Search results for "Tunnelling"
showing 10 items of 218 documents
Non-adiabatic pumping of single electrons affected by magnetic fields
2009
Non-adiabatic pumping of discrete charges, realized by a dynamical quantum dot in an AlGaAs/GaAs heterostructure, is studied under influence of a perpendicular magnetic field. Application of an oscillating voltage in the GHz-range to one of two top gates, crossing a narrow wire and confining a quantum dot, leads to quantized pumped current plateaus in the gate characteristics. The regime of pumping one single electron is traced back to the diverse tunneling processes into and out-of the dot. Extending the theory to multiple electrons allows to investigate conveniently the pumping characteristics in an applied magnetic field. In this way, a qualitatively different behavior between pumping ev…
Electron-hole duality and vortex rings in quantum dots
2004
In a quantum-mechanical system, particle-hole duality implies that instead of studying particles, we can get equivalent information by studying the missing particles, the so-called holes. Using this duality picture for rotating fermion condensates the vortices appear as holes in the Fermi see. Here we predict that the formation of vortices in quantum dots at high magnetic fields causes oscillations in the energy spectrum which can be experimentally observed using accurate tunnelling spectroscopy. We use the duality picture to show that these oscillations are caused by the localisation of vortices in rings.
Charge control in laterally coupled double quantum dots
2011
4 figuras, 4 páginas.-- PACS number(s): 78.67.Hc, 73.21.La, 78.55.Cr
Phase coherence of an atomic Mott insulator
2005
International audience; We investigate the phase coherence properties of ultracold Bose gases in optical lattices, with special emphasis on the Mott insulating phase. We show that phase coherence on short length scales persists even deep in the insulating phase, preserving a finite visibility of the interference pattern observed after free expansion. This behavior can be attributed to a coherent admixture of particle/hole pairs to the perfect Mott state for small but finite tunneling. In addition, small but reproducible ``kinks'' are seen in the visibility, in a broad range of atom numbers. We interpret them as signatures for density redistribution in the shell structure of the trapped Mott…
Magnetism and Hund's Rule in an Optical Lattice with Cold Fermions
2007
Artificially confined, small quantum systems show a high potential for employing quantum physics in technology. Ultra-cold atom gases have opened an exciting laboratory in which to explore many-particle systems that are not accessible in conventional atomic or solid state physics. It appears promising that optical trapping of cold bosonic or fermionic atoms will make construction of devices with unprecedented precision possible in the future, thereby allowing experimenters to make their samples much more "clean", and hence more coherent. Trapped atomic quantum gases may thus provide an interesting alternative to the quantum dot nanostructures produced today. Optical lattices created by stan…
State preparation and dynamics of ultracold atoms in higher lattice orbitals
2007
We report on the realization of a multi-orbital system with ultracold atoms in the excited bands of a 3D optical lattice by selectively controlling the band population along a given lattice direction. The lifetime of the atoms in the excited band is found to be considerably longer (10-100 times) than the characteristic time scale for inter-site tunneling, thus opening the path for orbital selective many-body physics with ultracold atoms. Upon exciting the atoms from an initial lowest band Mott insulating state to higher lying bands, we observe the dynamical emergence of coherence in 1D (and 2D), compatible with Bose-Einstein condensation to a non-zero momentum state.
Effect of the electromagnetic environment on arrays of small normal metal tunnel junctions: Numerical and experimental investigation
2000
We present results of a set of experiments to investigate the effect of dissipative external electromagnetic environment on tunneling in linear arrays of junctions in the weak tunneling regime. The influence of this resistance decreases as the number of junctions in the chain increases and ultimately becomes negligible. Further, there is a value of external impedance, typically \~5 k$\Omega$, at which the half-width of the zero-voltage dip in the conductance curve shows a maximum. Some new analytical formulae, based on the phase-correlation theory, along with numerical results will be presented.
Thermometry by Arrays of Tunnel Junctions
1994
We show that arrays of tunnel junctions between normal metal electrodes exhibit features suitable for primary thermometry in an experimentally adjustable temperature range where thermal and charging effects compete. $I\ensuremath{-}V$ and $\frac{\mathrm{dI}}{\mathrm{dV}}$ vs $V$ have been calculated for two junctions including a universal analytic high temperature result. Experimentally the width of the conductance minimum in this regime scales with $T$ and $N$, the number of junctions, and its value (per junction) agrees with the calculated one to within 3% for large $N$. The height of this feature is inversely proportional to $T$.
Competition between carrier recombination and tunneling in quantum dots and rings under the action of electric fields
2008
6 páginas, 3 figuras.-- Proceedings of the 7th International Conference on Physics of Light-Matter Coupling in Nanostructures.
Low-energy excitations from interacting tunneling units in the mean-field approximation
1991
Abstract The low-energy excitation spectrum of dilute concentrations of interacting tunneling quadrupoles randomly distributed in a non-polar medium was studied in the mean-field approximation. In particular the case of six-orientational tunneling quadrupoles (TQs) with a r−3 (elastic) interaction was considered. Because of the random position of the TQs, the internal field in a random variable and for relatively low concentrations has a Lorenzian probability distribution. The low-energy density of states is a constant and the low-energy excitations arise from the large internal fields, i.e. strongly interacting tunneling quadrupoles. The low-energy excitations were compared with those obta…