Topological constraints on magnetostatic traps

We theoretically investigate properties of magnetostatic traps for cold atoms that are subject to externally applied uniform fields. We show that Ioffe Pritchard traps and other stationary points of $B$ are confined to a two-dimensional curved manifold defined by $\det(\partial B_i/\partial x_j)=0$. We describe how stationary points can be moved over the manifold by applying external uniform fields. The manifold also plays an important role in the behavior of points of zero field. Field zeroes occur in two distinct types, in separate regions of space divided by the manifold. Pairs of zeroes of opposite type can be created or annihilated on the manifold. Finally, we give examples of the manifold for cases of practical interest.Comment: 7 pages, 5 figure

Introduction of ramp-type technology in HTS quasiparticle injection devices

Injection of quasiparticles with an energy larger than the superconducting gap into a superconducting strip results in breaking of Cooper-pairs and hence the suppression of the superconducting properties. Experiments using planar injection devices made of HTS materials with various barrier materials showed current gains varying from 2 up to 15 at 77 K. By changing the junction size and therefore the superconducting volume the current gain could be increased. A further reduction of the junction volume is very difficult using the planar device geometry. However, by applying the ramp-type technology it is possible to reduce the junction volume by at least one order of magnitude and a further increase in current gain is expected. Another advantage of this technology is the formation of in-situ barriers and electrodes and hence a better control of the junction characteristics should be possible, also the compatibility with the processes involved making RSFQ devices can be interesting for later applications. We have fabricated ramp-type injection devices, using various types of barriers. Characterization of these devices has been performed and the results of these experiments will be presented and discussed

HTS quasiparticle injection devices with large current gain at 77 K

Recent progress on the development of planar QP-injection devices using YBCO and STO as an epitaxial injection barrier will be discussed. The main problem for HTS injection devices is to grow reliably a well defined, ultra-thin tunneling barrier suitable for QP tunneling. For this purpose, we used inverted cylindrical magnetron sputtering to first optimize the smoothness of our YBCO films by controlling tightly an relevant sputtering conditions. We are able to prepare smooth (001) YBCO films on (001) STO substrates on a routine basis with an average roughness varying between 1 and 2 nm. With these flat YBCO films both planar as well as grain boundary junctions were fabricated using epitaxial STO barriers between 2 and 8 nm thick and a 50 nm of Au counter electrode. Planar junctions with 6 nm STO barriers were in most cases fully insulating, in some cases, a current gain of up to 7.4 at 77 K was obtained. For 3 nm STO barriers, the highest current gain was 15 at 81 K. The injection results also show a scaling behavior with junction size. Based on the present materials development and device understanding, we consider a current gain of up to 20 at 77 K possibl

Response of YBCO/PCBO/YBCO ramp type Josephson junctions to near MM wave irradiation

A high Tc Josephson device for high frequency detection applications is being developed, consisting of an YBCO/PBCO/YBCO ramp type junction and a broad band log-periodic antenna. In this contribution we present the response of such a device to (near) mm wave irradiation. Shapiro steps have been observed up to very high voltage values - nearly 4 mV at 10 K, at the maximum of the radiation power. The modulation of the step amplitudes shows very good resemblence with the predictions from the Resistively Shunted Junction model

Observation of Interactions between Trapped Ions and Ultracold Rydberg Atoms

We report on the observation of interactions between ultracold Rydberg atoms and ions in a Paul trap. The rate of observed inelastic collisions, which manifest themselves as charge transfer between the Rydberg atoms and ions, exceeds that of Langevin collisions for ground state atoms by about three orders of magnitude. This indicates a huge increase in interaction strength. We study the effect of the vacant Paul trap's electric fields on the Rydberg excitation spectra. To quantitatively describe the exhibited shape of the ion loss spectra, we need to include the ion-induced Stark shift on the Rydberg atoms. Furthermore, we demonstrate Rydberg excitation on a dipole-forbidden transition with the aid of the electric field of a single trapped ion. Our results confirm that interactions between ultracold atoms and trapped ions can be controlled by laser coupling to Rydberg states. Adding dynamic Rydberg dressing may allow for the creation of spin-spin interactions between atoms and ions, and the elimination of collisional heating due to ionic micromotion in atom-ion mixtures.Comment: 7 pages, 5 figures, including appendices. Note that the title has been changed in version

Fully permanent magnet atom chip for Bose-Einstein condensation

We describe a self-biased, fully permanent magnet atom chip used to study ultracold atoms and to produce a Bose-Einstein condensate (BEC). The magnetic trap is loaded efficiently by adiabatic transport of a magnetic trap via the application of uniform external fields. Radio frequency spectroscopy is used for in-trap analysis and to determine the temperature of the atomic cloud. The formation of a Bose-Einstein condensate is observed in time of flight images and as a narrow peak appearing in the radio frequency spectrum.Comment: changed title, substantial text modifications, journal reference adde

Material aspects for preparing HTS quasiparticle injection devices

Quasiparticle (QP) injection devices based on HTS could play an important role in future superconducting applications if material aspects can be better controlled. One reason why this kind of device received little attention in the past is the lack of an appropriate barrier for QP tunnelling. In a series of experiments, we used different barriers to test if they are suitable, i.e. if a current and possibly a voltage gain can be achieved. We improved the performance of planar YBCO/natural barrier/Au devices and a current gain of more than 6 at 40 K was observed. Most devices, however, showed signs of heating effects. Another barrier material was SrTiO3 with layers of 5-6 nm thickness. Current-voltage characteristics showed that the barriers were continuous and we observed current gains of up to 3 at 60 K. PrBa2 Cu3O7-x is an interesting candidate if one could overcome the problem of resonant inelastic tunnelling for QP. In a series of experiments we demonstrated that, even for 3 Mn thin PBCO barriers on a- and c-axis oriented YBa2Cu3O7-x, most devices showed at best a current gain of 1. However, we have indications that a current gain of 10 could be possible with unity voltage gai