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This Week at Physics

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Events on Friday, January 27th, 2017

Atomic Physics Seminar
Ultralow-Power Nonlinear Optics using Metastable Xenon in a Cavity
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Garrett Hickman, UMBC
Abstract: Single-photon cross phase shifts and other single-photon nonlinearities have numerous applications in all-optical quantum information processing. Several groups have experimentally achieved single-photon phase shifts on the order of pi. However, nonlinearities weaker than this have important applications as well. We introduce the idea of using metastable xenon gas in a high-finesse cavity to produce weak single-photon nonlinearities. This relatively simple and robust system avoids problems associated with the accumulation of alkali atoms on mirror surfaces, and is capable of approaching the strong coupling regime of cavity quantum electrodynamics. We demonstrate the feasibility of our approach with two proof-of-principle demonstrations, by measuring absorption saturation and cross-phase modulation using a cavity of moderately high finesse F=3,000. We find that the nonlinear effects occur at ultralow input power levels, proving that the presence of the cavity strongly enhances the inherent optical nonlinearities of metastable xenon. We close our discussion by reviewing our recent progress in building an improved cavity system, which is expected to produce enhanced single photon cross phase shifts.
Host: Saffman
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Physics Department Colloquium
A New Spin on Superconductivity
Time: 3:30 pm
Place: 2241 Chamberlin hall
Speaker: Amir Yacoby, Harvard University
Abstract: Nearly a hundred years after its discovery, superconductivity remains one of the most intriguing phases of matter. In 1957 Bardeen, Cooper and Schrieffer (BCS) presented their theory of superconductivity describing this state in terms of pairs of electrons arranged in a spatially isotropic wave function with no net momentum and a spin singlet configuration. Immediately thereafter, a search began to find materials with unconventional superconductivity where pairing deviates from conventional BCS theory.

One particular class of unconventional superconductors involves pairs arranged in triplet rather than singlet configurations. Such superconductors may enable dissipationless transport of spin and may also give rise to elementary excitations that do not obey the conventional Fermi or Bose statistics but rather have non-Abelian statistics where the exchange of two particles transforms the state of the system into a new quantum mechanical state.

In this talk I will describe some of our recent experiments that explore the proximity effect between a conventional superconductor and a semiconductor with strong spin-orbit interaction. Using supercurrent interference, we show that we can tune the induced superconductivity continuously from conventional to unconventional that is from singlet to triplet. Our results open up new possibilities for exploring unconventional superconductivity as well as new ways for detecting unconventional pairing in known materials.
Host: Mark Eriksson
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