127 research outputs found
Carbon Nanotube Based Bearing for Rotational Motions
We report the fabrication of a nanoelectromechanical system consisting of a
plate rotating around a multiwalled nanotube bearing. The motion is possible
thanks to the low intershell friction. Indeed, the nanotube has been engineered
so that the sliding happens between different shells. The plate rotation is
activated electrostatically with stator electrodes. The static friction force
is estimated at N/\AA.Comment: 4 pages, 3 figure
Impact of Channel Mixing on the Visibility of Two-particle Interferometry in Quantum Hall Edge States
We consider a two-particle interferometer, where voltage sources applied to
ohmic contacts inject electronic excitations into a pair of copropagating edge
channels. We analyze the impact of channel mixing due to inter-edge tunneling
on the current noise measured at the output of the interferometer. Due to this
mixing, the noise suppression typically expected for synchronized injecting
sources is incomplete, thereby reducing the visibility of the interference. We
investigate to which extent the impact of mixing on the noise visibility
depends on different shapes of the voltage drives. Furthermore, we compare a
simple model involving a single mixing point between the sources and the
quantum point contact to the more realistic case of a continuous distribution
of weak mixing points.Comment: 7 pages, 3 figures; accepted for publication in the proceedings of
the LT29 Conference (Sapporo, Japan
Violation of Kirchhoff's Laws for a Coherent RC Circuit
What is the complex impedance of a fully coherent quantum
resistance-capacitance (RC) circuit at GHz frequencies in which a resistor and
a capacitor are connected in series? While Kirchhoff's laws predict addition of
capacitor and resistor impedances, we report on observation of a different
behavior. The resistance, here associated with charge relaxation, differs from
the usual transport resistance given by the Landauer formula. In particular,
for a single mode conductor, the charge relaxation resistance is half the
resistance quantum, regardless of the transmission of the mode. The new
mesoscopic effect reported here is relevant for the dynamical regime of all
quantum devices
A high sensitivity ultra-low temperature RF conductance and noise measurement setup
We report on the realization of a high sensitivity RF noise measurement
scheme to study small current fluctuations of mesoscopic systems at milliKelvin
temperatures. The setup relies on the combination of an interferometric ampli-
fication scheme and a quarter-wave impedance transformer, allowing the mea-
surement of noise power spectral densities with GHz bandwith up to five orders
of magnitude below the amplifier noise floor. We simultaneously measure the
high frequency conductance of the sample by derivating a portion of the signal
to a microwave homodyne detection. We describe the principle of the setup, as
well as its implementation and calibration. Finally, we show that our setup
allows to fully characterize a subnanosecond on-demand single electron source.
More generally, its sensitivity and bandwith make it suitable for applications
manipulating single charges at GHz frequencies.Comment: The following article has been submitted to Review of Scientific
Instrument
The relaxation time of a chiral quantum R-L circuit
We report on the GHz complex admittance of a chiral one dimensional ballistic
conductor formed by edge states in the quantum Hall regime. The circuit
consists of a wide Hall bar (the inductor L) in series with a tunable resistor
(R) formed by a quantum point contact. Electron interactions between edges are
screened by a pair of side gates. Conductance steps are observed on both real
and imaginary parts of the admittance. Remarkably, the phase of the admittance
is transmission-independent. This shows that the relaxation time of a chiral
R-L circuit is resistance independent. A current and charge conserving
scattering theory is presented that accounts for this observation with a
relaxation time given by the electronic transit time in the c cuit
Influence of channel mixing in fermionic Hong-Ou-Mandel experiments
We consider an electronic Hong-Ou-Mandel interferometer in the integer quantum Hall regime, where the colliding electronic states are generated by applying voltage pulses (creating for instance levitons) to ohmic contacts. The aim of this work is to investigate possible mechanisms leading to a reduced visibility of the Pauli dip, i.e., the noise suppression expected for synchronized sources. It is known that electron-electron interactions cannot account for this effect and always lead to a full suppression of the Hong-Ou-Mandel noise. Focusing on the case of filling factor ?=2, we show instead that a reduced visibility of the Pauli dip can result from mixing of the copropagating edge channels, arising from tunneling events between them
An On-Demand Coherent Single Electron Source
We report on the electron analog of the single photon gun. On demand single
electron injection in a quantum conductor was obtained using a quantum dot
connected to the conductor via a tunnel barrier. Electron emission is triggered
by application of a potential step which compensates the dot charging energy.
Depending on the barrier transparency the quantum emission time ranges from 0.1
to 10 nanoseconds. The single electron source should prove useful for the
implementation of quantum bits in ballistic conductors. Additionally periodic
sequences of single electron emission and absorption generate a quantized
AC-current
Hanbury-Brown Twiss correlations to probe the population statistics of GHz photons emitted by conductors
soumis le 22 mars 2004We present the first study of the statistics of GHz photons in quantum circuits, using Hanbury-Brown and Twiss correlations. The superpoissonian and poissonian photon statistics of thermal and coherent sources respectively made of a resistor and a radiofrequency generator are measured down to the quantum regimeat milliKelvin temperatures. As photon correlations are linked to the second and fourth moments of current fluctuations, this experiment, which is based on current cryogenic electronics, may become a standard for probing electron/photon statistics in quantum conductor
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