221 research outputs found
Microscopic theory of indistinguishable single-photon emission from a quantum dot coupled to a cavity: The role of non-Markovian phonon-induced decoherence
We study the fundamental limit on single-photon indistinguishability imposed
by decoherence due to phonon interactions in semiconductor quantum dot-cavity
QED systems. Employing an exact diagonalization approach we find large
differences compared to standard methods. An important finding is that
short-time non-Markovian effects limit the maximal attainable
indistinguishability. The results are explained using a polariton picture that
yields valuable insight into the phonon-induced dephasing dynamics.Comment: published version, comments are very welcom
Measuring the effective phonon density of states of a quantum dot
We employ detuning-dependent decay-rate measurements of a quantum dot in a
photonic-crystal cavity to study the influence of phonon dephasing in a
solid-state quantum-electrodynamics experiment. The experimental data agree
with a microscopic non-Markovian model accounting for dephasing from
longitudinal acoustic phonons, and identifies the reason for the hitherto
unexplained difference between non-resonant cavity feeding in different
nanocavities. From the comparison between experiment and theory we extract the
effective phonon density of states experienced by the quantum dot. This
quantity determines all phonon dephasing properties of the system and is found
to be described well by a theory of bulk phonons.Comment: 5 pages, 3 figures, submitte
Quenching of phonon-induced processes in quantum dots due to electron-hole asymmetries
Differences in the confinement of electrons and holes in quantum dots are
shown to profoundly impact the magnitude of scattering with acoustic phonons in
materials where crystal deformation shifts the conduction and valence band in
the same direction. Using an extensive model that includes the non-Markovian
nature of the phonon reservoir, we show how the effect may be addressed by
photoluminescence excitation spectroscopy of a single quantum dot. We also
investigate the implications for cavity QED, i.e. a coupled quantum dot-cavity
system, and demonstrate that the phonon scattering may be strongly quenched.
The quenching is explained by a balancing between the deformation potential
interaction strengths and the carrier confinement and depends on the quantum
dot shape. Numerical examples suggest a route towards engineering the phonon
scattering.Comment: 5 pages, 5 figures, submitted for peer review, comments are welcom
Microscopic theory of phonon-induced effects on semiconductor quantum dot decay dynamics in cavity QED
We investigate the influence of the electron-phonon interaction on the decay
dynamics of a quantum dot coupled to an optical microcavity. We show that the
electron-phonon interaction has important consequences on the dynamics,
especially when the quantum dot and cavity are tuned out of resonance, in which
case the phonons may add or remove energy leading to an effective non-resonant
coupling between quantum dot and cavity. The system is investigated using two
different theoretical approaches: (i) a second-order expansion in the bare
phonon coupling constant, and (ii) an expansion in a polaron-photon coupling
constant, arising from the polaron transformation which allows an accurate
description at high temperatures. In the low temperature regime we find
excellent agreement between the two approaches. An extensive study of the
quantum dot decay dynamics is performed, where important parameter dependencies
are covered. We find that in general the electron-phonon interaction gives rise
to a greatly increased bandwidth of the coupling between quantum dot and
cavity. At low temperature an asymmetry in the quantum dot decay rate is
observed, leading to a faster decay when the quantum dot has a larger energy
than to the cavity. We explain this as due to the absence of phonon absorption
processes. Furthermore, we derive approximate analytical expressions for the
quantum dot decay rate, applicable when the cavity can be adiabatically
eliminated. The expressions lead to a clear interpretation of the physics and
emphasizes the important role played by the effective phonon density,
describing the availability of phonons for scattering, in quantum dot decay
dynamics. Based on the analytical expressions we present the parameter regimes
where phonon effects are expected to be important. Also, we include all
technical developments in appendices.Comment: published PRB version, comments are very welcom
Non-markovian model of photon-assisted dephasing by electron-phonon interactions in a coupled quantum-dot-cavity system
We investigate the influence of electron-phonon interactions on the dynamical
properties of a quantum-dot-cavity QED system. We show that non-Markovian
effects in the phonon reservoir lead to strong changes in the dynamics, arising
from photon-assisted dephasing processes, not present in Markovian treatments.
A pronounced consequence is the emergence of a phonon induced spectral
asymmetry when detuning the cavity from the quantum-dot resonance. The
asymmetry can only be explained when considering the polaritonic quasi-particle
nature of the quantum-dot-cavity system. Furthermore, a temperature induced
reduction of the light-matter coupling strength is found to be relevant in
interpreting experimental data, especially in the strong coupling regime.Comment: 4 pages, 4 figures, published in Physical Review Letters, changes
according to referees comments, comments are welcom
Overcoming phonon-induced dephasing for indistinguishable photon sources
Reliable single photon sources constitute the basis of schemes for quantum
communication and measurement based quantum computing. Solid state single
photon sources based on quantum dots are convenient and versatile but the
electronic transitions that generate the photons are subject to interactions
with lattice vibrations. Using a microscopic model of electron-phonon
interactions and a quantum master equation, we here examine phonon-induced
decoherence and assess its impact on the rate of production, and
indistinguishability, of single photons emitted from an optically driven
quantum dot system. We find that, above a certain threshold of desired
indistinguishability, it is possible to mitigate the deleterious effects of
phonons by exploiting a three-level Raman process for photon production
The Role of Autophagy in iNKT Cell Development
CD1d-restricted invariant natural killer T (iNKT) cells are innate-like T cells that express an invariant T cell receptor (TCR) Îą-chain and recognize self and foreign glycolipid antigens. They can rapidly respond to agonist activation and stimulate an extensive array of immune responses. Thymic development and function of iNKT cells are regulated by many different cellular processes, including autophagy, a self-degradation mechanism. In this mini review, we discuss the current understanding of how autophagy regulates iNKT cell development and effector lineage differentiation. Importantly, we propose that iNKT cell development is tightly controlled by metabolic reprogramming
Quantitative analysis of quantum dot dynamics and emission spectra in cavity quantum electrodynamics:Paper
We present detuning-dependent spectral and decay-rate measurements to study
the difference between spectral and dynamical properties of single quantum dots
embedded in micropillar and photonic-crystal cavities. For the micropillar
cavity, the dynamics is well described by the dissipative Jaynes-Cummings
model, while systematic deviations are observed for the emission spectra. The
discrepancy for the spectra is attributed to coupling of other exciton lines to
the cavity and interference of different propagation paths towards the detector
of the fields emitted by the quantum dot. In contrast, quantitative information
about the system can readily be extracted from the dynamical measurements. In
the case of photonic crystal cavities we observe an anti crossing in the
spectra when detuning a single quantum dot through resonance, which is the
spectral signature of strong coupling. However, time-resolved measurements
reveal that the actual coupling strength is significantly smaller than
anticipated from the spectral measurements and that the quantum dot is rather
weakly coupled to the cavity. We suggest that the observed Rabi splitting is
due to cavity feeding by other quantum dots and/or multiexcition complexes
giving rise to collective emission effects.Comment: 14 pages, 5 figures, submitte
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