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Academic Seminar (Course) Online SEMINAR:Topological Control of Light

Classification of materials based on their physical properties has shaped the development of modern civilisations. Using the right materials together with fine-tuning of their physical properties, has enabled novel engineered devices. Over the last decade, we have witnessed a new materials classification based on topological concepts. We can group materials using integer numbers associated with the symmetry of their electronic band structure. Recently those innovative concepts have been applied for optical systems to investigate topological phases of light on tailored optical materials. However, examples in the literature are passive optical systems with built-in topology. Active control of topology and device applications remains a challenge. This talk explores the topological control of light across different domains, demonstrating how topological singularities can be harnessed to manipulate electromagnetic waves. First, I will show how exceptional points (EPs) singularities in graphene-based terahertz devices enable precise control over light propagation. By tuning a gate voltage, we can modulate both the intensity and phase of terahertz pulses using a topological phase transition while crossing an EP. We were able to reconstruct the complex energy landscape and explore non-Hermitian physics behind the observed topological properties. In a second approach, we apply topological principles to thermal light. By controlling the reflection topology of thermal emitters, we observed a topological phase transition in thermal radiation by varying a single parameter. The critical point of zero reflection is topologically protected, and boundaries between spatial domains host interface states with near-unity thermal emissivity. Together, these examples illustrate rich physics of topological singularities providing new tools for controlling light, from the terahertz regime to thermal radiation, with potential applications in THz communications and thermal management.

16.10.2024 - All Day
Academic Seminar (Course) FENS L055 SEMINAR: Read/Write Implementations of Queues and Stacks with Relaxed...

Linearizability is the standard correctness criteria for implementations of concurrent objects. Roughly speaking, a linearizable implementation of an object gives the illusion that all operations happen sequentially, in some order that respects real-time. Unfortunately, it has been shown that linearizability is expensive to achieve for some concurrent objects, which include useful objects like queues and stacks. Concretely, any linearizable implementation for such objects requires expensive synchronization mechanisms. This negative result limits the scalability of linearizable implementations for some concurrent objects. One way to evade the impossibility result is to relax the semantics of the object to be implemented in order to use only lighter synchronization mechanisms, with the aim of achieving scalability. This talk is about a recently introduced relaxation for queues and stacks called multiplicity. Roughly speaking, multiplicity allows distinct dequeue/pop operations to take the same item only if they are concurrent. It will be shown that queues and stacks with multiplicity can be implemented using only the simplest read/write operations. A variant of multiplicity allows us to develop the fastest relaxed single-enqueuer queue implementations known so far, which has implications for work-stealing, a popular dynamic load balancing technique. This is a joint work with Miguel A Piña, Sergio Rajsbaum and Michel Raynal.

14.10.2024 - All Day
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