Alessandra Andreoni

Experimental Reconstruction of Photon Statistics without Photon Counting

Experimental reconstructions of photon number distributions of both continuous-wave and pulsed light beams are reported. Our scheme is based on on/off avalanche photo-detection assisted by maximum-likelihood estimation and does not involve photon counting. Reconstructions of the distribution for both semiclassical and quantum states of light are reported for single-mode as well as for multi-mode beams.

Role of H-bond formation in the photoreactivity of curcumin ∗

Curcumin is the main constituent of curry. In its ground state it shows chemo-preventive, chemo-therapeutic and anti-inflammatory effects. For its immunostimulating action it has been considered for the development of drugs suitable for treating AIDS and cystic fibrosis. Further biological action is induced in curcumin by photoactivation: in suitable environmen- tal conditions electronically excited curcumin can act as a singlet oxygen generator. Moreover, cytotoxicity is enhanced by light exposure and antibacterial effects are photosensitized. This work is aimed to understand the photobiological action of curcumin by elucidating the deactivation mechanisms of its first excited singlet state. In particular we find evidence of the role of tautomerization in the excited state by measuring fluorescence lifetimes and quantum yields for such compound dissolved in solvents of different polarity and H-bonding capability. Degradation quantum yield and singlet oxygen generation efficiency were also measured in acetonitrile and methanol. The results emphasize the strong dependence of the deactivation processes from the environment. The deactivation phenomenology can be fully explained by postulating intramolecular proton transfer in the cis enol conformer to be the leading non-radiative deactivation pathway.

Three-mode entanglement by interlinked nonlinear interactions in optical χ (2) media

We address the generation of fully inseparable three-mode entangled states of radiation by interlinked nonlinear interactions in χ(2) media. We show how three-mode entanglement can be used to realize symmetric and asymmetric telecloning machines, which achieve optimal fidelity for coherent states. An experimental implementation involving a single nonlinear crystal in which the two interactions take place simultaneously is suggested. Preliminary experimental results showing the feasibility and the effectiveness of the interaction scheme with a seeded crystal are also presented.

Sub-shot-noise photon-number correlation in a mesoscopic twin beam of light

We demonstrate sub-shot-noise photon-number correlations in a (temporal) multimode mesoscopic ({approx}10{sup 3} detected photons) twin beam produced by picosecond-pulsed spontaneous nondegenerate parametric down-conversion. We have separately detected the signal and idler distributions of photons collected in twin coherence areas and found that the variance of the photon-count difference goes below the shot-noise limit by 3.25 dB. The number of temporal modes contained in the twin beam, as well as the size of the twin coherence areas, depends on the pump intensity. Our scheme is based on spontaneous down-conversion and thus does not suffer from limitations due to the finite gain of the parametric process. Twin beams are also used to demonstrate the conditional preparation of a nonclassical (sub-Poissonian) state.

Self-consistent characterization of light statistics

We demonstrate the possibility of a self-consistent characterization of the photon-number statistics of a light field by using photoemissive detectors with internal gain simply endowed with linear input/output responses. The method can be applied to both microscopic and mesoscopic photon-number regimes. The detectors must operate in the linear range without the need for photon-counting capabilities.

Photon-number statistics with Silicon photomultipliers

We present a description of the operation of a multi-pixel detector in the presence of non-negligible dark-count and cross-talk effects. We apply the model to devise self-consistent calibration strategies to be performed on the very light under investigation.

Studies on curcumin and curcuminoids. XXXIV. Photophysical properties of a symmetrical, non-substituted curcumin analogue.

Curcumin is the main constituent of curry. In its ground state it shows chemo-preventive, chemo-therapeutic, anti-inflammatory and immune stimulating effects, and it is considered as a drug or drug model in the treatment of AIDS and cystic fibrosis. Further biological activity is induced in curcumin by light exposure: cytotoxicity is enhanced and photosensitized antibacterial effects are achieved. For the curcumin cis enol conformer, the fastest deactivation mechanism of the first excited singlet state is an excited-state intra-molecular proton transfer, which brings curcumin back to the ground state. This mechanism, as well as reketonization, interaction with the solvent and photodegradation, compete with the phototherapeutic action. The native compound curcumin carries phenolic hydroxyl and methoxy groups that influence the molecular charge distribution and hence the excited-state intra-molecular proton transfer rate in an unpredictable way. In this work we study static and time-resolved spectroscopic properties of a non-substituted curcuminoid that lacks both the phenolic hydroxyl and the phenolic methoxy groups. The photophysical properties of this compound are compared to those of native curcumin, in order to provide a rationale to the design of curcuminoids with molecular structures optimized for a photosensitizer.

Counting photoelectrons in the response of a photomultiplier tube to single picosecond light pulses

We demonstrate the capability of a commercial photomultiplier to produce distinguishable anodic-pulse charge values when 1, 2, or more photoelectrons leave the cathode within a time shorter than the pulse-response duration. We propose a method for precise reconstruction of the photoelectron statistics from the measured pulse-height spectra and discuss applications to the characterization of quantum states in the continuous-variable regime.

Studies on Curcumin and Curcuminoids. XXXIX. Photophysical Properties of Bisdemethoxycurcumin

The steady-state absorption and fluorescence, as well as the time-resolved fluorescence properties of bisdemethoxycurcumin dissolved in several solvents differing in polarity and H-bonding capability were measured. The photodegradation quantum yield of the compound in acetonitrile and methanol was determined. The bisdemethoxycurcumin decay mechanisms from the S1 state were discussed and compared with those of curcumin. The differences in S1 dynamics observed between bisdemethoxy-curcumin and curcumin could be ascribed to a difference in H-bond acceptor/donor properties of the phenolic OH and a difference in strength of the intramolecular H-bond in the keto-enol moiety within the two molecules.

Quantum and classical correlations of intense beams of light investigated via joint photodetection

We address joint photodetection as a method for discriminating between the classical correlations of a thermal beam divided by a beam splitter and the quantum entanglement of a twin beam obtained by parametric down-conversion. We show that for intense beams of light the detection of the difference photocurrent may be used, in principle, in order to reveal entanglement, while the simple measurement of the correlation coefficient is not sufficient. We have experimentally measured the correlation coefficient and the variance of the difference photocurrent for several classical and quantum states. Results are in good agreement with theoretical predictions taking into account the extra noise in the generated fields that is due to the pump laser fluctuations.