The excitations in organic materials are often described by Frenkel excitons, whose wave functions are tightly localized on the individual molecules, which results in short-range, nanoscale transport. However, under strong light-molecule coupling, new quantum states, known as cavity polaritons, are formed and the wave functions describing the coupled system extend over distances much larger than the molecular scale. Using time-resolved microscopy we directly show that this fundamental modification in the nature of the system induces long-range transport in organic materials and propagation over several microns. By following the motion of polaritons in real-time, we measure the propagation velocity of polaritons and we find that it is surprisingly lower than expected. Our approach sheds new light on the fundamental characteristics of polaritons and can provide critical information for the design of future organic-electronic devices, which will harness the polaritonic properties to overcome the poor conductance of organic materials.

We theoretically study and successfully observe the evolution of Gaussian and Airy surface gravity water wave packets propagating in an effective linear potential. This potential results from a homogeneous and time-dependent flow created by a computer-controlled water pump. For both wave packets we measure the amplitudes and the cubic phases appearing due to the linear potential. Furthermore, we demonstrate that the self-acceleration of the Airy surface gravity water wave packets can be completely canceled by a linear potential.

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Quantum information and communication technology will lead us to the new era of ultrafast and absolute-secure networks. With the emergence of quantum supremacy on the horizon, the security of various classical encryption systems soon may be deemed obsolete. As a remedy, quantum key distribution (QKD) is proposed as a novel quantumbased secret keys exchange, which is developed to solve the problems of legacy encryption. It is anticipated that QKD will provide stronger security for future communication systems even in the presence of malicious quantum attacks. As the QKD research and development is getting mature, the theoretical use cases of QKD in various industries are proliferating. In this treatise, we summarise the potential applications of QKD for future communication technology while highlighting the ongoing standardisation efforts essential for the sustainability and reliability of the near-future deployment. Additionally, we also present the various challenges faced by both discrete variable and continuous variable QKD schemes hindering their widespread implementation into our future communication networks.

We present the theoretical models and review the most recent results of a class of experiments in the field of surface gravity waves. These experiments serve as demonstration of an analogy to a broad variety of phenomena in optics and quantum mechanics. In particular, experiments involving Airy water-wave packets were carried out. The Airy wave packets have attracted tremendous attention in optics and quantum mechanics owing to their unique properties, spanning from an ability to propagate along parabolic trajectories without spreading, and to accumulating a phase that scales with the cubic power of time. Non-dispersive Cosine-Gauss wave packets and self-similar Hermite-Gauss wave packets, also well known in the field of optics and quantum mechanics, were recently studied using surface gravity waves as well. These wave packets demonstrated self-healing properties in water wave pulses as well, preserving their width despite being dispersive. Finally, this new approach also allows to observe diffractive focusing from a temporal slit with finite width.