University of Wisconsin-Madison Skip navigationDepartment of PhysicsSearchSite MapUW Home
 

 

UW Madison Homepage

 

Home

-----------------

Group Members

-----------------

Introduction to Cosmology

-----------------

Research Projects

-----------------

Scientific Papers

-----------------

Prospective Students

-----------------

For the Public

-----------------

Related Links

-----------------

Journal Club

Current Research Projects

Our research centers on precision measurements in observational cosmology.


Systematic Errors in CMB Power Spectra

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. Measuring the CMB polarization has become one of the major goals of CMB experiments. However, the polarized CMB signal is so small that its measurement requires not only very high instrumental sensitivity, but also exquisite control of systematics. In collaboration with Greg Tucker's group at Brown University, Ben Wandelt's group at the Institut d'Astrophysique (Paris) and Ted Bunn's group at University of Richmond, we are building a suite of simulation software to simulate CMB interferometric observations and to assess various systematic errors in CMB power spectra estimates by using maximum likelihood method and Gibbs sampling technique.

Kinetic Inductance Detectors for QUBIC

Kinetic Inductance Detectors (KIDs) use small superconducting resonant circuits to detect incident photons (P.K. Day, Nature (2003)). 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, critical temperature tolerance, and focal plane coverage. QUBIC is a planned CMB polarization telescope designed to search for the primordial B-mode anisotropy, a smoking gun for inflation. It will be deployed at the Concordia station in Antarctica in 2015.

3D 21 cm Simulations

We are developing general-purpose software to model systematic effects in interferometers to address three important issues facing interferometers consisting of hundreds to thousands of antennas. First, we will develop calibration algorithms, which require measuring the complex beam gain of each element as a function of frequency. Second, we will develop analysis techniques for large "data cubes" for removing foreground sources and recovering cosmological power spectra. Third, we will extend our simulation techniques for modeling and controlling systematic effects.

21 cm Tomography


Beam Pattern Measurements

We fabricated a model antenna in an effort to assist the experimental efforts on low redshift, 21cm intensity mapping observations for dark energy measurements as part of the Tianlai Project. Using LabVIEW automated instrument readout, we are testing the response of the model antenna in various locations. We hope to compare the beam pattern measurement of our antenna to that shown in CST simulations.

Low-temperature Heat Switch Design

Our research is motivated by precision control of heat flow in ultra-low temperature experiments. Specifically, the experiments in our lab are run at temperature of approximately 100 millikelvin. In order to reach the extremely low temperatures, an adiabatic demagnetization refrigerator (ADR) must be used. 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.


Past Projects

MBI: The Millimeter Wave Bolometric Interferometer
THM: A Transition-Edge Hot-Electron Microbolometer
Big Bang Blackbody Simulator
Stereolithographed Microwave Components
WSTAR
Giant Microwave Window
COMPASS: The first CMB polarization telescope optimized specifically for CMB polarization measurements at small angular scales
POLAR : A telescope optimized specifically for CMB polarization at large angular scales
TopHat
MSAM II
Neutron Calorimeter: for precision measurements of the energy spectrum of neutrons
Miniature Adiabatic Demagnetization Refrigerator
 


Last updated: 1/14
 

  © Website Admin: Peter Timbie | Contact: pttimbie@wisc.edu Top of Page