Quantum to classical walk transitions tuned by spontaneous emissions

We have realized a quantum walk in momentum space with rubidium spinor Bose-Einstein condensate by applying periodic kicking potential as operator and resonant microwave pulse coin toss operator. The generated walks appear to be stable for up ten steps then quickly transit classical due spontaneous emissions induced laser beams of the investigate these transitions introducing well-controlled an external light source during walks. Our findings demonstrate scheme control robustness can also applied other cold atom experiments involving emissions.