  We demonstrate the formation of a two-dimensional electron gas (2DEG) at the
$(100)$ surface of the $5d$ transition-metal oxide KTaO$_3$. From
angle-resolved photoemission, we find that quantum confinement lifts the
orbital degeneracy of the bulk band structure and leads to a 2DEG composed of
ladders of subband states of both light and heavy carriers. Despite the strong
spin-orbit coupling, our measurements provide a direct upper bound for
potential Rashba spin splitting of only $\Delta{k}_\parallel\sim\0.02$
\AA$^{-1}$ at the Fermi level. The polar nature of the KTaO$_3(100)$ surface
appears to help mediate formation of the 2DEG as compared to non-polar
SrTiO$_3(100)$.
