Quantum capacitive phase detector

We discuss how a single Cooper-pair transistor may be used to detect the superconducting phase difference by using the phase dependence of the input capacitance from gate to the ground. The proposed device has a low power dissipation because its operation is in principle free from quasiparticle generation. According to the sensitivity estimates the device may be used for efficient qubit readout in a galvanically isolated and symmetrized circuit.Comment: 5 pages, published for

Kalojen kasvu Kyrönjoella vuosina 2007-2010 : Vesistötöiden velvoitetarkkailu

Kyrönjoessa tehtyjen vesistötöiden vaikutusta kalojen kasvuun tutkittiin neljältä eri pyyntipaikalta vuosina 2007–10 saadusta koeverkkosaalisaineistosta. Keskeiset tutkimuslajit olivat ahven ja särki. Aineiston perusteella määritettiin lajien suhteelliset vuosiluokkien vahvuudet, verrattiin havaittuja keskipituuksia ja kuntokertoimia sekä tehtiin luutumanäytteiden perusteella takautuva kasvunmääritys. Vertailu suoritettiin joko kaikkien pyyntipaikkojen välillä tai Malkakosken padon ylä- ja alapuolella sijaitsevien paikkojen välillä. Suhteelliset vuosiluokkien vahvuudet jaksolla 1998–2008 vaihtelivat melko satunnaisesti ilman korrelaatiota käytettyyn pH- tai lämpötilaindeksiin. Vuosiluokkien vahvuuden vaihtelu ei antanut viitteitä myöskään vesistötöiden vaikutuksista kummankaan lajin lisääntymismenestykseen. 1-3-vuotiaiden ahventen ja särkien havaittu keskipituus oli selvästi suurempi Malkakosken alapuolisilla pyyntipaikoilla verrattuna yläpuolisiin. Sama suuntaus näkyi kuntokertoimissa, joskaan ei yhtä selvästi. Vanhemmilla kaloilla merkitseviä eroja padon eri puolilla ei ollut. Takautuvasti määritetyt pituudet olivat 1- ja 2-vuotiailla särjillä ja 2-4-vuotiailla lahnoilla suurempia padon alapuolisilla pyyntipaikoilla. Ahvenella ero näkyi vain 2-vuotiailla kaloilla, mitä vanhemmilla yksilöillä kasvu oli nopeampaa padon yläpuolella. Saadut tulokset näyttäisivät viittaavan hidastuneeseen kasvuun Malkakosken yläpuolisilla pyyntipaikoilla tai ainakin lisääntyneeseen kasvunopeuden eroon padon eri puolilla vuoden 2003 jälkeen. Aiemmissa seurantatuloksissa ero kasvunopeudessa on ollut pikemminkin päinvastainen, mikä saattaa selittyä 2000-luvun vaihteen voimaperäisten kaivu- ja perkaustöiden vaikutuksilla. Vuosina 2002 ja -03 tapahtunut vedenpinnan nosto Malkakosken padon kohdalla vaikuttaa kuitenkin heikentäneen yläpuolisen jokiosuuden ravinto- ja lisääntymisolosuhteita. Tämä saattaa johtua perkaustöiden haitallisista vaikutuksista rantavyöhykkeen kasvillisuuteen, kuten ulpukkavyöhykkeiden vähentymisestä niiden jäätyä liian syvään veteen. Myös muista syistä kuin vesistötöistä johtuvat vedenlaadun vaihtelut säätelevät voimakkaasti Kyrönjoen eliöyhteisöjä, joten aukottomien johtopäätösten tekeminen kunkin toimenpiteen vaikutusta arvioitaessa on ongelmallista

The Inductive Single-Electron Transistor (L-SET)

We demonstrate a sensitive method of charge detection based on radio-frequency readout of the Josephson inductance of a superconducting single-electron transistor. Charge sensitivity $1.4 \times 10^{-4}e/\sqrt{Hz}$, limited by preamplifier, is achieved in an operation mode which takes advantage of the nonlinearity of the Josephson potential. Owing to reactive readout, our setup has more than two orders of magnitude lower dissipation than the existing method of radio-frequency electrometry. With an optimized sample, we expect uncoupled energy sensitivity below $\hbar$ in the same experimental scheme.Comment: 10 page

Quantum device applications of mesoscopic superconductivity

The work involves a study of physical phenomena that take place at very small length scales, below one micro-meter. At temperatures roughly below one degree Kelvin, quantum-mechanical effects may rule in electronic transport. Macroscopic quantum-coherent effects that occur in metallic superconducting microstructures, are particularly intriguing. Large-scale quantum information processing is widely believed to be attainable utilizing such physical systems. This work concentrates on answering the question of how the described quantum-mechanical systems may be used as sensitive measuring devices. Considerable attention is paid to energy-storing metallic microstructures whose electrical properties resemble those of the familiar inductor or capacitor. This research involves primarily experimental investigations conducted around temperatures of 0.1 Kelvin. Methods both at low and at radio frequencies have been used. The experimental findings have been modelled theoretically, and theoretical concepts for new physical phenomena have been introduced. An inductively measured radio-frequency Cooper-pair transistor, the L-SET, has been developed and experimentally verified in this work. Being highly sensitive, fast, and non-invasive, the L-SET appears to be the most promising method for measuring electric charge. Sensitivity in charge measurements of 20 millionths of the electron charge (micro-e) within one second, and an input bandwidth of 100 MHz, have been demonstrated. It has been shown theoretically that the ultimate measurement accuracy is about 0.1 micro-e within a second. A new phase detector based on the Cooper-pair transistor has been proposed. This system has also been shown to be potentially usable as a quantum bit. A new type of radio-frequency single-electron transistor built using a multi-walled carbon nanotube has been fabricated and operated. Technologies have been developed in order to make the physical nano- or microstructures. A method has been presented to fabricate non-superconducting tunnel junctions. Consequences of the inverse superconducting proximity effect on the studied superconducting structures were considered. Measurement procedures were investigated for a new low-noise nanoamplifier, the Bloch-oscillating transistor. Single superconducting tunnel junctions were tested as detectors of energy states of the environment, or of noise.reviewe

Dielectric losses in multi-layer Josephson junction qubits

We have measured the excited state lifetimes in Josephson junction phase and transmon qubits, all of which were fabricated with the same scalable multi-layer process. We have compared the lifetimes of phase qubits before and after removal of the isolating dielectric, SiNx, and find a four-fold improvement of the relaxation time after the removal. Together with the results from the transmon qubit and measurements on coplanar waveguide resonators, these measurements indicate that the lifetimes are limited by losses from the dielectric constituents of the qubits. We have extracted the individual loss contributions from the dielectrics in the tunnel junction barrier, AlOx, the isolating dielectric, SiNx, and the substrate, Si/SiO2, by weighing the total loss with the parts of electric field over the different dielectric materials. Our results agree well and complement the findings from other studies, demonstrating that superconducting qubits can be used as a reliable tool for high-frequency characterization of dielectric materials. We conclude with a discussion of how changes in design and material choice could improve qubit lifetimes up to a factor of four.Comment: 10 pages, 4 figures,and 4 table

Charge sensitivity of the Inductive Single-Electron Transistor

We calculate the charge sensitivity of a recently demonstrated device where the Josephson inductance of a single Cooper-pair transistor is measured. We find that the intrinsic limit to detector performance is set by oscillator quantum noise. Sensitivity better than $10^{-6}$e$/\sqrt{\mathrm{Hz}}$ is possible with a high $Q$-value $\sim 10^3$, or using a SQUID amplifier. The model is compared to experiment, where charge sensitivity $3 \times 10^{-5}$e$/\sqrt{\mathrm{Hz}}$ and bandwidth 100 MHz are achieved.Comment: 3 page

Drinking water quality in the alpine pastures of the eastern Tibetan plateau

The need for water quality research on the Tibetan plateau has arisen after the rangeland was allocated and leased as pasture grounds to individual nomadic families in the 1990s. These policies changed the access to water sources. The imposed fencing of the pasture tenures makes the situation even more delicate. Nomadic families are now obliged to use only water sources existing on their own site. The restrictions have caused the urge to use all available water, which resulted in increasing water quality and quantity problems. In the past, natural water sources were in common use. During the Collective era, machine-dug wells near the collective settlements facilitated the procurement of drinking water. Based on recent investigations in Dzoge county (Sichuan province), the nomadic families of some regions considered the availability of adequate drinking water for humans and animals as their biggest problem. For this study, eight water samples were collected from the Dzoge county area. All samples were from different kinds of sources, but all in continuous use by humans and animals. The samples were analyzed for typical potable water quality factors (hygienic and technique-aesthetic). The results show that the Chinese national guideline values were exceeded for NO4-N and PO4-P in most open sampling locations. Those parameters do not spoil the water by themselves, but together with suspended solids and organic materials produce a great environment for bacteria like E. coli and fecal streptococci to grow. The result analysis and pictures seen from the location reveal that bacterial growth may be the biggest problem in water quality. Even primitive protection around the water source (i.e. concrete rings, wooden barriers around edges, covers) seem to have a great impact on water quality