The SPT-3G+ Experiment: Science Goals and Current Status of MKID Development

I will present an overview of the design and science goals of SPT-3G+, the fourth-generation survey camera for the South Pole Telescope (SPT) and then discuss the development of microwave kinetic inductance detectors (MKIDs) for SPT-3G+. The SPT is a 10-meter submillimeter (sub-mm) quality telescope designed to observe the cosmic microwave background (CMB), which has undertaken a series of large area mm-wavelength surveys (SPT-SZ, SPTpol, SPT-3G). The SPT-3G+ receiver is designed measure polarized light at 220, 285, and 345 GHz, and will map 1500 sq. degrees of sky, overlapping with the existing SPT-3G and BICEP Array surveys. The science goals for the SPT-3G and SPT-3G+ combined data sets include: constraining reionization through measurements of the kinematic Sunyaev-Zel'dovich effect, improving constraints on inflation through characterization of polarized galactic dust, extending SPT astrophysical transient observations into the sub-mm, and potentially observing the first Rayleigh scattering of the CMB off of neutral hydrogen in the early universe, which would provide constraints on recombination. The necessary sensitivity for this instrument will be achieved using MKIDs, which are highly multiplexable, allowing for high detector density in the focal plane.