Current Research Projects
Our research group of faculty, graduate students, postdocs and undergraduates studies the universe on the largest scales
and earliest times possible. In particular, we make maps of the cosmic microwave background radiation to attempt to learn
about the inflationary epoch during the first fraction of a second. And we use the 21 cm emission from neutral hydrogen gas
as a tool to make three-dimensional maps of the cosmos during the more recent epoch when the mysterious dark energy started
the accelerated expansion of the universe.
Cosmic microwave background (CMB) polarization measurements can give us extremely valuable information about our universe. Measurements
of these faint signals will play a major role in understanding the inflationary epoch and the distribution of matter and the evolution of
large scale structure. Arrays of thousands of background-limited detectors are required. Our approach involves Kinetic Inductance Detectors
(KIDs), which use small superconducting resonant circuits to detect incident photons (P.K. Day, Nature (2003)). The photons are absorbed,
breaking Cooper pairs and causing a change in the kinetic inductance which results in a shift in the resonant frequency of the circuit. KIDs
offer significant advantages over competitor detectors in terms of multiplexing, fabrication, and critical temperature tolerance.
The most significant challenge to 21 cm observations is extracting the small cosmological signal from strong foreground emission from our
Galaxy. We are developing general-purpose software that distinguishes the foregrounds from signal based on their differing statistics.
Over the past few years we have used the Green Bank Telescope in Green Bank, West Virginia, and the Parkes Radio Telescope in Australia
to map the 21 cm structure in the redshift range from 0.6 - 1.0 and from 0.054 - 0.107, respectively.
We are developing three new instruments optimized for 21 cm intensity mapping measurements. These are arrays of sensitive radio receivers
operating at a few hundred megahertz. Modeling the beam patterns of these arrays as function of frequency is essential for recovering
three-dimensional maps without systematic effects.
Much of our research requires cooling detectors to low temperatures. Specifically, the experiments in our lab are cooled to temperatures of
approximately 100 millikelvin using an adiabatic demagnetization refrigerator (ADR). However, in the process of using the ADR, residual heat
is generated which must be drawn off to a cold bath. The device used to connect and disconnect the salt pill to the cold bath, in our case a
helium bath, is called a heat switch. We developed a mechanical heat switch that is powered by a stepper motor.
MBI: The Millimeter Wave Bolometric Interferometer
THM: A Transition-Edge Hot-Electron Microbolometer
Big Bang Blackbody Simulator
Stereolithographed Microwave Components
Giant Microwave Window
The first CMB polarization telescope optimized specifically for CMB polarization measurements at small angular scales
A telescope optimized specifically for CMB polarization at large angular scales
for precision measurements of the energy spectrum of neutrons
Miniature Adiabatic Demagnetization Refrigerator