  Unveiling the emergence and prevalence of massive/bright galaxies during the
epoch of reionization and beyond, within the first 600 million years of the
Universe, stands as a pivotal pursuit in astronomy. Remarkable progress has
been made by JWST in identifying an immense population of bright galaxies,
which hints at exceptionally efficient galaxy assembly processes. However, the
underlying physical mechanisms propelling their rapid growth remain unclear.
With this in mind, millimeter and submillimeter-wave spectroscopic observations
of redshifted far-infrared spectral lines, particularly the [O III] 88 micron
and [C II] 158 micron lines, offers a crucial pathway to address this
fundamental query.
  To this end, we develop a dual-polarization sideband-separating
superconductor-insulator-superconductor (SIS) mixer receiver, FINER, for the
Large Millimeter Telescope (LMT) situated in Mexico. Harnessing advancements
from ALMA's wideband sensitivity upgrade (WSU) technology, FINER covers radio
frequencies spanning 120-360 GHz, delivering an instantaneous intermediate
frequency (IF) of 3-21 GHz per sideband per polarization, which is followed by
a set of 10.24 GHz-wide digital spectrometers. At 40% of ALMA's
light-collecting area, the LMT's similar atmospheric transmittance and FINER's
5 times wider bandwidth compared to ALMA culminate in an unparalleled spectral
scanning capability in the northern hemisphere, paving the way for finer
spectral-resolution detection of distant galaxies.
