Quantum walk of light in frequency space and its controlled dephasing

We implement, using a coherent source, a coined quantum walk of light in frequency space in a tabletop experiment utilizing a series of modified Michelson interferometers that incorporate polarization optics and acousto-optic modulators. Manipulating the phase of the radio frequency that governs the acousto-optic interaction, we achieve symmetric or asymmetric quantum walks. Introducing rapid random phase shifts electronically, while regulating the amplitude, we cause controlled dephasing and thus simulate a gradual transition from the quantum walk to the classical random walk.