Laurent Saminadayar

ABSTRACT The time τ φ over which an electron can maintain its phase coherence at low temperatures is of fundamental importance in mesoscopic systems. The observability of many phenomena, such as the Aharonov Bohm effect, the universal conductance fluctuations, the weak localisation correction to the conductance, persistent current in ringstructures and many more rely on a long enough phase coherence time. In disordered conductors and within the standard Fermi liquid picture, the phase coherence time is expected to diverge at zero temperature. However, most experiments show a saturating phase coherence time at low temperatures. This saturation has often been attributed to the presence of a small amount of magnetic impurities giving rise to the so-called Kondo effect. In this paper, we present a brief review of recent advances, both experimental and theoretical, in the understanding of dephasing by magnetic impurities in the framework of the Kondo effect. they have founded a research group devoted to the study of quantum (spin) transport in nanoscale devices at the Néel Institute, Grenoble, France. Their work concerns quantum coherence in Kondo systems and spin glasses, Kondo effect in semiconductor nanostructures and more recently spin based quantum bits and nanomechanics. The group has good expertise in very low temperature physics under high magnetic field, ultra-low noise transport measurements and micro-SQUID magnetometry. 2 C. Bäuerle et al. Pascal Degiovanni is CNRS researcher at the École Normale Supérieure of Lyon, in the condensed matter theory group. He has worked in decoherence problems in superconducting qubits, cavity QED and Luttinger liquids. He is now working on the development of quantum optics formalism for electrons. His expertise includes field theory methods in condensed matter physics as well as dissipative quantum dynamics.

We present a comprehensive experimental study of mesoscopic noise in a GaAs quantum point contact. In agreement with existing theory, we find that the measured noise power is strongly reduced from the full shot noise 2eI (I is the time-averaged current) expected for completely uncorrelated electron transport. Study of the temperature dependence of the noise clearly demonstrates the transition from

... 8 APRIL 1996 Experimental Test of the Quantum Shot Noise Reduction Theory A. Kumar, L. Saminadayar, and ... below 200 mK the thermalization length of electrons with phonons is largerthan the sample ... We thank P. Jacques for valuable technical help, P. Pari and P. Forget for ...

ABSTRACT We present measurements of the magnetic response of a network of connected mesoscopic GaAs/GaAlAs rings whose total size is much larger than the phase coherence length. We observe a clear magnetic response with a flux periodicity of h/e. Direct comparison with measurements on the same sample with isolated rings shows that the persistent current is only weakly affected by the connection of the rings.

ABSTRACT We present calculations of the quantum oscillations appearing in the transmission of a mesoscopic GaAs/GaAlAs ring isolated by quantum point contacts. We show that the device acts as an electronic Fabry–Perot spectrometer in the quantum Hall effect regime, and discuss the effect of the coherence length of edge states.

We present a comprehensive experimental study of mesoscopic noise in a GaAs quantum point contact. In agreement with existing theory, we find that the measured noise power is strongly reduced from the full shot noise 2eI (I is the time-averaged current) expected for completely uncorrelated electron transport. Study of the temperature dependence of the noise clearly demonstrates the transition from