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Prof. Daniel Leykam, Singapore University of Technology and Design, Singapore
Prof. Daniel Leykam, Singapore University of Technology and Design, Singapore
Title: Conical intersections and angular momentum
Title: Conical intersections and angular momentum
Abstract: Conical intersections occur between energy bands in certain two-dimensional periodic lattices. Wavepacket dynamics in the vicinity of a conical intersection mimics that of relativistic spinor particles, where the role of the particle spin is played by an internal spin-like "pseudospin" degree of freedom within the lattice. I will discuss intriguing relations between this pseudospin and other forms of angular momentum, focusing on the pseudospin-1/2 "Dirac cone" between two bands, which occurs in the electronic band structure of graphene. I will then show how Dirac cones can be generalised to pseudospin-1 and pseudospin-2 conical intersections using relatively simple and experimentally-feasible periodic lattice potentials. These findings are applicable to a variety of systems admitting mean field dynamics governed by Schrödinger-type equations, including photonic crystals, Bose-Einstein condensates in optical lattices, and structured optical microcavities.
Prof. Parinda Vasa, Indian Institute of Technology Bombay, India
Prof. Parinda Vasa, Indian Institute of Technology Bombay, India
Title: Emitters in proximity of plasmonic nano-cavity
Title: Emitters in proximity of plasmonic nano-cavity
Abstract: We'll discuss the experimental exploration of extremely narrow (~lambda/100), essentially 1D illumination conditions generated by plasmonic nano-cavity in probing and engineering nanoscale light-matter interactions over a broad spectral range.
Prof. Anshuman Kumar, Indian Institute of Technology Bombay, India
Prof. Anshuman Kumar, Indian Institute of Technology Bombay, India
Title: Sensing with Broken Symmetry: Revisiting Bound States in the Continuum
Title: Sensing with Broken Symmetry: Revisiting Bound States in the Continuum
Abstract: Metasurface with bound states in the continuum (BICs) offer exceptional potential for optical sensing due to their inherently high quality (Q) factors. However, the detection of symmetry-protected BICs remains experimentally challenging due to their non-radiative nature. Introducing slight asymmetry makes these resonances observable, though it reduces the Q-factor. In real devices, intrinsic material losses further affect the resonance behavior and sensing performance. While it is often assumed that sensing is optimized at the critical coupling when radiative and non-radiative losses are balanced, the precise conditions for achieving the best limit of detection (LOD) and figure-of-merit (FOM) remain under active discussion. In this work, we experimentally and theoretically investigate BIC-based sensing in the terahertz (THz) range. We demonstrate that the LOD exhibits a non-monotonic dependence on asymmetry, reaching an unexpected optimum where radiative and non-radiative losses are not equal. Moreover, we show that this optimum differs between reflection and transmission sensing schemes. Our results provide practical guidelines for optimizing Q-factor, sensitivity, and signal amplitude together, and contribute to a deeper understanding of the fundamental limits of BIC-based sensing.
Prof. Subhaskar Mandal, Indian Institute of Technology Bombay, India
Prof. Subhaskar Mandal, Indian Institute of Technology Bombay, India
Title: Axion Topological Photonic Crystals
Title: Axion Topological Photonic Crystals
Abstract: Axions are elusive particles that physicists have been pursuing for decades. Interestingly, in certain materials, analogous quasiparticles—known as axion insulators—can emerge. While axion insulators have been primarily explored in two dimensions, their rich three-dimensional properties remain largely unexplored. In this talk, I will present our realization of a 3D photonic crystal that emulates an axion insulator and describe how we probed its unique topological features. These include half-quantized Chern numbers on individual surfaces, chiral hinge states enabling unidirectional signal transport through the 3D structure, and even "mathematical operations" between fractional and integer Chern numbers. Together, these results highlight the potential of constructing complex 3D topological networks with light. I will conclude by discussing our key experimental findings and their implications for the future of topological photonics and robust light transport.
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