33 research outputs found
Stabilization of collapse and revival dynamics by a non-Markovian phonon bath
Semiconductor quantum dots (QDs) have been demonstrated to be versatile
candidates to study the fundamentals of light-matter interaction [1-3]. In
contrast with atom optics, dissipative processes are induced by the inherent
coupling to the environment and are typically perceived as a major obstacle
towards stable performances in experiments and applications [4].
In this paper we show that this is not necessarily the case. In fact, the
memory of the environment can enhance coherent quantum optical effects. In
particular, we demonstrate that the non-Markovian coupling to an incoherent
phonon bath has a stabilizing effect on the coherent QD cavity-quantum
electrodynamics (cQED) by inhibiting irregular oscillations and boosting
regular collapse and revival patterns. For low photon numbers we predict QD
dynamics that deviate dramatically from the well-known atomic Jaynes-Cummings
model. Our proposal opens the way to a systematic and deliberate design of
photon quantum effects via specifically engineered solid-state environments.Comment: 5 pages, 4 figure
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Triggered polarization-entangled photon pairs from a single quantum dot up to 30 K
The radiative biexciton-exciton decay in a semiconductor quantum dot (QD) has the potential of being a source of triggered polarization-entangled photon pairs. However, in most cases the anisotropy-induced exciton fine structure splitting destroys this entanglement. Here, we present measurements on improved QD structures, providing both significantly reduced inhomogeneous emission linewidths and near-zero fine structure splittings. A high-resolution detection technique is introduced which allows us to accurately determine the fine structure in the photoluminescence emission and therefore select appropriate QDs for quantum state tomography. We were able to verify the conditions of entangled or classically correlated photon pairs in full consistence with observed fine structure properties. Furthermore, we demonstrate reliable polarization-entanglement for elevated temperatures up to 30 K. The fidelity of the maximally entangled state decreases only a little from 72% at 4 K to 68% at 30 K. This is especially encouraging for future implementations in practical devices. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
Electrical control of the exciton-biexciton splitting in a single self-assembled InGaAs quantum dots
We report on single InGaAs quantum dots embedded in a lateral electric field
device. By applying a voltage we tune the neutral exciton transition into
resonance with the biexciton using the quantum confined Stark effect. The
results are compared to theoretical calculations of the relative energies of
exciton and biexciton. Cascaded decay from the manifold of single
exciton-biexciton states has been predicted to be a new concept to generate
entangled photon pairs on demand without the need to suppress the fine
structures splitting of the neutral exciton
Generation of two identical photons from a quantum dot in a microcavity
We propose and characterize a two-photon emitter in a highly polarised,
monochromatic and directional beam, realized by means of a quantum dot embedded
in a linearly polarized cavity. In our scheme, the cavity frequency is tuned to
half the frequency of the biexciton (two excitons with opposite spins) and
largely detuned from the excitons thanks to the large biexciton binding energy.
We show how the emission can be Purcell enhanced by several orders of magnitude
into the two-photon channel for available experimental systems.Comment: 5 pages, 4 figure
Electric-field-induced coherent coupling of the exciton states in a single quantum dot
The signature of coherent coupling between two quantum states is an
anticrossing in their energies as one is swept through the other. In single
semiconductor quantum dots containing an electron-hole pair the eigenstates
form a two-level system that can be used to demonstrate quantum effects in the
solid state, but in all previous work these states were independent. Here we
describe a technique to control the energetic splitting of these states using a
vertical electric field, facilitating the observation of coherent coupling
between them. Near the minimum splitting the eigenstates rotate in the plane of
the sample, being orientated at 45{\deg} when the splitting is smallest. Using
this system we show direct control over the exciton states in one quantum dot,
leading to the generation of entangled photon pairs
Engineering of quantum dot photon sources via electro-elastic fields
The possibility to generate and manipulate non-classical light using the
tools of mature semiconductor technology carries great promise for the
implementation of quantum communication science. This is indeed one of the main
driving forces behind ongoing research on the study of semiconductor quantum
dots. Often referred to as artificial atoms, quantum dots can generate single
and entangled photons on demand and, unlike their natural counterpart, can be
easily integrated into well-established optoelectronic devices. However, the
inherent random nature of the quantum dot growth processes results in a lack of
control of their emission properties. This represents a major roadblock towards
the exploitation of these quantum emitters in the foreseen applications. This
chapter describes a novel class of quantum dot devices that uses the combined
action of strain and electric fields to reshape the emission properties of
single quantum dots. The resulting electro-elastic fields allow for control of
emission and binding energies, charge states, and energy level splittings and
are suitable to correct for the quantum dot structural asymmetries that usually
prevent these semiconductor nanostructures from emitting polarization-entangled
photons. Key experiments in this field are presented and future directions are
discussed.Comment: to appear as a book chapter in a compilation "Engineering the
Atom-Photon Interaction" published by Springer in 2015, edited by A.
Predojevic and M. W. Mitchel
Generation and control of polarization-entangled photons from GaAs island quantum dots by an electric field
Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton–exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72±0.05