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ItemUltra-high Resolution Astronomical imaging using quantum properties of light(Georgia Institute of Technology, 2018-10-01) Kieda, David B.Ever since the first astronomical telescope observations made by Galileo (1610), optical astronomy has developed increasingly sophisticated methods for exploring the universe using only the classical (wave-description) properties of light. The quantum mechanical properties of light, including photon bunching and orbital angular momentum, carry substantially more information about the nature of the astronomical sources, yet these properties are currently not exploited. This talk will describe the development of a new astronomical capability which exploits the quantum properties of light. The technique has the potential to achieve < 100 micro-arc second angular resolution in the optical wavelengths; such high angular resolution would be sufficient to directly imaging the moons of Jupiter passing across the disk of a main sequence star ~8 light years away. We describe a conclusive demonstration of quantum photon bunching (Hanbury Brown-Twiss Interferometry) in the laboratory using simulated stars and binary systems. We describe the design of a future ultra-high resolution optical astronomical imaging observatory using existing and future arrays of Imaging Air Cherenkov Telescopes (IACTs). The talk describes the potential optical imaging resolution of the VERITAS IACT observatory array (Amado, Arizona) and the future CTA IACT Observatory (Canary Islands, Spain and Paranal, Chile).
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ItemSETI: Any Closer to a Discovery?(Georgia Institute of Technology, 2018-09-24) Shostak, SethAre we alone in the universe? The scientific hunt for extraterrestrial intelligence is now well into its fifth decade, and we still haven’t discovered any cosmic company. Could all this mean that finding biology beyond Earth, even if it exists, is a project for the ages – one that might take centuries or longer? New approaches and new technology for detecting sentient beings elsewhere suggest that there is good reason to expect that we could uncover evidence of sophisticated civilizations – the type of aliens we see in the movies and on TV – within a few decades. But why now, and what sort of evidence can we expect? And how will that affect humanity? Also, if we do find E.T., what would be the societal impact of learning that something, or someone, is out there?
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ItemThe American Physical Society Report on the Status of LGBT People in Physics(Georgia Institute of Technology, 2018-04-16) Atherton, TimIn this talk, I’ll discuss climatic issues faced by LGBT people in Physics, informed by findings of the recent American Physical Society report on the status of LGBT people in Physics. This report was prepared for the APS by an ad hoc committee of physicists, spanning a range of institutions types and career stages, and included information from focus groups held at APS meetings, the first ever climate survey of LGBT people in physics, and a set of in-depth interviews with individuals who self-identify as LGBT. Driven by this evidence, I’ll discuss implications for pedagogy, as well as collective and individual actions the community can take to alleviate the issues identified.
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ItemArch and scaffold: Hilbert space and transformation theory(Georgia Institute of Technology, 2018-04-02) Janssen, MichelIn early 1927, Paul Dirac and Pascual Jordan, independently of one another, published their versions of a general formalism tying the various forms of the new quantum theory together and giving the theory’s statistical interpretation in full generality. This formalism has come to be known as the Dirac-Jordan (statistical) transformation theory. A few months later, in response to these publications, John von Neumann published his Hilbert space formalism for quantum mechanics. The relation between the two formalisms can be captured in terms of a metaphor of arches and scaffolds that I have argued fits a number of instances of theory change in physics. What is unclear in this case is whether the story is best told with Hilbert space playing the role of the arch built on transformation theory as a scaffold to be dismantled once the arch could support itself, or with transformation theory playing the role of the arch and Hilbert space providing the scaffold built to prevent Jordan’s mathematically unsound arch from collapsing. Either way, a narrative for this episode in the history of quantum mechanics based on the arches-and-scaffolds metaphor illustrates the promise of borrowing ideas from the approach to evolutionary biology known as evodevo for reconstructing genealogies of theories rather than species.
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ItemIon Hydration and Effective Charge(Georgia Institute of Technology, 2018-03-26) Pincus, Philip A.Ions in water are typically understood to be hydrated, i.e. the appropriate water dipolar orientations point toward the charge (which is here taken to be of spherical symmetry). Depending on the specific charge, these oriented waters of hydration are tightly bound in up to three aqueous monolayers. The effective “hard core” radius of the ion together with its tightly bound water molecules is in the nanometer range. Because dipoles have zero net charge, the hydrated ion complex is generally viewed to have the samec harge as the unhydrated ion. We apply the Hone, Pincus1 view of hydrogen bonding in water to suggest that this may not be precisely correct and that there may be an effective charge which differs from the nominal charge. It is this effective charge that would be implicated in such phenomena as Debye screening.
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ItemLife in the Universe(Georgia Institute of Technology, 2018-03-12) Loeb, Abraham (Avi)Is life most likely to emerge at the present cosmic time around a star like the Sun? Loeb will review the habitability throughout cosmic history from the birth of the first stars 30 million years after the Big Bang to the death of the last stars in ten trillion years. Unless habitability around low mass stars is suppressed, life is most likely to emerge near stars with a tenth of a solar mass ten trillion years from now. Forthcoming searches for bio-signatures in the atmospheres of transiting Earth-mass planets around nearby low-mass stars will determine whether present-day life is indeed premature from a cosmic perspective.
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ItemMany-body Entanglement and Tensor Networks(Georgia Institute of Technology, 2018-02-12) Evenbly, GlenQuantum many-body systems are difficult to study because the space of possible many-body states is huge: its dimension grows exponentially in the system size. However, in recent years progress in our understanding of quantum entanglement has revealed that only a small region of this huge state space is actually relevant to the study of quantum many-body systems. Tensor networks are a powerful formalism developed to efficiently describe the states in this small, physically relevant region of the many-body state space. In this Colloquium I will (i) review our current understanding of many-body entanglement, (ii) introduce tensor networks as an efficient description of many-body states, and (iii) give an overview of the exciting developments within the tensor network program.
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ItemLocal temperature Ansatz: A novel quantum entanglement based approach for solving strongly correlated systems(Georgia Institute of Technology, 2018-02-05) Vaezi, AbolhassanThe exact solution to interacting quantum problems is, in general, an exponentially hard task due to the exponential growth of the Hilbert space with the system size. As a result, despite extensive research during the past several decades we still do not have a good understanding of strongly correlated systems even for the simplest ones such as the Hubbard model. We can only obtain exact results for special and very limited classes of models. For example, quantum Monte Carlo (QMC) method which evaluates path integrals stochastically is an exact and unbiased numerical method provided the notorious sign-problem is absent. In this talk, I will introduce our recently developed algorithm that can find the reduced density matrix associated with a finite subsystem of an infinite system. This paradigm was inspired by ideas from Hawking-Unruh radiation in black hole physics. As an example, I will demonstrate that this method can obtain the exact ground-state energy and scaling dimensions of the 1D Heisenberg model in the thermodynamic limit by solving a few sites problem. I will then show that within this new approach, the sign problem is practically circumvented and QMC can be applied to generic local models even at extremely low temperatures. I will finally show that this paradigm can also enhance the accuracy of matrix/tensor product states significantly by allowing gigantic bond dimensions.
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ItemThe crumpled state: crumpling dynamics and the evolution of damage networks(Georgia Institute of Technology, 2017-12-04) Rubinstein, ShmuelThe simple process of crumpling a sheet of paper with our hands results in a complex network of interconnected permanent creases of many sizes and orientations. Sheet preferentially bends along these creases, introducing history dependence to the process of crumpling. I will present an experimental study of the dynamics of crumpling. Specifically, I will first discuss how a crease network evolves when a thin elastoplastic sheet is repeatedly crumpled, opened up and then re-crumpled. Is there a maximally crumpled state after which the flat sheet can be deformed without further plastic damage? If time permits I will also I'll discuss the crumpling of soda cans, focusing on our attempts to characterize their stability in the case where on single defect dominates buckling.
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ItemSearch Levitation by Casimir forces in and out of equilibrium(Georgia Institute of Technology, 2017-11-27) Kardar, MehranA generalization of Earnshaw's theorem constrains the possibility of levitation by Casimir forces in equilibrium. The scattering formalism, which forms the basis of this proof, can be used to study fluctuation-induced forces for different materials, diverse geometries, both in and out of equilibrium. In the off-equilibrium context, I shall discuss non-classical heat transfer, and some manifestations of the dynamical Casimir effect.