The author will present an overview of the physics of polaritons, focusing on their quantum many-body properties. In particular, the author will illustrate recent results in two main areas: polariton Bose-Einstein condensation, and the controlled generation of quantum correlated polariton states. In particular, the author will discuss the physics of polaritons as a two-component interacting Bose gas and will illustrate the theoretical approach to the polariton condensate, predicting the phase diagram and the collective excitation spectrum.
The author will present an overview of the physics of polaritons, focusing on their quantum many-body properties. In particular, the author will illustrate recent results in two main areas: polariton Bose-Einstein condensation, and the controlled generation of quantum correlated polariton states. In particular, the author will discuss the physics of polaritons as a two-component interacting Bose gas and will illustrate the theoretical approach to the polariton condensate, predicting the phase diagram and the collective excitation spectrum.
The main scope of this thesis is the investigation of quantum properties of nonlinear, dissipative, optical and condensed matter systems. Compared with previous studies on this subjects, we reached several milestone of general interests for the theoretical and experimental community. \nThe main experimental platform we refer to in this thesis is microcavity polaritons: polaritons arise from the coupling of light with excitons in a quantum well, i.e., a 2D semiconductor material embedded in the microcavity. They have attracted the interest of the scientific community for their rich physics. Polaritons can form out-of-equilibrium Bose-Einstein condensates, they can experience superfluid phase transition and, due to their interaction via the excitonic component, they show a variety of phenomena which are typical of nonlinear physics, such as bistability and parametric scattering. \nIn particular, motivated by recent proposals about the generation of single photons from weakly nonlinear system, like the unconventional photon blockade, and by the production of squeezed states in polariton systems, we studied the possibility of obtaining antibunched light and other quantum states (like squeezed states and entangled states), when the nonlinear system shows some peculiar features: in particular we consider polariton soliton and cascade systems. \nFinally, when considering nonlinear incoherent processes, we investigate the effect of the PT-symmetry and the PT-symmetry breaking on the quantum state of the emitted light. \nHence, this research work has two main objectives: first, from the fundamental physics point of view, to understand the interplay between nonlinear phenomena and quantum optics, second to provide useful tools for future technological applications. Specifically, for the latter case, we demonstrate a theorem that links the measurement of intensity correlations with the occurrence of certain phase transitions, and we propose a setup to maximize the non-classicality of the light emitted by weakly non-linear systems via a cascade configuration. \n \n \n
Remarkable experimental advances in the past few decades have paved the way for a new era of ultra-cold physics. Experimentalists can now cool large samples of atoms down to temperatures where quantum mechanical effects dominate, and control their bulk geometrical structure and microscopic interactions with ease. The result is a wide open testing ground for quantum many-body physics. In this talk, I will provide an overview of the important concepts and methods that form the foundations of this field, before steering the discussion to Bose gases, or gases with constituents that obey Bose-Einstein statistics. At ultra-cold temperatures, gases of bosons condense into a single macroscopicquantum mechanical state, forming a Bose-Einstein condensate. One of the more interesting properties of Bose-Einstein condensates is that they are superfluid, and can exhibit dissipationless flow. If the bosons possess large dipole moments, their interaction character changes signifi cantly, as does their collective superfluid behavior. I will discuss some of the theoret ical and computational tools used to model Bose-Einstein condensates, demonstrate how dipolar interactions play a profound role in the basic properties of these novel superfluids, and provide an outlook for the future of this exciting field.
This reference book explains the fundamentals of Bose Einstein Condensation (BEC) in excitons and polaritons. It presents five chapters exploring fundamental concepts and recent developments on the subject. Starting with a historical overview of BEC, the book progresses into the origins and behaviors of excitons and polaritons. Chapters also cover the unique thermalization and relaxation kinetics of excitons, and the distinctive features of polaritons, such as lasing, superfluidity, and quantized vortices. The chapters dedicated to BEC in excitons and polaritons detail experimental techniques, theoretical modeling, recent advancements, and practical applications in a simplified way for beginners. This book serves as a resource for researchers, physicists, and students interested in the phenomena of BEC, providing insights into both the theoretical foundations and the practical implications of excitons and polaritons.
Exciton-polariton Bose-Einstein condensates (BECs) are newly emerged quantum systems that are capable of showing macroscopic quantum phenomena with intrinsic open-dissipative nature. The spatial distribution of the polariton density, without any external potential, can be controlled by the geometric shape of the pumping laser, enabling the investigation of polariton dynamics with topologically non-trivial configurations. Meanwhile, exciton-polaritons have spin degrees of freedom inherited from excitons and photons, making it a candidate for the realization of quantum logic gates. In this thesis, we will investigate theoretically the nonlinear dynamics of exciton-polariton BECs involving both polaritons' spatial degrees of freedom and spin degrees of freedom, and interactions between them. This thesis is organised as follows: In Chapter 1, we will present an overall review of exiton-polariton systems and important properties of polariton BECs and then introduce the dynamical equations with various interactions that will serve as the main theoretical tool for subsequent chapters. Several polariton pumping and trapping techniques appearing in later chapters will also be introduced. In Chapter 2, we will investigate the superfluidity properties of a single-component polariton condensate under an incoherent annular pumping configuration. By studying the stability properties of polariton persistent currents, we find that the persistent currents can exhibit dynamical instability and energetic-like instability according to different parameter region. A stability phase diagram will be given and its relation with the Landau's criterion will be discussed. In Chapter 3, we will investigate the spin dynamics of a two-component polariton condensate under a homogeneous pumping configuration. Owing to the Josephson coupling, there exist multiple steady state solutions that allow of controlled spin state switching. A desynchronized region where there exists no stable steady solution is found. In the desynchronized region, a desynchronized state beating periodically over time can exist, which will serve as a building block of spin waves presented in the next chapter. In Chapter 4, by combining results from the previous two chapters we will investigate generally the nonlinear dynamics of polariton condensates under an annular pumping configuration. The spin-orbit interaction provided by the Josephson coupling supports azimuthon states that have simultaneous modulations in both amplitude and phase. The azimuthon states, when viewed in a different polarization basis, form rotating spin waves that can be referred to as the optical ferris wheel. In Chapter 5, results from previous chapters will be extended to micocavities that support the anisotropic TE-TM splitting interaction. Rotating singularities (small-scale vortices) are found as a result. Their properties and experimental observation techniques will be discussed. Chapter 2-5 provide a theoretical framework for the nonlinear dynamics of polariton condensates. They rely mostly on optical trapping techniques and are ready to be tested in experiments. In Chapter 6, polaritons trapped by an engineered periodic mesa potential will be discussed. We will investigate the band structure of polaritons under the influence of the periodic potential together with discussions on the phase-modulated interference pattern which corresponds to the polariton Talbot patterns observed in experiments.
This work is an up-to-date and partially improved analysis of the basics of the mathe- matical description of Bose-Einstein condensation in terms of first principles of Quantum Mechanics. The main aims are: 1) to provide a compact, yet coherent overview: - of the basic mathematical tools used to formalise Bose-Einstein condensation, - of the mathematical techniques for studying several features of this physical phenomenon, - and of how such means emerge as the natural ones in connection with their physical interpretation; 2) to discuss and to place in the above perspective some new contributions and improvements: - on equivalent characterizations of Bose-Einstein condensation, - on the strength of the convergence for some currently available asymptotic results, - and on the effects of interparticle correlations on the energy and the dynamics of the many-body condensate.