CMB-S4 is the next-generation ground-based cosmic microwave background experiment.  With arrays of large- and small-aperture telescopes surveying the sky with hundreds of thousands of cryogenically-cooled superconducting detectors, CMB-S4 will deliver transformative discoveries in fundamental physics, cosmology, astrophysics, and astronomy.   Berkeley Lab is the lead laboratory for CMB-S4, and our group holds key roles across many aspects of the experiment.

Staff: Julian Borrill, Simone Ferraro, John Groh, Adrian Lee, Aritoki Suzuki, Clara Verges

Detecting or setting stringent upper limits on the energy scale of inflation is one of the biggest challenge of modern cosmology, and the key science goal of CMB-S4 ultra-deep survey. The success of this survey hinges on exquisite sensitivity and control of astrophysical and instrumental biases. We are strongly involved in performance forecasting for the experiment, which includes the development of component separation technique, to separate the CMB signal from the galactic foregrounds, as well as instrumental systematic studies, to set design and calibration requirements that will ensure the success of the survey.  We also work on CMB lensing reconstruction and delensing, which is crucial to revealing the inflationary signature in the CMB polarization.

While the focus of our group is on the CMB-S4 project, our members are also involved in Stage-3 CMB experiments, as the design of CMB-S4 must be guided by results, developments, and lessons learned from prior and ongoing experiments.  We are involved in the Simons Observatory, located in the Chilean Atacama,  that has started observations in 2023, and in the BICEP/Keck program, which has been operating telescopes at the South Pole for over 15 years. 

Staff: Julian Borrill, Simone Ferraro, John Groh, Adrian Lee, Aritoki Suzuki, Clara Verges

We are active in the analysis of current and future CMB data, as well as the development of new techniques to reduce possible astrophysical or instrumental systematic effects, while maximizing the amount of information that we can extract.  Secondary anisotropies, such as gravitational lensing by large-scale structure and the Sunyaev-Zel'dovich effect, allow us to use the CMB as a "backlight" revealing hidden matter in and around cosmic structures.  We use a variety of advanced statistical methods as well as Artificial Intelligence and Machine Learning approaches.  We often  analyze data from the Atacama Cosmology Telescope and will soon from the Simons Observatory's Large Aperture Telescope.

Staff: Simone Ferraro

Another major area of research is joint analyses with Large-Scale Structure surveys such as DESI and Rubin Observatory, among others. They can break important degeneracies between cosmological and astrophysical effects and probe the growth and evolution of structure across cosmic time, provide insights on the masses of neutrinos, and test our theories of how gravity works on the largest scales.

Staff: Simone Ferraro

Teasing the tiny cosmological signals out of massive CMB datasets requires a significant effort in simulating and analyzing the raw time-ordered data. This includes both the design of the algorithms and in their implementation on the most massively-parallel supercomputers. For 30 years, Physics and Computational Science staff in the Computational Cosmology Center have developed the necessary simulation and reduction tools, deployed them on the available resources (most notably the NERSC supercomputers), and applied them to data from satellite (Planck), balloon (BOOMERanG, MAXIMA), and ground-based (POLARBEAR, Simons Observatory, CMB-S4) experiments.

Staff: Julian Borrill, Reijo Keskitalo (Computational Science), Ted Kisner (Computional Science)

Superconducting Transition-edge sensors (TES) detectors have been the gold standard for highly-scalable background-limited detection of CMB radiation for several decades.  The Berkeley CMB group has a long history of key developments in CMB detector technology.  We have designed and delivered detectors for several generations of CMB experiments, and are currently leading the detector design and fabrication efforts for CMB-S4.  Other areas of focus include developing novel TES thin film materials and working with industry partners to increase fabrication throughput.

Staff: Adrian Lee, Aritoki Suzuki

Degree-scale CMB polarization anisotropies require extremely sensitive telescopes with well-controlled systematics.  To that end, we are developing telescopes with ~0.5 m diameter apertures that are appropriate for the large angular scales targeted by the CMB-S4 inflation survey.  As a key input to this process, we are also commissioning and analyzing data from similar telescopes in the Simons Observatory and BICEP Array.

Staff: John Groh, Adrian Lee, Aritoki Suzuki, Clara Verges

The scalability of the transition-edge sensor detectors used for CMB measurements is limited by their associated readout electronics .  Multiplexed readout is therefore a key enabling technology for current and future CMB experiments.  The Berkeley Lab group has developed and delivered multiplexed readout systems with several different architectures for several generations of CMB experiments, and continues to develop advanced readout schemes for future telescopes.  We are also studying how multiplexer systematic effects such as cross-talk manifest in observatory data.

Staff: John Groh, Adrian Lee, Aritoki Suzuki