Photonic quantum walk with ultrafast time-bin encoding

The quantum walk (QW) has proven to be a valuable testbed for fundamental inquiries in quantum technology applications such as quantum simulation and quantum search algorithms. Many benefits have been found by exploring implementations of QWs in various physical systems, including photonic platforms. Here, we propose a platform to perform quantum walks based on ultrafast time-bin encoding (UTBE) and all-optical Kerr gating. This platform supports the scalability of quantum walks to a large number of steps and walkers while retaining a significant degree of programmability. More importantly, ultrafast time bins are encoded at the picosecond time scale, far away from mechanical fluctuations. This enables the scalability of our platform to many modes while preserving excellent interferometric phase stability over extremely long periods of time without requiring active phase stabilization. Our 18-step QW is shown to preserve interferometric phase stability over a period of 50 h, with an overall walk fidelity maintained above 95%.