Vincenzo Ardizzone

Formation and control of Turing patterns in a coherent quantum fluid

A generalization of Turing patterns, originally developed for chemical reactions, to patterns in quantum fluids can be realized with microcavity polaritons. Theoretical concepts of formation and control, together with experimental observations, will be presented.

Strong reduction of exciton-phonon coupling in high crystalline quality single-wall carbon nanotubes: a new insight into broadening mechanisms and exciton localization

Carbon nanotubes are quantum sources whose emission can be tuned at telecommunication wavelengths by choosing the diameter appropriately. Most applications require the smallest possible linewidth. Therefore, the study of the underlying dephasing mechanisms is of utmost interest. Here, we report on the low-temperature photoluminescence of high crystalline quality individual single-wall carbon nanotubes synthesized by laser ablation (L-SWNTs) and emitting at telecom-munication wavelengths. A thorough statistical analysis of their emission spectra reveals a typical linewidth one order of magnitude narrower than that of most samples reported in the literature. The narrowing of the PL line of L-SWNTs is due to a weaker effective exciton-phonon coupling subsequent to a weaker localization of the exciton. These results suggest that exciton localization in SWNTs not only arises from interfacial effects, but that the intrinsic crystalline quality of the SWNT plays an important role. Photoluminescence (PL) emission in semiconducting carbon nanotubes arises from exciton recombination [1–3] and has been extensively studied in view of possible applications in opto-electronics, bio-imaging or photovoltaics [4–7]. Observation of photon antibunching in the near infrared [8, 9] suggests that SWNTs are also promising single-photon sources for the implementation of quantum information protocols. Interestingly, the PL emission energy (i.e. the excitonic recombination energy) strongly depends on the tube diameter and can be easily tuned in the telecommunication bands at 0.83 eV (1.5µm) by choosing SWNTs with a diameter of about 1-1.2 nm [10]. SWNTs could therefore make up a very versatile light source for quantum optics. Several studies suggested that the optical properties of SWNTs at low temperature are best described in terms of localized excitons (zero-dimensional confinement), leading to a quantum dot like behavior [11, 12]. Nevertheless, the nature of the traps responsible for this exciton localization is not elucidated yet. In order to address the issue of exciton localization, we studied carbon nanotubes produced by high-temperature synthesis methods such as electric arc or laser ablation methods, which are known for their higher crystalline quality, with a lower density of defects [13–17].

Control of Polariton Patterns in Semiconductor Microcavities

Polaritons in semiconductor microcavities can form patterns analogous to conventional Turing patterns, including two-spot and hexagon far field patterns. We present theoretical concepts of pattern formation and control, together with experimental observations.