Generation of Femtosecond Optical Vortices Entanglement

Femtosecond optical vortices feature helical phase fronts within their transverse modes and also display a fixed phase difference among the longitudinal modes. This multi‐dimensional manipulation of femtosecond laser pulses forms a fundamental basis for various applications. While multiple techniques exist for generating traditional femtosecond optical vortices, a notable void persists in the domain of continuous‐variable entanglement. This letter introduces the demonstration of femtosecond optical vortices entanglement accomplished through the synchronously pumped optical parametric oscillator, which is designed with a nonplanar ring cavity to compensate for astigmatism without introducing additional dispersion. The generated light field exhibits both temporal multimode structures, manifested as supermodes in the femtosecond optical frequency comb, and spatial multimode structures carrying orbital angular momentum. Orbital angular momentum entanglement is clearly observed in the first three‐order supermodes. The femtosecond optical vortices entanglement, serving as a precursor of potential, holds the crucial key to unlocking enhanced capabilities in advanced information processing, securing quantum communication, and even paving the way for the realization of multi‐parameter quantum metrology.