Before you can get in, you need to go to Four Island and help Lorelei defeat Team Rocket there. After that the man in front of the door will move, then you must Cut the door down, go down the holes that the Braille in the middle of the room indicates, and try to retrieve the Sapphire. Then that man will steal it and go to Team Rocket's Warehouse on Five Island, but he'll give you the second password to enter it.