Another way you can do this would be use the special $'string' expansion which is treated specially and expands string with backslash-escaped characters replaced as specified by the ANSI C standard (see under QUOTING of the bash(1) man page for more info).

You could therefore do something like this:
  grep "first"$'\t'"second" file.txt

This is also REALLY useful for weird characters (it supports \nnn, \U (unicode)) etc and the like.