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Colloquium Schedule

Spring 2020

Testing inflation and constraining cosmology with cosmic microwave background measurements

Kimmy Wu, University of Chicago
Tue., Feb. 11, 2020, 4:30 PM in Science Center 199

Inflation - the leading model for the earliest moments of the time, in which the Universe undergoes a period of rapid, accelerating expansion - generically predicts a background of primordial gravitational waves, which generate a B-mode component in the polarization of the cosmic microwave background (CMB). The measurement of such a B-mode signature would lend significant support to the paradigm of inflation. However, observed B modes also contain a component from the gravitational lensing of primordial E modes, which can obscure the measurement of the primordial B modes. We reduce the uncertainties in the B-mode measurement contributed from this lensing component by a technique called 'delensing.' In this talk, I will give an update on the current delensing effort on the BICEP/Keck data, using data from the South Pole Telescope (SPT) and the Planck satellite. This analysis will tighten the constraint on the amplitude of primordial gravitational waves, parameterized through the tensor-to-scalar ratio r that is related to the energy scale of inflation. For upcoming analyses, efficient delensing relies on high signal-to-noise measurements of the CMB lensing mass map. I will show the current state-of-the-art measurement of CMB lensing using SPTpol data, its inferred cosmological constraints, and its relevance for delensing. I will then discuss on-going efforts and novel methods in making lensing mass maps using new data/simulations from current and next-generation CMB experiments. After discussing the related challenges and opportunities, I will finish with an outlook on constraining r in this decade.

Superconducting nanowire single-photon detectors: physics and applications

Emma Wollman ('09), NASA Jet Propulsion Laboratory
Fri., Apr. 10, 2020, 12:30 PM in Science Center 199

Superconducting nanowire single-photon detectors, or SNSPDs, are able to detect single photons at wavelengths from the UV to mid-IR. SNSPDs have demonstrated detection efficiencies over 95%, timing resolution below 10 ps, and dark count rates less than 1e-3 counts/s. These characteristics make SNSPDs the detector of choice for applications ranging from fundamental tests of quantum mechanics to deep space laser communication. In this talk, I’ll describe the operational principle of SNSPDs and give some examples of their applications. In particular, I’ll focus on the Jet Propulsion Laboratory’s development of SNSPD arrays for deep space optical communication and for mid-IR astronomy.