Physics and Astronomy Seminar: Spring 2008 Schedule
Thursday, Feb 7, at 11.30 am, Student Union II, Room 7,
Title: Quantum computing with ultra-cold atoms in an optical lattice
Abstract: Ultra-cold neutral atoms can be confined in a space-periodic potential created by laser light and called an optical lattice. A novel type of optical lattice has been recently created at the National Institute of Standards and Technology (NIST) in which the lattice consists of a periodic array of double-well potentials [Sebby-Strabley, et al., Phys. Rev. A, vol. 73, pg. 033605 (2006)]. I will discuss how a system of ultra- cold atoms loaded into the NIST double-well optical lattice can be used to make an essential component of a quantum computer: a two-qubit universal gate.
Thursday, Feb 14, at 12 Noon , Research Building, Room 302 ( Interview Seminar for Planetary Science Candidate )
Title: Aurora in the lumpy bumpy magnetic fields of Mars
Abstract: Magnetometer observations from the Mars Global Surveyor spacecraft demonstrated that it has been billions of years since Mars possessed a significant global dynamo magnetic field. As a result, the planet?s extended atmosphere interacts directly with the solar wind, similar to the plasma interaction at Venus or comets. At Mars, especially, many independent lines of evidence suggest that this interaction has contributed substantially to the evolution of the climate. IInterestingly, strongly magnetized regions of the crust substantially All peperturb the interaction on both local and global scales. The presence of crustal fields has many interesting consequences, including the creation of localized pockets of protected atmosphere, atmospheric ?escape hatches? for particle deposition and escape, and auroral emission near crustal fields. I will give an overview of the interaction of the solar wind with the Martian atmosphere, including a discussion of three big picture science questions that study of this interaction addresses. I will then discuss in more detail two examples of the effects of crustal fields: a complex, variable magnetic field topology more similar to the Sun than to any other solar system object, and the observations and consequences of auroral processes operating near Mars.
Monday, Feb 18, at 12 Noon , Research Building, Room 302 ( Interview Seminar for Planetary Science Candidate )
Nader Haghighipour, Univ of Hawaii
Formation of Habitable Planets and the Origin of Water and Volatiles
ne of the outstanding issues in the formation of a habitable planet is the origin of water and organic materials. The widely accepted model of terrestrial planet formation, in which the collisional growth of Moon- to Mars-sized objects results in the formation of larger bodies, suggests that water and volatiles on a habitable planet may have their origins in the planet?s local environment. The models of the formation of Earth, however, suggest that Earth?s local environment was too hot to allow for the incorporation of water at the time of its formation. The Earth?s water seems to have been delivered to it by the collision of bodies originating in the outer regions of the asteroid belt. I will review current ideas on the origin of Earth?s water and present the results of our recent studies concerning the Earth?s volatiles parent bodies. I will also discuss the application of these ideas to extrasolar planetary systems, in particular systems in which unusual dynamical characteristics, such as the existence of close-in giant planets and, in several cases, the presence of a second star, have profound effects on the distribution of the building blocks of habitable planets. I will review the results of our recent simulations of habitable planet formation in such extreme environments, and show that it is indeed possible to form Earth-like objects, with substantial amounts of water, in the habitable zones of their stars. I will also discuss the possibility of the detection of extrasolar habitable bodies and present future directions for this research.Abstract:
Thursday, Feb 21, at 12 Noon , Research Building, Room 302 ( Interview Seminar for Planetary Science Candidate )
Jason Barnes, NASA Ames Res Center CA
Title: Cassini and the Case of Titan's Missing Ethane
Abstract: Saturn's moon Titan is only the fourth planetary body we have explored that has both a solid surface and a significant atmosphere. I will talk about new discoveries that have come from the Visual and Infrared Mapping Spectrometer instrument aboard the Cassini spacecraft regarding the nature of Titan's surface/atmosphere interactions. Photolysis of methane in the moon's atmosphere drives chemical reactions that lead to ethane and other higher-order hydrocarbons that form smog layers. However, when we peered through that smog we did not see the predicted 300-meter deep ocean of liquid ethane that would result from 4 billion years' worth of methane photolysis. Instead we see relatively small seas of methane/ethane clustered near both the north and south poles. At the equator lies a vast desert covered in the solar system's largest field of sand dunes. The dunes' spectral signature indicates that the sand is made of solid hydrocarbons, which account for a portion of the missing ethane. Confronted with only enough methane to last for 10 million years, and faced with extensive networks of gullies and channels carved over a much longer period, it seems that Titan's methane must be being replenished. I will show our best candidates for places where eruptions may have taken place that could help resupply the atmosphere's methane, and discuss the implications that these have for Titan's evolution.
Wed, Feb 27, at 12 Noon , Research Building, Room 302 ( Interview Seminar for Planetary Science Candidate )
David O?Brien, Plantary Science Insitute, AZ
Title: Terrestrial Planet Formation in the Solar System and Beyond
Abstract:The terrestrial planets in our Solar System pose several paradoxes. For example, despite being the product of repeated high-velocity collisions between Moon- to Mars-sized planetary embryos, the terrestrial planets have relatively low eccentricities and inclinations. As the Earth was forming, the solar nebula in its vicinity was too hot for ice to condense, yet the Earth today has abundant water. New, high-resolution N-body simulations that I have performed have begun to resolve many of these issues. Dynamical friction from a large population of small planetesimals is able to damp the eccentricities and inclinations of the growing planets, and a sufficient amount of water-bearing material from the outer asteroid belt is delivered to the Earth to explain its current water budget. Analyzing these simulations in the context of geochemical and meteoritic evidence shows that this scenario is consistent with Earth's Deuterium/Hydrogen (D/H) ratio and the abundances and isotop ic ratios of siderophile elements such as Osmium in the Earth's mantle. The remnant planetesimal population beyond Mars is consistent with the mass and orbital distribution of the present asteroid belt. I will give a summary of this work, and discuss how lessons learned from such detailed modeling of our Solar System can be applied towards better understanding the formation and evolution of terrestrial planets around other stars. Integrating dynamical models of terrestrial planet formation with chemical models of the condensation of solids in protoplanetary nebulae around other stars, many of which are chemically different from our Sun, allows for the prediction (in a statistical sense) of both the chemical and dynamical properties of terrestrial planets that may exist in those systems. I will present results for several extrasolar planetary systems, and discuss the diversity of possible extrasolar terrestrial planets, from those that are "Earth-like" to planets that may be very different than those in our Solar System.
Thursday, Feb 28, at 11.30 am , Research Building, Room 302
Title: Scattering and Guiding with Atom Walls
Abstract: We propose the possibility of using a wall of atoms to guide matter waves, e.g. electrons or other atoms, in a manner similar to which a fiber optic guides light. Such walls could be engineered from individual atoms by scanning tunneling microscopy, for instance. We model the atomic wall as a quasi-1D array of scatterers embedded in 2D; our theoretical study reveals the interplay of scattering phenomena with bands and conduction along the array. We discuss the conditions under which straight or curved arrays of atoms can guide a beam focused on one end of the array.
Friday, March 7, at 11.00 am, Research Building, Room 302
Victor Galitski, Univ of Maryland
Title:Vortex Dynamics and Fluctuations in Superconducting Films
Abstract: Superconductivity in two dimensions provides a unique area in which a fascinating variety of novel and fundamental phenomena occur. In this talk, I will review recent theoretical and experimental results on disordered films, which undergo a magnetic-field-tuned superconducting-insulator transition at low temperatures. I will focus on the unusual phases and fluctuation phenomena evident in the experimental studies of the field-tuned transition. First, I will explain how rare disorder fluctuations can enhance global superconductivity and increase the critical magnetic field at which samples become superconducting. Next, I will briefly summarize the recently developed theory of quantum superconducting fluctuations, which explains transport properties above the transition. At the end of my talk, I will focus on the low-temperature metallic phase observed in certain materials. This metallic state is truly mysterious and can not be explained by any conventional theory (in! ! volving bosonic vortices as basic excitations). I will argue that under certain circumstances the statistics of the vortices can change from bosonic to fermionic. Such a statistical transmutation may explain the nature of the metallic state. I will discuss possible experimental signatures of the resulting vortex Fermi liquid.
Thursday, March 20, at 11.30 am, Research Building, Room 302
Victor Yakovenko, Univ of Maryland
Title: Statistical Mechanics of Money, Income, and Wealth
Abstract: We propose an analogy between the thermal Boltzmann-Gibbs distribution of energy in physics and the equilibrium probability distribution of money in a closed economic system [1]. As a result of multiple money transfers between interacting economic agents, the system develops an exponential probability distribution of money, which corresponds to the state of maximal entropy. By analyzing income data from the IRS t miss it.I'm also auditing yo$ and the Census Bureau, we found that income distribution in the USA one of my application process$ has a well-defined two-class structure [2]. The majority of population (97-99%) belongs to the lower class characterized by the exponential Boltzmann-Gibbs ("thermal") distribution. The upper class (1-3% of population) has a Pareto power-law ("superthermal") distribution, whose parameters change in time with the rise and fall of stock market. We propose a concept of equilibrium inequality in a society, based on the principle of maximal entropy, and quantitatively demonstrate that it applies to the majority of population. For more references and computer animation video, see http://www2.physics.umd.edu/~yakovenk/econophysics/ and review article [3]. References: [1] A. A. Dragulescu and V. M. Yakovenko, "Statistical mechanics of money", European Physical Journal B 17, 723 (2000). [2] A. C. Silva and V. M. Yakovenko, "Temporal evolution of the `thermal' and `superthermal' income classes in the USA during 1983-2001", Europhysics Letters 69, 304 (2005). [3] V. M. Yakovenko, "Econophysics, Statistical Mechanics Approach to" arXiv:0709.3662.
Thursday April 3, at 11.30 am, Research Building, Room 302
Carl Williams, Chief, Atomic Physics Division, NIST
Title: From Quantum Information Science to Quantum Simulation
Abstract:
Quantum information science is described as a revolutionary development that has the potential of impacting the 21st century in a manner similar to what the laser and transistor had in the 20th century. How much of this is hype and why should one think that this might be a possibility? This talk will give a brief introduction into quantum information and its potential for affecting technology and innovation in the 21st century. I will try and give an argument of why such radical statements might be true and how difficult achieving them might be. After explaining why someone might expect that quantum information could be revolutionary and describing some of its better known impacts I will talk about one specific approach to quantum computing based on neutral atoms in optical lattices. After briefly describing how a neutral atom quantum computer might work I will focus on some of the iconic condensed matter Hamiltonians that might be simulated with these neutral atoms systems. I will briefly discuss the Bose-Hubbard Hamiltonian in a trap and then one or two situations for the 2-component Hubbard that are currently a focus of my research. Experimentally it is expected that one will begin to see the analog quantum simulation of these Hamiltonian in the laboratory since they are a major focal point of cold atom research and quantum information science.
Thursday April 17, at 11.30 am, Research Building, Room 302
Ludwig Mathey, NIST
Abstract:
We study the phase-locking transition of two coupled two-dimensional superfluids at finite temperature, and find that the superfluids have a strong tendency to
phase-lock. The phase-locking is accompanied by a sizeable increase of the transition temperature $T_{c}$ of the resulting double-layer superfluid to thermal Bose gas
transition, compared to the Kosterlitz-Thouless temperature $T_{KT}$ of the uncoupled 2D systems, which suggests a plausible way of observing the Kibble-Zurek
mechanism in two-dimensional cold atom systems by rapidly varying the tunneling rate between the superfluids. If there is also interaction between atoms in different
layers present we find additional phases, while no sliding phase, characterized by order or quasi long range order (QLRO) either in the symmetric or the antisymmetric
sector of the system.
This talk is based on Europhysics Letters, 81 (2008) 10008.
Thursday May 1, at 11.30 am, Research Building, Room 302 Title: Matter Wave Magic Abstract:
Louis de Broglie suggested in 1924 that particles, when observed close up, behave like waves. During the past decade, it has become possible to see
this relationship with unmistakable clarity. This is due to the attainment of Bose-Einstein condensation, an achievement recognized by the Nobel
Prize in Physics in 2001. I present some elementary visual demonstrations of matter waves, and explore the conections between matter and light.
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Thursday May 15, at 10.30 am, Research Building, Room 302 Title: Lipid Tubules: A Paradigm for Molecularly Engineering Structures" 