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Towards a n-electron source based on Lorentzian voltage pulses
Julie Dubois
Thu, Oct. 04th 2012, 10:30
Bât 774, Amphi Claude Bloch, Orme des Merisiers

Towards a n-electron source based on Lorentzian voltage pulses

Injecting a small controlled number of indistinguishable electrons in a quantum ballistic conductor opens the way to new kind of quantum experiments, involving interference with several electrons. This requires the implementation of a yet never done reliable source that can emit a coherent wave-packets of an arbitrary number of electrons above the Fermi sea.

Here we consider an electron source based on short time voltage pulses, which is expected to deliver q quanta of charge per pulse when the flux q=∫eV(t)dt/h is integer[i]. For most of the voltage pulses V(t), this charge is accompagnied by a statistical number N+ of quasi-particles (holes and electrons), the total charge of which being neutral. However, for Lorentzian-shaped voltage pulses, this extra neutral excitation remarkably vanishes, as shown by Ivanov et al.[ii]  This leads to a minimal excitation n-electron source, which a reliable number of emitted quasi-particles.

In this thesis we present a first attempt to experimentally implement this n-electron source. Sub-nanosecond pulses are applied on a quantum point contact (QPC) realized in a clean bidimensionnal electron gas of GaAs/AlGaAs heterostructure. When the single channel of the QPC is not perfectly transmitted, shot-noise occurs and reveals the excess number of quasi-particles emitted by the pulses N+. Thus the minimal excitation number of integer Lorentzian pulses can be tested. Moreover, shot-noise gives access to the spectroscopy of the photo-absorption and photon-emission processes that give rise to the excited quasi-particles. In our experiments, the sine, square and Lorentzian shape pulses are compared. The distinct quasi-particles excitations of Lorentzian voltage pulses is demonstrated and results, including finite temperature effects, are in quantitative agreement with the theoretical predictions.

[i] G.B. Lesovik and L.S. Levitov, Physical Review Letters, Vol. 72 (1994), pp. 538-541

[ii] Ivanov, Lee and Lesovik, Physical Review B, Vol. 56 (1997), pp. 6839-6850.



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