Find here the scientific production related to PoLLoC.
Minor embedding with Stuart-Landau oscillator networks
We theoretically implement a strategy from quantum computation architectures to simulate Stuart-Landau oscillator dynamics in all-to-all connected networks, also referred to as complete graphs. The technique builds upon the triad structure minor embedding which expands dense graphs of interconnected elements into sparse ones which can potentially be realized in future on-chip solid-state technologies with tunable edge weights. As a case study, we reveal that the minor embedding procedure allows simulating the XY model on complete graphs, thus bypassing a severe geometric constraint.
Universal scaling laws for charge-carrier interactions with quantum confinement in lead-halide perovskites
Lead halide perovskites open great prospects for optoelectronics and a wealth of potential applications in quantum optical and spin-based technologies. Precise knowledge of the fundamental optical and spin properties of charge-carrier complexes at the origin of their luminescence is crucial in view of the development of these applications. On nearly bulk Cesium-Lead-Bromide single perovskite nanocrystals, which are the test bench materials for next-generation devices as well as theoretical modeling, we perform low temperature magneto-optical spectroscopy to reveal their entire band-edge exciton fine structure and charge-complex binding energies. We demonstrate that the ground exciton state is dark and lays several millielectronvolts below the lowest bright exciton sublevels, which settles the debate on the bright-dark exciton level ordering in these materials. More importantly, combining these results with spectroscopic measurements on various perovskite nanocrystal compounds, we show evidence for universal scaling laws relating the exciton fine structure splitting, the trion and biexciton binding energies to the band-edge exciton energy in lead-halide perovskite nanostructures, regardless of their chemical composition. These scaling laws solely based on quantum confinement effects and dimensionless energies offer a general predictive picture for the interaction energies within charge-carrier complexes photo-generated in these emerging semiconductor nanostructures.
Many-body Correlations and Exciton Complexes in CsPbBr3 Quantum Dots
All-inorganic lead-halide perovskite (CsPbX3, X = Cl, Br, I) quantum dots (QDs) have emerged as a competitive platform for classical light-emitting devices (in the weak light-matter interaction regime, e.g., LEDs and laser), as well as for devices exploiting strong light-matter interaction at room temperature. Many-body interactions and quantum correlations among photogenerated exciton complexes play an essential role, e.g., by determining the laser threshold, the overall brightness of LEDs, and the single-photon purity in quantum light sources. Here, by combining cryogenic single-QD photoluminescence spectroscopy with configuration-interaction (CI) calculations, we address the size-dependent trion and biexciton binding energies. Trion binding energies increase from 7 meV to 17 meV for QD sizes decreasing from 30 nm to 9 nm, while the biexciton binding energies increase from 15 meV to 30 meV, respectively. CI calculations quantitatively corroborate the experimental results and suggest that the effective dielectric constant for biexcitons slightly deviates from the one of the single excitons, potentially as a result of coupling to the lattice in the multiexciton regime. Our findings provide a deep insight into the multiexciton properties in all-inorganic lead-halide perovskite QDs, essential for classical and quantum optoelectronic devices.
Electrically tunable Berry curvature and strong light-matter coupling in liquid crystal microcavities with 2D perovskite
The field of spinoptronics is underpinned by good control over photonic spin-orbit coupling in devices that have strong optical nonlinearities. Such devices might hold the key to a new era of optoelectronics where momentum and polarization degrees of freedom of light are interwoven and interfaced with electronics. However, manipulating photons through electrical means is a daunting task given their charge neutrality. In this work, we present electrically tunable microcavity exciton-polariton resonances in a Rashba-Dresselhaus spin-orbit coupling field. We show that different spin-orbit coupling fields and the reduced cavity symmetry lead to tunable formation of the Berry curvature, the hallmark of quantum geometrical effects. For this, we have implemented an architecture of a photonic structure with a two-dimensional perovskite layer incorporated into a microcavity filled with nematic liquid crystal. Our work interfaces spinoptronic devices with electronics by combining electrical control over both the strong light-matter coupling conditions and artificial gauge fields.
Annihilation of exceptional points from different Dirac valleys in a 2D photonic system
Topological physics relies on Hamiltonian’s eigenstate singularities carrying topological charges, such as Dirac points, and – in non-Hermitian systems – exceptional points (EPs), lines or surfaces. So far, the reported non-Hermitian topological transitions were related to the creation of a pair of EPs connected by a Fermi arc out of a single Dirac point by increasing non-Hermiticity. Such EPs can annihilate by reducing non-Hermiticity. Here, we demonstrate experimentally that an increase of non-Hermiticity can lead to the annihilation of EPs issued from different Dirac points (valleys). The studied platform is a liquid crystal microcavity with voltage-controlled birefringence and TE-TM photonic spin-orbit-coupling. Non-Hermiticity is provided by polarization-dependent losses. By increasing the non-Hermiticity degree, we control the position of the EPs. After the intervalley annihilation, the system becomes free of any band singularity. Our results open the field of non-Hermitian valley-physics and illustrate connections between Hermitian topology and non-Hermitian phase transitions.
Atomic-Level Description of Thermal Fluctuations in Inorganic Lead Halide Perovskites
A comprehensive microscopic description of thermally induced distortions in lead halide perovskites is crucial for their realistic applications, yet still unclear. Here, we quantify the effects of thermal activation in CsPbBr3 nanocrystals across length scales with atomic-level precision, and we provide a framework for the description of phase transitions therein, beyond the simplistic picture of unit-cell symmetry increase upon heating. The temperature increase significantly enhances the short-range structural distortions of the lead halide framework as a consequence of the phonon anharmonicity, which causes the excess free energy surface to change as a function of temperature. As a result, phase transitions can be rationalized via the soft-mode model, which also describes displacive thermal phase transitions in oxide perovskites. Our findings allow to reconcile temperature-dependent modifications of physical properties, such as changes in the optical band gap, that are incompatible with the perovskite time- and space-average structures.
Controlling the nucleation and growth kinetics of lead halide perovskite quantum dots
Colloidal lead halide perovskite (LHP) nanocrystals are of interest as photoluminescent quantum dots (QDs) whose properties depend on the size and shape. They are normally synthesized on subsecond time scales through hard-to-control ionic metathesis reactions. We report a room-temperature synthesis of monodisperse, isolable spheroidal APbBr3 QDs (A=Cs, formamidinium, methylammonium) that are size-tunable from 3 to over 13 nanometers. The kinetics of both nucleation and growth are temporally separated and drastically slowed down by the intricate equilibrium between the precursor (PbBr2) and the A[PbBr3] solute, with the latter serving as a monomer. QDs of all these compositions exhibit up to four excitonic transitions in their linear absorption spectra, and we demonstrate that the size-dependent confinement energy for all transitions is independent of the A-site cation.
Optically controlled polariton condensate molecules
A condensed-matter platform for analog simulation of complex two-dimensional molecular bonding configurations, based on optically trapped exciton-polariton condensates is proposed. The stable occupation of polariton condensates in the excited states of their optically configurable potential traps permits emulation of excited atomic orbitals. A classical mean-field model describing the dissipative coupling mechanism between p-orbital condensates is derived, identifying lowest-threshold condensation solutions as a function of trap parameters corresponding to bound and antibound π and σ bonding configurations, similar to those in quantum chemistry.
Spontaneous Formation of Time-Periodic Vortex Cluster in Nonlinear Fluids of Light
We demonstrate spontaneous formation of a nonlinear vortex cluster state in a microcavity exciton-polariton condensate with time-periodic sign flipping of its topological charges at the GHz scale. When optically pumped with a ring-shaped nonresonant laser, the trapped condensate experiences intricate high-order mode competition and fractures into two distinct trap levels. The resulting mode interference leads to robust condensate density beatings with periodic appearance of orderly arranged phase singularities. Our work opens new perspectives on creating structured free-evolving light, and singular optics in the strong light-matter coupling regime.
Screening nearest-neighbor interactions in networks of exciton-polariton condensates through spin-orbit coupling
We study the modification of the spatial coupling parameter between interacting ballistic exciton-polariton condensates in the presence of photonic spin-orbit coupling appearing from transverse electric–transverse magnetic (TE-TM) splitting in planar semiconductor microcavities. We propose a strategy to make the coupling strength between next-nearest neighbors stronger than between nearest neighbors, which inverts the conventional idea of the spatial coupling hierarchy between sites. Our strategy relies on the dominantly populated high-momentum components in the ballistic condensates which, in the presence of TE-TM splitting, lead to rapid radial precession of the polariton pseudospin. As a consequence, condensate pairs experience distance-periodic screening of their interaction strength, severely modifying their synchronization and condensation threshold solutions.