Advanced Photonics
Wave-particle duality in orbital angular momentum-based quantum delayed-choice experiment
Da-Wei Lyu, Qian-ke Wang, Jun Liu, Jian Wang
Abstract
Wave-particle duality is a foundational feature of quantum mechanics and can be demonstrated via delayed-choice and quantum delayed-choice (QDC) experiments. Photon-based implementations commonly rely on polarization or path degrees of freedom (DoFs), but these approaches present limitations: polarization is restricted to two dimensions, and the path-based schemes, although scalable, face increasing challenges in optical complexity and interferometric stability as the dimensionality grows. Here, we present a scalable QDC scheme leveraging the orbital angular momentum (OAM) of photons that overcomes these limitations. Instead of directly encoding paths in OAM states, we encode qubits in subsystems of the OAM DoF—specifically its signs and amplitudes—and realize a controlled-Hadamard gate with 98.73(2)% fidelity on these qubits using a diffractive neural network. This allows us to demonstrate the QDC experiment within the OAM subsystems and observe interference transitions between wave-like and particle-like behaviors in the space structured by these subsystems, with fidelities exceeding 99%. Our results show that wave-particle duality extends beyond intrinsic DoFs to qubits encoded in internal substructures of those DoFs, offering a broader perspective on the fundamental nature of quantum behavior.