  The Wideband Sensitivity Upgrade (WSU) is the top priority initiative for the
ALMA2030 Development Roadmap. The WSU will initially double, and eventually
quadruple, ALMA's system bandwidth and will deliver improved sensitivity by
upgrading the receivers, digital electronics and correlator. The WSU will
afford significant improvements for every future ALMA observation, whether it
is for continuum or spectral line science. The continuum imaging speed will
increase by a factor of 3 for the 2x bandwidth upgrade, plus any gains from
improved receiver temperatures. The spectral line imaging speed will improve by
a factor of 2-3. The improvements provided by the WSU will be most dramatic for
high spectral resolution observations, where the instantaneous bandwidth
correlated at 0.1-0.2 km/s resolution will increase by 1-2 orders of magnitude
in most receiver bands. The improved sensitivity and spectral tuning grasp will
open new avenues of exploration and enable more efficient observations. The
impact will span the vast array of topics that embodies ALMA's motto "In Search
of our Cosmic Origins". The WSU will greatly expand the chemical inventory of
protoplanetary disks, which will have profound implications for how and when
planets form. Observations of the interstellar medium will measure a variety of
molecular species to build large samples of clouds, cores and protostars. The
WSU will also enable efficient surveys of galaxies at high redshift. The first
elements of the WSU will be available later this decade, including a wideband
Band 2 receiver, a wideband upgrade to Band 6, new digitizers and digital
transmission system, and a new correlator. Other upgrades are under study,
including the newly developed ACA spectrometer and upgrades to Bands 9 and 10.
The gains enabled by the WSU will further enhance ALMA as the world leading
facility for millimeter/submillimeter astronomy. [Abridged]
