  Pre-stellar cores represent the initial conditions of star formation.
Although these initial conditions have been investigated in detail toward
low-mass pre-stellar cores, such initial conditions remain vastly unexplored
for massive star-forming regions. We report the detection of a cluster of
low-mass starless and pre-stellar core candidates in a massive protocluster
forming cloud, NGC6334S. With the ALMA observations at a $\sim$0.02 pc spatial
resolution, we identified 17 low-mass starless core candidates that do not show
any evidence of protostellar activity. These candidates present small velocity
dispersions, high fractional abundances of NH$_{2}$D, high NH$_{3}$ deuterium
fractionations, and are completely dark in the infrared wavelengths from 3.6 up
to 70~$\mu$m. Turbulence is significantly dissipated and the gas kinematics are
dominated by thermal motions toward these candidates. Nine out of the 17 cores
are gravitationally bound, and therefore are identified as pre-stellar core
candidates. The embedded cores of NGC6334S show a wide diversity in masses and
evolutionary stages.
