Engineering of Zeno Dynamics in Integrated Photonics

Observation of multiple topological bound states in the continuum in the photonic bilayer trimer lattice

A topological bound state in the continuum (TBIC) is a novel topological phase that has attracted significant attention. Different from conventional topological insulators (TIs), where boundary states reside within gaps, TBICs can support unconventional boundary states that remain isolated from the surrounding bulk states. In this work, we experimentally demonstrate multiple TBICs in photonic bilayer trimer lattices using femtosecond laser writing technology. By modulating the interlayer coupling between two trimer chains, we observe the emergence of two distinct types of TBICs. Moreover, we experimentally achieve the coexistence of in-gap topological states and TBICs and demonstrate the transformation between them. Our work unveils new insights into the flexible construction of TBICs, and this method can be easily applied to other one-dimensional topological structures, offering promising avenues for further research.

Dirac exciton-polariton condensates in photonic crystal gratings

Bound states in the continuum have recently been utilized in photonic crystal gratings to achieve strong coupling and ultralow threshold condensation of exciton-polariton quasiparticles with atypical Dirac-like features in their dispersion relation. Here, we develop the single- and many-body theory of these new effective relativistic polaritonic modes and describe their mean-field condensation dynamics facilitated by the interplay between protection from the radiative continuum and negative-mass optical trapping. Our theory accounts for tunable grating parameters giving full control over the diffractive coupling properties between guided polaritons and the radiative continuum, unexplored for polariton condensates. In particular, we discover stable cyclical condensate solutions mimicking a driven-dissipative analog of the zitterbewegung effect characterized by coherent superposition of ballistic and trapped polariton waves. We clarify important distinctions between the polariton nearfield and farfield explaining recent experiments on the emission characteristics of these long lived nonlinear Dirac polaritons.

Floquet parity-time symmetry in integrated photonics

Parity-time (PT) symmetry has been unveiling new photonic regimes in non-Hermitian systems, with opportunities for lasing, sensing and enhanced light-matter interactions. The most exotic responses emerge at the exceptional point (EP) and in the broken PT-symmetry phase, yet in conventional PT-symmetric systems these regimes require large levels of gain and loss, posing remarkable challenges in practical settings. Floquet PT-symmetry, which may be realized by periodically flipping the effective gain/loss distribution in time, can relax these requirements and tailor the EP and PT-symmetry phases through the modulation period. Here, we explore Floquet PT-symmetry in an integrated photonic waveguide platform, in which the role of time is replaced by the propagation direction. We experimentally demonstrate spontaneous PT-symmetry breaking at small gain/loss levels and efficient control of amplification and suppression through the excitation ports. Our work introduces the advantages of Floquet PT-symmetry in a practical integrated photonic setting, enabling a powerful platform to observe PT-symmetric phenomena and leverage their extreme features, with applications in nanophotonics, coherent control of nanoscale light amplification and routing.

Observation of higher-order topological corner states in photonic two-dimensional trimer lattices

We demonstrate the first, to the best of our knowledge, experimental observation of higher-order topological corner states in the photonic two-dimensional (2D) trimer lattices. Using a femtosecond laser direct writing technology, we experimentally fabricate a series of 2D trimer lattices with different open boundary conditions and thereby observe two kinds of 0D topological corner states, i.e., topological corner states and topological defect corner states. Interestingly, these corner states and defect corner states can not only exist in the bandgap but also coexist with the bulk states and show obvious localization properties. This work provides fresh perspectives on higher-order topology in artificial microstructures.

Accelerating Quantum Decay by Multiple Tunneling Barriers

A quantum particle constrained between two high potential barriers provides a paradigmatic example of a system sustaining quasi-bound (or resonance) states. When the system is prepared in one of such quasi-bound states, the wave function approximately maintains its shape but decays in time in a nearly exponential manner radiating into the surrounding space, the lifetime being of the order of the reciprocal of the width of the resonance peak in the transmission spectrum. Naively, one could think that adding more lateral barriers would preferentially slow down or prevent the quantum decay since tunneling is expected to become less probable and due to quantum backflow induced by multiple scattering processes. However, this is not always the case and in the early stage of the dynamics quantum decay can be accelerated (rather than decelerated) by additional lateral barriers, even when the barrier heights are arbitrarily large. The decay acceleration originates from resonant tunneling effects and is associated to large deviations from an exponential decay law. We discuss such a counterintuitive phenomenon by considering the hopping dynamics of a quantum particle on a tight-binding lattice with on-site potential barriers.

Efficient ultrafast laser writing with appropriate polarization

Appropriate polarization utilization makes the electric field vector direction and the statistically oriented localized states suitable for enhancing light-matter interactions so as to improve the efficiency of ultrafast laser writing, which will remarkably reduce the pulse energy and increase the processing speed for high density optical data storage, as well as manufacturing three-dimensional integrated optics and geometric phase optical elements.