  A scintillating bolometer based on a large cubic Li$_{2}$$^{100}$MoO$_4$
crystal (45 mm side) and a Ge wafer (scintillation detector) has been operated
in the CROSS cryogenic facility at the Canfranc underground laboratory in
Spain. The dual-readout detector is a prototype of the technology that will be
used in the next-generation $0\nu2\beta$ experiment CUPID. The measurements
were performed at 18 and 12 mK temperature in a pulse tube dilution
refrigerator. This setup utilizes the same technology as the CUORE cryostat
that will host CUPID and so represents an accurate estimation of the expected
performance. The Li$_{2}$$^{100}$MoO$_4$ bolometer shows a high energy
resolution of 6 keV FWHM at the 2615 keV $\gamma$ line. The detection of
scintillation light for each event triggered by the Li$_{2}$$^{100}$MoO$_4$
bolometer allowed for a full separation ($\sim$8$\sigma$) between
$\gamma$($\beta$) and $\alpha$ events above 2 MeV. The Li$_{2}$$^{100}$MoO$_4$
crystal also shows a high internal radiopurity with $^{228}$Th and $^{226}$Ra
activities of less than 3 and 8 $\mu$Bq/kg, respectively. Taking also into
account the advantage of a more compact and massive detector array, which can
be made of cubic-shaped crystals (compared to the cylindrical ones), this test
demonstrates the great potential of cubic Li$_{2}$$^{100}$MoO$_4$ scintillating
bolometers for high-sensitivity searches for the $^{100}$Mo $0\nu2\beta$ decay
in CROSS and CUPID projects.
