The rotational dynamics of CO single molecules solvated in small He clusters (CO@HeN ) has been studied using Reptation Quantum Monte Carlo for cluster sizes up to N = 30. Our results are in good agreement with the roto-vibrational features of the infrared spectrum recently determined for this system, and provide a deep insight into the relation between the structure of the cluster and its dynamics. Simulations for large N also provide a prediction of the effective moment of inertia of CO in the He nano-droplet regime, which has not been measured so far.

Exciton-polaritons in semiconductors are quasi-particles which have recently shown the capability to undergo phase transition into a coherent hybrid state of light and matter. The observation of such quasi-particles in organic microcavities has attracted increasing attention for their characteristic of reaching condensation at room temperature. In this work we demonstrate that the emission properties of organic polaritons do not depend on the overlap between the absorption and emission states of the molecule and that the emission dynamics are modified in the strong coupling regime, showing a significant enhancement of the photoluminescence intensity as compared to the bare dye. This paves the way to the investigation of molecules with large absorption coefficients but poor emission efficiencies for the realization of polariton condensates and organic electrically injected lasers by exploiting strong exciton-photon coupling regimes.2

We report observation of oscillations in the dynamics of a microcavity polariton condensate formed under pulsed non resonant excitation. While oscillations in a condensate have always been attributed to Josephson mechanisms due to a chemical potential unbalance, here we show that under some localisation conditions of the condensate, they may arise from relaxation oscillations, a pervasive classical dynamics that repeatedly provokes the sudden decay of a reservoir, shutting off relaxation as the reservoir is replenished. Using non-resonant excitation, it is thus possible to obtain condensate injection pulses with a record frequency of 0.1 THz. Light-matter particles-that arise from the strong interaction between the photonic field in a semiconductor microcavity and the exciton dipole in quantum wells (QWs)-have recently shown a variety of interesting phenomena related to non-equilibrium condensation. These particles, polaritons, have striking similarities with BoseEinstein condensates (BECs) of atomic gases, and, in other aspects, with photon lasers. Nonetheless, polaritons have demonstrated peculiarities of their own that set them apart from both quantum condensates and lasers. Recently many observation in fluid dynamics have shown such peculiar behaviors, related to the polaritonic dispersion on the one hand and its dissipative character on the other hand. Fundamental phenomena like condensation [1, 2], superfluidity [3][4][5], quantised vorticity [6,7], quantum turbulence [8,9] and phase transitions [10] have shown to deviate from conventional BEC, stimulating new models for the quantum dynamics of polariton condensates. These models consider some of the many parameters that are typical of polaritons, including the upper and lower dispersions, pumping, dissipation, spin, non-linearities, etc. One component that is seldom considered in details is the exciton reservoir. This, however, often plays an important role, even under resonant excitation [11,12], and in particular when it comes to polariton relaxation and condensation.We will show here how a polariton condensate formed by non-resonant excitation, in a confined region of space of a few micron squared, can exhibit marked oscillations of its population. While many oscillatory behaviours have been observed [13,14] or predicted [15] in the polariton literature, relating them to coherent and/or quantum phenomena, we report semi-classical oscillations due to the interplay between reservoir feeding and Bose stimulation. These oscillations fall in the class of so-called "relaxation oscillations" [16], that are well known in class B lasers [17], typically solid-state ones with a small active volume and slow-inversion decay [18], where they lead to the phenomenon of spiking [19]. The effect is an important class of self-oscillations [20]. In this form, it is analogous to the Tantalus cup oscillations, used by the Romans to measure time, or in natural phenomena such as rhythmic springs. The underlying principle is the following: passed a threshold, a siphon triggers...

In this paper, we present the implementation of a new class of optical pressure sensors in a robotic tactile-sensing system based on polydimethylsiloxane (PDMS). The sensor consists of a tapered optical fiber, where an optical signal goes across, embedded into a PDMS-gold nanocomposite material (GNM). By applying different pressure forces onto the PDMS-based nanocomposite, changes in the optical transmittivity of the fiber can be detected in real time due to the coupling between the GNM and the tapered fiber region. The intensity reduction of a transmitted light is correlated to the pressure force magnitude. Light intensity is converted into an electric signal by a system suitable for robotic implementation. High sensitivity using forces by applying weights of a few grams is proved. Sensitivity on the order of 5 g is checked. A detailed algorithm for the detection of roughness and shapes by means of a robotic finger is proposed.