Tunable superconducting microstrip resonators

We report on a simple yet versatile design for a tunable superconducting microstrip resonator. Niobium nitride is employed as the superconducting material and aluminum oxide, produced by atomic layer deposition, as the dielectric layer. We show that the high quality of the dielectric material allows to reach the internal quality factors in the order of Q(i) similar to 10(4) in the single photon regime. Q(i) rapidly increases with the number of photons in the resonator N and exceeds 10(5) for N similar to 10 - 50. A straightforward modification of the basic microstrip design allows to pass a current bias through the strip and to control its kinetic inductance. We achieve a frequency tuning delta f = 62 MHz around f(0) = 2.4 GHz for a fundamental mode and delta f = 164MHz for a third harmonic. This translates into a tuning parameter Q(i)delta f/f(0) = 150. The presented design can be incorporated into essentially any superconducting circuitry operating at temperatures below 2.5K

An ultra sensitive radio frequency single electron transistor working up to 4.2 K

We present the fabrication and measurement of a radio frequency single electron transistor (rf-SET), that displays a very high charge sensitivity of 1.9 microlectrons/sqrt(Hz) at 4.2 K. At 40 mK, the charge sensitivity is 0.9 and 1.0 microlectrons/sqrt(Hz) in the superconducting and normal state respectively. The sensitivity was measured as a function of radio frequency amplitude at three different temperatures: 40 mK, 1.8 K and 4.2 K.Comment: 13 pages, 4 figure

Galvanically split superconducting microwave resonators for introducing internal voltage bias

We present the design and performance of high-Q superconducting niobium nitride microwave resonators intended for use in hybrid quantum systems, coupling spin degrees of freedom to the cavity mode, both magnetically and electrically. We demonstrate a solution that allows to introduce static electric fields in the resonator without compromising the microwave performance. Quality factors above 10(5) remain unchanged in strong applied static electric fields above 10 MV/m and magnetic fields up to similar to 400 mT. By design, the configuration of the dc field matches that of the microwave field, especially advantageous for experiments on electrostatically controlled spin systems

Scaling of self-stimulated spin echoes

Self-stimulated echoes have recently been reported in the high cooperativity and inhomogeneous coupling regime of spin ensembles with superconducting resonators. In this work, we study their relative amplitudes using echo-silencing made possible by a fast frequency tunable resonator. The highly anisotropic spin linewidth of Er$^{3+}$ electron spins in the CaWO$_4$ crystal also allows to study the dependence on spin-resonator ensemble cooperativity. It is demonstrated that self-stimulated echoes primarily result from a combination of two large control pulses and the echo preceding it

Quantifying dynamics and interactions of individual spurious low-energy fluctuators in superconducting circuits

Understanding the nature and dynamics of material defects in superconducting circuits is of paramount importance for improving qubit coherence and parameter stability and much needed for implementing large-scale quantum computing. Here we present measurements on individual highly coherent environmental two-level systems (TLS). We trace the spectral diffusion of specific TLS and demonstrate that it originates from the TLS coupling to a small number of low energy incoherent fluctuators. From the analysis of these fluctuations, we access the relevant parameters of low energy fluctuators: Dipole moments, switching energies, and, more importantly, interaction energies. Our approach opens up the possibility of deducing the macroscopic observables in amorphous glassy media from direct measurements of local fluctuator dynamics at the microscopic level- A route towards substantiating commonly accepted, but so far phenomenological, models for the decohering environment

Prisutnost bakterija u zraku nastambi za svinje i neposrednom okolišu

This paper describes a bacteriological analysis of air samples taken from swine housing facilities and the immediate environment. The air volume of the samples was pre-programmed by a standard air sampler (MAS-100, Merck) and was directly impacted onto the bacteriologic agar surface (Petri dishes, standard diameter of 90 mm). The bacterial contamination in forty-eight samples was 2.59x105 CFU/m3 (ranging from 8.46x104 to 5.30x105 CFU/m3). Potentially pathogenic bacterial agents predominated in all samples (100%), while primarily pathogenic bacteria were isolated in a minor proportion of samples (33%–66%). Airborne bacterial contamination in samples (N=16) obtained from emptied facilities ranged from 1.8x103 CFU/m3 (that is, after coarse mechanical washing) to 0.8x102 CFU/m3 (upon completion of disinfection). Control measurements at different locations and distance from the farm (N=32) pointed to the presence of non-pathogenic airborne bacteria, ranging from 1.55x102 to 3.70x102 CFU/m3. The results of this preliminary study showed that the emission of potentially pathogenic bacteria from animal housing facilities to the immediate farm environment via aerosol was very low.Pored kontrole emisija štetnih plinova, vlage i čestica prašine u nastambama za životinje, važna je i detekcija ukupne bakterijske kontaminacije zraka. Od posebnog su značenja i moguće emisije u okoliš, osobito potencijalno ili primarno patogenih bakterija. U raspravi su prikazani rezultati prvih istraživanja bakterijske kontaminacije zraka u nastambama, kao i u neposrednom okolišu provedenih na jednoj farmi svinja. Programirani volumen zraka standardnim je skupljačem zraka (MAS-100-Merck) direktno naslojen na površine bakterioloških podloga (Petrijeve ploče promjera 90 mm). U pretraženih 48 uzoraka u nastambama ustanovljena je prosječna bakterijska kontaminacija zraka za farmu od 2,595 CFU/m3 (od 8,464 do 5,305). U svim su uzorcima dominantno bili prisutni Streptococcus spp., Micrococcus spp., Escherichia coli, Staphylococcus aureus i Streptococcus suis. U manjem broju uzoraka izdvojeni su potencijalno patogeni uzročnici Pasteurella multocida (66%), Actinobacillus suis (50%), hemolitični sojevi E. coli (41%) te Pasteurella haemolytica, Bordetella bronchiseptica i Actinobacillus pleuropneumoniae (33%). Mjerenjima u praznim objektima, prije useljenja životinja (16 uzoraka), ustanovljena je srednja kontaminacija zraka od 9,01 do 0,41 CFU/m3 s bakterijskim uzročnicima Streptococcus spp., Staphylococcus spp. i E. coli. Kontrolna mjerenja izvan objekata (32 uzorka) upozorila su na prosječnu kontaminaciju zraka od 0,261 CFU/m3 (od 0,151 do 0,371) i uz zastupljenost apatogenih uzročnika Bacillus subtilis, Bacillus cereus, E. coli, Streptococcus spp., Micrococcus spp. i Staphylococcus spp. Rezultati pokazuju da su neznatne emisije potencijalno patogenih bakterijskih uzročnika putem aerosola iz nastambi za svinje u neposredni okoliš. Unatoč sve sofisticiranijim uređajima za monitoring, ni danas još, u okviru programa animalne higijene, nisu određene granične vrijednosti za bakteriološku kontaminaciju zraka kao što je to slučaj s emisijom štetnih plinova NH3 i CO2

Magnetic field resilient superconducting fractal resonators for coupling to free spins

We demonstrate a planar superconducting microwave resonator intended for use in applications requiring strong magnetic fields and high quality factors. In perpendicular magnetic fields of 20 mT, the niobium resonators maintain a quality factor above 25 000 over a wide range of applied powers, down to single photon population. In parallel field, the same quality factor is observed above 160 mT, the field required for coupling to free spins at a typical operating frequency of 5 GHz. We attribute the increased performance to the current branching in the fractal design. We demonstrate that our device can be used for spectroscopy by measuring the dissipation from a pico-mole of molecular spins

Enhanced Josephson coupling in hybrid nanojunctions

We have fabricated NbN/Au nanogaps and bridged them with an Al superconductor using Ti as an interlayer. The nanodevices show a critical current density at 300 mK as high as 3 7106A/cm2, which is 30% higher than that of Al nanowires with the same lateral dimensions as the NbN-based devices. The response of the critical current as a function of the external magnetic field clearly showed a Fraunhofer-like behavior, indicating a Josephson coupling between the NbN electrodes through the Al barrier. The superconducting transport evolves into different transport regimes as a function of the temperature. These findings demonstrate the importance of using superconducting barriers in hybrid nanodevices to achieve very high Josephson current in nanodevices of great relevance in superconducting circuits requiring high integration density