250 research outputs found
Dephasing of Mollow Triplet Sideband Emission of a Resonantly Driven Quantum Dot in a Microcavity
Detailed properties of resonance fluorescence from a single quantum dot in a
micropillar cavity are investigated, with particular focus on emission
coherence in dependence on optical driving field power and detuning.
Power-dependent series over a wide range could trace characteristic Mollow
triplet spectra with large Rabi splittings of GHz. In
particular, the effect of dephasing in terms of systematic spectral broadening
of the Mollow sidebands is observed as a strong fingerprint
of excitation-induced dephasing. Our results are in excellent agreement with
predictions of a recently presented model on phonon-dressed QD Mollow triplet
emission in the cavity-QED regime
Spontaneously Localized Photonic Modes Due to Disorder in the Dielectric Constant
We present the first experimental evidence for the existence of strongly
localized photonic modes due to random two dimensional fluctuations in the
dielectric constant. In one direction, the modes are trapped by ordered Bragg
reflecting mirrors of a planar, one wavelength long, microcavity. In the cavity
plane, they are localized by disorder, which is due to randomness in the
position, composition and sizes of quantum dots located in the anti-node of the
cavity. We extend the theory of disorder induced strong localization of
electron states to optical modes and obtain quantitative agreement with the
main experimental observations.Comment: 6 page
Coherence dynamics and quantum-to-classical crossover in an exciton-cavity system in the quantum strong coupling regime
Interaction between light and matter generates optical nonlinearities, which are particularly pronounced in the quantum strong coupling regime. When a single bosonic mode couples to a single fermionic mode, a Jaynes-Cummings (JC) ladder is formed, which we realize here using cavity photons and quantum dot excitons. We measure and model the coherent anharmonic response of this strongly coupled exciton-cavity system at resonance. Injecting two photons into the cavity, we demonstrate a root 2 larger polariton splitting with respect to the vacuum Rabi splitting. This is achieved using coherent nonlinear spectroscopy, specifically four-wave mixing, where the coherence between the ground state and the first (second) rung of the JC ladder can be interrogated for positive (negative) delays. With increasing excitation intensity and thus rising average number of injected photons, we observe spectral signatures of the quantum-to-classical crossover of the strong coupling regime.Peer reviewe
Intensity fluctuations in bimodal micropillar lasers enhanced by quantum-dot gain competition
We investigate correlations between orthogonally polarized cavity modes of a
bimodal micropillar laser with a single layer of self-assembled quantum dots in
the active region. While one emission mode of the microlaser demonstrates a
characteristic s-shaped input-output curve, the output intensity of the second
mode saturates and even decreases with increasing injection current above
threshold. Measuring the photon auto-correlation function g^{(2)}(\tau) of the
light emission confirms the onset of lasing in the first mode with g^{(2)}(0)
approaching unity above threshold. In contrast, strong photon bunching
associated with super-thermal values of g^{(2)}(0) is detected for the other
mode for currents above threshold. This behavior is attributed to gain
competition of the two modes induced by the common gain material, which is
confirmed by photon crosscorrelation measurements revealing a clear
anti-correlation between emission events of the two modes. The experimental
studies are in excellent qualitative agreement with theoretical studies based
on a microscopic semiconductor theory, which we extend to the case of two modes
interacting with the common gain medium. Moreover, we treat the problem by an
extended birth-death model for two interacting modes, which reveals, that the
photon probability distribution of each mode has a double peak structure,
indicating switching behavior of the modes for the pump rates around threshold.Comment: 11 pages, 5 figures, submitted to Phys. Rev.
Conditional phase shift from a quantum dot in a pillar microcavity
Large conditional phase shifts from coupled atom-cavity systems are a key
requirement for building a spin photon interface. This in turn would allow the
realisation of hybrid quantum information schemes using spin and photonic
qubits. Here we perform high resolution reflection spectroscopy of a quantum
dot resonantly coupled to a pillar microcavity. We show both the change in
reflectivity as the quantum dot is tuned through the cavity resonance, and
measure the conditional phase shift induced by the quantum dot using an ultra
stable interferometer. These techniques could be extended to the study of
charged quantum dots, where it would be possible to realise a spin photon
interface
Nonlinear photoluminescence spectra from a quantum dot-cavity system: Direct evidence of pump-induced stimulated emission and anharmonic cavity-QED
We investigate the power-dependent photoluminescence spectra from a strongly
coupled quantum dot-cavity system using a quantum master equation technique
that accounts for incoherent pumping, pure dephasing, and fermion or boson
statistics. Analytical spectra at the one-photon correlation level and the
numerically exact multi-photon spectra for fermions are presented. We compare
to recent experiments on a quantum dot-micropiller cavity system and show that
an excellent fit to the data can be obtained by varying only the incoherent
pump rates in direct correspondence with the experiments. Our theory and
experiments together show a clear and systematic way of studying
stimulated-emission induced broadening and anharmonic cavity-QED.Comment: We have reworked our previous arXiv paper and submitted this latest
version for peer revie
Impact of phonons on dephasing of individual excitons in deterministic quantum dot microlenses
Optimized light-matter coupling in semiconductor nanostructures is a key to
understand their optical properties and can be enabled by advanced fabrication
techniques. Using in-situ electron beam lithography combined with a
low-temperature cathodoluminescence imaging, we deterministically fabricate
microlenses above selected InAs quantum dots (QDs) achieving their efficient
coupling to the external light field. This enables to perform four-wave mixing
micro-spectroscopy of single QD excitons, revealing the exciton population and
coherence dynamics. We infer the temperature dependence of the dephasing in
order to address the impact of phonons on the decoherence of confined excitons.
The loss of the coherence over the first picoseconds is associated with the
emission of a phonon wave packet, also governing the phonon background in
photoluminescence (PL) spectra. Using theory based on the independent boson
model, we consistently explain the initial coherence decay, the zero-phonon
line fraction, and the lineshape of the phonon-assisted PL using realistic
quantum dot geometries
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