Elisabeth Galopin

Bright solid-state sources of indistinguishable single photons

Bright sources of indistinguishable single photons are strongly needed for the scalability of quantum information processing. Semiconductor quantum dots are promising systems to build such sources. Several works demonstrated emission of indistinguishable photons while others proposed various approaches to efficiently collect them. Here we combine both properties and report on the fabrication of ultrabright sources of indistinguishable single photons, thanks to deterministic positioning of single quantum dots in well-designed pillar cavities. Brightness as high as 0.79±0.08 collected photon per pulse is demonstrated. The indistinguishability of the photons is investigated as a function of the source brightness and the excitation conditions. We show that a two-laser excitation scheme allows reducing the fluctuations of the quantum dot electrostatic environment under high pumping conditions. With this method, we obtain 82±10% indistinguishability for a brightness as large as 0.65±0.06 collected photon per pulse.

Direct Observation of Dirac Cones and a Flatband in a Honeycomb Lattice for Polaritons

Two-dimensional lattices of coupled micropillars etched in a planar semiconductor microcavity offer a workbench to engineer the band structure of polaritons. We report experimental studies of honeycomb lattices where the polariton low-energy dispersion is analogous to that of electrons in graphene. Using energy-resolved photoluminescence, we directly observe Dirac cones, around which the dynamics of polaritons is described by the Dirac equation for massless particles. At higher energies, we observe p orbital bands, one of them with the nondispersive character of a flatband. The realization of this structure which holds massless, massive, and infinitely massive particles opens the route towards studies of the interplay of dispersion, interactions, and frustration in a novel and controlled environment.

Macroscopic quantum self-trapping and Josephson oscillations of exciton polaritons

The Josephson effects that arise when two quantum states are coupled through a barrier are difficult to observe in optical systems because photon–photon interactions are so weak. Researchers have now demonstrated an optical realization of two such phenomena—macroscopic self-trapping and Josephson oscillations—using polariton condensates in overlapping microcavities.

Culture of mammalian cells on patterned superhydrophilic/superhydrophobic silicon nanowire arrays

Interfacing nanowires and living cells is highly interesting in various fields including biomedical implants, biosensors or drug delivery. Vertically aligned silicon nanowire (SiNW) arrays prepared by the stain etching technique were investigated in this study. Chemical modification with octadecyltrichlorosilane (OTS) led to the formation of superhydrophobic SiNW surface with a contact angle around 160°. A micropatterned superhydrophilic/superhydrophobic SiNW surface was fabricated using standard optical lithography techniques. Here we report on Chinese Hamster Ovary K1 (CHO) cell culture on patterned superhydrophilic/superhydrophobic silicon nanowire surfaces. It was found that the cells adhered selectively to the superhydrophilic regions while cell adhesion was almost completely suppressed on the superhydrophobic surface. Transmission electron microscopy analysis showed that the cell cytoplasmic projections penetrate the hydrophilic silicon nanowires layer and coat the nanowires, leading to an intimate surface contact and thus a strong adhesion. On the superhydrophobic surface, the cell cytoplasmic projections remained on the top of wires. The nonfouling of the superhydrophobic SiNW substrate was attributed to a stable Cassie–Baxter state, limiting the contact with the culture medium. Another interesting finding from this study is the corrosion of the superhydrophilic SiNW surface in phosphate-buffered saline (PBS) solution.

Polariton condensation in solitonic gap states in a one-dimensional periodic potential

Manipulation of nonlinear waves in artificial periodic structures leads to spectacular spatial features, such as generation of gap solitons or onset of the Mott insulator phase transition. Cavity exciton–polaritons are strongly interacting quasiparticles offering large possibilities for potential optical technologies. Here we report their condensation in a one-dimensional microcavity with a periodic modulation. The resulting mini-band structure dramatically influences the condensation process. Contrary to non-modulated cavities, where condensates expand, here, we observe spontaneous condensation in localized gap soliton states. Depending on excitation conditions, we access different dynamical regimes: we demonstrate the formation of gap solitons either moving along the ridge or bound to the potential created by the reservoir of uncondensed excitons. We also find Josephson oscillations of gap solitons triggered between the two sides of the reservoir. This system is foreseen as a building block for polaritonic circuits, where propagation and localization are optically controlled and reconfigurable.

Bosonic Condensation and Disorder-Induced Localization in a Flat Band.

We report on the engineering of a nondispersive (flat) energy band in a geometrically frustrated lattice of micropillar optical cavities. By taking advantage of the non-Hermitian nature of our system, we achieve bosonic condensation of exciton polaritons into the flat band. Because of the infinite effective mass in such a band, the condensate is highly sensitive to disorder and fragments into localized modes reflecting the elementary eigenstates produced by geometric frustration. This realization offers a novel approach to studying coherent phases of light and matter under the controlled interplay of frustration, interactions, and dissipation.

Realization of a Double-Barrier Resonant Tunneling Diode for Cavity Polaritons

We report on the realization of a double-barrier resonant tunneling diode for cavity polaritons, by lateral patterning of a one-dimensional cavity. Sharp transmission resonances are demonstrated when sending a polariton flow onto the device. We show that a nonresonant beam can be used as an optical gate and can control the device transmission. Finally, we evidence distortion of the transmission profile when going to the high-density regime, signature of polariton-polariton interactions.

Lasing in topological edge states of a one-dimensional lattice

Topology describes properties that remain unaffected by smooth distortions. Its main hallmark is the emergence of edge states localized at the boundary between regions characterized by distinct topological invariants. Because their properties are inherited from the topology of the bulk, these edge states present a strong immunity to distortions of the underlying architecture. This feature offers new opportunities for robust trapping of light in nano- and micrometre-scale systems subject to fabrication imperfections and environmentally induced deformations. Here, we report lasing in such topological edge states of a one-dimensional lattice of polariton micropillars that implements an orbital version of the Su–Schrieffer–Heeger Hamiltonian. We further demonstrate that lasing in these states persists under local deformations of the lattice. These results open the way to the implementation of chiral lasers in systems with broken time-reversal symmetry and, when combined with polariton interactions, to the study of nonlinear phenomena in topological photonics.Topologically protected lasing is reported in a lattice of polariton micropillars.

Localized surface plasmon-enhanced fluorescence spectroscopy for highly-sensitive real-time detection of DNA hybridization

Versatile and highly-sensitive detection of DNA hybridization is described using metal nanostructures-enhanced fluorescence (MEF) emission intensity when fluorescently-labeled DNA oligomers are covalently immobilized on a nanometer-thin amorphous silicon-carbon layer capping the metal nanostructures. The MEF structures are formed by thermal deposition of silver, gold or silver/gold thin films on glass surfaces and post-annealing at 500 degrees C. The choice of the metal film allows for tuning the optical properties of the interface. The metallic nanostructures are subsequently coated with an amorphous thin silicon-carbon alloy (a-Si(0.80)C(0.20): H) layer deposited by PECVD. Carboxydecyl groups are attached on these surfaces through hydrosilylation then reacted with amine-terminated single-stranded DNA oligomers, forming a covalent link. The immobilized DNA is hybridized with its complementary strand carrying a fluorescent label. Through optimization of the thickness of the a-Si(0.80)C(0.20): H alloy overlayer and by working close to resonance conditions for plasmon and fluorophore excitation, the hybridization of very dilute oligomers (5 fM) is easily detected, and the hybridization kinetics can be monitored in situ and in real-time.

All-optical phase modulation in a cavity-polariton Mach–Zehnder interferometer

We report on a new mechanism of giant phase modulation. The phenomenon arises when a dispersed photonic mode (slow light) strongly couples to an excitonic resonance. In such a case, even a small amount of optically injected carriers creates a potential barrier for the propagating exciton-polariton which provokes a considerable phase shift. We evidence this effect by fabricating an exciton-polariton Mach-Zehnder interferometer, modulating the output intensity by constructive or destructive interferences controlled by optical pumping of a micrometric size area. The figure of merit for a {\pi} phase shift, defined by the control power times length of the modulated region, is found at least one order of magnitude smaller than slow light photonic crystal waveguides.Quantum fluids based on light is a highly developing research field, since they provide a nonlinear platform for developing optical functionalities and quantum simulators. An important issue in this context is the ability to coherently control the properties of the fluid. Here we propose an all-optical approach for controlling the phase of a flow of cavity-polaritons, making use of their strong interactions with localized excitons. Here we illustrate the potential of this method by implementing a compact exciton–polariton interferometer, which output intensity and polarization can be optically controlled. This interferometer is cascadable with already reported polariton devices and is promising for future polaritonic quantum optic experiments. Complex phase patterns could be also engineered using this optical method, providing a key tool to build photonic artificial gauge fields.