Presumably the controller will be a PC, the program running in the PC will verify the swipe card is correct, and then send a signal telling the gate to open - plus it would store the card details and the time of entry. How you actually open the gate depends on how you want to - but I would suggest sending serial data from the PC and using a PIC near the gate to respond to it, and switch a relay that opens the gate.
If you don't want to record any details, you could do it all in a PIC, read the data, verify it, and open the gate.