Geometrical phases such as Pancharatnam and Berry phase, have been playing important role in classical wave and quantum physics. In topological photonics, the geometrical phases can be controlled with artificial gauge fields by designing lattice geometry of photonic crystals. Here, we theoretically and experimentally demonstrate that geometric phases can give rise to a new class of resonant states in topological ring resonators. Our simulations and analytical model reveal a hierarchy of the resonant modes and transformation of polarization states. Also, we provide experimental observations of the resonant states by infrared spectroscopy.
We have designed and experimentally realized a polaritonic topological insulator based on bulk transition metal dichalcogenide crystals (TMDC, ~40nm-thick WS2 film). We have demonstrated that due to their high refractive index and the presence of exciton modes in the optical range, they represent an excellent platform for topological polaritonics, offering both excellent confinement and strong light-matter interactions in a single material. The successful patterning of TMDC into the topological crystal was demonstrated and emergence of the topological polaritonic boundary modes was directly confirmed by the back focal plane imaging and real space imaging techniques.
Here we demonstrate that a unitary transformation due to nonuniform artificial gauge field enables a new class of topological boundary states carrying both spin and valley polarization. We show that such transformations also allow to tune radiative lifetimes of the hybrid spin-valley boundary modes. Then we demonstrate that gauge transformations, when applied adiabatically to the boundary modes, offer a mechanism for flipping the pseudo-spin without back reflection thus implementing an X-gate acting in synthetic Bloch subspaces spanned by pseudo-spins. Finally, we show that such adiabatic evolutions give rise to the geometrical phases, which offers a generic Phase-gate operation. Our results unveil a new versatile approach to control modes in topological photonics and also envisions topological materials as one of promising candidates for integrated quantum photonics applications.
In this work we propose a method to achieve improved topological edge sates by engineering an optimal profile of the transition at the boundary between topological and trivial domains. From experiment and simulation results we confirmed that the quality factor of edge state for smooth transition profile can be increased by more than an order compared to the edge state of a conventional step profile. At the same time the modes retained their topological resilience, which, when combined with the reduced radiative leakage, enables robust photonic transport over long distances even above the light line.
The WS2 monolayer encapsulated in two thin hBN layers was pumped at room temperature by a circularly polarized laser in order to excite one of the valleys (K or K’ valley). The refractivity spectra measured using both left- and right- CP probe with low intensity, revealed the nonreciprocal response at exciton resonance wavelength. Based on this effect, we propose a novel design of an isolator containing SiN ring resonator integrating an asymmetrically places WS2 monolayer. By applying the coupled mode theory and parameter extracted from the experiment, the isolation of the device was estimated to be ~20dB.
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