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Dynamically encircling exceptional points (EEPs) in non-Hermitian systems have been utilized to realize robust on-chip mode conversions by taking the advantage that the output states are usually fixed and independent of the input states. This highly protects one of the specific eigenstates, but restricts their practical applications requiring superposition states. Here, we realize an on-chip robust eigenstate generator using a depth-varying 3D waveguide to overpass the EEP system. It not only preserves the robustness of the EEP system to generate one determinate eigenstate, but also generates another two-level eigenstate and arbitrary superposition states. Furthermore, by ingeniously combining two identical generators with a symmetric Y combiner, both the all-optical XOR and OR logic operations insensitive to the variations in the input light are realized by the destructive or constructive interference between the two generators' near-neighboring output signals. This paper paves the way for applications of EEP systems to highly robust state manipulations and information processing in integrated photonic and quantum devices.

Boosting second-order optical nonlinear frequency conversion over subwavelength thickness has long been pursued through optical resonance in micro- and nanophotonics. However, the availability of thin film materials with high second-order nonlinearity is limited to III-V semiconductors, which have low transparency in the visible. Here, we experimentally demonstrated strongly enhanced second harmonic generation in one-dimensional heterostructure cavities on thin film lithium niobate. A guided-mode resonance resonator and distributed Bragg reflectors are combined for both efficient coupling and electromagnetic field localization. Over 1200 times second harmonic generation enhancement is experimentally realized compared with flat thin film lithium niobate through optimizing the trade-off between quality factor and mode volume, leading to a record high normalized conversion efficiency of 2.03×10-5 cm²/GW under 1.92 MW/cm² pump intensity. Our approach could inspire the miniaturization and integration of compact resonant nonlinear photonic devices on thin film lithium niobate. [ABSTRACT FROM AUTHOR]

To build universal quantum computers, an essential step is to realize the so-called controlled-NOT (CNOT) gate. Quantum photonic integrated circuits are well recognized as an attractive technology offering great promise for achieving large-scale quantum information processing, due to the potential for high fidelity, high efficiency, and compact footprints. Here, we demonstrate a supercompact integrated quantum CNOT gate on silicon by using the concept of symmetry breaking of a six-channel waveguide superlattice. The present path-encoded quantum CNOT gate is implemented with a footprint of 4.8×4.45  μm² (∼3λ×3λ) as well as a high-process fidelity of ∼0.925 and a low excess loss of <0.2  dB. The footprint is shrunk significantly by ∼10 000 times compared to those previous results based on dielectric waveguides. This offers the possibility of realizing practical large-scale quantum information processes and paving the way to the applications across fundamental science and quantum technologies. [ABSTRACT FROM AUTHOR]