Eric Sembrat's Test Bonanza

The recent advance in coherently controlling and manipulating strong, long-range Rydberg interactions has triggered extensive research in studying interesting many-body effects as, e.g. the use of Rydberg blockade effects for quantum information processing and crystal formation. In this talk I show that Rydberg interactions can be used to alter the photon statistics of a weak probe field after propagating in a coherently prepared atomic Rydberg gas under conditions of Electromagnetically Induced Transparency (EIT).

The Rydberg blockade mechanism leads to an effective two-level physics when two photons are separated by less than the blockade radius resulting in a strong anti-correlation of two photons given by an avoided volume. For large separations the repulsive long-range interaction between the Rydberg atoms induces repulsive interactions between the photons leading to quasi-crystalline states of photons. Confining the system to one dimension the low-energy physics of the excitations can be described in terms of a Luttinger Liquid.

Using DMRG simulations the Luttinger K-parameter is calculated and conditions on the formation of long-range ordered states are derived. Implications of the formation of such hard-sphere photons for the recent experiment of Pritchard et al. [Phys. Rev. Lett. 105, 193603 (2010)] and the observation of long-range correlations in future experiments will be discussed.

Blazar astronomy is rapidly progressing thanks in large part to the successes of the Fermi Gamma-ray Space Telescope and the ground-based gamma-ray telescopes. More than 1000 active galaxies have been detected at GeV energies, and nearly 50 at Very-High Energies (VHE,  > 100 GeV). We can now explore multiwavelength and multi-messenger connections in unprecedented detail, and derive the astroparticle implications of those results. In this presentation, leptonic and hadronic spectral modeling of blazars is reviewed with the intent of identifying ultra-high energy cosmic rays (UHECRs) in  the spectral energy distributions of these objects.  We consider a number of unusual results that could be explained by UHECRs in blazars:

(1) distinct spectral components revealed by deabsorption of blazar VHE spectra;
(2) flattening at moderate redshift in the Stecker-Scully relation showing the GeV - TeV spectral   index difference versus redshift;
(3) conflicting results for the location of the gamma-ray emission site in blazars;
(4) the unusually short variability times of luminous blazars.

The arguments for and against radio galaxies and blazars being the sources of the UHECRs are reviewed, and predictions for UHECR composition is made if BL Lac objects accelerate most of the UHECRs. Unusual effects of UHECR acceleration in blazars is illustrated by the strange case of 4C +21.35.  We also discuss effects of hypothetical axions, a dark matter candidate, in the interpretation of unusual blazar behavior, and a recent Fermi-LAT search for axions in occultations of bright AGNs by the Sun.

The history of the universe in a nutshell, from the Big Bang to now, and on to the future – John Mather will tell the story of how we got here, how the Universe began with a Big Bang, how it could have produced an Earth where sentient beings can live, and how those beings are discovering their history.  Mather was Project Scientist for NASA’s Cosmic Background Explorer (COBE) satellite, which measured the spectrum (the color) of the heat radiation from the Big Bang, discovered hot and cold spots in that radiation, and hunted for the first objects that formed after the great explosion.  He will explain Einstein’s biggest mistake, how Edwin Hubble discovered the expansion of the universe, how the COBE mission was built, and how the COBE data support the Big Bang theory.  He will also show NASA’s plans for the next great telescope in space, the James Webb Space Telescope.  It will look even farther back in time than the Hubble Space Telescope, and will peer inside the dusty cocoons where stars and planets are being born today. It is capable of examining Earth-like planets around other stars using the transit technique, and future missions may find signs of life. 

A triumph of contemporary physics is the highly successful description of the most fundamental constituents of Nature and their excitations. Recent theories of “topological insulators” [1,2] have shown that in the complex and emergent world of condensed matter physics, one can engineer the interplay between fundamental symmetries, band structure and spin-orbit coupling to create novel energy-spin-momentum relationships for band electrons and to yield effective realizations of exotic particles predicted but yet unobserved in Nature.  This Colloquium will describe the experimental routes we are pursuing in this context to build "detectors" for such particles, by coupling the surface states of a topological insulator with the gauge symmetry breaking effects of superconductivity [3] and the time-reversal symmetry breaking effect of magnetism [4.5].
1. M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82, 3045 (2010).
2. Xiao -Liang Qi and Shou-Cheng. Zhang, Rev. Mod. Phys. 83, 1057 (2011).
3. Duming Zhang et al., Phys. Rev. B 84, 165120 (2011).
4. Su-Yang Xu et al., Nature Physics 8, 616 (2012).
5. Duming Zhang et al., arxiv: 1206.2908.

Why does a piano sound like a piano? A similar question can be asked of virtually all musical instruments. A particular note, such as middle C, can be produced by a piano, a violin, and a clarinet.  Yet, it is easy for even a musically untrained listener to distinguish between these instruments.  One would like to understand why the sound of the “same” note depends greatly on the instrument.  In particular, we would like to understand what aspects of the piano are most critical in producing its musical tones.  The questions we will address in the talk include:

• Who invented the piano and why?
• Why does the piano have 88 keys and not more or fewer?
• How and why is the tone color of a loud note different from that of a soft note, and why is this important?
• Why are the bass strings on a piano made by wrapping a coil of wire around a central wire core?
• A piano tone is the sum of components that can be described by sine waves. The frequencies of these sine waves deviate a small amount from a simple harmonic series. What is the source of these deviations and why are they important?

After we have addressed all of these questions, we’ll be able to understand why a piano sounds like a piano.

Entropy can order shapes into complex structures, even in the absence of explicit attractive forces. As such, shape is important in the self assembly and crystallization of colloids, nanoparticles, proteins and viruses, and in the packing of granular matter.  Using computer simulations of nearly 200 different hard polyhedra, including families of tetrahedra, we demonstrate the emergence of entropic bonds and show how simple measures of building block shape and local order in fluid phases can predict crystals and quasicrystals, liquid crystals, rotator crystals, and glasses.  From these findings, we propose design rules for entropically patchy particles.

From the earliest days of the field of quantum information, trapped atomic ions have had great potential as qubits. Trapped-ion experiments have separately demonstrated the individual ingredients believed necessary for scalable quantum information processing, and, for small numbers of ions, many of these ingredients have been combined within the same experimental system. The central challenge going forward is to enlarge these systems, so that many more qubits can be controlled at a much higher level of accuracy. This will require advances in ion trap materials and designs; a higher level of integration between traps, optics, and control systems; and a greater degree of automation in the experiments. I will discuss work in several of these areas, including the coupling of ions in separate traps, a record-high fidelity single qubit gate, and recent progress in microfabricated ion trap technologies.

Spin electronics in its broadest definition is the study of systems where both the charge and the spin of the electron play a role.  The term was originally intended as a new technological concept, where traditionally the electron’s charge is important because transistors rely on currents and voltages, while the electron’s spin is important only in magnetic materials used for memory; spin electronics represents a new hybrid system.  Examples range from technological developments such as MRAM (magnetic random access memory) that are based on magnetic tunnel junctions, to some forms of quantum computing.  More broadly, spin electronics can be viewed as the visibility of and strong interactions between charge and spin in highly correlated electron materials such as high Tc superconductors, colossal magnetoresistance manganites, and doped semiconductors near the metal-insulator transition. 

I will discuss why these materials show such unusual spin-charge properties, and efforts to introduce magnetic moments into semiconducting materials, focusing particularly on our work on amorphous Si doped with magnetic ions such as Gd or Mn.  These alloys possess dramatic magnetic and transport properties due to electron-electron and electron-local moment interactions, including enormous (many orders of magnitude) negative magnetoresistance.  These amorphous materials provide an important counterpart to the more traditionally studied crystalline magnetically-doped semiconductors.

Extreme-mass-ratio binaries, composed of a small compact object (SCO) and supermassive black hole (SMBH), are eventual observational candidates for future space-based gravitational wave observatories.  Theoretically, these binaries are examples of the as-yet not thoroughly solved two-body problem in general relativity.  Extreme-mass-ratio inspiral (EMRI) calculations proceed by using black hole perturbation theory.  The gravitational field of the small mass affects its own orbit in the background geometry, leading to a radiation reaction that is formally divergent.  Regularization procedures tell how to compute the finite corrections to the SCOs orbit (the self force).  These require accurate knowledge of the perturbed metric.  We describe two, similar methods for computing the first-order gravitational perturbations and accurately determining the local perturbations in the metric.  Both involve use of mixed frequency domain/time domain methods.