Bose Einstein Condensation Of Excitons And Polaritons

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.

Bose-Einstein condensation of excitons is a unique effect in which the electronic states of a solid can self-organize to acquire quantum phase coherence. The phenomenon is closely linked to Bose-Einstein condensation in other systems such as liquid helium and laser-cooled atomic gases. This is the first book to provide a comprehensive survey of this field, covering theoretical aspects as well as recent experimental work. After setting out the relevant basic physics of excitons, the authors discuss exciton-phonon interactions as well as the behaviour of biexcitons. They cover exciton phase transitions and give particular attention to nonlinear optical effects including the optical Stark effect and chaos in excitonic systems. The thermodynamics of equilibrium, quasi-equilibrium, and nonequilibrium systems are examined in detail. The authors interweave theoretical and experimental results throughout the book, and it will be of great interest to graduate students and researchers in semiconductor and superconductor physics, quantum optics, and atomic physics.

In the past decade, there has been a burst of new and fascinating physics associated to the unique properties of two-dimensional exciton polaritons, their recent demonstration of condensation under non-equilibrium conditions and all the related quantum phenomena, which have stimulated extensive research work. This monograph summarizes the current state of the art of research on exciton polaritons in microcavities: their interactions, fast dynamics, spin-dependent phenomena, temporal and spatial coherence, condensation under non-equilibrium conditions, related collective quantum phenomena and most advanced applications. The monograph is written by the most active authors who have strongly contributed to the advances in this area. It is of great interests to both physicists approaching this subject for the first time, as well as a wide audience of experts in other disciplines who want to be updated on this fast moving field.

In 2006 researchers created the first polariton Bose-Einstein condensate at 19K in the solid state. Being inherently open quantum systems, polariton condensates open a window into the unpredictable world of physics beyond the “fifth state of matter”: the limited lifetime of polaritons renders polariton condensates out-of-equilibrium and provides a fertile test-bed for non-equilibrium physics. This book presents an experimental investigation into exciting features arising from this non-equilibrium behavior. Through careful experimentation, the author demonstrates the ability of polaritons to synchronize and create a single energy delocalized condensate. Under certain disorder and excitation conditions the complete opposite case of coexisting spatially overlapping condensates may be observed. The author provides the first demonstration of quantized vortices in polariton condensates and the first observation of fractional vortices with full phase and amplitude characterization. Finally, this book investigates the dynamics of polariton populations trapped in neighboring potential traps – and shows that coherent population oscillations are observed – in direct analogy to the AC Josephson effect. This book puts significant weight on both the details of the experimental techniques and the theoretical tools used pick apart the experimental findings making it an invaluable aide for condensed matter researchers interested in exciton-polaritons condensates.

Covering general theoretical concepts and the research to date, this book demonstrates that Bose-Einstein condensation is a truly universal phenomenon.

Volume 32 of the series addresses one of the most rapidly developing research fields in physics: microcavities. Microcavities form a base for fabrication of opto-electronic devices of XXI century, in particular polariton lasers based on a new physical principle with respect to conventional lasers proposed by Einstein in 1917. This book overviews a theory of all major phenomena linked microcavities and exciton-polaritons and is oriented to the reader having no background in solid state theory as well as to the advanced readers interested in theory of exciton-polaritons in microcavities. All major experimental discoveries in the field are addressed as well. · The book is oriented to a general reader and is easy to read for a non-specialist.· Contains an overview of the most essential effects in physics of microcavities experimentally observed and theoretically predicted during the recent decade such as:. · Bose-Einstein condensation at room temperature.· Lasers without inversion of population.· Microcavity boom: optics of the XXI century!· Frequently asked questions on microcavities and responses without formulas. · Half-light-half-matter quasi-particles: base for the future optoelectronic devices

Bose-Einstein condensation (BEC) is a remarkable manifestation of quantum mechani- cal behaviour where a macroscopic number of particles occupy a single particle ground state. Typical realizations of BEC occur at temperatures close to absolute zero. In this thesis, we propose a route towards full thermal equilibirum, room-temperature BEC of "half-light" - "half-matter" quasiparticles known as exciton-polaritons. Our proposed strategy uses three-dimensional photonic crystals to form the optical resonator; this leads to long lived confined optical modes. These long lived confined optical modes allow the condensates to reach full thermal equilibrium. Photonic crystal resonators ensure that the light-matter coupling strengths are significantly stronger than in conventional archi- tectures; this leads to BEC formation at higher temperatures. A central quantity in our work is the (lower) exciton-polariton dispersion depth. The dispersion depth is an energy scale that governs the limit on the critical temperature. Strategies for increasing the dispersion depth to facilitate room-temperature BEC will be discussed. We first examine exciton-polariton BEC in optical resonators composed of slanted pore photonic crystals. We consider InGaAs/InP quantum wells embedded in the res- onator to allow for light emission at a wavelength of approximately 1300 nm. In esti- mating the critical temperature, we ensure the use of modest exciton-polariton densities to avoid the saturation of the exciton resonance. Using three quantum wells, our study reveals that exciton-polariton BEC occurs for temperatures above 300 K and that our results are robust to both photonic and electronic disorder. Next, we investigate exciton-polariton BEC in optical resonators composed of wood- pile photonic crystals. We treat GaAs/AlAs quantum wells embedded in resonator to allow for the emission of light with a wavelength of approximately 750 nm. Due to the x-y symmetry of the woodpile photonic crystal, the exciton-polariton ground state exhibits a two-fold polarization degeneracy. We show that symmetry breaking lifts the degeneracy of the ground state and results in larger critical temperatures and higher condensate fractions, in comparison to a symmetrical woodpile structure. Our results show that for three quantum wells and a moderate exciton-polariton density that a BEC can be obtained at temperatures over 300 K; this condensate is robust to disorder.

Rapid development of microfabrication and assembly of nanostructures has opened up many opportunities to miniaturize structures that confine light, producing unusual and extremely interesting optical properties. This book addresses the large variety of optical phenomena taking place in confined solid state structures: microcavities. Realisations include planar and pillar microcavities, whispering gallery modes, and photonic crystals. The microcavities represent a unique laboratory for quantum optics and photonics. They exhibit a number of beautiful effects including lasing, superfluidity, superradiance, entanglement etc. Written by four practitioners strongly involved in experiments and theories of microcavities, it is addressed to any interested reader having a general physical background, but in particular to undergraduate and graduate students at physics faculties.

Coherent control has been at the heart of the study of physical chemistry. Great advancement has been achieved in the past few decades in coherent control of classical systems by using spatially and temporally shaped electromagnetic waves. In this dissertation, we extend the concept of coherent control to a purely quantum mechanical collective system, namely, microcavity exciton-polariton Bose-Einstein condensates. Microcavity exciton-polaritons, hereafter simply polaritons, are bosonic quasiparticles formed in a resonant semiconductor microcavity by coupling the excitonic polarizabilities in quantum wells to the transverse mode of the confined optical field in the cavity. The light-matter dual nature allows direct control of polaritons through either their excitonic or photonic components. By utilizing the fact that polariton-exciton and polariton-polariton interactions are repulsive, all-optical control of polaritons was realized. By shaping the intensity fronts of the optical beam incident on a microcavity, the potential landscape felt by polaritons can be easily tailored. This is the key ingredient of this dissertation work. The light-matter dual nature endows polaritons a very small effective mass that is one hundred million times less than that of a hydrogen atom, leading to the observation of quantum phenomena such as condensation, superfluidity and quantized vortices at temperatures ranging from tens of Kelvin up to room temperatures. However, debates persist over whether the observed phenomena can be related to Bose- Einstein condensation because polaritons are not in thermal equilibrium. By applying all-optical trapping to a high-quality microcavity structure, polaritons at both spatial and thermal equilibrium were achieved across a broad range of densities and bath temperatures, as evidenced by the observed equilibrium Bose-Einstein distributions. A phase diagram for Bose-Einstein condensation of polaritons was produced for the first time, which agrees with the predictions of basic quantum gas theory. The thermalization behavior depends crucially on the interactions among polaritons. By changing the underlying excitonic/photonic fractions in polaritons, the interaction strength of polaritons can be varied, leading to control between nonequilibrium and equilibrium behavior of the polariton gas. The interactions also play a crucial role in polaritonic device operations. However, an accurate measurement of the polariton-polariton interaction strength has been not possible because of the difficulty in separating polaritons and excitons that are created by the same optical excitation. After propagating to the center of a sufficiently large optically induced annular trap, polaritons were separated from the incoherent populations of free carriers and hot excitons. The polariton interaction strength was then extracted from energies measured as a function of the polariton density. The measured interaction strength was about two orders of magnitude larger than previous theoretical estimates, putting polaritons squarely into the strongly interacting regime. Optical control can also be utilized to directly manipulate polariton condensates. By tailoring the size and pumping intensity of the optical trap, polariton condensates can be switched among different high-order modes and the homogeneous condensate mode. The redistribution of spatial densities is accompanied by a superlinear increase in the emission intensity as a function of excitation power, implying that polariton condensates in this geometry could be exploited as a multistate switch. The parameters for reproducible switching between the high-order states in the optical trap have been measured experimentally, giving us a phase diagram for the mode switching. It will serve well to calibrate the implementation of an exciton-polaritonic multistate switch.

This volume provides a broad overview of the principal theoretical techniques applied to non-equilibrium and finite temperature quantum gases. Covering Bose-Einstein condensates, degenerate Fermi gases, and the more recently realised exciton-polariton condensates, it fills a gap by linking between different methods with origins in condensed matter physics, quantum field theory, quantum optics, atomic physics, and statistical mechanics.