15,189 research outputs found
Polarization correlated photons from a positively charged quantum dot
Polarized cross-correlation spectroscopy on a quantum dot charged with a
single hole shows the sequential emission of photons with common circular
polarization. This effect is visible without magnetic field, but becomes more
pronounced as the field along the quantization axis is increased. We interpret
the data in terms of electron dephasing in the X+ state caused by the
Overhauser field of nuclei in the dot. We predict the correlation timescale can
be increased by accelerating the emission rate with cavity-QED
Charge and spin state readout of a double quantum dot coupled to a resonator
State readout is a key requirement for a quantum computer. For
semiconductor-based qubit devices it is usually accomplished using a separate
mesoscopic electrometer. Here we demonstrate a simple detection scheme in which
a radio-frequency resonant circuit coupled to a semiconductor double quantum
dot is used to probe its charge and spin states. These results demonstrate a
new non-invasive technique for measuring charge and spin states in quantum dot
systems without requiring a separate mesoscopic detector
Observation of the Purcell effect in high-index-contrast micropillar
We have fabricated pillar microcavity samples with Bragg mirrors consisting
of alternate layers of GaAs and Aluminium Oxide. Compared to the more widely
studied GaAs/AlAs micropillars these mirrors can achieve higher reflectivities
with fewer layer repeats and reduce the mode volume. We have studied a number
of samples containing a low density of InGaAs/GaAs self assembled quantum dots
in a cavity and here report observation of a three fold enhancement in the
radiative lifetime of a quantum dot exciton state due to the Purcell effect
Oxide-apertured microcavity single-photon emitting diode
We have developed a microcavity single-photon source based on a single
quantum dot within a planar cavity in which wet-oxidation of a high-aluminium
content layer provides lateral confinement of both the photonic mode and the
injection current. Lateral confinement of the optical mode in optically pumped
structures produces a strong enhancement of the radiative decay rate. Using
microcavity structures with doped contact layers, we demonstrate a
single-photon emitting diode where current may be injected into a single dot
Sensitivity of the magnetic state of a spin lattice on itinerant electron orbital phase
Spatially extended localized spins can interact via indirect exchange
interaction through Friedel oscillations in the Fermi sea. In arrays of
localized spins such interaction can lead to a magnetically ordered phase.
Without external magnetic field such a phase is well understood via a
"two-impurity" Kondo model. Here we employ non-equilibrium transport
spectroscopy to investigate the role of the orbital phase of conduction
electrons on the magnetic state of a spin lattice. We show experimentally, that
even tiniest perpendicular magnetic field can influence the magnitude of the
inter-spin magnetic exchange.Comment: To be published in PhysicaE EP2DS proceedin
Giant Fluctuations of Coulomb Drag in a Bilayer System
We have observed reproducible fluctuations of the Coulomb drag, both as a
function of magnetic field and electron concentration, which are a
manifestation of quantum interference of electrons in the layers. At low
temperatures the fluctuations exceed the average drag, giving rise to random
changes of the sign of the drag. The fluctuations are found to be much larger
than previously expected, and we propose a model which explains their
enhancement by considering fluctuations of local electron properties.Comment: 10 pages, 4 figure
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