Events at Physics |
Events During the Week of March 22nd through March 29th, 2009
Monday, March 23rd, 2009
- R. G. Herb Condensed Matter Seminar
- Circuit QED<sup>2</sup>: Two amplifiers, two resonators, and two photons
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Matteo Mariantoni, Walther-Meissner-Institut and Technical University
- Abstract: In order to better understand the fundamental properties of quantum electrodynamics (QED), studying the zero-point fluctuations of microwave radiation represents an important task. In the first part of this talk, I present a full experimental characterization of the microwave vacuum fluctuations via the Planck distribution of noise at very low temperatures. I show a detailed study of the cross-over from thermal noise to vacuum quantum noise and quantify the vacuum fluctuations level for a narrow frequency band centered around 6 GHz. I also demonstrate the change of the vacuum fluctuations level with the carrier frequency. In addition, I present a new type of heterodyne detection particularly suitable for circuit QED systems. It is based on a microwave beam splitter and cross-correlation measurements and allows for a reconstruction of the entire covariance matrix of the vacuum fluctuations. Finally, I show that such a cross-correlation setup can be used for detecting entanglement in a two-resonator circuit QED system.
In the second part of the talk, I report on the observation of key signatures of a two-photon driven Jaynes-Cummings model, which unveils the upconversion dynamics of a superconducting flux qubit coupled to an on-chip resonator. The experimental results show a clear evidence for the coexistence of one- and two-photon driven level anticrossings of the qubit-resonator system. This results from the symmetry breaking of the system Hamiltonian, when parity becomes a not well-defined property. This experiment provides deep insight into the interplay of multiphoton processes and symmetries in a qubit-resonator system. - Host: Robert McDermott
Tuesday, March 24th, 2009
- Chaos & Complex Systems Seminar
- Dynamics of the white pine blister rust pathogen on wild gooseberry hosts
- Time: 12:05 pm
- Place: 4274 Chamberlin
- Speaker: Maria Newcomb, UW Department of Plant Pathology
- Abstract: The reductionist scientific approach has often been followed to increase our understanding of minimally- and intensively-managed systems for purposes of making informed management decisions. My doctoral research is on the dynamics of a host-pathogen interaction in a minimally-managed woodland system. This and other pathosystems could potentially be described as complex, chaotic, and/or poorly understood. I will present results from observational and manipulative studies on the interaction between a rust pathogen and its gooseberry hosts. Our hope is that results of individual experiments can be combined to build a better understanding of the whole system to better inform management decisions. We also recognize that features of complex and chaotic systems may either limit our abilities to put the parts together to understand the whole, or at least challenge us to interpret the combined results carefully. At the end of the talk I will invite the audience to participate in a discussion about the benefits and limitations of the reductionist experimental approach in complex plant-pathogen systems.
- Astronomy Colloquium
- The Magnetic Universe Revealed Through Radio Polarimetry
- Time: 3:45 pm
- Place: 6515 Sterling Hall
- Speaker: Bryan Gaensler, The University of Sydney
- Abstract: The evolution, structure and origin of magnetic fields are stillopen problems in physics and astrophysics. When and how were the first fields generated? Are present-day magnetic fields the result of standard dynamo action, or do they represent rapid or recent field amplification through other processes? What role do magnetic fields play in turbulence, cosmic ray acceleration and galaxy formation? I will explain how radio polarization surveys have the potential to address these questions. Specifically, I will present new Faraday rotation studies aimed at revealing the three-dimensional magnetic structure of the Milky Way, the Magellanic Clouds and distant galaxies. These studies pave the way to opening the full window to the magnetic Universe with the Square Kilometre Array and other future radio facilities.
- Host: Prof Snezana Stanirmirovic
Wednesday, March 25th, 2009
- No events scheduled
Thursday, March 26th, 2009
- R. G. Herb Condensed Matter Seminar
- What can we learn from spin-dependent shot noise in semiconductor and graphene nanostructures?
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Branislav Nikolic, University of Delaware
- Abstract: I review recent studies of the shot noise of spin-polarized charge currents and pure spin currents in multiterminal semiconductor nanostructures with spin-orbit couplings or zigzag graphene nanoribbons attached to metallic electrodes. Akin to early utilization of noise in mesoscopic devices, where random time-dependent current fluctuations contain much more information about the transport than revealed through average current and conductance, spin-dependent shot noise emerges as a rich electrical tool to probe spin as magnetic degree of freedom. The Fano factor (noise-to-current ratio) of such noise can quantify decoherence of transported spins, or reveal the origin of the spin Hall effect (SHE) in simply-connected devices and probe interference effects in SHE induction in multiply-connected Aharonov-Casher rings. Finally, while the conventional spin-degenerate shot noise has very recently become important experimental tool to study ballistic transport through evanescent modes in graphene samples attached to metallic electrodes, in ribbons with zigzag edges which favor edge magnetic ordering when Coulomb interaction is "turned on", modification of the shot noise can be exploited to detect this unusual form of low-dimensional carbon-based magnetism.
- Host: Irena Knezevic, Elect. & Comp. Engineering
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- M-flation
- Time: 4:00 pm
- Place: 4274 Chamberlin
- Speaker: Amjad Ashoorioon, University of Michigan
- Abstract: We propose an inflationary scenario, M-flation, in which inflation is driven by three NXN Hermitian matrices Phi_i, i=1,2,3. The inflationary potential of our model in the most general form involves a commutator squared term, a cubic term involving product of a commutator with the field and a quadratic ``mass'' term. This class of potentials are strongly motivated by string theory. We show that one can consistently restrict the classical dynamics to a sector in which the Phi_i are proportional to the NXN irreducible representation of SU(2). In this sector our model effectively behaves as an N-flation with order N^2 number of fields, and therefore remove the fine-tunings associated with super-Planckian field and/or unnaturally small couplings in the chaotic type inflationry scenarios. Due to the matrix nature of the scalars 3N^2-1$ other scalar fields also affect the inflationary dynamics. These have the observational effects such as production of entropy (non-adiabatic) perturbations on cosmic microwave background. Moreover, the existence of these other scalars provides us with a natural preheating model for our setup.<br>
- Host: Dan Chung
Friday, March 27th, 2009
- No events scheduled