Colloquia are held on Mondays at 4:00pm (Refreshments at 3:30pm) in Barus & Holley 168. Past colloquia from the current and previous years, including many videos, can be found on the Past Physics Colloquia page.
September 15, 2014 -- Seth Lloyd (MIT)
Nature is the great nanotechnologist: life is based on a myriad of interlinked mechanisms that operate at the molecular scale. The dynamics of these mechanisms are governed by quantum mechanics. Quantum mechanics famously exhibits strange and counterintuitive effects based on quantum coherence and entanglement. Does such `quantum weirdness' play a role in the functioning of living systems? Recent experimental investigations of photosynthesis indicate that quantum coherence may play an important role in optimizing energy transport in photosynthetic complexes. This talk presents a general theory that shows how quantum coherence can dramatically enhance energy transport in photosynthesis and in artificial systems. Optimal energy transport takes place at the point where the timescales for dynamic and static disorder converge, a phenomenon called the quantum Goldilocks effect.
September 22, 2014 -- Vijay Balasubramanian (UPenn)
"The Maps Inside Your Head"
How do our brains make sense of a complex and unpredictable world? In this talk, I will discuss a physicist's approach to the neural topography of information processing in the brain. First I will review the brain's architecture, and how neural circuits map out the sensory and cognitive worlds. Then I will describe how highly complex sensory and cognitive tasks are carried out by the cooperative action of many specialized neurons and circuits, each of which has a simple function. I will illustrate my remarks with one sensory example and one cognitive example. For the sensory example, I will consider the sense of smell ("olfaction"), whereby humans and other animals distinguish vast arrays of odor mixtures using very limited neural resources. For the cognitive example, I will consider the "sense of place", that is, how animals mentally represent their physical location. Both examples demonstrate that brains have evolved neural circuits that exploit sophisticated principles of mathematics - principles that scientists have only recently discovered.
September 29, 2014 -- David Goldhaber-Gordon (Stanford University)
October 6, 2014 -- Valerie Connaughton (NASA)
October 20, 2014 -- Valery Pokrovsky (Texas A&M University)
"Bose-Einstein condensation of spin waves in YIG "
In 2006 the experimental group from University of Münster (Germany) had discovered the phenomenon of Bose-‐Einstein condensation of spin waves (magnons) in a ferromagnet YIG (Yttrium-‐Iron garnet) at room temperature. They pumped low-‐energy magnons with external electro-‐ magnetic field in GHz range of frequency in a film of YIG. More recently (2012) the same group discovered a low-‐contrast interference pattern in the intensity of signal generated by the condensed magnons. This interference demonstrates the coherence between two condensates corresponding to two minima of magnons energy. Surprisingly, the oscillations displayed very low contrast that had no explanation in the framework of existing theories. In the work by Fuxiang Li, W.M. Saslow and VLP [Scientific Reports 3, 01372 (2013)] we proposed a theory explaining the coherence and low level of contrast. Our theory predicts that in thinner films it is possible to observe a different state of condensates with 100% contrast. The transition between the two states can be driven by a weak magnetic field. We predict the phase trapping between two condensates with two possible states 0 and π. Its experimental observation is feasible with traditional means (Brilloin scattering of light). Theory also predicts a new type of low-‐energy
October 27, 2014 -- Nandini Trivedi (Ohio State University)
November 3, 2014 -- Scott Watson (Syracuse University)
November 10, 2014 -- Patrick Lee (MIT) Host: Dima Feldman
November 17, 2014 -- Eric Mazur (Harvard University)
November 24, 2014 --James Olsen (Princeton University)
December 1, 2014 -- Savvas Koushiappas (Brown University)