  Following the idea of nucleon clustering and light-nuclei production in
relativistic heavy-ion collisions close to the QCD critical-end point, we
address the quantum effects affecting the interaction of several nucleons at
finite temperature. For this aim we use the $K$-harmonics method to
four-nucleon states ($\alpha$ particle), and also develop a novel semiclassical
"flucton" method at finite temperature, based on certain classical paths in
Euclidean time, and apply it to two- and four-particle configurations. To study
possible effects on the light-nuclei production close to the QCD critical
point, we also made such calculations with modified internuclear potentials.
For heavy-ion experiments, we propose new measurements of light-nuclei
multiplicity ratios which may show enhancements due to baryon preclustering. We
point out the special role of the $\mathcal{O}(50)$ four-nucleon excitations of
$\alpha$-particle, feeding into the final multiplicities of $d,t$, $^3$He and
$^4$He, and propose to directly look for their two-body decays.
