If atoms can be in two places at one time, why can't we use this to travel through space instantly?

Atoms are too large to be in two places 'at once'.

There are no known physical systems, larger than single photons or electrons to my knowledge, that behave this way.

The possible exception is electrons inside an atom which have 'clouds of probability', and are not localizable to a specific location in space without performing some type of observation. Until they are 'observed', they can in some sense be said to be in many locations 'at once', although that is a rather sloppy and colloquial way to describe the details.

Copyright 1997 Dr. Sten Odenwald