377 research outputs found
Growth and structural characterization of pyramidal site-controlled quantum dots with high uniformity and spectral purity
This work presents some fundamental features of pyramidal site-controlled
InGaAs Quantum Dots (QDs) grown by MetalOrganic Vapour Phase Epitaxy on
patterned GaAs (111)B substrate. The dots self-form inside pyramidal recesses
patterned on the wafer via pre-growth processing. The major advantage of this
growth technique is the control it provides over the dot nucleation posi-tion
and the dimensions of the confined structures onto the sub-strate. The
fundamental steps of substrate patterning and the QD forma-tion mechanism are
described together with a discussion of the structural particulars. The
post-growth processes, including sur-face etching and substrate removal, which
are required to facili-tate optical characterization, are discussed. With this
approach extremely high uniformity and record spectral purity are both
achieved
Impact of classical forces and decoherence in multi-terminal Aharonov-Bohm networks
Multi-terminal Aharonov-Bohm (AB) rings are ideal building blocks for quantum
networks (QNs) thanks to their ability to map input states into controlled
coherent superpositions of output states. We report on experiments performed on
three-terminal GaAs/Al_(x)Ga_(1-x)As AB devices and compare our results with a
scattering-matrix model including Lorentz forces and decoherence. Our devices
were studied as a function of external magnetic field (B) and gate voltage at
temperatures down to 350 mK. The total output current from two terminals while
applying a small bias to the third lead was found to be symmetric with respect
to B with AB oscillations showing abrupt phase jumps between 0 and pi at
different values of gate voltage and at low magnetic fields, reminiscent of the
phase-rigidity constraint due to Onsager-Casimir relations. Individual outputs
show quasi-linear dependence of the oscillation phase on the external electric
field. We emphasize that a simple scattering-matrix approach can not model the
observed behavior and propose an improved description that can fully describe
the observed phenomena. Furthermore, we shall show that our model can be
successfully exploited to determine the range of experimental parameters that
guarantee a minimum oscillation visibility, given the geometry and coherence
length of a QN.Comment: 7 pages, 8 figure
Probing the local temperature of a 2DEG microdomain with a quantum dot: measurement of electron-phonon interaction
We demonstrate local detection of the electron temperature in a
two-dimensionalmicrodomain using a quantum dot. Our method relies on the
observation that a temperature bias across the dot changes the functional form
of Coulomb-blockade peaks. We apply our results to the investigation of
electron-energy relaxation at subkelvin temperatures, find that the energy flux
from electrons into phonons is proportional to the fifth power of temperature,
and give a measurement of the coupling constant.Comment: 5 pages, 4 figure
Immunity of intersubband polaritons to inhomogeneous broadening
We demonstrate that intersubband (ISB) polaritons are robust to inhomogeneous
effects originating from the presence of multiple quantum wells (MQWs). In a
series of samples that exhibit mid-infrared ISB absorption transitions with
broadenings varying by a factor of 5 (from 4 meV to 20meV), we have observed
polariton linewidths always lying in the 4 - 7 meV range only. We have
experimentally verified the dominantly inhomogeneous origin of the broadening
of the ISB transition, and that the linewidth reduction effect of the polariton
modes persists up to room-temperature. This immunity to inhomogeneous
broadening is a direct consequence of the coupling of the large number of ISB
oscillators to a single photonic mode. It is a precious tool to gauge the
natural linewidth of the ISB plasmon , that is otherwise masked in such MQWs
system , and is also beneficial in view of perspective applications such as
intersubband polariton lasers
A quantum Hall Mach-Zehnder interferometer far beyond the equilibrium
We experimentally realize quantum Hall Mach-Zehnder interferometer which
operates far beyond the equilibrium. The operation of the interferometer is
based on allowed intra-edge elastic transitions within the same Landau sublevel
in the regime of high imbalances between the co-propagating edge states. Since
the every edge state is definitely connected with the certain Landau sublevel,
the formation of the interference loop can be understood as a splitting and a
further reconnection of a single edge state. We observe an Aharonov-Bohm type
interference pattern even for low-size interferometers. This novel interference
scheme demonstrates high visibility even at millivolt imbalances and survives
in a wide temperature range.Comment: As accepted by PR
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