformationen entwickeln, die einen natürlichen Eindruck erwecken.This paper deals with the occurrence of Sempervivum globiferum subsp. globiferum (Sprouting Houseleek, Hen and chicks, Beard of Jove) in Middle Germany (Saxony, Saxony-Anhalt and Thuringia). It tries to get conclusions from the discovered pattern of distribution in this region. Among the frequently cultivated Sempervivum tectorum can be also found Sempervivum globiferum as traditional plantation on walls and pillars of entrance doors of old buildings in the core of villages. Conspicuous spreading of use of S. globiferum instead of S. tectorum or occurrences in common can be seen in villages of river valleys of Elster in Saxony, Saxony-Anhalt and Thuringia, of Unstrut up to the southern area of Harz Mountains and in the region of Ilm river in Thuringia. Indeed there is a good agreement with the occurrence of cultivated S. globiferum plants and regions, where in historic times friendly contacts have taken place between Germans and ethnic groups from eastern regions (probably mainly Slavs). Wildness of S. globiferum arises never in the deep regions on the left side of the Elbe river, but rather in mountain areas, where stable quasi native populations are formed on rock formations

Atomic cluster state build up with macroscopic heralding

We describe a measurement-based state preparation scheme for the efficient build up of cluster states in atom-cavity systems. As in a recent proposal for the generation of maximally entangled atom pairs [Metz et al., Phys. Rev. Lett. 97, 040503 (2006)], we use an electron shelving technique to avoid the necessity for the detection of single photons. Instead, the successful fusion of smaller into larger clusters is heralded by an easy-to-detect macroscopic fluorescence signal. High fidelities are achieved even in the vicinity of the bad cavity limit and are essentially independent of the concrete size of the system parameters.Comment: 14 pages, 12 figures; minor changes, mainly clarification

Nano Positioning of Single Atoms in a Micro Cavity

The coupling of individual atoms to a high-finesse optical cavity is precisely controlled and adjusted using a standing-wave dipole-force trap, a challenge for strong atom-cavity coupling. Ultracold Rubidium atoms are first loaded into potential minima of the dipole trap in the center of the cavity. Then we use the trap as a conveyor belt that we set into motion perpendicular to the cavity axis. This allows us to repetitively move atoms out of and back into the cavity mode with a repositioning precision of 135 nm. This makes possible to either selectively address one atom of a string of atoms by the cavity, or to simultaneously couple two precisely separated atoms to a higher mode of the cavity.Comment: 4 pages 5 figure

Time-resolved and state-selective detection of single freely falling atoms

We report on the detection of single, slowly moving Rubidium atoms using laser-induced fluorescence. The atoms move at 3 m/s while they are detected with a time resolution of 60 microseconds. The detection scheme employs a near-resonant laser beam that drives a cycling atomic transition, and a highly efficient mirror setup to focus a large fraction of the fluorescence photons to a photomultiplier tube. It counts on average 20 photons per atom.Comment: 6 pages, 7 figure

Analyzing quantum jumps of one and two atoms strongly coupled to an optical cavity

We induce quantum jumps between the hyperfine ground states of one and two Cesium atoms, strongly coupled to the mode of a high-finesse optical resonator, and analyze the resulting random telegraph signals. We identify experimental parameters to deduce the atomic spin state nondestructively from the stream of photons transmitted through the cavity, achieving a compromise between a good signal-to-noise ratio and minimal measurement-induced perturbations. In order to extract optimum information about the spin dynamics from the photon count signal, a Bayesian update formalism is employed, which yields time-dependent probabilities for the atoms to be in either hyperfine state. We discuss the effect of super-Poissonian photon number distributions caused by atomic motion.Comment: 12 pages, 13 figure

Ground state cooling in a bad cavity

We study the mechanical effects of light on an atom trapped in a harmonic potential when an atomic dipole transition is driven by a laser and it is strongly coupled to a mode of an optical resonator. We investigate the cooling dynamics in the bad cavity limit, focussing on the case in which the effective transition linewidth is smaller than the trap frequency, hence when sideband cooling could be implemented. We show that quantum correlations between the mechanical actions of laser and cavity field can lead to an enhancement of the cooling efficiency with respect to sideband cooling. Such interference effects are found when the resonator losses prevail over spontaneous decay and over the rates of the coherent processes characterizing the dynamics.Comment: 6 pages, 5 figures; J. Mod. Opt. (2007

Ultracold atoms in optical lattices generated by quantized light fields

We study an ultracold gas of neutral atoms subject to the periodic optical potential generated by a high-$Q$ cavity mode. In the limit of very low temperatures, cavity field and atomic dynamics require a quantum description. Starting from a cavity QED single atom Hamiltonian we use different routes to derive approximative multiparticle Hamiltonians in Bose-Hubbard form with rescaled or even dynamical parameters. In the limit of large enough cavity damping the different models agree. Compared to free space optical lattices, quantum uncertainties of the potential and the possibility of atom-field entanglement lead to modified phase transition characteristics, the appearance of new phases or even quantum superpositions of different phases. Using a corresponding effective master equation, which can be numerically solved for few particles, we can study time evolution including dissipation. As an example we exhibit the microscopic processes behind the transition dynamics from a Mott insulator like state to a self-ordered superradiant state of the atoms, which appears as steady state for transverse atomic pumping.Comment: 17 pages, 10 figures, Published versio

Cavity QED with a Bose-Einstein condensate

Cavity quantum electrodynamics (cavity QED) describes the coherent interaction between matter and an electromagnetic field confined within a resonator structure, and is providing a useful platform for developing concepts in quantum information processing. By using high-quality resonators, a strong coupling regime can be reached experimentally in which atoms coherently exchange a photon with a single light-field mode many times before dissipation sets in. This has led to fundamental studies with both microwave and optical resonators. To meet the challenges posed by quantum state engineering and quantum information processing, recent experiments have focused on laser cooling and trapping of atoms inside an optical cavity. However, the tremendous degree of control over atomic gases achieved with Bose-Einstein condensation has so far not been used for cavity QED. Here we achieve the strong coupling of a Bose-Einstein condensate to the quantized field of an ultrahigh-finesse optical cavity and present a measurement of its eigenenergy spectrum. This is a conceptually new regime of cavity QED, in which all atoms occupy a single mode of a matter-wave field and couple identically to the light field, sharing a single excitation. This opens possibilities ranging from quantum communication to a wealth of new phenomena that can be expected in the many-body physics of quantum gases with cavity-mediated interactions.Comment: 6 pages, 4 figures; version accepted for publication in Nature; updated Fig. 4; changed atom numbers due to new calibratio

Vacuum-stimulated cooling of single atoms in three dimensions

Taming quantum dynamical processes is the key to novel applications of quantum physics, e.g. in quantum information science. The control of light-matter interactions at the single-atom and single-photon level can be achieved in cavity quantum electrodynamics, in particular in the regime of strong coupling where atom and cavity form a single entity. In the optical domain, this requires permanent trapping and cooling of an atom in a micro-cavity. We have now realized three-dimensional cavity cooling and trapping for an orthogonal arrangement of cooling laser, trap laser and cavity vacuum. This leads to average single-atom trapping times exceeding 15 seconds, unprecedented for a strongly coupled atom under permanent observation.Comment: 4 pages, 4 figure

Towards quantum computing with single atoms and optical cavities on atom chips

We report on recent developments in the integration of optical microresonators into atom chips and describe some fabrication and implementation challenges. We also review theoretical proposals for quantum computing with single atoms based on the observation of photons leaking through the cavity mirrors. The use of measurements to generate entanglement can result in simpler, more robust and scalable quantum computing architectures. Indeed, we show that quantum computing with atom-cavity systems is feasible even in the presence of relatively large spontaneous decay rates and finite photon detector efficiencies.Comment: 14 pages, 6 figure