We present an experiment where a reconfigurable photonic processor fabricated in glass by femtosecond laser micromachining is used for the generation of four-photons GHZ entangled states, with high efficiency and fidelity. The chip is used in synergy with a bright and quasi-deterministic source of single photons based on semiconductor quantum dot. The very efficient interfacing of these two platforms is ensured by the excellent connectivity between glass photonic circuits and standard optical fibers. In addition, in order to benchmark the quality of the generated states, this processor is used to implement a quantum secret sharing protocol on chip.
THz coherent acoustic phonons on a scale of sub-picoseconds in temporal-periodicities and nanometers in wavelengths are promising in various fields such as nanometrology/nanoimaging, THz devices and heat management. By merging advanced ultrafast laser spectroscopy and sophisticated nanotechnologies, the excitation and detection of bulk coherent acoustic phonons in the THz regime have been accomplished. Nevertheless, coherent surface acoustic waves (SAWs) realized by metallic gratings deposited on a substrate, are still below 100 GHz. In this report, we take advantage of the cleaved superlattice (SL) surface with immediately reachable nanometer periodicity and atomic-level interface quality to monitor SAWs by femtosecond lasers. Rayleigh SAWs above 100 GHz and bulk surface skimming acoustic waves up to 1THz, with deeply sub-optical-wavelength periodicities, are observed on cleaved Al0.3Ga0.7As/GaAs SLs and cleaved In0.2Ga0.8N/GaN SLs, respectively. The observations open a path towards THz opto-acoustic/acousto-optic transducers.
Semiconductor quantum dots have emerged as excellent artificial atoms to both generate and manipulate quantum light. When embedded in cavities, they can generate single photons and entangled photons with unparalleled efficiency and high quantum purity. In this talk, I will discuss how such devices can be used to generate strings of many entangled photons. The method, leveraging the spin-selective optical transition in a charged quantum dot, leads to the generation of indistinguishable photons in linear cluster states or GHZ states at high rates, realizing an important milestone for scaling-up optical quantum technologies.
Integrated quantum photonics is a key tool towards large scale quantum technologies. In this work we present an AlGaAs-based photonic circuit for on-chip generation and manipulation of broadband polarization-entangled photon pairs. The quantum state is generated by Type-II spontaneous parametric down conversion in AlGaAs Bragg reflection waveguides at telecom wavelengths and room temperature. Polarization entangled photons are manipulated over a frequency band of around 50 nm by an integrated polarizing beam splitter. We demonstrate Hong-Ou-Mandel visibility of 80% for a quantum device where the photon pairs generation and manipulation are implemented in a single chip.
In-rich InGaN/GaN nanowires (NWs) are key optoelectronic materials, which can close the green gap of the light emitting diodes and can be used in efficient high-bandgap solar cells for integration in tandem devices. Realization of these devices requires as a first step the optimization of the NW structure and their electrical parameters. Electron Beam Induced Current (EBIC) microscopy is well suited to probe nanoscale devices with a high resolution and to extract the material parameters.
Here, we analyze the electrical properties of axial GaN and InGaN/GaN n-p and p-n junction NWs using EBIC microscopy. III-N NWs were grown on Si(111) substrates by molecular beam epitaxy using Mg as a p-dopant and Si as an n-dopant. The growth conditions were adjusted to optimize the doping order with an abrupt axial junction without a parasitic radial overgrowth. From the EBIC analysis of the GaN p-n junctions, the doping level and the minorities carrier diffusion lengths were extracted. Next, a p-GaN/i-InGaN/n-GaN junction containing an In-rich InGaN segment [1] was grown yielding a flat and strong EBIC signal in the InGaN NW portion. NW arrays were then contacted and their behavior under visible light was analyzed.
[1] Morassi et al., Cryst. Growth Des., 2545, 18 2018
“Photonics Multiannual Strategic Roadmap 2014-2020” mentions flexible electronics, light sources, displays, sensors and solar cells as key emerging technologies with a high expected growth of the market share. Technologies based on organic semiconductors still suffer from a short lifetime and low efficacy as compared to their inorganic counterparts. To make a flexible device from inorganic semiconductors one should shrink the size of the active elements and to integrate them on mechanically-flexible substrates. This can be achieved using control-by-design nanowires.
In this work, we address the growth of nitride nanowires on novel substrates and the fabrication and characterization of flexible devices based on nitride nanowires. First, we will discuss the epitaxy of GaN nanowires on graphene-on-SiO2 substrates. We show that without any catalyst or intermediate layer, the nanowires grow on graphene with an excellent selectivity compared to the uncovered SiO2 surface. Taking advantage of this selectivity, we demonstrate that organized arrays of nanowires can be synthesized by structuring the graphene layer. Next, we will discuss the approach for nanowire lift-off, transfer into polymer-embedded membranes and flexible contacting. The realization and characterization of flexible light sources, photodetectors and piezogenerators will be presented.
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