  We report neutron scattering, pressure-dependent AC calorimetry, and AC
magnetic susceptibility measurements of triangular lattice NaYbSe$_2$. We
observe a continuum of scattering, which is reproduced by matrix product
simulations, and no phase transition is detected in any bulk measurements.
Comparison to heat capacity simulations suggest the material is within the
Heisenberg spin liquid phase. AC Susceptibility shows a significant 23~mK
downturn, indicating a gap in the magnetic spectrum. The combination of a gap
with no detectable magnetic order, comparison to theoretical models, and
comparison to other $A$YbSe$_2$ compounds all strongly indicate NaYbSe$_2$ is
within the quantum spin liquid phase. The gap also allows us to rule out a
gapless Dirac spin liquid, with a gapped $\mathbb{Z}_2$ liquid the most natural
explanation.
