Ballistic transport of electrons far from equilibrium is investigated in a cold two-dimensional electron system. In a three-terminal device, we realize an electronic version of the Venturi effect that enables us to build an avalanche amplifier based on non-equilibrium electrons. This device might be developed further to create a non-invasive charge detector. A preliminary model based on numerical calculations using a random phase approximation is in agreement with our data.
[more] We study a mesoscopic disordered quasi-1D ring weakly coupled to leads, where the Aharonov-Bohm effect and weak-localization of the electrons lead to so-called Altshuler-Aronov-Spivak (AAS) oscillations of the conductance. The dephasing time limits the amplitude of these oscillations and we analyze its dependence on temperature T in the presence of electron interactions. Using an influence functional for quantum Nyquist noise, which takes into account the Pauli blocking of the Fermi sea, we describe the crossover for the dephasing time from diffusive or ergodic 1D to 0D behavior as T drops below the Thouless energy. The crossover to 0D, predicted earlier for 2D and 3D systems, has so far eluded experimental observation. We show that the ring geometry holds promise of meeting this longstanding challenge, since the crossover manifests itself not only in the smooth part of the magnetoconductance but also in the amplitude of the AAS oscillations. This allows to filter out distorting contributions due to dephasing in the leads.
[more] We propose an approach to investigate non-equilibrium photon dynamics driven by mechanical motion in a recently developed optomechanical setup with a membrane between two mirrors. The presence of a photon in the left or the right half of the cavity can be identified with the two states of a two-level system, loosely speaking. Mechanical driving can shuttle photons between the two halves of the cavity and opens up the whole domain of strongly driven quantum systems to the field of optomechanics. Depending on the driving strength we predict the possibility to observe an Autler-Townes splitting as well as Landau-Zener-Stueckelberg dynamics originally known from atomic two-state systems.
[more] We show that a realistic description of the classic Kondo systems of iron impurities in the noble metals gold and silver is given by the fully screened, 3-channel spin 3/2 Kondo model. It yields excellent agreement between theory and experiment for the temperature dependence of both the resistivity and the decoherence rate, studied via weak localization. This result sets a benchmark for the level of quantitative understanding attainable for the Kondo effect in real materials.
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