The precise characterization of the polarized fluctuations of the 3K Cosmic Microwave Background (CMB) appears today to be a major scientific challenge to further progress in the understanding of the primordial Universe. The so-called cosmological B modes in the CMB polarization are thought to have been generated by inflation in the very early Universe and would provide unique information about the origin of the Universe and fundamental laws of physics at very high energies. The weakness of the expected signals, a few nK for the B-Mode, requires a detection chain which must be highly sensitive together with an extreme immunity to instrumental systematic effects that are generally higher by a few orders of magnitude.

CMB-S4 (stage 4) is a 4th generation ground based instrument aiming at observing the polarized sky and especially the CMB with ultimate sensitivity. To achieve this goal, the experiment will use about 500 000 cryogenic detectors distributed over 85 optics tubes deployed on a multiple small (SAT) and large (LAT) aperture telescopes, which will operate from Chile and Antarctica. This will make it the largest and most advanced CMB observatory ever constructed. CMB-S4 has recently been ranked as the top priority for the next decade by the US Particle Physics Project Prioritization Panel (P5).

The detection chain will be based on Transition Edge Sensor arrays cooled to 100mK and readout in a Time Domain Multiplexing scheme using Superconducting Quantum Interference Devices (SQUIDs). This detection chain requires advanced, low-noise readout electronics that is being designed. As part of this effort, the APC team in collaboration with Stanford and Berkeley is studying the warm front-end readout electronics. An Application Specific Integrated Circuit (ASIC) developed for another project will be tested with S4 prototype detectors before designing a specific ASIC for CMB-S4. A prototype of this detection chain will be installed and tested at APC in a dilution fridge. The Ph.D student will take part of this development phase together with characterizations. The research activity will be done in the context of a collaboration with SLAC on the CMB S4 warm front-end read-out, and also with Berkeley Lab and UC Berkeley on the detection chain and the CMB S4 instrument. The modeling of the detection chain including the readout system will also be developed to be integrated in the CMB-S4 simulation pipeline in order to check for potential systematic effects. 

This PhD is funded through a CNRS international program. The PhD student is expected to share work between APC in Paris and Centre Pierre Binetruy in Berkeley as a function of project needs.