Bound states in the continuum (BICs)
are peculiar topological states that, when realized in a planar photonic crystal lattice, are symmetry-protected from radiating in the far field despite lying ...within the light cone
. These BICs possess an invariant topological charge given by the winding number of the polarization vectors
, similar to vortices in quantum fluids such as superfluid helium and atomic Bose-Einstein condensates. In spite of several reports of optical BICs in patterned dielectric slabs with evidence of lasing, their potential as topologically protected states with theoretically infinite lifetime has not yet been fully exploited. Here we show non-equilibrium Bose-Einstein condensation of polaritons-hybrid light-matter excitations-occurring in a BIC thanks to its peculiar non-radiative nature, which favours polariton accumulation. The combination of the ultralong BIC lifetime and the tight confinement of the waveguide geometry enables the achievement of an extremely low threshold density for condensation, which is reached not in the dispersion minimum but at a saddle point in reciprocal space. By bridging bosonic condensation and symmetry-protected radiation eigenmodes, we reveal ways of imparting topological properties onto macroscopic quantum states with unexplored dispersion features. Such an observation may open a route towards energy-efficient polariton condensation in cost-effective integrated devices, ultimately suited for the development of hybrid light-matter optical circuits.
Charge generation and transport in (CH sub(3)NH sub(3))PbI sub(3-x)Cl sub(x) sensitized mesostructured solar cells are investigated. A highly efficient charge generation is directly proven by time ...correlated single photon counting analysis. Photoinduced absorption and transient photovoltage investigations depict double charge recombination dynamics. To explain the high device performances according to those spectroscopic observations, we suggest the existence of two complementary paths for electron transport, involving either TiO sub(2) or perovskite matrixes.
All-optical polariton transistor Ballarini, D; De Giorgi, M; Cancellieri, E ...
Nature communications,
2013, Volume:
4, Issue:
1
Journal Article
Peer reviewed
Open access
Although optical technology provides the best solution for the transmission of information, all-optical devices must satisfy several qualitative criteria to be used as logic elements. In particular, ...cascadability is difficult to obtain in optical systems, and it is assured only if the output of one stage is in the correct form to drive the input of the next stage. Exciton-polaritons, which are composite particles resulting from the strong coupling between excitons and photons, have recently demonstrated huge non-linearities and unique propagation properties. Here we show that polariton fluids moving in the plane of the microcavity can operate as input and output of an all-optical transistor, obtaining up to 19 times amplification and demonstrating the cascadability of the system. Moreover, the operation as an AND/OR gate is shown, validating the connectivity of multiple transistors in the microcavity plane and opening the way to the implementation of polariton integrated circuits.
Spin-glass theory is one of the leading paradigms of complex physics and describes condensed matter, neural networks and biological systems, ultracold atoms, random photonics and many other research ...fields. According to this theory, identical systems under identical conditions may reach different states. This effect is known as replica symmetry breaking and is revealed by the shape of the probability distribution function of an order parameter named the Parisi overlap. However, a direct experimental evidence in any field of research is still missing. Here we investigate pulse-to-pulse fluctuations in random lasers, we introduce and measure the analogue of the Parisi overlap in independent experimental realizations of the same disordered sample, and we find that the distribution function yields evidence of a transition to a glassy light phase compatible with a replica symmetry breaking.
We define landslide Early Warning Systems and present practical guidelines to assist end-users with limited experience in the design of landslide Early Warning Systems (EWSs). In particular, two flow ...chart-based tools coming from the results of the SafeLand project (7th Framework Program) have been created to make them as simple and general as possible and in compliance with a variety of landslide types and settings at single slope scale. We point out that it is not possible to cover all the real landslide early warning situations that might occur, therefore it will be necessary for end-users to adapt the procedure to local peculiarities of the locations where the landslide EWS will be operated.
Turbulent phenomena are among the most striking effects that both classical and quantum fluids can exhibit. Although classical turbulence is ubiquitous in nature, the observation of quantum ...turbulence requires the precise manipulation of quantum fluids such as superfluid helium or atomic Bose–Einstein condensates. Here we demonstrate the turbulent dynamics of a two-dimensional quantum fluid of exciton–polaritons, hybrid light–matter quasiparticles, both by measuring the kinetic energy spectrum and showing the onset of vortex clustering. We demonstrate that the formation of clusters of quantum vortices is triggered by the increase of the incompressible kinetic energy per vortex, showing the tendency of the vortex-gas towards highly excited configurations despite the dissipative nature of our system. These results lay the basis for investigations of quantum turbulence in two-dimensional fluids of light.The turbulent dynamics of a 2D quantum fluid of exciton–polaritons is measured in a planar AlGaAs microcavity after a pulsed optical excitation. Clear evidence of both the onset of vortex clustering and inverse energy cascade is provided.
Although photons in vacuum are massless particles that do not appreciably interact with each other, significant interactions appear in suitable nonlinear media, leading to hydrodynamic behaviours ...typical of quantum fluids. Here, we show the generation and manipulation of vortex-antivortex pairs in a coherent gas of strongly dressed photons (polaritons) flowing against an artificial potential barrier created and controlled by a light beam in a semiconductor microcavity. The optical control of the polariton flow allows us to reveal new quantum hydrodynamical phenomenologies such as the formation of vortex pairs upstream from the optical barrier, a case of ultrashort time excitation of the quantum flow, and the generation of vortices with counterflow trajectories. Additionally, we demonstrate how to permanently trap and store quantum vortices hydrodynamically generated in the wake of a defect. These observations are supported by time-dependent simulations based on the non-equilibrium Gross-Pitaevskii equation.
CdSe nanocrystals of well‐defined sizes (so‐called magic‐size clusters, MSCs) have been grown with progressively larger sizes. During the synthesis, the relative populations of the different families ...of MSCs vary, as smaller clusters evolve into larger clusters. The time evolution of the various MSCs (see figure) is modeled by taking into account their much higher stability over nanocrystals of any intermediate size. A blue‐light‐emitting diode based on these MSCs is also presented.
Data regarding the possible relationship of insomnia and EDS with mortality are inconclusive. The aim of this study was to investigate the association between these sleep complaints and the risk of ...long-term (20 years) all-cause mortality in older adults. Between April 2000 and March 2001, 750 subjects aged 65 years and older, who resided in the seventh district of Udine, were recruited. Data on sociodemographic characteristics, past medical history, and pharmacological treatment were collected. Dementia was diagnosed using a comprehensive neurological and neuroradiological assessment. Older adults were interviewed by neuropsychologists trained in sleep disturbances in order to assess the presence of sleep complaints. Vital status was followed over 20 years until March 2020. Older male adults affected by insomnia and EDS were significantly more likely to die over the follow-up period. Indeed, males reporting poor sleep and daytime somnolence had a 60% and 48% higher chance of dying than subjects who were not affected by these sleep complaints, respectively. The HR was attenuated after adjusting for confounding variables among insomniacs, whereas that of somnolent men strengthened. Differently from men, insomnia and EDS did not have any impact on mortality in older women. In conclusion, older male adults affected by insomnia and EDS had a significant increased risk of mortality, which is independent of cancer, depression, dementia, cardiovascular diseases, and sleeping pill use.
•We investigated whether insomnia and excessive daytime sleepiness increase the risk of long-term mortality in older adults.•Older male adults with insomnia and excessive daytime sleepiness were significantly more likely to die.•Differently from men, insomnia and excessive daytime sleepiness did not have any impact on mortality in older women.
A collection of more than 1800 carbonized papyri, discovered in the Roman 'Villa dei Papiri' at Herculaneum is the unique classical library survived from antiquity. These papyri were charred during ...79 A.D. Vesuvius eruption, a circumstance which providentially preserved them until now. This magnificent collection contains an impressive amount of treatises by Greek philosophers and, especially, Philodemus of Gadara, an Epicurean thinker of 1st century BC. We read many portions of text hidden inside carbonized Herculaneum papyri using enhanced X-ray phase-contrast tomography non-destructive technique and a new set of numerical algorithms for 'virtual-unrolling'. Our success lies in revealing the largest portion of Greek text ever detected so far inside unopened scrolls, with unprecedented spatial resolution and contrast, all without damaging these precious historical manuscripts. Parts of text have been decoded and the 'voice' of the Epicurean philosopher Philodemus is brought back again after 2000 years from Herculaneum papyri.
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