Novel techniques to cool and rotate Bose-Einstein condensates in time-averaged adiabatic potentials

We report two novel techniques for cooling and rotating Bose-Einstein condensates in a dilute rubidium vapour that highlight the control and versatility afforded over cold atom systems by time-averaged adiabatic potentials (TAAPs). The intrinsic loss channel of the TAAP has been successfully employed to evaporatively cool a sample of trapped atoms to quantum degeneracy. The speed and efficiency of this process compares well with that of conventional forced rf-evaporation. In an independent experiment, we imparted angular momentum to a cloud of atoms forming a Bose-Einstein condensate by introducing a rotating elliptical deformation to the TAAP geometry. Triangular lattices of up to 60 vortices were created. All findings reported herein result from straightforward adjustments of the magnetic fields that give rise to the TAAP.Comment: The first two authors contributed equally to this wor

Trapping Ultracold Atoms in a Time-Averaged Adiabatic Potential

We report the first experimental realization of ultracold atoms confined in a time-averaged, adiabatic potential (TAAP). This novel trapping technique involves using a slowly oscillating ($\sim$ kHz) bias field to time-average the instantaneous potential given by dressing a bare magnetic potential with a high frequency ($\sim$ MHz) magnetic field. The resultant potentials provide a convenient route to a variety of trapping geometries with tunable parameters. We demonstrate the TAAP trap in a standard time-averaged orbiting potential trap with additional Helmholtz coils for the introduction of the radio frequency dressing field. We have evaporatively cooled 5 $\times 10^4$ atoms of $^{87}$Rb to quantum degeneracy and observed condensate lifetimes of over \unit[3]{s}.-Comment: 4 pages, 6 figure

In Situ Treatment of a Scanning Gate Microscopy Tip

In scanning gate microscopy, where the tip of a scanning force microscope is used as a movable gate to study electronic transport in nanostructures, the shape and magnitude of the tip-induced potential are important for the resolution and interpretation of the measurements. Contaminations picked up during topography scans may significantly alter this potential. We present an in situ high-field treatment of the tip that improves the tip-induced potential. A quantum dot was used to measure the tip-induced potential.Comment: 3 pages, 1 figure, minor changes to fit published versio

Measurement of the Tip-Induced Potential in Scanning Gate Experiments

We present a detailed experimental study on the electrostatic interaction between a quantum dot and the metallic tip of a scanning force microscope. Our method allowed us to quantitatively map the tip-induced potential and to determine the spatial dependence of the tip's lever arm with high resolution. We find that two parts of the tip-induced potential can be distinguished, one that depends on the voltage applied to the tip and one that is independent of this voltage. The first part is due to the metallic tip while we interpret the second part as the effect of a charged dielectric particle on the tip. In the measurements of the lever arm we find fine structure that depends on which quantum state we study. The results are discussed in view of scanning gate experiments where the tip is used as a movable gate to study nanostructures.Comment: 7 pages, 5 figures, minor changes to fit published versio

Effects of Size, Caudal Autotomy, and Predator Kairomones on the Foraging Behavior of Alleghany Mountain Dusky Salamanders (Desmognathus ochrophaeus)

Prey must balance the conflicting demands of foraging and defensive behavior. Foraging under the threat of predation may be further complicated among species that engage in caudal autotomy, the loss of a portion of the tail at preformed breakage planes, because the tail may serve as an important energy storage organ and contribute to motility, culminating in a trade-off between foraging and predator avoidance. As a result of the advantages conferred by the presence of a tail, individuals that have recently undergone autotomy may be more motivated to forage despite elevated levels of threat indicated by predator kairomones. We used a full factorial design to evaluate the combined effects of body size, exposure to predator kairomones, and experience with autotomy on the latency to strike at Drosophila prey, number of strikes, and prey captured per strike by Allegheny Mountain dusky salamanders (Desmognathus ochrophaeus). In our study, caudal autotomy was the only significant main effect and influenced both the latency to attack prey and the number of strikes attempted. In terms of latency to attack prey, there was a significant interaction between body size and autotomy such that small salamanders (≤3.2 cm SVL) without tails delayed their foraging behavior. In terms of the number of strikes toward prey, there was a significant interaction between autotomy and exposure to predator kairomones such that individuals with intact tails exhibited a greater number of strikes, with the exception of the large (\u3e3.2 cm SVL) salamanders, which performed fewer strikes when exposed to the snake kairomones. There was no significant effect on foraging efficiency, although the trend in the data suggests that autotomized individuals forage more efficiently. This study was designed to evaluate the confluence of factors related to size, caudal autotomy, and exposure to stimuli from predators and hints at the magnitude of caudal autotomy on antipredator decision- making. Our data suggest that despite the importance of tail tissue for energy storage, locomotion, and mating, salamanders without tails are cautious when foraging under elevated risk

Imaging Coulomb Islands in a Quantum Hall Interferometer

In the Quantum Hall regime, near integer filling factors, electrons should only be transmitted through spatially-separated edge states. However, in mesoscopic systems, electronic transmission turns out to be more complex, giving rise to a large spectrum of magnetoresistance oscillations. To explain these observations, recent models put forward that, as edge states come close to each other, electrons can hop between counterpropagating edge channels, or tunnel through Coulomb islands. Here, we use scanning gate microscopy to demonstrate the presence of quantum Hall Coulomb islands, and reveal the spatial structure of transport inside a quantum Hall interferometer. Electron islands locations are found by modulating the tunneling between edge states and confined electron orbits. Tuning the magnetic field, we unveil a continuous evolution of active electron islands. This allows to decrypt the complexity of high magnetic field magnetoresistance oscillations, and opens the way to further local scale manipulations of quantum Hall localized states

NIKA: A millimeter-wave kinetic inductance camera

Current generation millimeter wavelength detectors suffer from scaling limits imposed by complex cryogenic readout electronics. To circumvent this it is imperative to investigate technologies that intrinsically incorporate strong multiplexing. One possible solution is the kinetic inductance detector (KID). In order to assess the potential of this nascent technology, a prototype instrument optimized for the 2 mm atmospheric window was constructed. Known as the N\'eel IRAM KIDs Array (NIKA), it was recently tested at the Institute for Millimetric Radio Astronomy (IRAM) 30-meter telescope at Pico Veleta, Spain. The measurement resulted in the imaging of a number of sources, including planets, quasars, and galaxies. The images for Mars, radio star MWC349, quasar 3C345, and galaxy M87 are presented. From these results, the optical NEP was calculated to be around $1 \times 10^{-15}$ W$/$Hz$^{1/2}$. A factor of 10 improvement is expected to be readily feasible by improvements in the detector materials and reduction of performance-degrading spurious radiation.Comment: Accepted for publication in Astronomy & Astrophysic

Inductively guided circuits for ultracold dressed atoms

Recent progress in optics, atomic physics and material science has paved the way to study quantum effects in ultracold atomic alkali gases confined to non-trivial geometries. Multiply connected traps for cold atoms can be prepared by combining inhomogeneous distributions of DC and radio-frequency electromagnetic fields with optical fields that require complex systems for frequency control and stabilization. Here we propose a flexible and robust scheme that creates closed quasi-one-dimensional guides for ultracold atoms through the ‘dressing’ of hyperfine sublevels of the atomic ground state, where the dressing field is spatially modulated by inductive effects over a micro-engineered conducting loop. Remarkably, for commonly used atomic species (for example, 7Li and 87Rb), the guide operation relies entirely on controlling static and low-frequency fields in the regimes of radio-frequency and microwave frequencies. This novel trapping scheme can be implemented with current technology for micro-fabrication and electronic control

Lever arm of a metallic tip in scanning gate experiments

Abstract We present a scanning gate experiment on the electrostatic interaction between a semiconductor quantum dot and the metallic tip of a scanning force microscope. With the help of a feedback mechanism we can map the lever arm of the tip, using the quantum dot in a given quantum state as a sensitive electrometer. Besides the geometrically expected shape at length scales of hundreds of nanometers, we observe fine structure on much shorter length scales. r 2007 Elsevier B.V. All rights reserved. There are relatively few studies about an important factor common to all scanning gate experiments, namely the electrostatic potential that the tip induces in the sample. The importance of the tip potential for the interpretation of scanning gate measurements has been mentioned in some of the first studies [5] but only recently a technique was demonstrated allowing to determine it with high precision. In Ref. [6] we used a quantum dot as a very sensitive potentiometer to study the tip-induced potential. We demonstrated how, with the help of a feedback mechanism, one can map the tip potential with high spatial and energetical resolution. Additionally, we showed how the tip's lever arm on the quantum dot can be mapped and used to better understand the properties of the tip potential. In these measurements we found fine structure which illustrates how the scanning gate technique may yield local information about the quantum dot. Here we show a measurement reproducing the main findings. The measurement conditions were identical as in Ref. We used a quantum dot prepared on a GaAs/AlGaAs heterostructure with a two-dimensional electron gas residing 34 nm below the surface. The quantum dot was patterned by local anodic oxidation of the GaAs surface at room temperature. Subsequently, we evaporated a thin Ti film on the sample surface and this film was again patterned by local anodic oxidation We scanned the SFM tip at a constant height of about 200 nm over the sample surface. The dot was tuned into the Coulomb blockade regime, and we used a feedback mechanism to apply a voltage to a plunger gate such that one of the quantized energy levels of the dot always stayed in resonance with the chemical potential of the source and drain leads. The voltage on the plunger gate corresponds to the tip potential and with this technique we could ensure ARTICLE IN PRESS www.elsevier.com/locate/physe 1386-9477/$ -see front matter

Single SQUID Multiplexer for Arrays of Voltage-biased Superconducting Bolometers

Abstract. We describe a frequency domain superconducting quantum interference device (SQUID) multiplexer which monitors a row of low-temperature sensors simultaneously with a single SQUID. Each sensor is ac biased with a unique frequency and all the sensor currents are added in a superconducting summing loop. A single SQUID measures the current in the summing loop, and the individual signals are lock-in detected after the room temperature SQUID electronics. The current in the summing loop is nulled by feedback to eliminate direct crosstalk. In order to avoid the accumulation of Johnson noise in the summing loop, a tuned bandpass filter is inserted in series with each sensor. For a 32-channel multiplexer for Voltage-baised Superconducting Bolometer (VSB) with a time constant ~1msec, we estimate that bias frequencies in the range from ~500kHz to ~600kHz are practical. The major limitation of our multiplexing scheme is in the slew rate of a readout SQUID. We discuss a "carrier nulling" technique which could be used to increase the number of sensors in a row or to multiplex faster bolometers by reducing the required slew rate for a readout SQUID