Fall, 2013 Physics Colloquia

September 27, 2013 (Friday) 4:00-5:00p.m. Small Hall 110

Speaker: Prof. Keith R. Dienes, University of Arizona
Host: Prof. Marc Sher
Title: Probing the String Landscape: Implications, Applications and Altercations

Abstract: We are currently in the throes of a potentially huge paradigm shift in physics. Motivated by recent developments in string theory and the discovery of the so-called "string landscape," physicists are beginning to question the uniqueness of fundamental theories of physics and the methods by which such theories might be understood and investigated. In this colloquium, I will give a non-technical introduction to the nature of this paradigm shift and the history of how it developed. I will also discuss some of the questions to which it has led, and the nature of the controversies it has spawned.

October 4, 2013 (Friday) 4:00-5:00p.m. Small Hall 110

Speaker: Dr. Samindranath Mitra, Editor of Physical Review Letters
Host: Prof. Enrico Rossi
Title: Hows and Whys of Publishing in PRL

Abstract: How do its editors determine which papers to publish in PRL? What how-tos should you know as an author and a referee? Why should you submit your work to us? How are journals in general and PRL in particular reorienting amid increasing competition and other challenges? I plan to address these and related issues during my presentation and the subsequent discussion.

October 18, 2013 (Friday) 4:00-5:00p.m. Small Hall 110

Speaker: Eugene Mele, University of Pennsylvania
Host: Prof. Enrico Rossi
Title: Topological Physics in Band Insulators

Abstract: Topological insulators are a recently discovered quantum electronic phase of matter. This talk will give a brief overview of the known electronic phases of matter, focusing on the unique properties of topological insulators and their discovery from a careful consideration of the low energy electronic physics of single-layer graphene. Closely related ideas are then used to analyze the electronic behavior of multilayer graphenes including gapped bilayer graphene and "twisted" graphenes where topological considerations introduce unexpectedly rich low energy physics.

October 25, 2013 (Friday) 3:00-4:00p.m. Small Hall 110

Speaker: Thomas R. Gentile, NIST (National Institute of Standards & Tech)
Host: Prof. Todd Averett
Title: Polarized 3He spin filters for neutron science

Abstract: The large spin dependence of the absorption cross section for neutrons by 3He gas provides a method to polarize neutron beams. For certain applications, such polarized 3He-based neutron "spin filters" have advantages over conventional neutron optical polarizing methods. Spin filters operate at all neutron wave- lengths, can cover a large angular range and/or a large energy range, and decouple neutron polarization from energy selection. Both spin-exchange optical pumping (SEOP) and metastability-exchange optical pumping (MEOP) are currently being employed to polarize 3He spin filters at various neutron facilities worldwide. I will focus on the development and application of SEOP-based neutron spin filters at the National Institute of Standards and Technology, Center for Neutron Research (NCNR). The combination of long relaxation time spin filter cells, high power spectrally narrowed diode lasers, and the use of Rb/K mixtures have allowed us to reach 3He polarizations up to 85% in spin filter cells ~1 liter in volume. Studies have revealed limits to the achievable polarization from temperature-dependent relaxation and unexplained magnetic field dependence for relaxation in SEOP cells. Applications include neutron scattering methods such as triple-axis spectrometry and small angle neutron scattering, and fundamental neutron physics. In most neutron scattering applications, cells are transported to the beam line and stored in a magnetically shielded solenoid or box. A recent focus has been apparatus for wide-angle neutron polarization analysis. A measurement of the spin-dependence of the neutron-3He scattering length was performed with a small, polarized 3He cell in a neutron interferometer and a 3He spin filter for accurate neutron polarimetry. Use of spin filters in high flux neutron beams have revealed beam-induced alkali-metal relaxation and long term effects on SEOP spin filter cells.

November 1, 2013 (Friday) 4:00-5:00p.m. Small Hall 110

Speaker: Marina Artuso, Syracuse University
Host: Prof. Marc Sher
Title: New physics in charm and beauty decays: the LHCb perspective

Abstract: Charm and beauty decays provide indirect probes of new physics at very high mass scales. The LHCb is the first dedicated experiment to explore this physics in a hadron machine, and its first phase has already produced a great variety of very interesting results. Highlights of the most interesting achievements will be summarized, as well as prospects for the next data taking cycle and the planned LHCb upgrade.

November 8, 2013 (Friday) 4:00-5:00p.m. Small Hall 110

Speaker: Nandini Trivedi, Ohio State University
Host: Prof. Enrico Rossi
Title: Probing quantum phase transitions

Abstract: At a quantum phase transition, one ground state evolves into a different one by passing through a quantum critical region with enhanced spatial and temporal fluctuations. I will discuss several ways of probing the quantum critical fluctuations in a system of strongly interacting bosons in optical lattices using deviations from the fluctuation-dissipation theorem. I will also discuss some novel ways of using atom-photon entanglement to detect correlated phases.

November 15, 2013 (Friday) 4:00-5:00p.m. Small Hall 110

Speaker: John Howell, Unviversity of Rochester
Host: Prof. Irina Novikova
Title: Entropy, Information and Compressive Sensing in the Quantum Domain

Abstract: Compressive sensing utilizes sparsity to realize efficient image reconstruction. It is a valuable processing technique when cost, power, technology or computational overhead are limited or high. In the quantum domain technology usually limits efficient acquisition of weak or fragile signals. We have used compressive sampling for low-flux laser Radar [1], photonic phase transitions, high resolution biphoton ghost imaging [2], Ghost object tracking [3] and high dimensional entanglement characterization [4]. As shown below, we were able to efficiently and rapidly reconstruct high dimensional joint probability functions of biphotons in momentum and position. With conventional raster scanning this process would take approximately a year, but using double-pixel compressive sensing, the pictures were acquired in a few hours with modest flux.

November 22, 2013 (Friday) 4:00-5:00p.m. Small Hall 111

Speaker: Olivier Pfister, Unviversity of Virginia
Host: Prof. Irina Novikova
Title: The quantum optical frequency comb as a (really large) quantum computing register

Abstract: The race to build a practical quantum computer demands that one address the challenges of decoherence and scalability. I present our nonincremental progress toward the latter. In 2004, our group proposed to use the vast set of resonant eigenmodes of an optical cavity (a.k.a. the quantum optical frequency comb) as the many Qbits (or, rather, Qmodes) of a quantum computing register. Since then, we have proven theoretically that an optical parametric oscillator (OPO, an optical cavity containing a dispersive two-photon-emitting medium) can be used to generate large-scale multipartite entanglement. I will present our recent measurement of a 60-Qmode cluster state in a single OPO, which constitutes a world record in quantum state preparation for quantum computing.