Strong Purcell Effect on a Neutral Atom Trapped in an Open Fiber Cavity.

We observe a sixfold Purcell broadening of the D_{2} line of an optically trapped ^{87}Rb atom strongly coupled to a fiber cavity. Under external illumination by a near-resonant laser, up to 90% of the atom's fluorescence is emitted into the resonant cavity mode. The sub-Poissonian statistics of the cavity output and the Purcell enhancement of the atomic decay rate are confirmed by the observation of a strongly narrowed antibunching dip in the photon autocorrelation function. The photon leakage through the higher-transmission mirror of the single-sided resonator is the dominant contribution to the field decay (κ≈2π×50 MHz), thus offering a high-bandwidth, fiber-coupled channel for photonic interfaces such as quantum memories and single-photon sources.

Fast Nondestructive Parallel Readout of Neutral Atom Registers in Optical Potentials.

We demonstrate the parallel and nondestructive readout of the hyperfine state for optically trapped ^{87}Rb atoms. The scheme is based on state-selective fluorescence imaging and achieves detection fidelities >98% within 10 ms, while keeping 99% of the atoms trapped. For the readout of dense arrays of neutral atoms in optical lattices, where the fluorescence images of neighboring atoms overlap, we apply a novel image analysis technique using Bayesian inference to determine the internal state of multiple atoms. Our method is scalable to large neutral atom registers relevant for future quantum information processing tasks requiring fast and nondestructive readout and can also be used for the simultaneous readout of quantum information stored in internal qubit states and in the atoms' positions.

Switching photochromic molecules adsorbed on optical microfibres.

The internal state of organic photochromic spiropyran molecules adsorbed on optical microfibres is optically controlled and measured by state-dependent light absorption. Repeated switching between the states is achieved by exposure to the evanescent field of a few nanowatts of light guided in the microfibre. By adjusting the microfibre evanescent field strength the dynamic equilibrium state of the molecules is controlled. Time-resolved photoswitching dynamics are measured and modelled with a rate equation model. We also study how many times the photochromic system can be switched before undergoing significant photochemical degradation.

Deterministic delivery of a single atom.

We report the realization of a deterministic source of single atoms. A standing-wave dipole trap is loaded with one or any desired number of cold cesium atoms from a magneto-optical trap. By controlling the motion of the standing wave, we adiabatically transport the atom with submicrometer precision over macroscopic distances on the order of a centimeter. The displaced atom is observed directly in the dipole trap by fluorescence detection. The trapping field can also be accelerated to eject a single atom into free flight with well-defined velocities.

Continued imaging of the transport of a single neutral atom.

We have continuously imaged the controlled motion of a single atom as well as of a small number of distinguishable atoms with observation times exceeding one minute. The Cesium atoms are confined to potential wells of a standing wave optical dipole trap which allows to transport them over macroscopic distances. The atoms are imaged by an intensified CCD camera, and spatial resolution near the diffraction limit is obtained.

Single atoms in an optical dipole trap: towards a deterministic source of cold atoms

We describe a simple experimental technique which allows us to store a small and deterministic number of neutral atoms in an optical dipole trap. The desired atom number is prepared in a magneto-optical trap overlapped with a single focused Nd:YAG laser beam. Dipole trap loading efficiency of 100% and storage times of about one minute have been achieved. We have also prepared atoms in a certain hyperfine state and demonstrated the feasibility of a state-selective detection via resonance fluorescence at the level of a few neutral atoms. A spin relaxation time of the polarized sample of 4.2+/-0.7 s has been measured. Possible applications are briefly discussed.

Neuromuscular properties and functional aspects of taped ankles.

We used electromyographic and goniometric methods to test 40 subjects to describe the neuromuscular and biomechanical adaptation of the ankle with respect to application of two different adhesive tapes and to exercises. The neuromuscular responses to inversion injury simulation, together with the mechanical displacements of the joint complex, were analyzed before and after controlled athletic exercises. The proprioceptive amplification ratio was calculated on the basis of the integrated reflex electromyographic results and on the maximum inversion amplitude. Relevant stability gains were achieved immediately after applying tape. There was reduced tape stability after athletic exercise for one of the two tape materials tested. No further loosening was detected, even after prolonged wearing of tape (24 hours). Compared with the unprotected ankle, the taped ankle had a significant increase in the proprioceptive amplification ratio. Both fatigue and mechanical loosening may be responsible for the significant reduction in this ratio immediately after exercise. After the 24-hour interval, the ratio was increased, which could be explained by physiologic neuromuscular regeneration and mechanical restabilization of the tape itself. The sensitivity of the proprioceptive amplification ratio, both to external stabilization and to internal fatigue, supports its potential value to quantify functional joint stability.

Elements of a systematic search in animal behavior and model simulations.

Starting from a position paper by Hans Bremermann, general aspects of search behavior are envisaged: locomotion itself, the capability of orientation and possible storage of information about the 'goals' of a search. The importance of stochasticity in these processes is briefly discussed. In particular, experimental findings and theoretical concepts on the homing search of desert isopods (Hemilepistus reaumuri) are presented. Using the general framework of stochastic differential equations for the angular turning rate of a migrating individual, search paths with characteristic loops and meanders can be modelled and simulated. Search success is quantified by measuring the degree of path overlap and by computing an index of area search intensity. Quantities are plotted versus path length, both for observed isopod data and for typical simulated search paths. Certain elements of a systematic search are described and explained by a hypothesis about temporal locomotion control, based on the isopod's ability for path integration and directional compensation. Finally, possible effects of orientational cues are mentioned.

Cytoplasm dynamics and cell motion: two-phase flow models.

The motion of amoeboid cells is characterized by cytoplasmic streaming and by membrane protrusions and retractions which occur even in the absence of interactions with a substratum. Cell translocation requires, in addition, a transmission mechanism wherein the power produced by the cytoplasmic engine is applied to the substratum in a highly controlled fashion through specific adhesion proteins. Here we present a simple mechano-chemical model that tries to capture the physical essence of these complex biomolecular processes. Our model is based on the continuum equations for a viscous and reactive two-phase fluid model with moving boundaries, and on force balance equations that average the stochastic interactions between actin polymers and membrane proteins. In this paper we present a new derivation and analysis of these equations based on minimization of a power functional. This derivation also leads to a clear formulation and classification of the kinds of boundary conditions that should be specified at free surfaces and at the sites of interaction of the cell and the substratum. Numerical simulations of a one-dimensional lamella reveal that even this extremely simplified model is capable of producing several typical features of cell motility. These include periodic 'ruffle' formation, protrusion-retraction cycles, centripetal flow and cell-substratum traction forces.

Functional properties of adhesive ankle taping: neuromuscular and mechanical effects before and after exercise.

The purpose of the study was to investigate effects of adhesive ankle taping. Using electromyographic, goniometric, and thermologic methods, different ankle tapes were tested before and after athletic exercise in simulated inversion trauma. Twelve subjects with stable ankle joints performed five trials: with two different materials, with two taping techniques, and one trial without tape as control. After the simulated inversion trauma, approximately 35% of the initial maximum inversion amplitude was decreased by ankle taping. Depending on the technique, there was a loss of tape stability < or =14% after 30 min of athletic exercise. Thermologic analysis revealed a postexercise 6 degrees C temperature increase in the foot, especially under the tape. Initially, interpreted as the primary effect, the improved joint stabilization is based on mechanical stiffness caused by the adhesive tape. Joint stability was influenced positively by neuromuscular proprioceptive and physiological processes, characterized by relatively increased electromyographic activation.

[Biomechanics of actomyosin-dependent mobility of keratinocytes]. / Biomekhanika aktomiozinzavisimoi podvizhnosti keratinotsitov.

Migration of epidermal skin cells, keratinocytes, plays an important role in processes as wound healing or melanoma formation. Thus, characterization of their spontaneous motility in vitro could give indications about abnormalities of the responsible motor system, namely the cortical actomyosin layer and its interaction with the plasma membrane. Videomicroscopical observations and image data evaluations of keratinocytes spread on glass have revealed typical patterns of peripheral shape changes as rhythmical protrusions and retractions of lamellipodia, periodic waves of ruffles moving towards the cell body and, finally, pulsating or rotating waves of cell protrusions. We present two models of the behavior of actomyosin network taken as a highly viscous reactive and contractive polymer fluid. One describes the dynamics of lamellipodial protrusions transversal to the cell periphery, the other considers a simplified circular model along the whole cell circumference. Simulations of these partial differential equation models reproduce the observed spatio-temporal patterns.

Comparison of acceleration signals of simulated and real-world backward falls.

Most of the knowledge on falls of older persons has been obtained from oral reports that might be biased in many ways. Fall simulations are widely used to gain insight into circumstances of falls, but the results, at least concerning fall detection, are not convincing. Variation of acceleration and maximum jerk of 5 real-world backward falls of 4 older persons (mean age 68.8 years) were compared to the corresponding signals of simulated backward falls by 18 healthy students. Students were instructed to "fall to the back as if you were a frail old person" during experiment 1. In experiment 2, students were instructed not to fall, if possible, when released from a backward lean. Data acquisition was performed using a tri-axial acceleration sensor. In experiment 1, there was significantly more variation within the acceleration signals and maximum jerk was higher in the real-world falls, compared to the fall simulation. Conversely, all values of acceleration and jerk were higher for the fall simulations, compared to real-world falls in experiment 2. The present findings demonstrate differences between real-world falls and fall simulations. If fall simulations are used, their limitations should be noted and the protocol should be adapted to better match real-world falls.

[Phyllodes tumour of the seminal vesicle - case report of a rare tumour entity]. / Phylloider Low-Grade-Tumor der Samenblase - Fallbericht einer seltenen Tumorentität.

Neoplasms of the seminal vesicles are rare. Here we report on a patient with a low-grade phyllodes tumour of the seminal vesicle. The patient was admitted to our hospital with a tumour in the excavatio rectovesicalis diagnosed by CT scan. He had no symptoms. For further diagnosis we took transrectal ultrasound-guided biopsies, the histopathological examination showed no malignant features. One month later a follow-up CT scan demonstrated a significant enlargement of the tumour. Therefore we decided to perform a surgical exploration. During surgery we found a partially necrotic mass involving the prostate, the urinary bladder and the rectum. Both radical cystoprostatectomy with ileal conduit and anterior resection of the rectum with colostomy were necessary. Histologically the specimen showed a low-grade phyllodes tumour of the left seminal vesicle. One year after surgery the follow-up was completely normal without any residual or recurrent tumour. Frequency, histology, diagnostic investigations, therapy and prognosis of this rare tumour entity are discussed with respect to the actual literature.

Nearest-neighbor detection of atoms in a 1D optical lattice by fluorescence imaging.

We overcome the diffraction limit in fluorescence imaging of neutral atoms in a sparsely filled one-dimensional optical lattice. At a periodicity of 433 nm, we reliably infer the separation of two atoms down to nearest neighbors. We observe light induced losses of atoms occupying the same lattice site, while for atoms in adjacent lattice sites, no losses due to light induced interactions occur. Our method points towards characterization of correlated quantum states in optical lattice systems with filling factors of up to one atom per lattice site.

Quantum jumps and spin dynamics of interacting atoms in a strongly coupled atom-cavity system.

We experimentally investigate the spin dynamics of one and two neutral atoms strongly coupled to a high finesse optical cavity. We observe quantum jumps between hyperfine ground states of a single atom. The interaction-induced normal-mode splitting of the atom-cavity system is measured via the atomic excitation. Moreover, we observe the mutual influence of two atoms simultaneously coupled to the cavity mode.

Cold-atom physics using ultrathin optical fibers: light-induced dipole forces and surface interactions.

The strong evanescent field around ultrathin unclad optical fibers bears a high potential for detecting, trapping, and manipulating cold atoms. Introducing such a fiber into a cold-atom cloud, we investigate the interaction of a small number of cold cesium atoms with the guided fiber mode and with the fiber surface. Using high resolution spectroscopy, we observe and analyze light-induced dipole forces, van der Waals interaction, and a significant enhancement of the spontaneous emission rate of the atoms. The latter can be assigned to the modification of the vacuum modes by the fiber.

Inserting two atoms into a single optical micropotential.

We recently demonstrated that strings of trapped atoms inside a standing wave optical dipole trap can be rearranged using optical tweezers [Y. Miroshnychenko, Nature 442, 151 (2006)]. This technique allows us to actively set the interatomic separations on the scale of the individual trapping potential wells. Here, we use such a distance-control operation to insert two atoms into the same potential well. The detected success rate of this manipulation is 16(-3)(+4)%, in agreement with the predictions of a theoretical model based on our experimental parameters.

Submicrometer position control of single trapped neutral atoms.

We optically detect the positions of single neutral cesium atoms stored in a standing wave dipole trap with a subwavelength resolution of 143 nm rms. The distance between two simultaneously trapped atoms is measured with an even higher precision of 36 nm rms. We resolve the discreteness of the interatomic distances due to the 532 nm spatial period of the standing wave potential and infer the exact number of trapping potential wells separating the atoms. Finally, combining an initial position detection with a controlled transport, we place single atoms at a predetermined position along the trap axis to within 300 nm rms.