67 research outputs found
Collective optomechanical effects in cavity quantum electrodynamics
We investigate a cavity quantum electrodynamic effect, where the alignment of
two-dimensional freely rotating optical dipoles is driven by their collective
coupling to the cavity field. By exploiting the formal equivalence of a set of
rotating dipoles with a polymer we calculate the partition function of the
coupled light-matter system and demonstrate it exhibits a second order phase
transition between a bunched state of isotropic orientations and a stretched
one with all the dipoles aligned. Such a transition manifests itself as an
intensity-dependent shift of the polariton mode resonance. Our work, lying at
the crossroad between cavity quantum electrodynamics and quantum optomechanics,
is a step forward in the on-going quest to understand how strong coupling can
be exploited to influence matter internal degrees of freedom.Comment: 6 pages, 3 figure
Strong coupling of ionising transitions
We demonstrate that a ionising transition can be strongly coupled to a
photonic resonance. The strong coupling manifests itself with the appearance of
a narrow optically active resonance below the ionisation threshold. Such a
resonance is due to electrons transitioning into a novel bound state created by
the collective coupling of the electron gas with the vacuum field of the
photonic resonator. Applying our theory to the case of bound-to-continuum
transitions in microcavity-embedded doped quantum wells, we show how those
strong-coupling features can be exploited as a novel knob to tune both optical
and electronic properties of semiconductor heterostructures.Comment: 10 pages, 7 figure
Protective effects of the postbiotic deriving from cow's milk fermentation with L. paracasei CBA L74 against Rotavirus infection in human enterocytes
: Rotavirus (RV) is the leading cause of acute gastroenteritis-associated mortality in early childhood. Emerging clinical evidence suggest the efficacy of the postbiotic approach based on cow's milk fermentation with the probiotic Lacticaseibacillus paracasei CBAL74 (FM-CBAL74) in preventing pediatric acute gastroenteritis, but the mechanisms of action are still poorly characterized. We evaluated the protective action of FM-CBAL74 in an in vitro model of RV infection in human enterocytes. The number of infected cells together with the relevant aspects of RV infection were assessed: epithelial barrier damage (tight-junction proteins and transepithelial electrical resistance evaluation), and inflammation (reactive oxygen species, pro-inflammatory cytokines IL-6, IL-8 and TNF-α, and mitogen-activated protein kinase pathway activation). Pre-incubation with FM-CBA L74 resulted in an inhibition of epithelial barrier damage and inflammation mediated by mitogen-activated protein kinase pathway activation induced by RV infection. Modulating several protective mechanisms, the postbiotic FM-CBAL74 exerted a preventive action against RV infection. This approach could be a disrupting nutritional strategy against one of the most common killers for the pediatric age
An engineered planar plasmonic reflector for polaritonic mode confinement
It was recently demonstrated that, in deep subwavelength gap resonators
coupled to two-dimensional electron gases, coupling to propagating plasmons can
lead to energy leakage and prevent the formation of polaritonic resonances.
This process, akin to Landau damping, limits the achievable field confinement
and thus the value of light-matter coupling strength. In this work, we show how
plasmonic subwavelength reflectors can be used to create an artificial energy
stopband in the plasmon dispersion, confining them and enabling the recovery of
the polaritonic resonances. Using this approach we demonstrate a normalized
light-matter coupling ratio of {\Omega}/{\omega} = 0.35 employing a single
quantum well with a gap size of {\lambda}/2400 in vacuum.Comment: 13 pages, 3 figure
Excitons bound by photon exchange
In contrast to interband excitons in undoped quantum wells, doped quantum
wells do not display sharp resonances due to excitonic bound states. In these
systems the effective Coulomb interaction between electrons and holes typically
only leads to a depolarization shift of the single-electron intersubband
transitions. Non-perturbative light-matter interaction in solid-state devices
has been investigated as a pathway to tune optoelectronic properties of
materials. A recent theoretical work [Cortese et al., Optica 6, 354 (2019)]
predicted that, when the doped quantum wells are embedded in a photonic cavity,
emission-reabsorption processes of cavity photons can generate an effective
attractive interaction which binds electrons and holes together, leading to the
creation of an intraband bound exciton. Spectroscopically, this bound state
manifests itself as a novel discrete resonance which appears below the
ionisation threshold only when the coupling between light and matter is
increased above a critical value. Here we report the first experimental
observation of such a bound state using doped GaAs/AlGaAs quantum wells
embedded in metal-metal resonators whose confinement is high enough to permit
operation in strong coupling. Our result provides the first evidence of bound
states of charged particles kept together not by Coulomb interaction, but by
the exchange of transverse photons. Light-matter coupling can thus be used as a
novel tool in quantum material engineering, tuning electronic properties of
semiconductor heterostructures beyond those permitted by mere crystal
structures, with direct applications to mid-infrared optoelectronics
Sculpting ultrastrong light-matter coupling through spatial matter structuring
The central theme of cavity quantum electrodynamics is the coupling of a
single optical mode with a single matter excitation, leading to a doublet of
cavity polaritons which govern the optical properties of the coupled structure.
Especially in the ultrastrong coupling regime, where the ratio of the vacuum
Rabi frequency and the quasi-resonant carrier frequency of light,
, approaches unity, the polariton
doublet bridges a large spectral bandwidth , and further
interactions with off-resonant light and matter modes may occur. The resulting
multi-mode coupling has recently attracted attention owing to the additional
degrees of freedom for designing light-matter coupled resonances, despite added
complexity. Here, we experimentally implement a novel strategy to sculpt
ultrastrong multi-mode coupling by tailoring the spatial overlap of multiple
modes of planar metallic THz resonators and the cyclotron resonances of
Landau-quantized two-dimensional electrons, on subwavelength scales. We show
that similarly to the selection rules of classical optics, this allows us to
suppress or enhance certain coupling pathways and to control the number of
light-matter coupled modes, their octave-spanning frequency spectra, and their
response to magnetic tuning. This offers novel pathways for controlling
dissipation, tailoring quantum light sources, nonlinearities, correlations as
well as entanglement in quantum information processing
Real-space nanophotonic field manipulation using non-perturbative lightâmatter coupling
The achievement of large values of the lightâmatter coupling in nanoengineered photonic structures can lead to multiple photonic resonances contributing to the final properties of the same hybrid polariton mode. We develop a general theory describing multi-mode lightâmatter coupling in systems of reduced dimensionality, and we explore their phenomenology, validating our theoryâs predictions against numerical electromagnetic simulations. On one hand, we characterize the spectral features linked with the multi-mode nature of the polaritons. On the other hand, we show how the interference between different photonic resonances can modify the real-space shape of the electromagnetic field associated with each polariton mode. We argue that the possibility of engineering nanophotonic resonators to maximize multi-mode mixing, and to alter the polariton modes via applied external fields, could allow for the dynamical real-space tailoring of subwavelength electromagnetic fields
Best friends: children use mutual gaze to identify friendships in others
This study examined childrenâs ability to use mutual eye gaze as a cue to friendships in others. In Experiment 1, following a discussion about friendship, 4-, 5-, and 6-year-olds were shown animations in which three cartoon children looked at one another, and were told that one target character had a best friend. Although all age groups accurately detected the mutual gaze between the target and another character, only 5- and 6-year-olds used this cue to infer friendship. Experiment 2 replicated the effect with 5- and 6-year-olds when the target character was not explicitly identified. Finally, in Experiment 3, where the attribution of friendship could only be based on synchronized mutual gaze, 6-year-olds made this attribution, while 4- and 5-year-olds did not. Children occasionally referred to mutual eye gaze when asked to justify their responses in Experiments 2 and 3, but it was only by the age of 6 that reference to these cues correlated with the use of mutual gaze in judgements of affiliation. Although younger children detected mutual gaze, it was not until 6 years of age that children reliably detected and justified mutual gaze as a cue to friendship
Tuning materials' properties by non-perturbative cavity quantum electrodynamics
When in a quantum optical system the coupling between matter and cavity mode becomes comparable to the bare excitation frequency, we enter a non-perturbative coupling regime, as perturbation theory fails describing the systemâs dynamics. While recent advances in Cavity Quantum Electrodynamics allowed to achieve very high values of the coupling strength, thanks to the resonators properties optimization and the employment of solid-state devices, an ever growing interest has been shown about the possibility of significantly modify materialsâ properties. It has been demonstrated that the chemical structure of molecules strongly coupled to a photon mode can be altered, which opens the possibility to manipulate and control chemical reactions. The aim of this thesis is to explore non-perturbative regimes on several quantum systems, and to investigate the effects of the coupling upon their properties, such as internal degrees of freedom or electronic states structure. I first developed a novel theory to determine the polariton spectrum of a dipolar ensamble in which a Ising-like dipole-dipole interaction in the 2 non-perturbative regime is considered. A further important focus is the investigation of the saturation effects due to the inclusion of the inter-dipole interaction, and the interplay between the latter and light-matter coupling strength. I also explored specifically the influence of the coupling on the rotational degrees of freedom of an ensemble of two-dimensional freely rotating dipoles, all coupled to a single cavity mode, finding that they are driven by the collective light-matter coupling to undergo a crossover between an isotropic and an aligned phase. I then investigated the case of cavity-embedded doped quantum wells, demonstrating that not only it is possible to couple a discrete cavity mode and bound-to-continuum transitions, but also that a novel bound exciton state appears, induced by the coupling strength. This results shows how lightâmatter coupling can be used to tune both optical and electronic properties of semiconductor heterostructures beyond those permitted by mere crystal properties. Finally, I explored the physics of an array of THz metamaterial resonators coupled to cyclotron resonances of a two-dimensional electron gas, developing a multiple-mode theory that takes in account the interaction between multiple photon modes mediated by the electrons. My results show that this cross-interaction, due to the strong two-dimensional geometry of the optically active medium, leads to the hybridization of different uncoupled photon modes, and manifests as a visible change of the distribution of the coupled electromagnetic field
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