Weekly Colloquium

Most weeks during the semester, we host a scholar for a one-day visit. The visit culminates with a public talk on a topic of contemporary physics or astronomy. Students are welcome to these talks, and seniors are required to attend at least nine over the course of a year. Near the end of each semester, honors thesis students give public lectures on their work.   

Our Astronomy program is part of the Five College Astronomy Department, which hosts its own colloquium series Thursdays at 3:45 pm at UMass. 

  • Contact colloquium organizer Alice Simmoneau with any questions about colloquia, or being added to our mailing list.

October 2019

Tue, Oct 1, 2019

Gopal Narayanan, UMass: “The Event Horizon Telescope: The Story Behind the First Image of a Super-Massive Black Hole”

The Event Horizon Telescope (EHT) is a Very Long Baseline Interferometry (VLBI) array composed of radio telescopes operating around the world and operating at short millimeter wavelengths. This globe-spanning telescope can resolve the event horizons of the nearest super-massive black holes. At millimeter wavelengths, the photons that originate from deep within the gravitational well of the black hole can travel unimpeded and be detectable by the EHT.

In April 2017, the EHT performed observations of two super-massive black holes, SgrA* and M87*, using eight telescopes around the world. And on April 10, 2019, 100 years after Sir Arthur Eddington famously provided observational proof of Einstein's Theory of General Relativity, the EHT collaboration presented the first images of the shadow and event horizon of the super-massive black hole in M87.

In this talk, I will recount the story of this remarkable scientific advance, the novel instrumentation that enables EHT science, and the role that UMass and the Large Millimeter Telescope (LMT) played in this effort. I will also chart out the next steps for this project.

Tue, Oct 8, 2019

Chandrasekhar Ramanathan, Dartmouth: “Engineering the Dynamics of Electron and Nuclear Spins in Solids”

Quantum technologies could enable transformative advances in applications such as computing, cryptography and sensing, while furthering our understanding of chemistry and materials design. However, as we construct ever larger and more complex quantum devices, a key challenge is to control them in a way that preserves their fragile quantum nature.

In this talk, Chandrasekhar Ramanathan will describe ongoing efforts in our group to control the dynamics of both electron and nuclear spins in solids using magnetic resonance techniques. These electron and nuclear spin system are excellent platforms for the study of quantum dynamics, due to their long coherence and relaxation times. He will also discuss our efforts to hyperpolarize nuclear spins in semiconductors via dynamic nuclear polarization (DNP) techniques, and discuss how the enhanced nuclear spin signal can be used to probe the local physics and chemistry.

Tue, Oct 22, 2019

Brian Daly, Vassar: “Picosecond Laser Ultrasonics: A Sound Way to Study Nanostructures”

Ultrafast lasers produce pulses of light at extremely regular intervals (about 13 nanoseconds apart) that are less than a picosecond in duration. These lasers allow us to study very fast phenomena in crystals and solid nanostructures. The work that my group at Vassar does involves using these lasers to generate and detect ultrasound that is roughly 1,000 times higher in frequency than traditional medical or industrial ultrasound. Since ultrasound can serve as a nondestructive probe of the size or mechanical properties of buried structures, this so called “picosecond ultrasound” should be a great way to study and image the nanoscale structures that form the backbone of all of our modern electronic devices. In this talk, Professor Daly will describe a number of investigations (some very applied, some very fundamental) that we have pursued over the past decade with this optical experiment.

Tue, Oct 29, 2019

Myriam Sarachik, City College of New York: “SURPRISE: Just Because You Think You’re Heading Toward a Quantum Phase Transition Does Not Mean You Will Get There”

Measurements of the Hall coefficient, resistivity, magnetoresistance, magnetic response and thermopower in two-dimensional strongly interacting electron systems have established that, contrary to expectations, a metal-insulator transition occurs at a critical electron density nc and a metallic phase exists in 2-D. One intriguing mystery has been that, by contrast with the dramatic divergences that have been observed for all other physical properties, the magnetoresistance has exhibited smooth and uneventful behavior approaching and crossing nc.

In this talk, I will present new data and a different new analysis of the magnetoresistance of the strongly interacting 2-D electron system in a silicon MOSFET for a broad range of electron densities. Our surprising results should trigger a re-examination of past work.