Scaling Of The Coulomb Energy Due To Quantum Fluctuations In The Charge Of A Quantum Dot

The charging energy of a quantum dot is measured through the effect of its potential on the conductance of a second dot. This technique allows a measurement of the scaling of the dot's charging energy with the conductance of the tunnel barriers leading to the dot. We find that the charging energy scales quadratically with the reflection probability of the barriers. In a second experiment we study the transition from a single to a double-dot which exhibits a scaling behavior linear in the reflection probability. The observed power-laws agree with a recent theory.Comment: 5 pages, uuencoded and compressed postscript file, with figure

Preamble Design for Data-Aided Synchronization of Single Side Band Continuous Phase Modulation

International audienceIn this paper, we calculate the Cramer-Rao bound (CRB) for single side band continuous phase modulation signals (SSB-FSK). The CRB is useful to design an optimum preamble sequence to jointly estimate the frequency offset, symbol timing, and carrier phase. The goal is to find preamble sequences that minimize the CRBs of all estimated parameters. The results provide some useful preambles, which can be added to data packets for synchronization in burst-mode SSB-FSK transmissions. © 2020 URSI

Noise in Carbon Nanotubes in the Kondo regime

The Kondo effect is a very active subject in condensed matter physics and a paradigm for strongly correlated electronic system s. It arises as a resonant antiferromagnetic coupling between the spin of an impurity with the spin of the conduction electrons in the host matrix. In nanoscale conductors like carbon nanotube devices, the spin impurity is formed in a strong Coulomb blockade region where charge is quenched. Such artificial impurities offer new perspectives for the study of the Kondo effect, in particular in out-of-equilibrium situations. We report here on {\it current noise} measurements in a carbon nanotube quantum dot tuned to the Kondo regime. A strong enhancement of the current noise is observed within the Kondo resonance compared to simple non-interacting theories. While the measured conductances come close to the unitary limit $2 e^2/h$, the noise is not suppressed as in a coherent conduc tor but remains sizeable. This effect can not be accounted for, either by a resonant level model, or by a simple SU(2) Kondo mode l. This emphasizes the importance of the doubly degenerate orbital degree of freedom (in addition to the spin degeneracy) in the dot related to clockwise and counterclockwise motion around the nanotube. Moreover, the addition of this orbital pseudo-spin with the true spin could lead to Kondo screening with an enhanced SU(4) symmetry. In fact, using an interacting slave-boson mean field (SBMFT) approach with SU(4) symmetry to describe the Kondo effect, we can account~\cite{delattre:09} for both conductance and noise measurements with a rather good agreement. Noisy Kondo impurities Nature Physics 5 (2009) 208-21