Abstract: We present the first experimental realization of a widely frequency tunable, non-degenerate three-wave mixing device for quantum signals at GHz frequency. It is based on a new superconducting building-block consisting of a ring of four Josephson junctions shunted by a cross of four linear inductances. The phase configuration of the ring remains unique over a wide range of magnetic fluxes threading the loop. It is thus possible to vary the inductance of the ring with flux while retaining a strong, dissipation-free, and noiseless non-linearity. The device has been operated in amplifier mode and its noise performance has been evaluated by using the noise spectrum emitted by a voltage biased tunnel junction at finite frequency as a test signal. The unprecedented accuracy with which the crossover between zero-point-fluctuations and shot noise has been measured provides an upper-bound for the noise and dissipation intrinsic to the device.
Abstract: This article discusses three experiments on the properties of electronic transport at the mesoscopic scale. The first one allowed to measure the energy exchange rate between electrons in a metal contaminated by a very weak concentration of magnetic impurities. The role played by magnetic impurities in the Kondo regime on those energy exchanges is quantitatively investigated, and the global measured exchange rate is larger than expected. The second experiment is a measurement of the current-phase relation in a system made of two superconductors linked through a single atom. We thus provide quantitative support for the recent description of the mesoscopic Josephson effect. The last experiment is a measurement of the asymmetry of the current fluctuations in a mesoscopic conductor, using a Josephson junction as a threshold detector.
Abstract: We have used a manipulation stage to electrically contact individual nanotube bundles coated with metal nanoparticles for in-situ studies in a transmission electron microscope. When electrical current is passed through a bundle, unusual mass transport is observed along that bundle. Nanocrystals melt and disappear from a given section, with a correlated growth of similar nanoparticles further along the bundle. This unusual phenomenon, termed nanowicking, may provide a method for controlled nanoscale mass transport.
Abstract: Amplifiers are crucial in every experiment carrying out a very sensitive measurement. However, they always degrade the information by adding noise. Quantum mechanics puts a limit on how small this degradation can be. Theoretically, the minimum noise energy added by a phase-preserving amplifier to the signal it processes amounts at least to half a photon at the signal frequency. In this article, we show that we can build a practical microwave amplifying circuit that fulfills the minimal requirements to reach this quantum limit. The readout of solid-state qubits, and more generally, the measurement of very weak signals in various areas of science, can benefit from this new superconducting device. We also discuss how our circuit can be the basic buiding block for a variety of practical applications such as frequency conversion with and without photon number gain, dynamic cooling and production of entangled signal pairs.
