Optical stark effect and coherent gain of excitons in a semiconductor microcavity

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High-efficiency single-photon detection in the microwave domain is a key enabling technology for various quantum applications. However, the extremely low energy of microwave photons presents a fundamental challenge, preventing direct photon-to-charge conversion as achieved in optical systems using semiconductors. Here, we demonstrate continuous microwave photon detection with an efficiency approaching 70% in the single-photon regime. We use a hybrid system comprising a gate-defined double quantum dot (DQD)

Semiclassical trajectory-based methods are computational techniques that approximate solutions to the time-dependent Schrödinger equation by using information from classical trajectories equipped with evolving phases or width matrices. These additional structures to the classical trajectory enable semiclassical methods to go beyond purely classical descriptions and to capture quantum effects, at least approximately. While single-trajectory semiclassical methods, such as the thawed Gaussian approximation,

We introduce a variational Monte Carlo framework that combines neural-network quantum states with the Lorentz integral transform technique to compute the dynamical properties of self-bound quantum many-body systems in continuous Hilbert spaces. While broadly applicable to various quantum systems, including atoms and molecules, in this initial application we focus on the photoabsorption cross section of light nuclei, where benchmarks against numerically exact techniques are available. Our accurate theoretica

Quantum process learning is a fundamental primitive that draws inspiration from machine learning with the goal of better studying the dynamics of quantum systems. One approach to quantum process learning is quantum compilation, whereby an analog quantum operation is digitized by compiling it into a series of basic gates. While there has been significant focus on quantum compiling for discrete-variable systems, the continuous-variable (CV) framework has received comparatively less attention. We present an ex

Quantum emitters, such as quantum dots and organic molecules, are vital components in many modern optical devices, including displays and sensing systems. In the visible spectrum, these emitters are highly efficient in light emission, but their performance declines significantly with decreasing optical gap due to the energy-gap law, limiting their use especially for infrared applications. To overcome this, coupling them with plasmonic particles can significantly enhance light emission by leveraging field co

This thesis investigates quantum many-body systems in and out of equilibrium, with a dual focus on open-system theory and advanced computational methods. Taken together, the results articulate a unifying perspective: in both classical/analog simulations and digital algorithms for many-body quantum systems, the relevant physics often concentrates in small, dynamically selected pockets of the Liouville or Hilbert space. By exposing this structure - whether as noise-protected logical manifolds in bosonic modes

Learning faithful representations of quantum states is crucial to fully characterizing the variety of manybody states created on quantum processors.While various tomographic methods, such as classical shadow andmatrix product state (MPS) tomography have shown promise in characterizing a wide class of quantum states, they face unique limitations in detecting topologically ordered two-dimensional states. To address this problem, we implement and study a heuristic tomographic method that combines variational o

Purpose – Since pulsed lasers are mainly used in selective laser sintering (SLS) – contrarily to selective laser melting (SLM) – only the exterior of the powder particles is molten while their core stays solid. The purpose of this paper is to investigate the binding mechanism between two particles of titanium powder. Design/methodology/approach – A dedicated experimental setup is used to isolate the particles. They are then irradiated by the laser. SEM micrographs are taken at each step and image analysis i

Among the different fields of research in nuclear magnetic resonance (NMR) which are currently investigated in the Laboratory of Biomolecular Magnetic Resonance (LRMB), two subjects that are closely related to each other are presented in this article. On the one hand, we show how to populate long-lived states (LLS) that have long lifetimes T_LLS which allow one to go beyond the usual limits imposed by the longitudinal relaxation time T_1. This makes it possible to extend NMR experiments to longer time-scale

We report on the growth by metalorganic vapor phase epitaxy of a InGaN/GaN resonant-cavity light emitting diode (RCLED) emitting at 454 nm and incorporating a 12-pair Al0.82In0.18N/GaN distributed Bragg reflector as bottom mirror. A(1-x)In(x)N layers with an Al content around x similar to 0.17 are lattice matched to GaN, thus avoiding strain-related issues in the subsequent active layers while keeping a high refractive index contrast of 7%, comparable to that achievable in the Al0.5Ga0.5N/GaN system. Device

Over the past decade a new family of optoelectronic devices has emerged whose performance is enhanced by placing the active device structure inside a Fabry–Perot resonantmicrocavity [P. E. Green, IEEE Spectrum 13 (2002)]. The increased optical field allows photodetectors to be made thinner and therefore faster, while simultaneously increasing the quantum efficiency at the resonant wavelengths. We have demonstrated a variety of resonant cavity enhanced (RCE) photodetectors in compound semiconductors [B. Yang

Doping of organic light-emitting devices using highly luminescent molecules is a well-established strategy to improve brightness, efficiency and lifetime or to adjust emission color and color purity. Laser dyes from the pyran-containing donor-acceptor family are particularly interesting for emission in the yellow and red spectral domain. In solution, these polar dyes show marked solvatochromic shifts in the absorption and emission. The fluorescence quantum efficiency also depends strongly on solvent polarit

Recombination dynamics in a variety of InGaN/GaN quantum systems has been studied by time resolved photoluminescence (PL). We have discovered that the time-decay of PL exhibits a scaling law: the nonexponential shape of this decay is preserved for quantum wells and quantum boxes of various sizes while their decay time varies over several orders of magnitude. To explain these results, we propose an original model for electron-hole pair recombination in these systems, combining the effects of internal electri

The dissociation of methane on a nickel catalyst is a key step in steam reforming of natural gas for hydrogen production. Despite substantial effort in both experiment and theory, there is still no atomic-scale description of this important gas-surface reaction. We report quantum state-resolved studies, using pulsed laser and molecular beam techniques, of vibrationally excited methane reacting on the nickel (100) surface. For doubly deuterated methane (CD2H2), we observed that the reaction probability with

We have demonstrated ultrafast coherent control of excitons and exciton-polaritons in semiconductor quantum nanostructures. An InGaAs/AlGaAs multi-quantum-well Bragg structure and an AlGaAs/GaAs crescent-shaped quantum wire structure were used as samples for the control of the exciton-polariton and excitons in the nanostructure. In the multi-quantum-well Bragg sample, a two-stage decay due to the super-radiant exciton-polariton mode is clearly observed under the resonance conditions. Highly sensitive cohere

An investigation of the parametric amplification and its coherent control in a semiconductor micro-cavity is presented. The time and angle resolved pump and probe experiments show that several ps after pumping parametric scattering is still phase coherent. The experimental data are in qualitative agreement with the numerical data obtained from a relatively simple theoretical model based on three polarisation components, pump, probe, and idler. This model also predicts that under particular circumstances, th

The photoluminescence (PL) and PL-excitation (PLE) spectra of InyCa1-yAs/AlxGa1-xAs compressively strained V-groove quantum wires (QWR's) are compared to that of lattice-matched GaAs/AlyGa1-xAs QWR's with the same wire geometry. The PL is preferentially polarized along the QWR axis and the PL anisotropy increases with increasing indium content y. The observed PLE anisotropy also increases with y at the ground subband transition but is nearly independent of excited subband indices, unlike the case of lattice

High-efficiency top-emitting InGaAs/AlGaAs microcavity light-emitting diodes (MCLEDs) have been optimized and fabricated. The structures were grown using molecular beam epitaxy on GaAs substrates. They consist of a three-period Be-doped distributed Bragg reflector (DBR) centred at 950 nm wavelength, a cavity containing three InGaAs quantum wells and a 15-period Si-doped DBR. Different values for the wavelength detuning between the spontaneous emission line and Fabry-Perot cavity mode were explored, between

We investigate the mechanisms leading to the optical non-linearities observed on a strongly excited semiconductor microcavity containing quantum wells. This study of a coupled exciton-cavity system is possible owing to the availability of a sample of exceptionally high quality, permitting to exclude effects of disorder and inhomogeneous broadening. Sub-picosecond pump and probe experiments are performed, in the regime of an incoherent exciton gas of high density. For such a gas the dephasing due to collisio

State-selected spectra of the OH stretch overtones of methanol in the range of upsilon(1) = 3-8 reveal spectral splittings and broadenings that result from vibrational couplings within the molecule. We employ a two-color excitation technique in which an infrared pulse promotes jet-cooled methanol molecules to a single rotational state in upsilon(1) = 1 or 2 and a second visible or near-infrared laser pulse is scanned to record a vibrational overtone spectrum. The final vibrationally excited species are dete

Optical stark effect and coherent gain of excitons in a semiconductor microcavity

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