Talks

Here you can find the Abstract of the Talks given during the Workshop.

List of Talks

  1. Dynamical Photonic Structures using EIT, Francesco Bariani
  2. Public Understanding of Science and Science Communication, Michela Guglielmino
  3. Quantum Monte Carlo study of the 2-D electron gas in presence of Rashba interaction, Alberto Ambrosetti
  4. Density Profiles of a Trapped Polarized Fermi Gas, Gianluca Bertaina
  5. Nonlinear optical properties of Silicon nanocrystals at 1550 nm and their application, Rita Spano
  6. Interplay between surface tension and local amorphous order in the Mosaic picture of glass transition, Giacomo Gradenigo
  7. Dynamics of criterion setting under feedback control in human perception, Davide Tabarelli
  8. Whispering Gallery Mode resonators based on Silicon nanocrystal in a Silicon Oxide host, Alessandro Pitanti
  9. Guiding light in silicon : new materials and building blocks, Romain Guider: the talk was suspended because of health problem of the speaker
  10. Strong CP-violation in external magnetic fields: vacuum polarization and vacuum birefringence, Raffaele Millo
  11. Effective Field Theory and Quantum Monte Carlo Methods in nuclear physic, Paolo Armani
  12. Chandrasekhar-Clogston limit in Fermi mixtures with unequal masses at Unitarity, Ingrid Bausmerth
  13. Physical techniques on lipidomics, Tommaso Sandron
  14. EXAFS studies of negative thermal expansion Zincblende Materials,AbdelAll Naglaa
  15. Physically and chemically synthesized TiO2 composite thin films for hydrogen production by photocatalytic water splitting, Rupali Dholam

Dynamical Photonic Structures using EIT

Author Francesco Bariani

Short Abstract
The interference effect between different excitation schemes of a quantum system is one of the remarkable features of Quantum Mechanics. Electromagnetically Induced Transparency (EIT) is a spectacular demonstration of this property which provides the possibility to inhibit the absorption of light in an otherwise optically thick medium while hugely slowing down the radiation.
This phenomenon offers the possibility to play with light by varying in time the optical response of an EIT medium while a wavepacket is inside it. In order to tackle the problem, we have studied the band diagram, the reflectivity and the scattering properties of such a system.

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Public Understanding of Science and Science Communication

Author Michela Guglielmino

Short Abstract
Public understanding of Science and, consequently, science communication are themes of increasing importance for the scientific community: people are more and more involved in making decisions and choices about the future and development of research, about scientific applications and about possible ethical limits.
How can we improve people’s understanding and knowledge of the scientific method, of the way science develops and grows, of how it changes our daily lives, so that they can make an informed choice when required?
A level, among many others, at which we can make some difference, is school education. For this reason I am going to investigate the value of merging the curricular teaching of physics with practical activities related to astrophysics, as, for example, measuring a stellar spectrum via a normal digital camera and then evaluating temperature and chemical composition of the emitting object.

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Quantum Monte Carlo study of the 2-D electron gas in presence of Rashba interaction

Author Alberto Ambrosetti

Abstract
The Rashba interaction, an electric field induced spin orbit coupling has been observed in semiconductor heterostructures depending on their symmetry. Due to the possibility of controlling spin by applied voltage wide interest raised on such systems as possible candidates for spintronics devices.
Diffusion Monte Carlo is used for studying the ground state energy of the homogeneus case at T=0. Because of the spin-orbit nature of Rashba interaction a normal apprach cannot be used and therefore a specific imaginary time propagator has been developed and implemented.

Density Profiles of a Trapped Polarized Fermi Gas

Author Gianluca Bertaina

Short Abstract
Ultracold gases are a very active field of research. A cloud of alkali atoms is cooled down to temperatures of the order of 100 nK, avoiding its solidification thanks to lasers and magnetic fields. At this very low temperatures quantum effects start to be evident, showing unusual phenomena like superfluidity. One of the challenges have been the realization of the so called BCS-BEC crossover between a superfluid of attracting fermions and a superfluid of biatomic molecules.

We theoretically investigate the density profiles of a trapped Fermi gas as a function of polarization and interaction strength. The system shows a shell structure with possibly both a superfluid and a normal part. We provide comparison to the density profiles observed by the MIT group.

Future work will deal with neutral Fermi gases in two dimensions, using Quantum Monte Carlo methods to study the ground state of the system.

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Nonlinear optical properties of Silicon nanocrystals at 1550 nm and their application

Author Rita Spano

Short Abstract
A new generation of all-optical devices based on Silicon nanocrystals (Si-nc) as non linear active material is under development. The key features of Si-nc are their compatibility with the CMOS fabrication processes, their possible large scale production and their potential large Kerr effect. Si-nc are currently better known because of their efficient visible emission. However a few studies have already reported that they can be used for nonlinear optical applications at 800 nm both in the form of porous Silicon or embedded in a SiO2 matrix. In the framework of transparent optical network, the evaluation of the nonlinear response of Si-nc at telecom wavelengths is needed for a proper design of the structural parameters aimed at optimization of the performance of the final device.

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Interplay between surface tension and local amorphous order in the Mosaic picture of glass transition

Author Giacomo Gradenigo

Short Abstract
The exponential divergence of relaxation time in supercoleed liquids is a clue of an underlying glass transition. This is a continuous transition, with no latent heat: according to the theory of critical phenomena a divergent correlation length is expected to be found. Mosaic model is aimed to describe glass transition introducing such a divergent lengthscale. According to Mosaic this lenghtscale is the critical size of droplets of different amorphous phases that coexhist in the system just above the transition point. The formation of droplets is favoured by entropic reasons and disturbed by a surface energy cost: the competition between these two effects determines the critical size of droplets. A detailed study of droplets surface cost is thus central to Mosaic. We investigated numerically the surface cost for different droplets size at different temperatures. Our results support Mosaic scenario and give also evidences of a crossover from activated (supercooled liquid) to non-activated (liquid) relaxational dynamic.

Dynamics of criterion setting under feedback control in human perception

Author Davide Tabarelli

Short Abstract
Signal Detection Theory (SDT) provides a reliable theoretical model to interpret and investigate human perception, in particular as regards discrimination and classification experiments. The theory accounts for the contribution of endogenous and exogenous noise by assuming a normal distributed neural representation of external stimuli. Moreover, in order to explain the dichotomic nature of observer's motor response, the existence of a internal criterion is assumed: the observer's outcome is then determined by the comparison between the internally encoded criterion and the neural response. Although it is known that an observer can change his/her criterion, typically in tasks aiming at maximizing the percentage of correct responses, how the neural system sets and maintains this criterion is still an open issue. A possible method to retrieve important information about the criterion setting mechanism is to investigate its dynamics. We investigate the criterion dynamics in a orientation "yes-no", one-interval experiment within the visual modality inducing criterion changes by means of feedback techniques. To account for the observed criterion dynamics we used the the simplest model for a closed-loop system i.e: a low-pass-filtered amplifier described by a single pole gain function in the frequency domain and characterized by a time constant and an amplitude. This model has an immediate physical interpretation. Data have been analyzed on a trial-by-trial basis by means of maximum likelihood estimation techniques (MLE); likelihood-based spectral analysis of the dynamics were also performed. Besides experiments, numerical simulations have been carried out in order to test and calibrate the method. Results confirms the reliability of the model and of the developed experimental techniques.

Whispering Gallery Mode resonators based on Silicon nanocrystal in a Silicon Oxide host

Author Alessandro Pitanti

Short Abstract
High quality monolithic resonators such as micro-disks, rings and toroids are triggering an intensive and rapidly evolving research. In such structures, due to total internal reflection, the light propagates in azimuthally simmetric mode, called whispering-gallery modes (WGM). Optically passive microdisks, based on transparent materials with negligible absorption losses, lead to extremely high quality factors (Q ~ 106 to 1010), offering applications in spectroscopy and sensing. On the contrary, optically active resonator systems, such as III-V semiconductor quantum dot microdisk lasers, report active Qs of 103-104 in the visible and near infrared wavelength range.
The recent challenges in silicon photonics towards using nanocrystalline Si (nc-Si) as an integrated light source have boosted an intensive research in the last decade. The aim of this research is to exploit the Si-nc as emitters embedded in a WGM microdisk active resonator, enabling an easy energy charge of the cavity due to the strong photoluminescence of the Si quantum dots in the visible range.

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Guiding light in silicon : new materials and building blocks

Author Romain Guider

Short Abstract
Waveguides are a very interesting component in nanophotonic integrated circuits. They are of course necessary for interconnects, but a lot of elements are also based on waveguides. This presentation will describe the study of new nanoSilicon waveguides and some others nanophotonics structures, more particularly the ring and disk resonators. We will study three various type of materials, one new in term of waveguide (SiOC) and two well-known for waveguides applications (Silicon On Insulator and SOI Slot waveguides).

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Strong CP-violation in external magnetic fields: vacuum polarization and vacuum birefringence

Author Raffaele Millo

Abstract
There are compelling theoretical arguments suggesting that strong interactions would violate CP-symmetry. Nonetheless, strong CP- violating hadronic processes have never been observed. In this talk we show how Effective Field Theory approach enables to determine effects of CP-violation on QCD and QED vacuum, in the presence of external magnetic fields. This would lead to macroscopic and hence observable effects: the external field would polarize quantum fluctuations and induce an electric field along the direction of the magnetic field. We study the magnitude of this effect induced by the primordial large-scale magnetic fields, and by the magnetic fields in the vicinity of neutron stars: the polarization induced by a magnetar could accelerate electric charges up to energies of the order the MeV.
From these results it is immediate to compute the QCD contribution to the CP-odd photon-photon low-energy effective coupling. This term triggers a non zero CP-violating vacuum birefringence: implications on the PVLAS experiments are discussed.

Effective Field Theory and Quantum Monte Carlo Methods in nuclear physic

Author Paolo Armani

Abstract
It's studied the ground state of many nucleon systems, starting from an ab-initio Effective Field Theory Lagrangian with Monte Carlo methods.

Chandrasekhar-Clogston limit in Fermi mixtures with unequal masses at Unitarity

Author Ingrid Bausmerth

Short Abstract
Using many-body diagrammatic techniques and ab initio Monte Carlo results we analyze the bulk phase diagram of a unitary Fermi gas at zero temperature with population imbalance and unequal masses. The phase diagram permits to identify different regions where the gas is superfluid, partially polarized or fully polarized. The asymmetry in the phase diagram, caused by the mass imbalance, and its effect on the Chandrasekhar-Clogston limit for the critical polarization are explicitly discussed. The equation of state of the superfluid and normal phases is employed, within the local density approximation, to predict novel phase separated configurations in the presence of armonic trapping potentials.

Physical techniques on lipidomics

Author Tommaso Sandron

Abstract
In recent years the interest in the research on lipids (lipidomics) is broadly increased due to the increased knowledge of the crucial role of these molecules in cell, tissue and organ physiology. It's however still difficult to obtain chemical and structure informations due to the complexity of lipids and the lack of powerful tools for their analysis. An important improvement in this direction has been achieved by new analytical approaches such as mass spectrometry and NMR spectroscopy, that make lipidomics a promising field of biomedical research. In this talk, by showing some latest applications, the potential of these techniques and their great complementarity will be discussed.

EXAFS studies of negative thermal expansion Zincblende Materials"

Author AbdelAll Naglaa

Short Abstract
Extended X-ray absorption fine structure (EXAFS) can represent a powerful probe of the local behaviour of negative thermal expansion (NTE) materials, thanks to the possibility of measuring the expansion of selected inter-atomic bonds and the perpendicular relative atomic displacements. The thermal expansions measured by EXAFS and by Bragg scattering have a different physical meaning. The effectiveness of EXAFS for NTE on crystals with the zincblende structure are presented and critically compared.

Physically and chemically synthesized TiO2 composite thin films for hydrogen production by photocatalytic water splitting

Author Rupali Dholam

Short Abstract
TiO2 has been most preferred material as a photocatalyst for water splitting to produce hydrogen by solar light irradiation. In the present work TiO2 films have been synthesized by radio frequency magnetron sputtering and sol-gel method. Photoelectrochemical cell with chemical bias, involving photoanode in form of TiO2 film deposited on conducting indium tin oxide (ITO) film and Pt as cathode, is developed. The effect of conducting ITO layer on photo-voltage is studied by varying the thickness of ITO films. Under visible light irradiation constant H2 generation rate is obtained for long period of time by both the TiO2 films because of the separated evolution of H2 and O2 gas, thus eliminating the back-reaction effect. Sputter-deposited film as compared to sol–gel synthesized film showed better H2 generation rate, mainly explained in terms of the higher visible light absorption achieved by oxygen vacancies created in the TiO2 film by the energetic target ions during deposition in pure Ar gas pressure.