Optical properties of ensembles of coupled three-level quantum emitters are investigated in linear and non-linear regimes. The model of the Maxwell–Liouville von Neumann equations is implemented to explore the reflection, transmission, and absorption of a thin layer of atom-like emitters at low and high densities. The stimulated Raman adiabatic passage is analysed in systems of coupled quantum emitters of various densities. It is shown that coupling via local electromagnetic fields shifts the energy levels and modifies propagating fields leading to a mixed final population distribution and appearance of new absorption resonances. Strong femtosecond pulses induce population inversion in emitters leading to optical gain.
Optical properties of ensembles of coupled three-level quantum emitters are investigated in linear and non-linear regimes. The model of the Maxwell–Liouville von Neumann equations is implemented to explore the reflection, transmission, and absorption of a thin layer of atom-like emitters at low and high densities. The stimulated Raman adiabatic passage is analysed in systems of coupled quantum emitters of various densities. It is shown that coupling via local electromagnetic fields shifts the energy levels and modifies propagating fields leading to a mixed final population distribution and appearance of new absorption resonances. Strong femtosecond pulses induce population inversion in emitters leading to optical gain.
Optical properties of ensembles of coupled three-level quantum emitters are investigated in linear and non-linear regimes. The model of the Maxwell–Liouville von Neumann equations is implemented to explore the reflection, transmission, and absorption of a thin layer of atom-like emitters at low and high densities. The stimulated Raman adiabatic passage is analysed in systems of coupled quantum emitters of various densities. It is shown that coupling via local electromagnetic fields shifts the energy levels and modifies propagating fields leading to a mixed final population distribution and appearance of new absorption resonances. Strong femtosecond pulses induce population inversion in emitters leading to optical gain.
Optical properties of ensembles of three-level quantum emitters coupled to plasmonic systems are investigated employing a self-consistent model. It is shown that the stimulated Raman adiabatic passage (STIRAP) technique can be successfully adopted to control optical properties of hybrid materials with collective effects present and playing an important role in light-matter interactions. We consider a core-shell nanowire composed of a silver core and a shell of coupled quantum emitters and utilize a STIRAP scheme to control the scattering efficiency of such a system in a frequency and spatially dependent manner. After the STIRAP-induced population transfer to the final state takes place, the core-shell nanowire exhibits two sets of Rabi splittings with Fano line shapes, indicating strong interactions between two different atomic transitions driven by plasmon near-fields.
The structure of a solution of the generalized Maxwell–Bloch system of equations describing the strongly pumped interacting two-level atoms is discussed. This structure is represented by means of the corresponding differential equations for each contributing process. The interaction between the processes is introduced through the interaction integral and is illustrated by the specific system of graphs. The method allows one to describe the quantum-field-induced long-range interaction prevailing over short-range collisions and causing the broadening, narrowing, and shifts of an absorption line shape. The description is given in terms of the interaction integrals which couple the collective atomic polarization and population inversion. The contributions from different effects are analyzed with the use of the additivity of the corresponding absorption/reemission rates.
The interaction between light and matter is fundamental to developments in quantum optics and information. Over recent years enormous progress has been made in controlling the interface between light and single emitters including ions, atoms, molecules, quantum dots and ensembles. For many systems, inter-particle interactions are typically negligible. However, if the emitters are separated by less than the emission wavelength, resonant dipole--dipole interactions modify the radiative decay rate and induce a splitting or shift of the resonance. Here we map out the transition between individual dipoles and a strongly interacting ensemble by increasing the density of atoms confined in a layer with thickness much less than the emission wavelength. We find two surprising results: whereas for a non-interacting ensemble the opacity increases linearly with atomic density, for an interacting ensemble the opacity saturates, i.e., a thin dipolar layer never becomes opaque regardless of how many scatterers are added. Secondly, the relative phase of the dipoles produces an abrupt change in the optical transmission around the thickness λ/4.
Reduced abstract. This Thesis explores emergent cooperative phenomena in collective light-matter systems. We study ensembles of interacting quantum emitters coherently driven by a laser field and coupled to photonic structures, focusing on the hybrid description of emitters dressed by light. The interplay among quantum emitters, coherent driving, and photonic environments reveals a rich landscape of cooperative effects. While single-emitter dressing has been widely studied, we address collective phenomena in two non-identical emitters modelled as two-level systems. Strong interaction forms a dimer exhibiting superradiant and subradiant states, with two-photon resonances directly connecting ground and doubly excited states. This nonlinear process, central to the Thesis, enables new regimes of cooperative light-matter physics. Analytical studies show how interactions reshape observables such as emission intensity, photon statistics, and spectra, offering implications for quantum metrology. The sensitivity of two-photon processes to emitter distance and driving strength enables high-precision sensing and sub-wavelength imaging. Unexpectedly, we find that off-resonant virtual states may gain population through dissipation, redefining their role in open systems. To capture this, we develop a hierarchical adiabatic elimination method for metastable dynamics. We also analyze entanglement in emitters coupled to a lossy cavity, identifying five mechanisms, including the frequency-resolved Purcell effect introduced here. This selective enhancement stabilizes cooperative states and enables scalable entanglement. Our models, tailored to solid-state platforms such as quantum dots and molecular aggregates, address challenges like inhomogeneous broadening and decoherence, demonstrating the feasibility of harnessing cooperative light-matter effects for quantum technologies.
The appearance of quantum interference in the microscopic world is one of the deepest mysteries at the very root of quantum mechanics. When light interacts with atoms, it can induce transitions by way of distinct but indistinguishable pathways and yield unexpected and often counter-intuitive results. Electromagnetically Induced Transparency (EIT), Coherent Population Trapping (CPT), and Lasing Without Inversion (LWI) are modern examples of phenomena where the traditional rules that govern absorption and dispersion undergo major revisions. Spectacular consequences of this new state of affairs include the ability of a light beam to propagate through a normally absorbing medium with little or no absorption, or to undergo amplification even if the active medium is not prepared in a state of population inversion. Light signals have been shown to travel with strongly subluminal group velocities of only a handful of meters per second and, even, to propagate at speed greater than the ordinary speed of light, but without violation of causality or of the established rules that control the transfer of optical information through space. Three-level atoms can interact with two coherent electromagnetic fields according to three different systems, known as Cascade, Lambda and Vee systems. The propagation of a weak probe field can be deeply affected by the presence of a second stronger beam, the so-called coupling field. Transparency windows, splitting of emission and absorption lines and enormously enhanced dispersion have been documented in numerous experiments. In this thesis we explore the physical origin of the transparency induced in these systems by the simultaneous interplay of the coupling and probe fields. We focus our attention on the Cascade system and study its two configurations, Cascade-EIT and Cascade-AT. We develop a variety of complementary approaches for the description of these two configurations, some semiclassical and others fully quantum mechanical. We prove the existence of quantum interference in Electromagnetically Induced Transparency and also the surprising absence of interference in a closely related phenomenon, known as the Autler-Townes effect. Finally we complement the traditional machinery of theoretical quantum optics with techniques borrowed from quantum scattering theory, and offer what we believe is the most convincing physical evidence for the appearance, or for the absence, of quantum interference effects.