Superconducting Antenna-Coupled Detectors and Readouts for CMB polarimetry in PICO

We propose to develop high-sensitivity millimeter-wave detector arrays for CMB polarimetry. The detector arrays use planar antennas to implement optical coupling, polarization discrimination, and spectral band definition. The array architecture relies exclusively on lithographed thin film structures and eschews three-dimensional and massive fore-optics such as contacting lenses or feed horns. The antenna arrays’ coherent microstrip feeds can tailor synthesized beams that would not be possible with lenses and feed horns. In particular, antenna arrays can couple to top-hat (uniform) illuminations resulting in substantially higher packing of pixel densities than can be achieved with coupling optics with Guassian profiles. The received optical signals couple to transition-edge sensor (TES) bolometers, read with multiplexed SQUID current amplifiers This program will advance technology readiness for the Inflation Probe mission in NASA's Physics of the Cosmos (PCOS) program and specifically the NASA PICO mission, recently studied by an international team of CMB scientists. PICO is a fourth-generation CMB satellite that will measure the polarization of the CMB to astrophysical limits, characterizing the inflationary potential, mapping large scale structure through polarization induced by gravitational lensing, and mapping the Galactic magnetic fields through polarized emission of galactic dust. Gravitational waves produced in the early universe's inflationary expansion may have generated detectable odd symmetry B-mode polarization patterns in the CMB whose amplitude can constrain inflation's energy scale. These degree-scale B-modes are distinct from the even symmetry E-modes sourced by inflationary scalar field variations. Intervening large scale structure also induces arcminute B-modes, spatially correlated at degree scales. This large scale structure is sensitive to the dark energy equation of state and the neutrino mass hierarchy. Observations with these detectors in suborbital experiments have placed the world's leading constraints on inflationary B-modes, limiting r<0.06. Ground based experiments using these detectors have demonstrated precise control of systematic errors subdominant to statistical errors. The achieved map depths on small patches of the sky are comparable to PICO's target depths over the entire sky. In a long duration balloon flight in 2015, these detectors demonstrated instantaneous sensitivity, stability, and cosmic ray immunity approaching PICO's needs. New arrays at 220 and 270GHz are now providing the most sensitive characterization of galactic dust through millimeter wave polarization. Beginning in 2020, new 30GHz and 40GHz arrays will produce the most sensitive characterization of galactic synchrotron emission through millimeter wave polarization. We propose to advance specific aspects of the detectors to ensure their technology readiness for space applications, including both PICO and other international satellite opportunities. We will increase pixel densities with circular footprint antennas, we will extend the range of multi-color pixels into the mid-frequency range with 150-220GHz dual color prototypes, we will develop 100mK bolometers and test cosmic ray susceptibility, we will modify our time division readout system to read 128 rows in a set with a chopped voltage bias, and we will demonstrate arrays of antenna-coupled TKIDs as an enhancing technology for PICO.

The Strategic Astrophysics Technology program (SAT) supports focused development efforts for key technologies to the point at which they are ready to feed into major missions in the three science themes of the Astrophysics Division: Exoplanet Exploration, Cosmic Origins, and the Physics of the Cosmos. This program is specifically designed to address middle technology readiness level (TRL) "gaps" between levels 3 and 6: the maturation of technologies that have been established as feasible, but which are not yet sufficiently mature to incorporate into flight missions without introducing an unacceptable level of risk. NASA does not require a data management plan for proposals to SAT.

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