  Based on lattice non-relativistic QCD (NRQCD) studies we present results for
Bethe-Salpeter amplitudes for $\Upsilon(1S)$, $\Upsilon(2S)$ and $\Upsilon(3S)$
in vacuum as well as in quark-gluon plasma. Our study is based on 2+1 flavor
$48^3 \times 12$ lattices generated using the Highly Improved Staggered Quark
(HISQ) action and with a pion mass of $161$ MeV. At zero temperature the
Bethe-Salpeter amplitudes follow the expectations based on non-relativistic
potential models. At non-zero temperatures, the interpretation of
Bethe-Salpeter amplitudes turns out to be more nuanced, but consistent with our
previous lattice QCD study of excited Upsilons in quark-gluon plasma.
