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Understanding the stress transfer mechanisms from a polymer matrix to two-dimensional reinforcements is essential for the preparation of high performance nanocomposites. In this study, the interfacial stress transfer from a flexible polymer substrate to monolayer and few-layer molybdenum disulfide MoS2 under tension has been investigated. Layer-dependent and strain-dependent photoluminescence (PL) spectroscopy were used to examine the stress transfer efficiency., Comment: 29 pages

$\textbf{Purpose}$: To develop a clinical CEST MR fingerprinting (CEST-MRF) method for brain tumor quantification using EPI acquisition and deep learning reconstruction. $\textbf{Methods}$: A CEST-MRF pulse sequence originally designed for animal imaging was modified to conform to hardware limits on clinical scanners while keeping scan time $\leq$ 2 minutes. Quantitative MRF reconstruction was performed using a deep reconstruction network (DRONE) to yield the water relaxation and chemical exchange parameters. The feasibility of the 6 parameter DRONE reconstruction was tested in simulations in a digital brain phantom. A healthy subject was scanned with the CEST-MRF sequence, conventional MRF and CEST sequences for comparison. Reproducibility was assessed via test-retest experiments and the concordance correlation coefficient (CCC) calculated for white matter (WM) and grey matter (GM). The clinical utility of CEST-MRF was demonstrated in 4 patients with brain metastases in comparison to standard clinical imaging sequences. Tumors were segmented into edema, solid core and necrotic core regions and the CEST-MRF values compared to the contra-lateral side. $\textbf{Results}$: The DRONE reconstruction of the digital phantom yielded a normalized RMS error of $\leq$ 7% for all parameters. The CEST-MRF parameters were in good agreement with those from conventional MRF and CEST sequences and previous studies. The mean CCC for all 6 parameters was 0.98$\pm$0.01 in WM and 0.98$\pm$0.02 in GM. The CEST-MRF values in nearly all tumor regions were significantly different (P=0.05) from each other and the contra-lateral side. $\textbf{Conclusion}$: Combination of EPI readout and deep learning reconstruction enabled fast, accurate and reproducible CEST-MRF in brain tumors., Comment: 9 figures, 1 table

Silicon-based tracking detectors have been used in several important applications, such as in cancer therapy using particle beams, and for the discovery of new elementary particles at the Large Hadron Collider at CERN. III-V semiconductor materials are an attractive alternative to silicon for this application, as they have some superior physical properties. They could meet the demands for fast timing detectors allowing time-of-flight measurements with ps resolution while being radiation tolerant and cost-efficient. As a material with a larger density, higher atomic number Z and much higher electron mobility than silicon, GaAs exhibits faster signal collection and a larger signal per {\mu}m of sensor thickness. In this work, we report on the fabrication of n-in-n GaAs thin-film devices intended to serve next-generation high-energy particle tracking detectors. Molecular beam epitaxy (MBE) was used to grow high-quality GaAs films with doping levels sufficiently low to achieve full depletion for detectors with an active thickness of 10 {\mu}m. The signal collection speed of the detector structures was assessed using the transient current technique (TCT). To elucidate the structural properties of the detector, Kelvin probe force microscopy (KPFM) was used, which confirmed the formation of the junction in the detector and revealed residual doping in the intrinsic layer. Our results suggest that GaAs thin films are suitable candidates to achieve thin and radiation-tolerant tracking detectors., Comment: 15 pages, 12 figures

The BraTS 2021 challenge celebrates its 10th anniversary and is jointly organized by the Radiological Society of North America (RSNA), the American Society of Neuroradiology (ASNR), and the Medical Image Computing and Computer Assisted Interventions (MICCAI) society. Since its inception, BraTS has been focusing on being a common benchmarking venue for brain glioma segmentation algorithms, with well-curated multi-institutional multi-parametric magnetic resonance imaging (mpMRI) data. Gliomas are the most common primary malignancies of the central nervous system, with varying degrees of aggressiveness and prognosis. The RSNA-ASNR-MICCAI BraTS 2021 challenge targets the evaluation of computational algorithms assessing the same tumor compartmentalization, as well as the underlying tumor's molecular characterization, in pre-operative baseline mpMRI data from 2,040 patients. Specifically, the two tasks that BraTS 2021 focuses on are: a) the segmentation of the histologically distinct brain tumor sub-regions, and b) the classification of the tumor's O[6]-methylguanine-DNA methyltransferase (MGMT) promoter methylation status. The performance evaluation of all participating algorithms in BraTS 2021 will be conducted through the Sage Bionetworks Synapse platform (Task 1) and Kaggle (Task 2), concluding in distributing to the top ranked participants monetary awards of $60,000 collectively., Comment: 19 pages, 2 figures, 1 table

The resistance to failure through tearing is a crucial mechanical property for the application of different elastomers. In this work, graphene nanoplatelets (GNPs) were introduced into a fluoroelastomer (FKM) matrix with the aim of improving its tear resistance. The fracture energy through tearing was evaluated using the pure shear test. It was found that the tearing energy increased linearly with the volume fraction of the GNPs. At the maximum GNP content, the tearing resistance was 3 times higher, suggesting efficient toughening from the GNPs. Theoretical analysis of the micromechanics was conducted by considering debonding and pull-out of the nanoplatelets as possible toughening mechanisms. It was determined quantitatively that the main toughening mechanism was debonding of the interface rather than pull-out. The formation of cavities at flake ends during the deformation, as confirmed by scanning electron microscopy, was found to contribute to the remarkably high interfacial debonding energy (~1 kJ/m2).

High-performance sealing materials that can guard key components against high pressure gases and liquid chemicals while withstanding mechanical deformation are of utmost importance in a number of industries. In this present work, graphene nanoplatelets (GNPs) were introduced into a fluoroelastomer (FKM) matrix to improve its mechanical and barrier properties and test its suitability for sealing applications. Nanocomposites filled with different loadings of GNPs were prepared and compared with their counterparts loaded with carbon black (CB). GNPs were dispersed homogeneously with a high degree of in-plane alignment. The tensile and barrier properties of the FKM were improved significantly by the addition of GNPs. Micromechanical modelling based on the shear-lag/rule-of-mixtures theory was used to analyse the reinforcing efficiency of the GNPs. Upon the addition of the GNPs, the elastomer was able to swell anisotropically in liquids, a fact that can be used to tune the swelling properties for sealing applications. In terms of gas permeability, a modification of the well-established Nielsen's theory was introduced to analyse the CO2 permeability for the bulk composite samples. The significantly improved mechanical, thermal and barrier properties at relatively low filler loadings, reveal that the FKM/GNP nanocomposites produced are very promising for use in advanced sealing applications.

There has been a massive growth in the study of transition metal dichalcogenides (TMDs) over the past decade, based upon their interesting and unusual electronic, optical and mechanical properties, such as tuneable and strain-dependent bandgaps. Tungsten disulfide (WS2), as a typical example of TMDs, has considerable potential in applications such as strain engineered devices and the next generation multifunctional polymer nanocomposites. However, controlling the strain, or more practically, monitoring the strain in WS2 and the associated micromechanics have not been so well studied. Both photoluminescence spectroscopy (PL) and Raman spectroscopy have been proved to be effective but PL cannot be employed to characterise multilayer TMDs while it is difficult for Raman spectroscopy to reveal the band structure. In this present study, photoluminescence and Raman spectroscopy have been combined to monitor the strain distribution and stress transfer of monolayer WS2 on a flexible polymer substrate and in polymer nanocomposites. It is demonstrated that WS2 still follows continuum mechanics on the microscale and that strain generates a non-uniform bandgap distribution even in a single WS2 flake through a simple strain engineering. It is shown that these flakes could be useful in optoelectonic applications as they become micron-sized PL emitters with a band gap that can be tuned by the application of external strain to the substrate. The analysis of strain distributions using Raman spectroscopy is further extended to thin-film few-layer WS2 polymer nanocomposites where it is demonstrated that the stress can be transferred effectively to WS2 flakes. The relationship between the mechanical behaviour of single monolayer WS2 flakes and that of few-layer flakes in bulk composites is investigated.

Most polymers are long-lasting and produced from monomers derived from fossil fuel sources. Bio-based and/or biodegradable plastics have been proposed as a sustainable alternative. Amongst those available, polyhydroxyalkanoate (PHA) shows great potential across a large variety of applications but is currently limited to packaging, cosmetics and tissue engineering due to its relatively poor physical properties. An expansion of its uses can be accomplished by developing nanocomposites where PHAs are used as the polymer matrix. Herein, a PHA biopolyester was melt blended with graphene nanoplatelets (GNPs) or with a 1:1 hybrid mixture of GNPs and carbon nanofibers (CNFs). The resulting nanocomposites exhibited enhanced thermal stability while their Young's modulus roughly doubled compared to pure PHA. The hybrid nanocomposites percolated electrically at lower nanofiller loadings compared to the GNP-PHA system. The electrical conductivity at 15 wt.% loading was ~ 6 times higher than the GNP-based sample. As a result, the electromagnetic interference shielding performance of the hybrid material was around 50% better than the pure GNPs nanocomposites, exhibiting shielding effectiveness above 20 dB, which is the threshold for common commercial applications. The thermal conductivity increased significantly for both types of bio-nanocomposites and reached values around 5 W K-1 m-1 with the hybrid-based material displaying the best performance. Considering the solvent-free and industrially compatible production method, the proposed multifunctional materials are promising to expand the range of application of PHAs and increase the environmental sustainability of the plastic and plastic electronics industry., Comment: 26 pages

Electrically conductive, polymeric materials that maintain their conductivity even when under significant mechanical deformation are needed for actuator electrodes, conformable electromagnetic shielding, stretchable tactile sensors and flexible energy storage. The challenge for these materials is that the percolated, electrically conductive networks tend to separate even at low strains, leading to significant piezoresistance. Herein, deformable conductors were fabricated by spray-coating a nitrile substrate with a graphene-elastomer solution. The coatings showed only slight increase in electrical resistance after thousands of bending cycles and repeated folding-unfolding events. The deformable conductors doubled their electrical resistance at 12% strain and were washable without changing their electrical properties. The conductivity-strain behaviour was modelled by considering the nanofiller separation upon deformation. To boost the conductivity at higher strains, the production process was adapted by stretching the nitrile substrate before spraying, after which it was released. This adaption meant that the electrical resistance doubled at 25 % strain. The electrical resistance was found sufficiently low to give a 1.9 dB/{\mu}m shielding in the 8-12 GHz electromagnetic band. The physical and electrical properties, including the EM screening, of the flexible conductors, were found to deteriorate upon cycling but could be recovered through reheating the coating., Comment: 29 pages, 6 figures

A comprehensive study has been undertaken on the dimensional swelling of graphene-reinforced elastomers in liquids. Anisotropic swelling was observed for samples reinforced with graphene nanoplatelets (GNPs), induced by the in-plane orientation of the GNPs. Upon the addition of the GNPs, the diameter swelling ratio of the nanocomposites was significantly reduced, whereas the thickness swelling ratio increased and was even greater than that of the unfilled elastomers. The swelling phenomenon has been analyzed in terms of a modification of the Flory-Rhener theory. The newly-derived equations proposed herein, can accurately predict the dependence of dimensional swelling (diameter and thickness) on volume swelling, independent of the type of elastomer and solvent. The anisotropic swelling of the samples was also studied in combination with the evaluation of the tensile properties of the filled elastomers. A novel theory that enables the assessment of volume swelling for GNP-reinforced elastomers, based on the filler geometry and volume fraction has been developed. It was found that the swelling of rubber nanocomposites induces a biaxial constraint from the graphene flakes.

The biaxial mechanical properties constitute another remarkable advantage of graphene, but their evaluation has been overlooked in polymer nanocomposites. Herein, we provided an innovative and practical method to characterise biaxial reinforcement from graphene via swelling of elastomers, where graphene nanoplatelets were controlled to be oriented in-plane. The in-plane-aligned graphene imposed a biaxial constraining force to the elastomer during the swelling process that led to the anisotropic swelling behaviour of the bulk nanocomposites.

In order to realise the potential of graphene nanocomposites it is vital to control the degree of dispersion and achieve a strong graphene polymer interface. Herein, we developed a facile grafting to functionalisation approach for graphene nanoplatelets. NH2-terminated graphene nanoplatelets, NH2 GNPs, prepared by a diazonium coupling were used as a platform to covalently graft PMMA chains to the surface of graphene through an amidation between the NH2 groups and PMMA chains, PMMA NH GNPs. A degree of PMMA grafting of 3.8 wt, one chain per 40 carbon atoms, was found to both improve the dispersion of the GNPs in a PMMA matrix and give strong graphene-polymer interfaces compared to as-provided GNPs. Thus, 2 wt of PMMA NH GNPs in PMMA was found to increase the elastic modulus, strength and strain at break of PMMA, whereas the incorporation of unmodified GNPs showed poor levels of reinforcement at all loadings. Furthermore, Tg and Td of PMMA were increased by 15 C and 29 C, respectively, by adding 5 wt of PMMA NH GNPs, whereas incorporating unmodified GNPs led to smaller increases. This work offers the possibility of controlling the properties of graphene-polymer composites through chemically tuning the graphene-polymer interface, which will have broad implications in the field of nanocomposites., Comment: 33 pages, 6 figures

Electromagnetic interference (EMI) shielding coating materials with thicknesses in the microscale are required in many sectors, including communications, medical, aerospace and electronics, to isolate the electromagnetic radiation emitted from electronic equipment. We report a spray, layer-by-layer (LbL) coating approach to fabricate micron thick, highly-ordered and electrically-conductive coatings with exceptional EMI shielding effectiveness (EMI SE >4830 dB/mm), through the alternating self-assembly of negatively-charged reduced graphene oxide (RGO) and a positively-charged polyelectrolyte (PEI). The microstructure and resulting electrical properties of the (PEI/RGO)n LbL structures are studied as function of increasing mass of graphene deposited per cycle (keeping the PEI content constant), number of deposited layers (n), flake diameter and type of RGO. A strong effect of the lateral flake dimensions on the electrical properties is observed, which also influences the EMI SE. A maximum EMI SE of 29 dB is obtained for a 6 um thick (PEI/RGO)10 coating with 19 vol.% loading of reduced electrochemically-exfoliated graphene oxide flakes with diameters ~3um. This SE performance exceeds those previously reported for thicker graphene papers and bulk graphene/polymer composite films with higher RGO or graphene nanoplatelets contents, which represents an important step towards the fabrication of thin and light-weight high-performance EMI shielding structures., Comment: 34 pages,7 figures

The development of scalable Out of Autoclave (OoA) in situ thermoset curing methods are required to overcome important drawbacks related to the autoclave based processing methods typically used in industry. The incorporation of graphene, an electrothermal carbon nanomaterial with the ability to transform electric energy into heat through Joule heating, emerges as a promising route to replace the conventional processing methods. In this work the electrical behaviour of both uncured and oven cured GNPs/epoxy composites with loadings of up to 10 wt% were evaluated and electrical percolation thresholds were established for both. Above the critical loading found for oven cured materials (8.5 wt%) the electrically conducting networks of GNPs formed in the matrix showed the ability to act as integrated nanoheaters when an electric current was passed through them, successfully curing the composites by Joule heating. Composites prepared by this OoA curing method (as an alternative to the traditional oven based one) at 10 wt% loading of GNPs were also prepared and compared to the oven cured ones. They showed more compact composite structures, with less microvoids and a preferred orientation of the GNPs in the matrix relative to the oven cured material at identical loading, as revealed by electron microscopy and polarized Raman spectroscopy, respectively. This microstructure and anisotropy induced by the electrically induced (i.e. OoA) cure led to GNPs/epoxy composites with superior electrical and mechanical properties (revealed by tensile testing). The well distributed GNP nanoparticles acting as nanoheaters integrated in a thermosetting matrix, in combination with excellent mechanical and electrical performances achieved for the overall graphene/epoxy composites and the simplicity associated to the method, should open the door to novel industrial applications., Comment: 29 pages, 8 figures

Graphene is considered an ideal filler for the production of multifunctional nanocomposites; as a result, considerable efforts have been focused on the evaluation and modeling of its reinforcement characteristics. In this work, we modelled successfully the mechanical percolation phenomenon, observed on a thermoplastic elastomer (TPE) reinforced by graphene nanoplatelets (GNPs), by designing a new set of equations for filler contents below and above the percolation threshold volume fraction (Vp). The proposed micromechanical model is based on a combination of the well-established shear-lag theory and the rule-of-mixtures and was introduced to analyse the different stages and mechanisms of mechanical reinforcement. It was found that when the GNPs content is below Vp, reinforcement originates from the inherent ability of individual GNPs flakes to transfer stress efficiently. Furthermore, at higher filler contents and above Vp, the nanocomposite materials displayed accelerated stiffening due to the reduction of the distance between adjacent flakes. The model derived herein, was consistent with the experimental data and the reasons why the superlative properties of graphene cannot be fully utilized in this type of composites, were discussed in depth., Comment: 29 pages, 12 figures

The deformation and fracture behaviour of one-atom-thick mechanically exfoliated graphene has been studied in detail. Monolayer graphene flakes with different lengths, widths and shapes were successfully prepared by mechanical exfoliation and deposited onto poly(methyl methacrylate) (PMMA) beams. The fracture behaviour of the monolayer graphene was followed by deforming the PMMA beams. Through in-situ Raman mapping at different strain levels, the distributions of strain over the graphene flakes were determined from the shift of the graphene Raman 2D band. The failure mechanisms of the exfoliated graphene were either by flake fracture or failure of the graphene/polymer interface. The fracture of the flakes was observed from the formation of cracks identified from the appearance of lines of zero strain in the strain contour maps. It was found that the strength of the monolayer graphene flakes decreased with increasing flake width. The strength dropped to less than 10 GPa for large flakes, much lower than the reported value of 130 GPa for monolayer graphene, thought to be due to the presence of defects. It is shown that a pair of topological defects in monolayer graphene will form a pseudo crack and the effect of such defects upon the strength of monolayer graphene has been modelled using molecular mechanical simulations., Comment: 16 pages, 11 figures

In this work, we design and implement a strong physical uncloneable function from an array of individual resonant tunnelling diodes that were previously described to have a unique response when challenged. The system demonstrates the exponential scalability of its responses when compared to the number of devices present in the system, with an expected large set of responses while retaining a 1:1 relationship with challenges. Using a relatively small set of 16 devices, 256 responses are shown to have promising levels of distinctness and repeatability through multiple measurements., Comment: 2 pages, 2 figures, 1 table

The ability to uniquely identify an object or device is important for authentication. Imperfections, locked into structures during fabrication, can be used to provide a fingerprint that is challenging to reproduce. In this paper, we propose a simple optical technique to read unique information from nanometer-scale defects in 2D materials. Flaws created during crystal growth or fabrication lead to spatial variations in the bandgap of 2D materials that can be characterized through photoluminescence measurements. We show a simple setup involving an angle-adjustable transmission filter, simple optics and a CCD camera can capture spatially-dependent photoluminescence to produce complex maps of unique information from 2D monolayers. Atomic force microscopy is used to verify the origin of the optical signature measured, demonstrating that it results from nanometer-scale imperfections. This solution to optical identification with 2D materials could be employed as a robust security measure to prevent counterfeiting., Comment: 14 pages, 5 figures

Random number generation is crucial in many aspects of everyday life, as online security and privacy depend ultimately on the quality of random numbers. Many current implementations are based on pseudo-random number generators, but information security requires true random numbers for sensitive applications like key generation in banking, defence or even social media. True random number generators are systems whose outputs cannot be determined, even if their internal structure and response history are known. Sources of quantum noise are thus ideal for this application due to their intrinsic uncertainty. In this work, we propose using resonant tunnelling diodes as practical true random number generators based on a quantum mechanical effect. The output of the proposed devices can be directly used as a random stream of bits or can be further distilled using randomness extraction algorithms, depending on the application., Comment: 11 pages, 4 figures, 1 table

We propose a scheme for coupling 2D materials to an engineered cavity based on a defective rod type photonic crystal lattice. We show results from numerical modelling of the suggested cavity design, and propose using the height profile of a 2D material transferred on top of the cavity to maximise coupling between exciton recombination and the cavity mode. The photonic structure plays a key role in enhancing the launch efficiency, by improving the directionality of the emitted light to better couple it into an external optical system. When using the photonic structure, we measured an increase in the extraction ratio by a factor of 3.4. We investigated the variations in the flux spectrum when the radius of the rods is modified, and when the 2D material droops to a range of different heights within the cavity. We found an optimum enhancement when the rods have a radius equal to 0.165 times the lattice constant, this enhancement reduces when the radius is reduced or increased. Finally, we discuss the possible use of solid immersion lenses, in combination with our photonic structure, to further enhance the launch efficiency and to improve vertical confinement of the cavity mode., Comment: 7 pages, 4 figures

The recent discovery of semiconducting two-dimensional materials has led to the prediction of a revolution in the field of optoelectronics, driven by the introduction of a series of new components that are just a few atoms thick. Key remaining challenges for producing practical devices from these materials lie in improving the coupling of light into and out of single atomic layers, and in making these layers robust to the influence of their surrounding environment. We present a solution to tackle both of these problems simultaneously, by deterministically placing a micro-lens directly onto the surface of these materials. These lenses are dynamically tuned to increase the coupling of light, whilst controlling chromatic aberration, before being set in place with UV light. We show that this approach enhances photoluminescence of tungsten diselenide (WSe2) monolayers by up to 300%, and nearly doubles the imaging resolution of the system. Furthermore, this solution fully encapsulates the monolayer, preventing it from physical damage and degradation in air. The optical solution we have developed could become a key enabling technology for the mass production of ultra-thin optical devices, such as quantum light emitting diodes., Comment: 12 pages, 6 figures

The deformation of monolayer graphene, produced by chemical vapor deposition (CVD), on a polyester film substrate has been investigated through the use of Raman spectroscopy. It has been found that the microstructure of the CVD graphene consists of a hexagonal array of islands of flat monolayer graphene separated by wrinkled material. During deformation, it was found that the rate of shift of the Raman 2D band wavenumber per unit strain was less than 25% of that of flat flakes of mechanically-exfoliated graphene, whereas the rate of band broadening per unit strain was about 75% of that of the exfoliated material. This unusual deformation behavior has been modeled in terms of mechanically-isolated graphene islands separated by the graphene wrinkles, with the strain distribution in each graphene island determined using shear lag analysis. The effect of the size and position of the Raman laser beam spot has also been incorporated in the model. The predictions fit well with the behavior observed experimentally for the Raman band shifts and broadening of the wrinkled CVD graphene. The effect of wrinkles upon the efficiency of graphene to reinforce nanocomposites is also discussed., Comment: ACS Nano (2015)

We report in this work on the spectral purity of pyramidal site-controlled InGaAs/AlGaAs Quantum Dots grown by metalorganic vapour phase epitaxy on(111)B oriented GaAs substrates. Extremely sharp emission peaks were found, showing linewidths surprisingly narrow (~27{\mu}eV) and comparable to those which can be obtained by Molecular Beam Epitaxy in an ultra-high vacuum environment. A careful reactor handling is regarded as a crucial step toward the fabrication of high optical quality systems., Comment: ICMOVPE 2010 Proceeding

This work presents some fundamental features of pyramidal site-controlled InGaAs Quantum Dots (QDs) grown by MetalOrganic Vapour Phase Epitaxy on patterned GaAs (111)B substrate. The dots self-form inside pyramidal recesses patterned on the wafer via pre-growth processing. The major advantage of this growth technique is the control it provides over the dot nucleation posi-tion and the dimensions of the confined structures onto the sub-strate. The fundamental steps of substrate patterning and the QD forma-tion mechanism are described together with a discussion of the structural particulars. The post-growth processes, including sur-face etching and substrate removal, which are required to facili-tate optical characterization, are discussed. With this approach extremely high uniformity and record spectral purity are both achieved.

We investigate the dependence of the low-temperature photoluminescence linewidths from InP-lattice-matched InGaAs/InAlAs quantum wells on the low-angle misorientation from the (100) surface of the host InP substrate. Quantum wells were grown on InP substrates misorientated by 0, 0.2, 0.4 and 0.6 degrees; 0.4 degrees was found to consistently result in the narrowest peaks, with the optimal spectral purity of ~4.25 meV found from a 15nm quantum well. The width of the emission from the 15nm quantum well was used to optimize the growth parameters. Thick layers of Si-doped InGaAs were then grown and found to have bulk, low temperature (77 K), electron mobilities up to \mu ~ 3.5 x 10^4 cm2/Vs with an electron concentration of ~1 x 10^16.

We investigate the evolution of quantum correlations over the lifetime of a multi-photon state. Measurements reveal time-dependent oscillations of the entanglement fidelity for photon pairs created by a single semiconductor quantum dot. The oscillations are attributed to the phase acquired in the intermediate, non-degenerate, exciton-photon state and are consistent with simulations. We conclude that emission of photon pairs by a typical quantum dot with finite polarisation splitting is in fact entangled in a time-evolving state, and not classically correlated as previously regarded.

We show storage of the circular polarisation of an optical field, transferring it to the spin-state of an individual electron confined in a single semiconductor quantum dot. The state is subsequently readout through the electronically-triggered emission of a single photon. The emitted photon shares the same polarisation as the initial pulse but has a different energy, making the transfer of quantum information between different physical systems possible. With an applied magnetic field of 2 Tesla, spin memory is preserved for at least 1000 times more than the exciton's radiative lifetime., Comment: 7 pages, 4 figures

We demonstrate the on-demand emission of polarisation-entangled photon pairs from the biexciton cascade of a single InAs quantum dot embedded in a GaAs/AlAs planar microcavity. Improvements in the sample design blue shifts the wetting layer to reduce the contribution of background light in the measurements. Results presented show that >70% of the detected photon pairs are entangled. The high fidelity of the (|HxxHx>+|VxxVx>)/2^0.5 state that we determine is sufficient to satisfy numerous tests for entanglement. The improved quality of entanglement represents a significant step towards the realisation of a practical quantum dot source compatible with applications in quantum information., Comment: 9 pages. Paper is available free of charge at http://www.iop.org/EJ/abstract/1367-2630/8/2/029/, see also 'A semiconductor source of triggered entangled photon pairs', R. M. Stevenson et al., Nature 439, 179 (2006)