Three-Dimensional Electrical Control of the Excitonic Fine Structure for a Quantum Dot in a Cavity

The excitonic fine structure plays a key role for the quantum light generated by semiconductor quantum dots, both for entangled photon pairs and single photons. Controlling the excitonic fine structure has been demonstrated using electric, magnetic, or strain fields, but not for quantum dots in optical cavities, a key requirement to obtain high source efficiency and near-unity photon indistinguishability. Here, we demonstrate the control of the fine structure splitting for quantum dots embedded in micropillar cavities. We propose and implement a scheme based on remote electrical contacts connected to the pillar cavity through narrow ridges. Numerical simulations show that such a geometry allows for a three-dimensional control of the electrical field. We experimentally demonstrate tuning and reproducible canceling of the fine structure, a crucial step for the reproducibility of quantum light source technology.

Bright Polarized Single-Photon Source Based on a Linear Dipole

Semiconductor quantum dots in cavities are promising single-photon sources. Here, we present a path to deterministic operation, by harnessing the intrinsic linear dipole in a neutral quantum dot via phonon-assisted excitation. This enables emission of fully polarized single photons, with a measured degree of linear polarization up to 0.994±0.007, and high population inversion-85% as high as resonant excitation. We demonstrate a single-photon source with a polarized first lens brightness of 0.50±0.01, a single-photon purity of 0.954±0.001, and single-photon indistinguishability of 0.909±0.004.

Hong-Ou-Mandel Interference with Imperfect Single Photon Sources

Hong-Ou-Mandel interference is a cornerstone of optical quantum technologies. We explore both theoretically and experimentally how unwanted multiphoton components of single-photon sources affect the interference visibility, and find that the overlap between the single photons and the noise photons significantly impacts the interference. We apply our approach to quantum dot single-photon sources to access the mean wave packet overlap of the single-photon component. This study provides a consistent platform with which to diagnose the limitations of current single-photon sources on the route towards the ideal device.

Sequential generation of linear cluster states from a single photon emitter

Light states composed of multiple entangled photons—such as cluster states—are essential for developing and scaling-up quantum computing networks. Photonic cluster states can be obtained from single-photon sources and entangling gates, but so far this has only been done with probabilistic sources constrained to intrinsically low efficiencies, and an increasing hardware overhead. Here, we report the resource-efficient generation of polarization-encoded, individually-addressable photons in linear cluster states occupying a single spatial mode. We employ a single entangling-gate in a fiber loop configuration to sequentially entangle an ever-growing stream of photons originating from the currently most efficient single-photon source technology—a semiconductor quantum dot. With this apparatus, we demonstrate the generation of linear cluster states up to four photons in a single-mode fiber. The reported architecture can be programmed for linear-cluster states of any number of photons, that are required for photonic one-way quantum computing schemes.

Generating photonic cluster states using a single non-heralded source and a single entangling gate would optimise scalability and reduce resource overhead. Here, the authors generate up to 4-photon cluster states using a quantum dot coupled to a fibre loop, with a fourfold generation rate of 10 Hz.

Genotoxic and enzymatic effects of fluoranthene in microsomes and freshly isolated hepatocytes from sole (Solea solea)

The fluoranthene (Fluo) is one of the most abundant polycyclic aromatic hydrocarbons (PAHs) in human food and in marine compartments. However, the existing data on its genotoxicity is poor and controversial. The aim of this study was to assess in vitro the potential genotoxicity of Fluo in sole and its possible effect on CYP450 modulation. Freshly isolated hepatocytes were exposed for 24 h to a range of Fluo concentrations from 0.5 to 50 μM in both culture flasks and microplate wells. The ethoxyresorufin-O-deethylase (EROD) activity was measured as an indicator of the activity of the cytochrome P450 1A1 (CYP1A1). The genotoxic effects were evaluated by measuring both DNA strand breaks and DNA adducts by the alkaline comet assay and the postlabeling technique respectively. Calf thymus DNA was also exposed to Fluo in the presence of sole liver microsomes in order to check for Fluo DNA adduct formation. In sole hepatocytes, Fluo was shown to induce a decrease in the EROD activity in a concentration-dependent manner. A significant genotoxic effect was observed in terms of DNA strand breakage from an exposure concentration of 5 μM: despite a concentration-dependent effect was observed, it did not follow a linear dose-response. The response was similar whatever the way of exposure in flasks or in wells. One reproducible adduct was detected in the hepatocytes exposed to the highest concentrations of Fluo. The formation of Fluo adducts was confirmed by the detection of one reproducible adduct following in vitro exposure of calf thymus DNA to 100 and 200 μM of Fluo in the presence of sole microsomes. These results demonstrate the potential of sole hepatocytes to metabolize Fluo in 24 h into reactive species, able to induce genotoxicity by DNA strand breakage and DNA adduct formation. Moreover, a miniaturized cell exposure system was validated for further experiments using fewer amounts of hepatocytes and contaminants, and allowing exposure to PAH metabolites.

[Cystadenocarcinoma complicating urachal cysts. A case report and review of the literature (author's transl)]

A 50-year-old man developed a cystadenocarcinoma on a large urachal cyst. Only 15 similar cases have been reported in the published literature, equivalent to less than 10 p. cent of cancers of the urachus. These tumours present certain clinical, radiological, endoscopic, ultrasonographic, and pathological characteristics. As against solid urachal tumours, there is little controversy as to their vestigial origin from the remains of the allantoid canal. Their prognosis is poor, regional recurrences and pulmonary metastases, and complicated or uncomplicated urachal cysts should therefore be systematically excised.