17 research outputs found
Semiconductor quantum dot - a quantum light source of multicolor photons with tunable statistics
We investigate the intensity correlation properties of single photons emitted
from an optically excited single semiconductor quantum dot. The second order
temporal coherence function of the photons emitted at various wavelengths is
measured as a function of the excitation power. We show experimentally and
theoretically, for the first time, that a quantum dot is not only a source of
correlated non-classical monochromatic photons but is also a source of
correlated non-classical \emph{multicolor} photons with tunable correlation
properties. We found that the emitted photon statistics can be varied by the
excitation rate from a sub-Poissonian one, where the photons are temporally
antibunched, to super-Poissonian, where they are temporally bunched.Comment: 4 pages, 2 figure
Optical spectroscopy of single quantum dots at tunable positive, neutral and negative charge states
We report on the observation of photoluminescence from positive, neutral and
negative charge states of single semiconductor quantum dots. For this purpose
we designed a structure enabling optical injection of a controlled unequal
number of negative electrons and positive holes into an isolated InGaAs quantum
dot embedded in a GaAs matrix. Thereby, we optically produced the charge states
-3, -2, -1, 0, +1 and +2. The injected carriers form confined collective
'artificial atoms and molecules' states in the quantum dot. We resolve
spectrally and temporally the photoluminescence from an optically excited
quantum dot and use it to identify collective states, which contain charge of
one type, coupled to few charges of the other type. These states can be viewed
as the artificial analog of charged atoms such as H, H, H,
and charged molecules such as H and H. Unlike higher
dimensionality systems, where negative or positive charging always results in
reduction of the emission energy due to electron-hole pair recombination, in
our dots, negative charging reduces the emission energy, relative to the
charge-neutral case, while positive charging increases it. Pseudopotential
model calculations reveal that the enhanced spatial localization of the
hole-wavefunction, relative to that of the electron in these dots, is the
reason for this effect.Comment: 5 figure
Single Photons on Pseudo-Demand from Stored Parametric Down-Conversion
We describe the results of a parametric down-conversion experiment in which
the detection of one photon of a pair causes the other photon to be switched
into a storage loop. The stored photon can then be switched out of the loop at
a later time chosen by the user, providing a single photon for potential use in
a variety of quantum information processing applications. Although the stored
single photon is only available at periodic time intervals, those times can be
chosen to match the cycle time of a quantum computer by using pulsed
down-conversion. The potential use of the storage loop as a photonic quantum
memory device is also discussed.Comment: 8 pages, 7 Figs., RevTe
Enhanced sequential carrier capture into individual quantum dots and quantum posts controlled by surface acoustic waves
Individual self-assembled Quantum Dots and Quantum Posts are studied under
the influence of a surface acoustic wave. In optical experiments we observe an
acoustically induced switching of the occupancy of the nanostructures along
with an overall increase of the emission intensity. For Quantum Posts,
switching occurs continuously from predominantely charged excitons (dissimilar
number of electrons and holes) to neutral excitons (same number of electrons
and holes) and is independent on whether the surface acoustic wave amplitude is
increased or decreased. For quantum dots, switching is non-monotonic and shows
a pronounced hysteresis on the amplitude sweep direction. Moreover, emission of
positively charged and neutral excitons is observed at high surface acoustic
wave amplitudes. These findings are explained by carrier trapping and
localization in the thin and disordered two-dimensional wetting layer on top of
which Quantum Dots nucleate. This limitation can be overcome for Quantum Posts
where acoustically induced charge transport is highly efficient in a wide
lateral Matrix-Quantum Well.Comment: 11 pages, 5 figure
Sub-microsecond correlations in photoluminescence from InAs quantum dots
Photon correlation measurements reveal memory effects in the optical emission
of single InAs quantum dots with timescales from 10 to 800 ns. With above-band
optical excitation, a long-timescale negative correlation (antibunching) is
observed, while with quasi-resonant excitation, a positive correlation
(blinking) is observed. A simple model based on long-lived charged states is
presented that approximately explains the observed behavior, providing insight
into the excitation process. Such memory effects can limit the internal
efficiency of light emitters based on single quantum dots, and could also be
problematic for proposed quantum-computation schemes.Comment: 8 pages, 8 figure