Quantum transitions induced by the third cumulant of current fluctuations

We investigate the transitions induced by external current fluctuations on a small probe quantum system. The rates for the transitions between the energy states are calculated using the real-time Keldysh formalism for the density matrix evolution. We especially detail the effects of the third cumulant of current fluctuations inductively coupled to a quantum bit and propose a setup for detecting the frequency-dependent third cumulant through the transitions it induces.Comment: 4 pages, 3 figure

Lääkejäämät jätevedessä

Tiivistelmä. Lääkkeiden käyttö lisääntyy jatkuvasti, mikä lisää myös lääkepäästöjä ympäristöön. Lääkeaineita joutuu viemäriin, kun ne poistuvat käytön jälkeen ihmisten ja eläinten elimistöstä, tai jos lääkkeitä hävitetään virheellisesti viemäriin. Jäteveteen tulee lääkepäästöjä myös teollisuudesta. Lääkeaineet kuormittavat jätevedenpuhdistamoita, eikä niitä saada nykyisin käytössä olevilla puhdistusprosesseilla kokonaan puhdistettua jätevedestä, joten osa päätyy vesistöön. Lääkeaineiden parempaan poistamiseen jätevedestä on kehitetty uusia menetelmiä, mutta kustannukset jarruttavat niiden käyttöönottoa. Lääkeaineet ovat haitallisia ympäristölle. Sukupuolihormonit häiritsevät kalojen lisääntymistoimintaa, mielialalääkkeet vaikuttavat niiden käyttäytymiseen, antibiootit tappavat luonnon mikrobeja ja aiheuttavat antibioottiresistenssiä, ja tulehduskipulääkkeet voivat olla vesieliöille tappavan myrkyllisiä. Lääkeaineet vaikuttavat vesiekosysteemissä kokonaisiin ravintoverkkoihin, ja uhkaavat näin ekosysteemin tasapainoa. Jäteveden puhdistusprosesseja tulisi kehittää paremmin lääkeaineiden puhdistamiseen soveltuviksi. Lääkeaineiden poistamiselle jätevedestä ei tällä hetkellä ole jätevedenpuhdistamoiden ympäristöluvissa erikseen velvoitetta. EU-lainsäädäntöön ollaan kuitenkin lisäämässä raja-arvot tiettyjen lääkeaineiden puhdistumille. Lääkejäämien määrää jätevedessä voitaisiin vähentää myös edistämällä lääkkeiden rationaalista käyttöä, karsimalla turhia ja päällekkäisiä lääkityksiä sekä valistamalla ihmisiä lääkkeiden oikeaoppisesta hävittämisestä

Mesoscopic persistent currents in a strong magnetic field

Recent precision measurements of mesoscopic persistent currents in normal-metal rings rely on the interaction between the magnetic moment generated by the current and a large applied magnetic field. Motivated by this technique, we extend the theory of mesoscopic persistent currents to include the effect of the finite thickness of the ring and the resulting penetration of the large magnetic field. We discuss both the sample-specific typical current and the ensemble-averaged current which is dominated by the effects of electron-electron interactions. We find that the magnetic field strongly suppresses the interaction-induced persistent current and so provides direct access to the independent-electron contribution. Moreover, the technique allows for measurements of the entire distribution function of the persistent current. We also discuss the consequences of the Zeeman splitting and spin-orbit scattering, and include a detailed and quantitative comparison of our theoretical results to experimental data.Comment: 12 pages, 7 figure

The Josephson heat interferometer

The Josephson effect represents perhaps the prototype of macroscopic phase coherence and is at the basis of the most widespread interferometer, i.e., the superconducting quantum interference device (SQUID). Yet, in analogy to electric interference, Maki and Griffin predicted in 1965 that thermal current flowing through a temperature-biased Josephson tunnel junction is a stationary periodic function of the quantum phase difference between the superconductors. The interplay between quasiparticles and Cooper pairs condensate is at the origin of such phase-dependent heat current, and is unique to Josephson junctions. In this scenario, a temperature-biased SQUID would allow heat currents to interfere thus implementing the thermal version of the electric Josephson interferometer. The dissipative character of heat flux makes this coherent phenomenon not less extraordinary than its electric (non-dissipative) counterpart. Albeit weird, this striking effect has never been demonstrated so far. Here we report the first experimental realization of a heat interferometer. We investigate heat exchange between two normal metal electrodes kept at different temperatures and tunnel-coupled to each other through a thermal `modulator' in the form of a DC-SQUID. Heat transport in the system is found to be phase dependent, in agreement with the original prediction. With our design the Josephson heat interferometer yields magnetic-flux-dependent temperature oscillations of amplitude up to ~21 mK, and provides a flux-to-temperature transfer coefficient exceeding ~ 60mK/Phi_0 at 235 mK [Phi_0 2* 10^(-15) Wb is the flux quantum]. Besides offering remarkable insight into thermal transport in Josephson junctions, our results represent a significant step toward phase-coherent mastering of heat in solid-state nanocircuits, and pave the way to the design of novel-concept coherent caloritronic devices.Comment: 4+ pages, 3 color figure

Influence of forest management changes and reuse of peat production areas on water quality in a northern river

In Northern Finland, the most significant land use challenges are related to bioenergy production from peat extraction and forest biomass. Increasing societal demand for bioenergy may increase production rates. However, environmental impacts of peat extraction are of increasing concern, which has led to a decline in production, thereby freeing up these areas for other uses. Using storylines for different societal futures and process-based models (PERSiST and INCA), we simulated the effect of simultaneous land use change and climate change on water quality (phosphorus, nitrogen and suspended sediments concentration). Conversion of peat extraction areas to arable land, together with climate change, may pose a risk for deterioration of ecological status. On the other hand, continuous forestry may have positive impacts on water quality. Suspended sediment concentrations in the river do not exceed water quality requirements for salmonids, but nitrogen concentrations may exceed threshold values especially during high flows. A storyline emphasizing sustainable development in energy pro-duction led to the best outcome in terms of water protection

Ultra-Sensitive Hot-Electron Nanobolometers for Terahertz Astrophysics

The background-limited spectral imaging of the early Universe requires spaceborne terahertz (THz) detectors with the sensitivity 2-3 orders of magnitude better than that of the state-of-the-art bolometers. To realize this sensitivity without sacrificing operating speed, novel detector designs should combine an ultrasmall heat capacity of a sensor with its unique thermal isolation. Quantum effects in thermal transport at nanoscale put strong limitations on the further improvement of traditional membrane-supported bolometers. Here we demonstrate an innovative approach by developing superconducting hot-electron nanobolometers in which the electrons are cooled only due to a weak electron-phonon interaction. At T<0.1K, the electron-phonon thermal conductance in these nanodevices becomes less than one percent of the quantum of thermal conductance. The hot-electron nanobolometers, sufficiently sensitive for registering single THz photons, are very promising for submillimeter astronomy and other applications based on quantum calorimetry and photon counting.Comment: 19 pages, 3 color figure