278 research outputs found
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Coherently Controlled Quantum Emitters In Cavities
Semiconductor nanostructures such as quantum dots (QDs) have offered unique opportunities to investigate quantum optical effects in solid-state systems. These include quantum interference, Rabi oscillations, as well as photon antibunching, and were previously observable only in isolated atoms or ions. In addition, QDs can be integrated into optical microcavities, making them attractive for applications in quantum information processing and high efficiency quantum light sources. Despite much progress towards these goals, one area that was little explored is coherent control of such solid-state quantum emitters in cavities. The main technical hurdle lies in overcoming the laser background scattering. By using a sample structure in which QDs are embedded in a planar Fabry-Perot cavity and by using an orthogonal excitation geometry, we have achieved a nearly complete elimination of laser background scattering. This in turn allows us to show resonantly controlled light emission of quantum dots in the cavity including (a) Rabi flopping using pulse control, (b) direct observation of Mollow triplets in the frequency domain, and (c) simultaneously measured first-order and second order photon-photon correlations.Physic
Hydration of a side-chain-free n-type semiconducting ladder polymer driven by electrochemical doping
We study the organic electrochemical transistors (OECTs) performance of the
ladder polymer, poly(benzimidazobenzophenanthroline) (BBL) in an attempt to
better understand how an apparently hydrophobic side-chain-free polymer is able
to operate as an OECT with favorable redox kinetics in an aqueous environment.
We examine two BBLs of different molecular masses from different sources. Both
BBLs show significant film swelling during the initial reduction step. By
combining electrochemical quartz crystal microbalance (eQCM) gravimetry,
in-operando atomic force microscopy (AFM), and both ex-situ and in-operando
grazing incidence wide-angle x-ray scattering (GIWAXS), we provide a detailed
structural picture of the electrochemical charge injection process in BBL in
the absence of any hydrophilic side-chains. Compared with ex-situ measurements,
in-operando GIWAXS shows both more swelling upon electrochemical doping than
has previously been recognized, and less contraction upon dedoping. The data
show that BBL films undergo an irreversible hydration driven by the initial
electrochemical doping cycle with significant water retention and lamellar
expansion that persists across subsequent oxidation/reduction cycles. This
swelling creates a hydrophilic environment that facilitates the subsequent fast
hydrated ion transport in the absence of the hydrophilic side-chains used in
many other polymer systems. Due to its rigid ladder backbone and absence of
hydrophilic side-chains, the primary BBL water uptake does not significantly
degrade the crystalline order, and the original dehydrated, unswelled state can
be recovered after drying. The combination of doping induced hydrophilicity and
robust crystalline order leads to efficient ionic transport and good stability.Comment: 24 pages, 5 figure
Electro-elastic tuning of single particles in individual self-assembled quantum dots
We investigate the effect of uniaxial stress on InGaAs quantum dots in a
charge tunable device. Using Coulomb blockade and photoluminescence, we observe
that significant tuning of single particle energies (~ -0.5 meV/MPa) leads to
variable tuning of exciton energies (+18 to -0.9 micro-eV/MPa) under tensile
stress. Modest tuning of the permanent dipole, Coulomb interaction and
fine-structure splitting energies is also measured. We exploit the variable
exciton response to tune multiple quantum dots on the same chip into resonance.Comment: 16 pages, 4 figures, 1 table. Final versio
Fast Purcell-enhanced single photon source in 1,550-nm telecom band from a resonant quantum dot-cavity coupling
High-bit-rate nanocavity-based single photon sources in the 1,550-nm telecom
band are challenges facing the development of fibre-based long-haul quantum
communication networks. Here we report a very fast single photon source in the
1,550-nm telecom band, which is achieved by a large Purcell enhancement that
results from the coupling of a single InAs quantum dot and an InP photonic
crystal nanocavity. At a resonance, the spontaneous emission rate was enhanced
by a factor of 5 resulting a record fast emission lifetime of 0.2 ns at 1,550
nm. We also demonstrate that this emission exhibits an enhanced anti-bunching
dip. This is the first realization of nanocavity-enhanced single photon
emitters in the 1,550-nm telecom band. This coupled quantum dot cavity system
in the telecom band thus provides a bright high-bit-rate non-classical single
photon source that offers appealing novel opportunities for the development of
a long-haul quantum telecommunication system via optical fibres.Comment: 16 pages, 4 figure
Tunable Indistinguishable Photons From Remote Quantum Dots
Single semiconductor quantum dots have been widely studied within devices
that can apply an electric field. In the most common system, the low energy
offset between the InGaAs quantum dot and the surrounding GaAs material limits
the magnitude of field that can be applied to tens of kVcm^-1, before carriers
tunnel out of the dot. The Stark shift experienced by the emission line is
typically 1 meV. We report that by embedding the quantum dots in a quantum well
heterostructure the vertical field that can be applied is increased by over an
order of magnitude whilst preserving the narrow linewidths, high internal
quantum efficiencies and familiar emission spectra. Individual dots can then be
continuously tuned to the same energy allowing for two-photon interference
between remote, independent, quantum dots
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
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MAGIC: Marine ARM GPCI Investigation of Clouds
The second Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF2) will be deployed aboard the Horizon Lines cargo container ship merchant vessel (M/V) Spirit for MAGIC, the Marine ARM GPCI1 Investigation of Clouds. The Spirit will traverse the route between Los Angeles, California, and Honolulu, Hawaii, from October 2012 through September 2013 (except for a few months in the middle of this time period when the ship will be in dry dock). During this field campaign, AMF2 will observe and characterize the properties of clouds and precipitation, aerosols, and atmospheric radiation; standard meteorological and oceanographic variables; and atmospheric structure. There will also be two intensive observational periods (IOPs), one in January 2013 and one in July 2013, during which more detailed measurements of the atmospheric structure will be made
Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM
Transmission spectroscopy of exoplanets has revealed signatures of water
vapor, aerosols, and alkali metals in a few dozen exoplanet atmospheres.
However, these previous inferences with the Hubble and Spitzer Space Telescopes
were hindered by the observations' relatively narrow wavelength range and
spectral resolving power, which precluded the unambiguous identification of
other chemical speciesin particular the primary carbon-bearing molecules.
Here we report a broad-wavelength 0.5-5.5 m atmospheric transmission
spectrum of WASP-39 b, a 1200 K, roughly Saturn-mass, Jupiter-radius exoplanet,
measured with JWST NIRSpec's PRISM mode as part of the JWST Transiting
Exoplanet Community Early Release Science Team program. We robustly detect
multiple chemical species at high significance, including Na (19),
HO (33), CO (28), and CO (7). The non-detection
of CH, combined with a strong CO feature, favours atmospheric models
with a super-solar atmospheric metallicity. An unanticipated absorption feature
at 4m is best explained by SO (2.7), which could be a tracer
of atmospheric photochemistry. These observations demonstrate JWST's
sensitivity to a rich diversity of exoplanet compositions and chemical
processes.Comment: 41 pages, 4 main figures, 10 extended data figures, 4 tables. Under
review in Natur
Voltage-Dependent Gating in a “Voltage Sensor-Less” Ion Channel
An unusual mechanism of ion channel regulation generates voltage-dependent gating in the absence of a canonical voltage-sensing domain
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