Godefroy Leménager

Polariton Superfluids Reveal Quantum Hydrodynamic Solitons

A condensed-matter system is used to study superfluid dynamics. A quantum fluid passing an obstacle behaves differently from a classical one. When the flow is slow enough, the quantum gas enters a superfluid regime, and neither whirlpools nor waves form around the obstacle. For higher flow velocities, it has been predicted that the perturbation induced by the defect gives rise to the turbulent emission of quantized vortices and to the nucleation of solitons. Using an interacting Bose gas of exciton-polaritons in a semiconductor microcavity, we report the transition from superfluidity to the hydrodynamic formation of oblique dark solitons and vortex streets in the wake of a potential barrier. The direct observation of these topological excitations provides key information on the mechanisms of superflow and shows the potential of polariton condensates for quantum turbulence studies.

Room temperature-dipolelike single photon source with a colloidal dot-in-rod

We propose colloidal CdSe/CdS dots in rods as nonclassical sources for quantum information technology. Such nanoemitters show specific properties such as strongly polarized emission of on-demand single photons at room temperature, dipolelike behavior and mono-exponential recombination rates, making us envision their suitability as sources of single photons with well defined quantum states in quantum cryptography based devices.

Non-blinking single-photon generation with anisotropic colloidal nanocrystals: towards room-temperature, efficient, colloidal quantum sources.

Blinking and single-photon emission can be tailored in CdSe/CdS core/shell colloidal dot-in-rods. By increasing the shell thickness it is possible to obtain almost non-blinking nanocrystals, while the shell length can be used to control single-photon emission probability.

Exciton Fine Structure of CdSe/CdS Nanocrystals Determined by Polarization Microscopy at Room Temperature

We present a method that allows determining the band-edge exciton fine structure of CdSe/CdS dot-in-rods samples based on single particle polarization measurements at room temperature. We model the measured emission polarization of such single particles considering the fine structure properties, the dielectric effect induced by the anisotropic shell, and the measurement configuration. We use this method to characterize the band-edge exciton fine structure splitting of various samples of dot-in-rods. We show that, when the diameter of the CdSe core increases, a transition from a spherical like band-edge exciton symmetry to a rod-like band edge exciton symmetry occurs. This explains the often reported large emission polarization of such particles compared to spherical CdSe/CdS emitters.

Three-dimensional cage-like microscaffolds for cell invasion studies

Cancer cell motility is one of the major events involved in metastatic process. Tumor cells that disseminate from a primary tumor can migrate into the vascular system and, being carried by the bloodstream, transmigrate across the endothelium, giving rise to a new tumor site. However, during the invasive process, tumor cells must pass through the extracellular matrix, whose structural and mechanical properties define the parameters of the migration process. Here, we propose 3D-complex cage-like microstructures, realized by two-photon (TP) direct laser writing (DLW), to analyze cell migration through pores significantly smaller than the cell nucleus. We found that the ability to traverse differently sized pores depends on the metastatic potential and on the invasiveness of the cell lines, allowing to establish a pore-area threshold value able to discriminate between non-tumorigenic and tumorigenic human breast cells.

Single colloidal quantum dots as sources of single photons for quantum cryptography

Colloidal nanocrystals, i.e. quantum dots synthesized trough wet-chemistry approaches, are promising nanoparticles for photonic applications and, remarkably, their quantum nature makes them very promising for single photon emission at room temperature. In this work we describe two approaches to engineer the emission properties of these nanoemitters in terms of radiative lifetime and photon polarization, drawing a viable strategy for their exploitation as room-temperature single photon sources for quantum information and quantum telecommunications.

Nanofabricated 3D cage-like structures for cancer cell discrimination

Some cellular mechanisms such as migration and invasion, are determined and regulated by cell mechanical properties, especially during embryonic development or tumorigenesis. In these cases, cells attitude to undergo deformation and to displace their whole body is a crucial point for survival and metastasis formation. Extracellular environment three-dimensionality is a key feature influencing cell mechanics, and micro- and nano-fabricated structures represent a promising tool to study cell behavior. Here we engineer 3D- cage-like microstructures realized by two-photon polymerization to analyze cell migration through pores significantly smaller than the cell nucleus. We found that cells spontaneously interact with the cages by applying force at the cell-cage contact points while rearranging their cytoskeleton. The ability to traverse pores of different area depends on the invasiveness of the cell lines, allowing to discriminate between cells with different invasive potential.

Room-temperature non-blinking single photon nanoemitters

In this work we propose rod-shaped core/shell CdSe/CdS colloidal nanocrystals as efficient non-classical light sources. These nanoemitters show peculiar features such as pronounced photoluminescence stability and high single-photon emission efficiency at room-temperature, making us envision their possible employment as single-photon sources for quantum communications protocols.

Effect of shell size on single photon emission performances of core/shell dot-in-rods colloidal nanocrystals

CdSe/CdS dot-in-rod (DR) nanocrystals, i.e. semiconductor nanoparticles consisting of a CdSe spherical core surrounded by a rod-shaped CdS shell, recently emerged as efficient sources of non-classical light for quantum cryptography applications. This paper discusses the influence of shell size on DRs quantum emission properties, showing that shell elongation has detrimental effects on DRs single photon emission effectiveness.

Colloidal quantum light sources based on asymmetric semiconductor nanocrystals

We report on the development of efficient and low cost single photon sources for quantum communications. The work discusses the suitability of colloidal nanocrystals as sources of quantum light as well as it draws out possible solutions to overtake the drawbacks of these emitters, such as blinking and polarization.