Aharonov-Bohm cages in the GaAlAs/GaAs system

Aharonov-Bohm oscillations have been observed in a lattice formed by a two dimensional rhombus tiling. This observation is in good agreement with a recent theoretical calculation of the energy spectrum of this so-called T3 lattice. We have investigated the low temperature magnetotransport of the T3 lattice realized in the GaAlAs/GaAs system. Using an additional electrostatic gate, we have studied the influence of the channel number on the oscillations amplitude. Finally, the role of the disorder on the strength of the localization is theoretically discussed.Comment: 6 pages, 11 EPS figure

A V-shape superconducting artificial atom based on two inductively coupled transmons

Circuit quantum electrodynamics systems are typically built from resonators and two-level artificial atoms, but the use of multi-level artificial atoms instead can enable promising applications in quantum technology. Here we present an implementation of a Josephson junction circuit dedicated to operate as a V-shape artificial atom. Based on a concept of two internal degrees of freedom, the device consists of two transmon qubits coupled by an inductance. The Josephson nonlinearity introduces a strong diagonal coupling between the two degrees of freedom that finds applications in quantum non-demolition readout schemes, and in the realization of microwave cross-Kerr media based on superconducting circuits.Comment: 5 pages, 3 figure

Probing Spin-Charge Separation in Tunnel-Coupled Parallel Quantum Wires

Interactions in one-dimensional (1D) electron systems are expected to cause a dynamical separation of electronic spin and charge degrees of freedom. A promising system for experimental observation of this non-Fermi-liquid effect consists of two quantum wires coupled via tunneling through an extended uniform barrier. Here we consider the minimal model of an interacting 1D electron system exhibiting spin-charge separation and calculate the differential tunneling conductance as well as the density-density response function. Both quantities exhibit distinct strong features arising from spin-charge separation. Our analysis of these features within the minimal model neglects interactions between electrons of opposite chirality and applies therefore directly to chiral 1D electron systems realized, e.g., at the edge of integer quantum-Hall systems. Physical insight gained from our results is useful for interpreting current experiment in quantum wires as our main conclusions still apply with nonchiral interactions present. In particular, we discuss the effect of charging due to applied voltages, and the possibility to observe spin-charge separation in a time-resolved experiment.Comment: 9 pages, 3 figures, expanded version with many detail

Alteration of superconductivity of suspended carbon nanotubes by deposition of organic molecules

We have altered the superconductivity of a suspended rope of single walled carbon nanotubes, by coating it with organic polymers. Upon coating, the normal state resistance of the rope changes by less than 20 percent. But superconductivity, which on the bare rope shows up as a substantial resistance decrease below 300 mK, is gradualy suppressed. We correlate this to the suppression of radial breathing modes, measured with Raman Spectroscopy on suspended Single and Double-walled carbon nanotubes. This points to the breathing phonon modes as being responsible for superconductivity in carbon nanotubes

Epitaxial rhenium microwave resonators

International audienceWe have fabricated rhenium microwave resonators from epitaxial films. We have used thin films of different structural quality depending on their growth conditions. The resonators were coupled to a microwave transmission line which allows the measurement of their resonance frequencies and internal quality factors. From the resonance frequency at low temperature , the effective penetration depth and the London penetration depth of the rhenium film are extracted