57 research outputs found
Covalently Binding the Photosystem I to Carbon Nanotubes
We present a chemical route to covalently couple the photosystem I (PS I) to
carbon nanotubes (CNTs). Small linker molecules are used to connect the PS I to
the CNTs. Hybrid systems, consisting of CNTs and the PS I, promise new
photo-induced transport phenomena due to the outstanding optoelectronic
properties of the robust cyanobacteria membrane protein PS I
Electrical control of spontaneous emission and strong coupling for a single quantum dot
We report the design, fabrication and optical investigation of electrically
tunable single quantum dot - photonic crystal defect nanocavities operating in
both the weak and strong coupling regimes of the light matter interaction.
Unlike previous studies where the dot-cavity spectral detuning was varied by
changing the lattice temperature, or by the adsorption of inert-gases at low
temperatures, we demonstrate that the quantum confined Stark effect can be
employed to quickly and reversibly switch the dot-cavity coupling simply by
varying a gate voltage. Our results show that exciton transitions from
individual dots can be tuned by ~4 meV relative to the nanocavity mode before
the emission quenches due to carrier tunneling escape. This range is much
larger than the typical linewidth of the high-Q cavity modes (~0.10 meV)
allowing us to explore and contrast regimes where the dots couple to the cavity
or decay by spontaneous emission into the 2D photonic bandgap. In the weak
coupling regime, we show that the dot spontaneous emission rate can be tuned
using a gate voltage, with Purcell factors >=7. New information is obtained on
the nature of the dot-cavity coupling in the weak coupling regime and
electrical control of zero dimensional polaritons is demonstrated for the
highest-Q cavities (Q>=12000). Vacuum Rabi splittings up to ~0.13 meV are
observed, much larger than the linewidths of either the decoupled exciton or
cavity mode. These observations represent a voltage switchable optical
non-linearity at the single photon level, paving the way towards on-chip dot
based nano-photonic devices that can be integrated with passive optical
components
A Correlation between the Emission Intensity of Self-Assembled Germanium Islands and the Quality Factor of Silicon Photonic Crystal Nanocavities
We present a comparative micro-photoluminescence study of the emission
intensity of self-assembled germanium islands coupled to the resonator mode of
two-dimensional silicon photonic crystal defect nanocavities. The emission
intensity is investigated for cavity modes of L3 and Hexapole cavities with
different cavity quality factors. For each of these cavities many nominally
identical samples are probed to obtain reliable statistics. As the quality
factor increases we observe a clear decrease in the average mode emission
intensity recorded under comparable optical pumping conditions. This clear
experimentally observed trend is compared with simulations based on a
dissipative master equation approach that describes a cavity weakly coupled to
an ensemble of emitters. We obtain evidence that reabsorption of photons
emitted into the cavity mode is responsible for the observed trend. In
combination with the observation of cavity linewidth broadening in power
dependent measurements, we conclude that free carrier absorption is the
limiting effect for the cavity mediated light enhancement under conditions of
strong pumping.Comment: 8 pages, 5 figure
Emitters of -photon bundles
We propose a scheme based on the coherent excitation of a two-level system in
a cavity to generate an ultrabright CW and focused source of quantum light that
comes in groups (bundles) of photons, for an integer tunable with the
frequency of the exciting laser. We define a new quantity, the \emph{purity} of
-photon emission, to describe the percentage of photons emitted in bundles,
thus bypassing the limitations of Glauber correlation functions. We focus on
the case and show that close to 100% of two-photon emission and
90% of three-photon emission is within reach of state of the art cavity QED
samples. The statistics of the bundles emission shows that various
regimes---from -photon lasing to -photon guns---can be realized. This is
evidenced through generalized correlation functions that extend the standard
definitions to the multi-photon level.Comment: Introduce the n-th order N-photon correlation functions. Reorganized
to emphasize the N-photon emitter, now extended to the antibunching regime,
rather than only coherent emission as previsoul
Direct measurement of plasmon propagation lengths on lithographically defined metallic waveguides on GaAs
We present optical investigations of rectangular surface plasmon polariton
waveguides lithographically defined on GaAs substrates. The plasmon propagation
length is directly determined using a confocal microscope, with independent
polarization control in both excitation and detection channels. Surface plasmon
polaritons are launched along the waveguide using a lithographically defined
defect at one end. At the remote end of the waveguide they scatter into the
far-field, where they are imaged using a CCD camera. By monitoring the length
dependence of the intensity of scattered light from the waveguide end, we
directly extract the propagation length, obtaining values ranging from LSPP =
10-40 {\mu}m depending on the waveguide width (w=2-5 {\mu}m) and excitation
wavelength (760-920 nm). Results are in good accord with theoretical
expectations demonstrating the high quality of the lithographically defined
structures. The results obtained are of strong relevance for the development of
future semiconductor based integrated plasmonic technologies
Atomistic defect states as quantum emitters in monolayer MoS
Quantum light sources in solid-state systems are of major interest as a basic
ingredient for integrated quantum device technologies. The ability to tailor
quantum emission through deterministic defect engineering is of growing
importance for realizing scalable quantum architectures. However, a major
difficulty is that defects need to be positioned site-selectively within the
solid. Here, we overcome this challenge by controllably irradiating
single-layer MoS using a sub-nm focused helium ion beam to
deterministically create defects. Subsequent encapsulation of the ion bombarded
MoS flake with high-quality hBN reveals spectrally narrow emission lines
that produce photons at optical wavelengths in an energy window of one to two
hundred meV below the neutral 2D exciton of MoS. Based on ab-initio
calculations we interpret these emission lines as stemming from the
recombination of highly localized electron-hole complexes at defect states
generated by the helium ion bombardment. Our approach to deterministically
write optically active defect states in a single transition metal
dichalcogenide layer provides a platform for realizing exotic many-body
systems, including coupled single-photon sources and exotic Hubbard systems.Comment: Main: 9 pages, 3 figures + SI: 19 pages, 10 figure
- …