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April, 04/21/2015
Events and times subject to change

April 23, 2015 Thursday 4:00 PM  +
Meyer 122
Physics Colloquia (colloquia)

Julio Fernandez
Columbia University

The Physics of Titin and Muscle Function

Current theories of muscle contraction largely exclude titin, the largest protein in the human body, which determines the passive elasticity of muscles. I will show how to construct the free energy of a titin-like model protein, and how we can use this free energy to predict the behavior of titin in intact tissues. I will demonstrate the use of single molecule force-spectroscopy techniques to probe the folding of titin domains and measure the contribution that they make to the force generated by a contracting muscle. I will show that the folding of single titin domains can generate in excess of 100zJ of contractile energy, which is larger than the mechanical energy delivered by the power stroke of a myosin motor. Hence, the folding of titin Ig domains is an important contributor to the force generated by a contracting muscle.

April 30, 2015 Thursday 4:00 PM  +
Meyer 122
Physics Colloquia (colloquia)

Marc Kamionkowski

Inflation: There's Room at the Bottom

The idea that the Universe underwent a period of superluminal expansion, known as inflation, has gained considerable traction with the advent of precise measurements over the past decade+. One of the key predictions of inflation is a spectrum of primordial density fluctuations that remains nearly scale-invariant over 15-25 decades in distance scale. The near scale-invariance of primordial perturbations over the roughly 3 decades over which the spectrum has been measured so far remains one of the theory's greatest successes. Still, it is interesting to think whether that spectrum can be measured over the remaining 12-22 decades, all of it at distance scales smaller than those that can be probed by the cosmic microwave background or galaxy surveys. I will discuss some ideas for accessing these smaller scales.

May 7, 2015 Thursday 4:00 PM  +
Meyer 122
Physics Colloquia (colloquia)

Ivan Schuller


May 19, 2015 Tuesday 2:00 PM  +
Meyer 6th Floor Conference Room
Physics Colloquia (colloquia)

Jacqueline Bloch
Laboratoire de Photonique et de Nanostructures, LPN/CNRS

Manipulating Polariton Quantum Fluids in Semiconductor Microcavities

At the frontier between non-linear optics and Bose Einstein condensates, semiconductor microcavities have opened a new research field, both for fundamental studies of bosonic quantum fluids in a driven dissipative system, and for the development of new devices for all optical information processing. Optical properties of semiconductor microcavities are governed by bosonic quasi-particles named cavity polaritons, which are light-matter mixed states. Cavity polaritons propagate like photons, but interact strongly with their environment via their matter component. Patterning of semiconductor microcavities on a micron scale allows confining polaritons in photonic circuits or in lattices.
After a general introduction on cavity polaritons, I will illustrate the diversity of physical problems that can be addressed in this non-linear photonic system using patterned microstructures.I will show that taking advantage of the giant non-linearities induced by polariton interaction it is possible to realize photonic circuits in which coherent polaritons are propagated and optically manipulated.
The second part of the talk will be dedicated to the physics of polaritons in lattices. I will show that we can implement complex Hamiltonians and thus develop a new platform for quantum emulation. For instance, we have demonstrated a fractal energy spectrum for polaritons by engineering a quasi-periodic lattice. It becomes possible to explore the physics of non-linear wavepackets in such complex environment. Polaritons are also very promising for the investigation of graphene physics using honeycomb lattices. For instance, Dirac cones are directly imaged in the polariton far field emission. Finally we recently fabricated lattices holding non dispersive bands. In such flat bands, kinetic energy frustration dramatically modifies the spontaneous spatial coherence of polariton condensates.
[1] Spontaneous formation and optical manipulation of extended polariton condensates, E. Wertz, et al., Nat. Phys. 6, 860 (2010)
[2] Realization of a double barrier resonant tunneling diode for cavity polaritons, H-.S. Nguyen et al., Phys. Rev. Lett. 110, 236601 (2013)
[3] All-optical phase modulation in a cavity-polariton Mach-Zehnder interferometer, C. Sturm et al., Nature Commun. 5, 3278 (2014)
[4] Fractal energy spectrum of a polariton gas in a Fibonacci quasi-periodic potential, D. Tanese et al., Phys. Rev. Lett. 112, 146404 (2014)
[5] Direct observation of Dirac cones and a flatband in a honeycomb lattice for polaritons, T. Jacqmin et al., Phys. Rev. Lett. 112, 116402 (2014)
[6] Spin-Orbit Coupling for Photons and Polaritons in Microstructures, V.G. Sala et al., Phys. Rev. X 5, 011034 (2015)