QUaD, an acronym for QUEST at DASI, was a ground-based cosmic microwave background (CMB) polarization experiment at the South Pole. QUEST was the original name attributed to the bolometer detector instrument, while DASI is a famous CMB interferometry experiment credited with the first detection of CMB polarization. QUaD used the existing DASI mechanical infrastructure but replaced the DASI interferometric array with a bolometer detector at the end of a cassegrain optical system. The mount has housed the Keck Array since 2011.