  We report 31 GHz CARMA observations of IDCS J1426.5+3508, an
infrared-selected galaxy cluster at z = 1.75. A Sunyaev-Zel'dovich decrement is
detected towards this cluster, indicating a total mass of M200 = (4.3 +/- 1.1)
x 10^{14} Msun in agreement with the approximate X-ray mass of ~5 x 10^{14}
Msun. IDCS J1426.5+3508 is by far the most distant cluster yet detected via the
Sunyaev-Zel'dovich effect, and the most massive z >= 1.4 galaxy cluster found
to date. Despite the mere ~1% probability of finding it in the 8.82 deg^2 IRAC
Distant Cluster Survey, IDCS J1426.5+3508 is not completely unexpected in LCDM
once the area of large, existing surveys is considered. IDCS J1426.5+3508 is,
however, among the rarest, most extreme clusters ever discovered, and indeed is
an evolutionary precursor to the most massive known clusters at all redshifts.
We discuss how imminent, highly sensitive Sunyaev-Zel'dovich experiments will
complement infrared techniques for statistical studies of the formation of the
most massive galaxy clusters in the z > 1.5 Universe, including potential
precursors to IDCS J1426.5+3508.
