Fractal photonic anomalous Floquet topologicalinsulators to generate multiple quantum chiraledge states

Anomalous Floquet topological insulators with vanishing Chern numbers but supporting chiral edge modes are attracting more and more attention.Since the existing anomalous Floquet topological insulators usually support only one kind of chiral edge mode even at a large lattice size,they are unscalable and unapplicable for multistate topological quantum systems.Recently,fractal topological insulators with self-similarity have been explored to support more nontrivial modes.Here,we demonstrate the first experimental realization of fractal photonic anomalous Floquet topological insulators based on dual Sierpinski carpet consisting of directional couplers using the femtosecond laser direct writing.The fabricated lattices support much more kinds of chiral edge states with fewer waveguides and enable perfect hopping of quantum states with near unit transfer efficiency.Instead of zero-dimensional bound modes for quantum state transport in previous laser direct-written topological insulators,we generate multiple propagating single-photon chiral edge states in the fractal lattice and observe high-visibility quantum interferences.These suggest the successful realization of highly indistinguishable single-photon chiral edge states,which can be applied in various quantum operations.This work provides the potential for enhancing the multi-fold manipulation of quantum states,enlarging the encodable quantum information capacity in a single lattice via high-dimensional encoding and many other fractal applications.

On-chip path encoded photonic quantum Toffoli gate

The quantum Toffoli gate is one of the most important three-qubit gates,but it is challenging to construct a chip according to the complicated traditional circuit.Using the optimized 3D configuration with an overpass waveguide to reduce the circuit complexity,we successfully fabricate an on-chip path encoded photonic quantum Toffoli gate enabled by the 3D capability of the femtosecond laser direct writing(FLDW)for the first time to our knowledge,whose truth-table fidelity is higher than 85.5%.Furthermore,a path encoded four-qubit controlled-controlled-controlled NOT gate is written to confirm the scalability of this resource-saving technique.This work paves the way for the FLDW of more complex and powerful photonic quantum computation chips.