Periodic Reporting for period 4 - ANDLICA (Anderson Localization of Light by Cold Atoms)
Reporting period: 2024-04-01 to 2024-09-30
The goal of this ERC-ADG project is to understand a long standing question about Anderson localization of light in three dimensions. This topic appear at first sight to be an easy problem, as it can be formulated as a classical optic problem. When considering the scattering medium however, it is a genuine (classical) many body problem with no analytical solution. Initial universal predictions were believed for decades to be valid for all types of systems. However more recently, the community came to understand that details of how photons propagate are crucial and completely change the features. As no experiment so far has observed Anderson localization of light in three dimensions, it is important to clarify under which conditions such an effect can exist.
This line of research is part of the ongoing effort to understand details of coherent photonic transport, in particular in presence of disorder or defects.
The main objective of this project is to observe Anderson localization of light in cold atomic samples, which appear to be a promising platform allowing for detailed control of many relevant parameters and an ab initio modeling.
This line of research is part of the ongoing effort to understand details of coherent photonic transport, in particular in presence of disorder or defects.
The main objective of this project is to observe Anderson localization of light in cold atomic samples, which appear to be a promising platform allowing for detailed control of many relevant parameters and an ab initio modeling.
A new experiment on laser cooled and trapped Ytterbium atoms has been constructed. A novel in situ preparation and detection scheme has been implemented, allowing to avoid boundary effects, known to be a limitation for the detection of Anderson localization.
Two different approaches towards Anderson localization of light in three dimensions are under implementation in the experiment.
The first one is based on so-called diagonal disorder, closely related to the initial paper by P. Anderson on random site energies. The theoretical prediction has been studied in detailed extending the well-known coupled dipole model to incorporate diagonal disorder. The experimental implementation of controlled diagonal disorder for cold atoms is based on the use of an ancillary excited atom state allowing for spatial dependent resonant frequencies of the atoms. This light shift laser has been already used in the in situ preparation scheme of optical excitation.
The second approach is based on fluctuations in atomic positions and require high spatial densities and the additional application of a large magnetic bias field to reduce the detrimental effect of near field dipole-dipole coupling in such dense regimes. Initial experiments so far have not yet reached the required density, partially due to light assisted collisions. Experimental efforts to reach the required density will include transverse collimation of the atomic beam and time dependent compression schemes. The hard to implement large magnetic bias field will be replaced by yet another use of the light shift laser, having already allowed to realize all optical induced Faraday rotation with large Zeeman dependant energy shift implemented in microsecond timescales.
Two different approaches towards Anderson localization of light in three dimensions are under implementation in the experiment.
The first one is based on so-called diagonal disorder, closely related to the initial paper by P. Anderson on random site energies. The theoretical prediction has been studied in detailed extending the well-known coupled dipole model to incorporate diagonal disorder. The experimental implementation of controlled diagonal disorder for cold atoms is based on the use of an ancillary excited atom state allowing for spatial dependent resonant frequencies of the atoms. This light shift laser has been already used in the in situ preparation scheme of optical excitation.
The second approach is based on fluctuations in atomic positions and require high spatial densities and the additional application of a large magnetic bias field to reduce the detrimental effect of near field dipole-dipole coupling in such dense regimes. Initial experiments so far have not yet reached the required density, partially due to light assisted collisions. Experimental efforts to reach the required density will include transverse collimation of the atomic beam and time dependent compression schemes. The hard to implement large magnetic bias field will be replaced by yet another use of the light shift laser, having already allowed to realize all optical induced Faraday rotation with large Zeeman dependant energy shift implemented in microsecond timescales.
Optical pumping of atoms into long lived states via higher excited levels is a novel and promising effect, which has not been anticipated at the beginning of this project.
The results obtained during the project have proved the potential of the light shift laser for a large variety of applications: (i) in situ preparation of an optical excitation, (ii) all optical Faraday rotation creating an effective magnetic field, (iii) implementation of controlled spatial frequency control of atoms, for lattice or random potential.
Beyond this experimental progress, theoretical studies during the project include the systematic study of Anderson localization with diagonal disorder and investigations beyond the single excitation sector, with entanglement studies and intensity correlations in random atomic media..
The results obtained during the project have proved the potential of the light shift laser for a large variety of applications: (i) in situ preparation of an optical excitation, (ii) all optical Faraday rotation creating an effective magnetic field, (iii) implementation of controlled spatial frequency control of atoms, for lattice or random potential.
Beyond this experimental progress, theoretical studies during the project include the systematic study of Anderson localization with diagonal disorder and investigations beyond the single excitation sector, with entanglement studies and intensity correlations in random atomic media..