  We report the discovery of an extremely young protostar, SMM11, located in
the associated submillimeter condensation SMM11 in the Serpens Main cluster
using the Atacama Large Millimeter/submillimeter Array (ALMA) during its Cycle
3 at 1.3 mm and an angular resolution of ~0.5"~210 AU. SMM11 is a Class 0
protostar without any counterpart at 70 um or shorter wavelengths. The ALMA
observations show 1.3 mm continuum emission associated with a collimated 12CO
bipolar outflow. Spitzer and Herschel data show that SMM11 is extremely cold
(T_bol=26 K) and faint (L_bol<~0.9 Lsun). We estimate the inclination angle of
the outflow to be ~80 deg, almost parallel to the plane of the sky, from simple
fitting using wind-driven-shell model. The continuum visibilities consist of
Gaussian and power-law components, suggesting a spherical envelope with a
radius of ~600 AU around the protostar. The estimated low C18O abundance,
X(C18O)=1.5-3x10^-10, is also consistent with its youth. The high outflow
velocity, a few 10 kms^-1 at a few 1000 AU, is much higher than theoretical
simulations of first hydrostatic cores and we suggest that SMM11 is a
transitional object right after the second collapse of the first core.
