The project aimed at uncovering topological behavior in nanophotonic systems, in particular by breaking time-reversal symmetry through nano-optomechanical interactions. Such behavior is normally alien to both photons and phonons as they do not interact with magnetic fields, in contrast to electrons. It can lead to highly sought-after functionality such as one-way transport and states that are protected against scattering from disorder. As such, it is appealing to introduce these principles in nanophotonic and nanomechanical systems, which are rich in applications related to sensing and information processing.
In on-chip silicon nanophotonic systems, we observed various topological states of phonons and photons, bearing analogy to the quantum Hall effect, the quantum spin Hall effect, and the quantum valley Hall effect known in electronic materials. We demonstrated the ability of such states to control nonreciprocal transport of signals as well as thermal flows, and propagation robust against scattering from defects. Moreover, by combining broken time-reversal symmetry with non-Hermitian dynamics, we discovered new phases of matter and physical mechanisms, including a geometric phase that controls non-Hermitian dynamics in parametrically driven systems, and a bosonic Kitaev-Majorana chain that establishes a non-Hermitian topological phase with intriguing applications as a sensor and amplifier. Finally, we uncovered rich dynamical behavior in nonlinear nano-optomechanical networks controlled with laser fields.
This project demonstrated a suite of new physical phenomena in topological bosonic systems. It showcased the power of on-chip silicon nanophotonic and nanomechanical systems to study such phenomena, with potential applications in various domains, and possible analogues in many other wave systems and metamaterials.
