Carole Diederichs

Parametric oscillation in vertical triple microcavities

Optical parametric oscillation is a nonlinear process that enables coherent generation of ‘signal’ and ‘idler’ waves, shifted in frequency from the pump wave. Efficient parametric conversion is the paradigm for the generation of twin or entangled photons for quantum optics applications such as quantum cryptography, or for the generation of new frequencies in spectral domains not accessible by existing devices. Rapid development in the field of quantum information requires monolithic, alignment-free sources that enable efficient coupling into optical fibres and possibly electrical injection. During the past decade, much effort has been devoted to the development of integrated devices for quantum information and to the realization of all-semiconductor parametric oscillators. Nevertheless, at present optical parametric oscillators typically rely on nonlinear crystals placed into complex external cavities, and pumped by powerful external lasers. Long interaction lengths are typically required and the phase mismatch between the parametric waves propagating at different velocities results in poor parametric conversion efficiencies. Here we report the demonstration of parametric oscillation in a monolithic semiconductor triple microcavity with signal, pump and idler waves propagating along the vertical direction of the nanostructure. Alternatively, signal and idler beams can also be collected at finite angles, allowing the generation of entangled photon pairs. The pump threshold intensity is low enough to envisage the realization of an all-semiconductor electrically pumped micro-parametric oscillator.

Ultra-coherent single photon source

We present an original type of single photon source in solid state, based on the coherent laser light scattering by a single InAs quantum dot. We demonstrate that the coherence of the emitted single photons is tailored by the resonant excitation with a spectral linewidth below the radiative limit. Our ultra-coherent source opens the way for integrated quantum devices dedicated to the generation of single photons with high degrees of indistinguishability.

Room-Temperature Polariton Lasing in All-Inorganic Perovskite Nanoplatelets

Polariton lasing is the coherent emission arising from a macroscopic polariton condensate first proposed in 1996. Over the past two decades, polariton lasing has been demonstrated in a few inorganic and organic semiconductors in both low and room temperatures. Polariton lasing in inorganic materials significantly relies on sophisticated epitaxial growth of crystalline gain medium layers sandwiched by two distributed Bragg reflectors in which combating the built-in strain and mismatched thermal properties is nontrivial. On the other hand, organic active media usually suffer from large threshold density and weak nonlinearity due to the Frenkel exciton nature. Further development of polariton lasing toward technologically significant applications demand more accessible materials, ease of device fabrication, and broadly tunable emission at room temperature. Herein, we report the experimental realization of room-temperature polariton lasing based on an epitaxy-free all-inorganic cesium lead chloride perovskite nanoplatelet microcavity. Polariton lasing is unambiguously evidenced by a superlinear power dependence, macroscopic ground-state occupation, blueshift of the ground-state emission, narrowing of the line width and the buildup of long-range spatial coherence. Our work suggests considerable promise of lead halide perovskites toward large-area, low-cost, high-performance room-temperature polariton devices and coherent light sources extending from the ultraviolet to near-infrared range.

Correlated fluorescence blinking in two-dimensional semiconductor heterostructures

‘Blinking’, or ‘fluorescence intermittency’, refers to a random switching between ‘ON’ (bright) and ‘OFF’ (dark) states of an emitter; it has been studied widely in zero-dimensional quantum dots and molecules, and scarcely in one-dimensional systems. A generally accepted mechanism for blinking in quantum dots involves random switching between neutral and charged states (or is accompanied by fluctuations in charge-carrier traps), which substantially alters the dynamics of radiative and non-radiative decay. Here, we uncover a new type of blinking effect in vertically stacked, two-dimensional semiconductor heterostructures, which consist of two distinct monolayers of transition metal dichalcogenides (TMDs) that are weakly coupled by van der Waals forces. Unlike zero-dimensional or one-dimensional systems, two-dimensional TMD heterostructures show a correlated blinking effect, comprising randomly switching bright, neutral and dark states. Fluorescence cross-correlation spectroscopy analyses show that a bright state occurring in one monolayer will simultaneously lead to a dark state in the other monolayer, owing to an intermittent interlayer carrier-transfer process. Our findings suggest that bilayer van der Waals heterostructures provide unique platforms for the study of charge-transfer dynamics and non-equilibrium-state physics, and could see application as correlated light emitters in quantum technology.

Local Field Effects in the Energy Transfer between a Chromophore and a Carbon Nanotube: A Single-Nanocompound Investigation

Energy transfer in noncovalently bound porphyrin/carbon nanotube compounds is investigated at the single-nanocompound scale. Excitation spectroscopy of the luminescence of the nanotube shows two resonances arising from intrinsic excitation of the nanotube and from energy transfer from the porphyrin. Polarization diagrams show that both resonances are highly anisotropic, with a preferred direction along the tube axis. The energy transfer is thus strongly anisotropic despite the almost isotropic absorption of porphyrins. We account for this result by local field effects induced by the large optical polarizability of nanotubes. We show that the local field correction extends over several nanometers outside the nanotubes and drives the overall optical response of functionalized nanotubes.

Design for a triply resonant vertical-emitting micro-optical parametric oscillator

An approach is proposed for the realization of a vertical-cavity surface-emitting semiconductor micro-optical parametric oscillator that relies on the use of third-order excitonic nonlinearity in isotropic semiconductors. We demonstrate that a planar triple microcavity structure can be designed to provide triple resonance for the parametric frequencies together with built-in cavity phase-matching for all waves at normal incidence. An example is given of a monolithic structure consisting of three strongly coupled AlGaAs∕GaAs lambda microcavities including single InGaAs quantum wells. Applications to the generation of twin photons or entangled photon pairs are discussed.

Universal non-resonant absorption in carbon nanotubes

Photoluminescence excitation measurements in semi-conducting carbon nanotubes show a systematic non-resonant contribution between the well known excitonic resonances. Using a global analysis method, we were able to delineate the contribution of each chiral species including its tiny non-resonant component. By comparison with the recently reported excitonic absorption cross-section on the S22 resonance, we found a universal non-resonant absorbance which turns out to be of the order of one half of that of an equivalent graphene sheet. This value as well as the absorption line-shape in the non-resonant window is in excellent agreement with microscopic calculations based on the density matrix formalism. This non-resonant absorption of semi-conducting nanotubes is essentially frequency independent over 0.5 eV wide windows and reaches approximately the same value betweeen the S11 and S22 resonances or between the S22 and S33 resonances. In addition, the non-resonant absorption cross-section turns out to be the same for all the chiral species we measured in this study. From a practical point of view, this study puts firm basis on the sample content analysis based on photoluminescence studies by targeting specific excitation wavelengths that lead to almost uniform excitation of all the chiral species of a sample within a given diameter range. In contrast to graphene, single-wall carbon nanotubes (SWNTs) show marked resonances in their optical spectrum that primarily reflect the one-dimensional quantum confinement of carriers. These resonances that combine one-dimensional and excitonic characteristics have been extensively investigated and are widely used as finger prints of the (n, m) species [1]. However, spectroscopic studies reveal that the absorption of nanotubes does not vanish between resonances and consists of a wealth of tiny structures, such as phonon side-bands, crossed exci-tons (S ij), or higher excitonic states [2–5]. In ensemble measurements, the non-resonant absorption is even more congested due to the contribution of residual catalyst or amorphous carbon and due to light scattering [6]. In total , a relatively smooth background showing an overall increase with photon energy is observed, from which it is challenging to extract any quantitative information. In this study, we show that thorough photolumines-cence excitation (PLE) measurements yield a much finer insight into the non-resonant absorption of carbon nan-otubes, that reveals the universal features of light-matter interaction in carbon nano-structures [7]. In particular, we show that the non-resonant absorption of SWNTs per unit area well above the S 11 or S 22 resonances reaches an universal value of 0.013±0.003 in good agreement with the value α √ 3 (where α is the fine structure constant) predicted by a simple band-to-band theory. Our study of non-resonant absorption is based on the global analysis of PLE maps of ensembles of carbon nan-otubes that allows us to deconvolute the contribution of each (n, m) species while keeping a high signal to noise

Room temperature long-range coherent exciton polariton condensate flow in lead halide perovskites

Long-range coherent polariton condensate flow is observed in all-inorganic perovskite microcavities. Novel technological applications significantly favor alternatives to electrons toward constructing low power–consuming, high-speed all-optical integrated optoelectronic devices. Polariton condensates, exhibiting high-speed coherent propagation and spin-based behavior, attract considerable interest for implementing the basic elements of integrated optoelectronic devices: switching, transport, and logic. However, the implementation of this coherent polariton condensate flow is typically limited to cryogenic temperatures, constrained by small exciton binding energy in most semiconductor microcavities. Here, we demonstrate the capability of long-range nonresonantly excited polariton condensate flow at room temperature in a one-dimensional all-inorganic cesium lead bromide (CsPbBr3) perovskite microwire microcavity. The polariton condensate exhibits high-speed propagation over macroscopic distances of 60 μm while still preserving the long-range off-diagonal order. Our findings pave the way for using coherent polariton condensate flow for all-optical integrated logic circuits and polaritonic devices operating at room temperature.

Room Temperature Coherently Coupled Exciton–Polaritons in Two-Dimensional Organic–Inorganic Perovskite

Two-dimensional (2D) organic-inorganic perovskite semiconductors with natural multiquantum well structures and confined 2D excitons are intriguing for the study of strong exciton-photon coupling, due to their large exciton binding energy and oscillation strength. This strong coupling leads to a formation of the half-light half-matter bosonic quasiparticle called exciton-polariton, consisting of a linear superposition state between photonic and excitonic states. Here, we demonstrate room temperature strong coupling in exfoliated wavelength-tunable 2D organic-inorganic perovskite semiconductors embedded into a planar microcavity, exhibiting large energetic splitting-to-line width ratios (>34.2). Angular-dependent spectroscopy measurements reveal that hybridized polariton states act as an ultrafast and reversible energy oscillation, involving 2D perovskite exciton, cavity modes (CM), and Bragg modes of the distributed Bragg reflector. Meanwhile, sizable hybrid particles dominantly couple to the measured optical field through the CMs. Our findings advocate a considerable promise of 2D organic-inorganic perovskite to explore fundamental quantum phenomena such as Bose-Einstein condensation, superfluidity, and exciton-polariton networks.

Generation of quantum correlated photon pairs from a vertical triple microcavity

We study the statistics of twin photons emitted by a vertical triple microcavity. We measured the intensity correlations of the signal and idler by measuring the noise spectra. Quantum correlated photon modes are observed.