It really depends on how the teleportation works. If it’s folding spacetime to make it so that I can step instantaneously through the gap, that’s definitely still me. If it’s just like a portal cutting temporarily through Hell ala WH40k or Event Horizon, it’s probably still me, but I might be suffering from demonic posession. If I’m being completely atomized, converted to electricity, and transmitted to the other tube to be reconstituted as an exact copy, then I am a copy.