Technically its called a "baffle gate", but not many people know that, not even native speakers. People just refer to them as "ticket gates" or even just "gates". For example: "I missed my train, because my ticket wouldn't work at the gate", people will infer from context what kind of gate you're talking about. If they have a rotating bar (like this: https://5.imimg.com/data5/TN/LQ/MY-9772935/turnstyle-tripod-with-access-card-500x500.jpg ) instead of sliding doors, then its called a "turnstyle"