James J. (Jamie) Bock
Research InterestsExperimental Cosmology
- Gruber Foundation Cosmology Prize (Planck team), 2018
- AAS Joseph Weber Award for Astronomical Instrumentation, 2016
- NASA Distinguished Service Medal, 2014
- SPIE George W. Goddard Award, 2014
- Jet Propulsion Laboratory Fellow, 2012
- NASA Exceptional Technology Achievement Medal, JPL 2009
- Presidential Early Career Award for Scientists and Engineers, 2001
- NASA Exceptional Achievement Medal, JPL 2000
My research program develops unique experiments to study the early universe.
The cosmic microwave background comes from the time photons last substantially interacted with matter in the universe, when free electrons and protons combined to form neutral hydrogen. Measurements of the minute temperature variations on the CMB give us a snapshot of the universe at this time called recombination, about 380,000 years after the Big Bang. CMB temperature variations are sensitive to the geometry and composition of the universe, and serve as the experimental foundation for our modern conception of cosmology. The figure below shows the all-sky measurement of spatial fluctuations at 143 GHz from the Planck satellite. The variations are dominated by the CMB over most of this image, except in the plane of the Galaxy visible as the stripe across the center. These state of the art CMB measurements were enabled by novel low-temperature bolometers developed by our group at Caltech and JPL.
CMB polarization may allow us to probe the state of the universe at even earlier times. Inflation is an exponential expansion of space-time that occurred a small fraction of a second after the Big Bang. Conceived in the 1980s, the theory of inflation was motivated to explain the approximate flatness of the universe and the extreme spatial uniformity of the CMB. Inflation is likely the outcome of exotic physics, such as a phase transition associated with GUT energy scales. In the intervening 3 decades, increasingly capable CMB experiments have verified the spatial power, statistics, and polarization signatures predicted by basic models of inflation. Inflation also can produce a background of gravitational waves, with an amplitude that depends on the physical process driving inflation. These gravitational waves leave fingerprints in the CMB in a polarization pattern with a distinctive curl property that changes sign when viewed in a mirror.
The experimental cosmology group is leading a new generation of instruments to search for inflationary polarization. The BICEP Array (above) is the latest phase of the experiment, which is developing a new generation of powerful receivers at 30/40, 95, 150 and 220/270 GHz for observations from the South Pole, an excellent site for millimeter-wave measurements. The first of these receivers has been observing at 30/40 GHz since 2020. The new receivers build upon state-of-the-art polarization data obtained from BICEP3 and the previous-generation Keck Array which lead the field in constraints on inflationary polarization. BICEP Array has started a collaboration with the South Pole Telescope, providing access to arcminute polarization data and to remove the gravitational lensing polarization signal to reach higher levels of sensitivity. We are now in a very exciting phase of this program, achieving sensitivity levels that will either detect inflationary polarization or supply new constraints on inflationary theory.
The group is developing new detector technology for the large array formats needed for the next generation of experiments. The detectors use an inductor in a resonating circuit to sense the temperature of a bolometer. Thermally-generated quasi-particles change the inductance. These Thermal Kinetic Inductance Detectors (TKIDs) are similar to photon-coupled KID devices, but can be better optimized for noise performance. Single devices have achieved photon-limited noise performance to the ~0.1 Hz frequencies needed for CMB observations. Hundreds of TKIDs can be multiplexed on a single coax cable, scaling to large formats much more gracefully than current SQUID-based multiplexors. A prototype camera operating TKID arrays is currently in development.
I am the principal investigator of SPHEREx, a mission selected by NASA as a Medium Explorer in February 2019, designed to map the entire sky in near-infrared spectroscopy. SPHEREx, expected to launch in the 2024-25 timeframe, will probe the physics of inflation by measuring non-Gaussianity by studying large-scale structure, surveying a large cosmological volume and complementing high-z surveys optimized to constrain dark energy. Non-Gaussianity tests if inflation was driven by multiple fields, complementing the CMB polarization measurements generally related to single-field inflation. The origin of water and biogenic molecules will be investigated in all phases of planetary system formation - from molecular clouds to young stellar systems with protoplanetary disks - by measuring ice absorption spectra. SPHEREx will chart the origin and history of galaxy formation through a deep survey mapping large-scale spectro-spatial power in two deep fields located near the ecliptic poles. SPHEREx will create spectra (0.75 – 5 um at R = 35-130) with high sensitivity using a cooled telescope with a wide field-of-view for large mapping speed. With over a billion detected galaxies, hundreds of millions of high-quality stellar and galactic spectra the archive will enable diverse scientific investigations and enable many synergistic analysis with other large scale structure surveys over the next decade. SPHEREx also presents future opportunities for line-intensity mapping measurements and further tests of cosmology in conjunction with next-generation CMB experiments.
Members of the group also have access to two specialized experiments developing the method of ‘intensity mapping', using information in the spatial structure of intensity variations to measure galaxy clustering. The key here is that intensity mapping uses a small wide-field instrument to map large-scale structure, instead of a large telescope to detect individual galaxies. The CIBER2 sounding rocket experiment applies intensity mapping to study the near-infrared extragalactic background, measuring background fluctuations in 6 infrared/optical bands to constrain the cosmic history of energy released by star formation, and searching for the background associated with first stars during the epoch of reionization. TIME studies fluctuations in line emission from singly ionized carbon, redshifted from 158 um rest frame into the millimeter-wave. Measuring fluctuations in line emission gives 3-dimensional information in redshift slices. TIME seeks to detect C+ fluctuations from the epoch of reionization, using a stack of novel 2-dimensional waveguide grating spectrometers to perform millimeter-wave imaging spectroscopy.
Additional info can be found on the Observational Cosmology Group web page.