Associate Professor of Physics and Astronomy
Cosmology, astrophysics, and fundamental physics: studying inflation, dark energy, dark matter, neutrinos, galaxy clusters, and galaxy evolution using cosmic microwave background and sub-mm measurements. Detector arrays and applied superconductivity: low-temperature detector arrays, superconducting detectors, transition-edge sensor bolometers, SQUID measurement systems, device physics, sub-Kelvin refrigeration. Astronomical optics and receivers: optics design, optical coatings, material properties, cryogenic instruments.
Our research focuses on developing new instrumentation to study the formation and evolution of the universe through precision measurements of microwave radiation. Past measurements of the cosmic microwave background (CMB) provided an exquisite picture of the early universe, which combined with astronomical observations at other wavelengths led to strong evidence that we live in a dark energy and dark matter dominated universe; however, we still do not fully understand fundamental aspects of the universe. What are dark energy and dark matter? Did inflation occur in the early universe, and can we understand it? How did the primordial fluctuations evolve into galaxies, stars, and planets? What physical models best describe the past, present, and future of the cosmos?
The instruments we develop help address aspects of these questions through more sensitive observations at millimeter and sub-millimeter wavelengths. We survey the CMB temperature and polarization in unprecedented detail, enabling a wide range of science objectives, including: new constraints on the physics of inflation, new probes of dark energy and modified gravity, characterization of the dark matter distribution, measurements of the neutrino mass sum, and the discovery of both galaxy clusters and high-redshift galaxies.
In 2008 observations began with the six-meter Atacama Cosmology Telescope (ACT), located at 5190 meters elevation in the Chilean desert. The ACT data has led to a variety of results, including first detections of the power spectrum of CMB gravitational lensing as well as the kinematic Sunyaev-Zel'dovich effect. We are now working on ACTPol - the first polarization sensitive receiver for ACT - and the Advanced ACTPol upgrade. We are working on characterizing the instrument, running observations, developing detectors and instrumentation for the Advanced ACTPol upgrade, and analyzing ACTPol data, including cross-correlating the data with measurements from other observatories that span the electromagnetic spectrum. We are also collaborating on the upcoming CCAT-prime, Simons Observatory, and CMB-S4 projects to measure the CMB with far better sensitivity than the ACT.
Another exciting aspect of our research is that advances in millimeter and sub-millimeter radiation measurements are largely being driven by the development of new superconducting and optical techniques. We have helped to design, build, and deploy some of the largest arrays of superconducting detectors yet, with thousands of transition-edge sensor (TES) detectors cooled to sub-Kelvin temperatures. TES detectors are becoming a widely used technology spanning eight orders of magnitude in detection energy (from CMB bolometers to gamma ray microcalorimeters). Arrays of TESes are generally measured using multiplexed superconducting quantum interference devices (SQUIDs). We are working on new detector and SQUID measurement technologies to enable readout of even larger superconducting detector arrays, and are developing new optics and instrument designs to couple to these arrays in next generation observatories. We also work in the Cornell Nanoscale Facility developing new optics and detector microfabrication techniques that can be tested and integrated in our laboratory.
Steve K. Choi, Matthew Hasselfield, Shuay-Pwu Patty Ho, Brian Koopman, et al. "The Atacama Cosmology Telescope: A Measurement of the Cosmic Microwave Background Power Spectra at 98 and 150 GHz” (2020). arXiv:2007.07289
T. Herter, et al. "The CCAT-Prime Submillimeter Observatory," Decadal Survey white paper (2019). arXiv:1909.02587
P. A. Gallardo, N. F. Cothard, R. Puddu, R. Dunner, B. J. Koopman, M. D. Niemack, S. Simon, E. J. Wollack "Far sidelobes from baffles and telescope support structures in the Atacama Cosmology Telescope," Proc. SPIE 10708, 107083Y (2018). SPIE , arXiv:1808.05101
A. Mittal, F. de Bernardis, M. D. Niemack "Optimizing measurements of cluster velocities and temperatures for CCAT-prime and future surveys," Journal of Cosmology and Astroparticle Physics (2018). arXiv:1708.06365
F. De Bernardis, S. Aiola, E. M. Vavagiakis, M. D. Niemack, N. Battaglia, et al. Detection of the pairwise kinematic Sunyaev-Zel'dovich effect with BOSS DR11 and the Atacama Cosmology Telescope, arXiv:1607.02139 (2016). arXiv
S. Naess, M. Hasselfield, J. McMahon, M. D. Niemack, et al. The Atacama Cosmology Telescope: CMB Polarization at 200ℓ9000, Journal of Cosmology and Astroparticle Physics 10, 007 (2014). JCAP link , arXiv