Colloquium Spring 2012

Following Terms

January 9
Emerging Quantum Optical Networks
Joseph Kerckhoff
NIST & University of Colorado


Economic and environmental pressures continually push information systems smaller and to operate at lower energies. As a consequence, optical technologies are increasingly utilized to connect computing devices over short distances. For similar reasons and in view of recent advances in nanophotincs, large scale electro-optical integration in processors could also be advantageous. These trends raise some fundamental hardware questions however. For example, the energy equivalent of today’s CMOS logic operation is a countable number of photons. How could we control a physical optical "bit" with significant quantum noise? Can the full quantum complexity and emergent behavior of an optical network be engineered? The stability problem is illustrated by a recent experiment in which quantum fluctuations destabilize bistability (a canonical context for digital logic) in an ultra-low energy, highly non-linear optical device. On the other hand, the emergence of a new binary switching phenomena in this device is also compelling. I will discuss a proposal for stabilizing related devices with a simple, on-chip and alloptical feedback network, utilizing a nascent theory of quantum optical circuits that resembles a noncommutative generalization of electrical circuit theory. Finally, I will describe a potential all-optical feedback network capable of stabilizing an unknown quantum superposition state without external oversight or even a regulating "clock", demonstrating the wide scope of quantum optical control.

January 16
Martin Luther King Jr. Holiday

January 23
Strong Light-Matter Interactions in Semiconductor Quantum Dots Coupled to Photonic Crystals
Edo Waks
Nanophotonics Group
Electrical & Computer Engineering
University of Maryland


Two dimensional photonic crystals have been recognized as a highly promising scalable platform for compact integrated photonics. Another important aspect of photonic crystals is their ability to localize and trap light to spatial volumes on the order of a cubic wavelength, resulting in extremely high electromagnetic intensities. Recently, it has been shown that by embedding a single quantum dot (QD) in the high field region of photonic crystal cavities it becomes possible to achieve strong light-matter interactions at the single photon/single atom level. These unprecedented interaction strengths open up the possibility for creating nonlinear optical effects approaching the single photon level. In addition, they can be exploited to engineer unique quantum mechanically entangled states of light and matter that enable scalable quantum networks. In this talk, I will discuss our work on coupling indium arsenide (InAs) QDs to photonic crystal structures for creating nonlinear optical interactions at low photon numbers, and for storing and transferring quantum information from QD spin to photons for quantum networking. I will describe an experimental demonstration of giant optical Stark shifts with only 10 photons of energy by using a strongly coupled cavity-QD system, as well as a recent demonstration of alloptical switching with only 150 photons of control energy. I will then describe our work on coupling QD spin to light in order to realize a quantum transistor that can exhibit the quantum mechanical property of entanglement. The quantum transistor could enable a novel class of opto-electronic devices that serve as a fundamental building block for quantum computers and quantum networks.

January 30
Today's colloquium by Richard G. Harris, D-Wave Systems has been rescheduled to February 13.

February 6
The Origin of the Universe and the Arrow of Time
Sean Carroll
Senior Research Associate
Moore Center for Theoretical Cosmology and Astrophysics
Physics Department
California Institute of Technology


Over a century ago, Boltzmann and others provided a microscopic understanding for the tendency of entropy to increase. But this understanding relies ultimately on an empirical fact about cosmology: the early universe had a very low entropy. Why was it like that? Cosmologists aspire to provide a dynamical explanation for the observed state of the universe, but have had very little to say about the dramatic asymmetry between early times and late times. I will discuss whether the problem of low-entropy initial conditions can be alleviated within the context of a multiverse.

February 13
Introduction to D-Wave One Processor
Richard G. Harris
D Wave Systems, Inc.


The D Wave One is a prototype computing platform that harnesses a physical process referred to as quantum annealing. The technology is built on a superconducting chip composed of analog devices that enable a quantum annealing algorithm and digital components that apply programmable on-chip flux biases. This lecture will provide a high level introduction to the D-Wave One processor architecture and a discussion of the promises and challenges that have been encountered. I will conclude with a brief glimpse of a second generation processor currently in development.

February 20
President's Day Holiday

February 27
Energy Technology Innovation and Public Policy
Prof. Venkatesh Narayanamurti
The Narayanamurti Group
Department of Physics
Harvard University


The talk will discuss the main ingredients for nurturing successful science and technological innovation institutions, drawing on lessons from the past, and the need to create new structures to bridge the basic-applied dichotomy. It will revisit the Vannevar Bush paradigm, Science the Endless Frontier for a research –innovation ecosystem appropriate for the 21st century. A major part of the talk will include reviewing the results of a 3-year study at Harvard University to develop actionable recommendations for transforming the U.S. energy innovation system, which spans work at universities, national labs and industry.

March 5
Strong correlations and disorder in bosonic systems
Tommaso Roscilde
Assistant Professor
Laboratoire de Physique
Ecole Normale Superierure de Lyon


The study of strongly interacting quantum particles in a disordered environment is one of the hardest problems in condensed matter, and nonetheless it applies to a large variety of physical systems (liquid He in porous media, granular superconductors, cold atoms in random optical potentials, disordered magnetic systems, etc.). The coexistence of disorder and strong interactions gives rise to a rich showcase of novel phases, including insulating phases in which particles are trapped by disorder (localized phases), and conducting phases in which quantum tunneling assisted by the interactions allow the particles to escape localization. These phenomena are still relatively poorly understood for fermionic particles. In the case of bosons, on the other hand, we observe a recent explosion of theoretical and experimental studies which can unveil the nature of insulating and conducting phases, and of the quantum phase transition connecting them. It is very charming to observe that widely different physical systems (whose energy scales could differ by more than ten orders of magnitude) allow one to tackle the common problem of reconstructing the universal phase diagram of disordered bosons with interaction. In this presentation I will review some of the progresses and open problems in the domain of disordered bosons with interaction, as well as our recent results, focusing on the theory of cold atoms in random or quasi-periodic potentials, and of magnetic quasiparticles in chemically doped magnetic insulators.

March 19
The BioRC Biomimetric Real-Time Cortex Project
Alice C. Parker
Ming Hsieh Department of Electrical Engineering


This talk describes the BioRC project, beginning with the challenges facing the construction of a synthetic cortex. The talk then describes collaborative work with Chongwu Zhou on working carbon nanotube synapses (the mechanisms supporting communication between neurons). The talk will then survey the scope of the BioRC project. Time permitting, the talk will also describe progress in incorporating interactions between glial cells and neurons, implementation of noisy/chaotic neurons, and implementing structural plasticity.

March 26
Coated Nanoparticles in Solution and at Interfaces
Dr. Gary Grest
Center for Integrated Nanotechnologies
Sandia National Lab


Among the most prevalent ways to control the assembly and integration of nanoparticles is to coat them with organic molecules whose specific functionalized groups modifies their inter particle interactions as well as the interaction of nanoparticles with their surrounding, while retaining their inherent properties. While it is often assumed that uniformly coating spherical nanoparticles with short organic will lead to symmetric nanoparticles, I will show using explicit-atom molecular dynamics simulations of model nanoparticles that the high curvature of small nanoparticle and the relatively short dimensions of the coating can produce highly asymmetric coating arrangements. In solution geometric properties dictate when a coating’s spherical symmetry will be unstable and that the chain end group and the solvent play a secondary role in determining the properties of surface patterns. At the water-vapor interface the anisotropic nanoparticle coatings seen in bulk solvents are reinforced by interactions at the interface. The coatings are significantly distorted and oriented by the surface and depend strongly on the amount of free volume provided by the geometry, end group, and solvent properties. At an interface any inhomogeneity or asymmetry tends to orient with the surface so as to minimize free energy. These asymmetric and oriented coatings are expected to have a dramatic effect on the interactions between nanoparticles and can influence the structures of aggregated nanoparticles which self-assemble in the bulk and at surfaces.

April 2
Benchmarking quantum annealing with 108 qubits on DWave One
Sergio Boixo
Information Sciences Institute


The architecture and some of the design principles of DWave One, a programmable quantum optimizer with 108 functional qubits, will be reviewed. This chip implements quantum annealing to find the ground state of spin glass Hamiltonians. Recent data will be presented from the benchmarking being carried out at ISI - USC, and how it compares against classical algorithms. Finally, preliminary experiments will be presented which we believe directly support the conclusion that this chip is using quantum resources for information processing.

April 9
Controlling the rate of axon outgrowth: a potential axon guidance mechanism?
Samantha J. Butler

April 16
Structural Control of Charge Flow Through Biomacromolecules
David Beratan
Beratan Research Group
Duke University


The last 20 years have witnessed impressive developments in our understanding of biological electron transfer reaction mechanisms. Eclipsing early pictures of biomacromolecules as static and structureless one-dimensional square tunneling barriers, atomistic views point to a rich landscape for thermally fluctuating tunneling pathways, incoherent hopping chains, and mixed transport mechanisms, depending upon structure, energetics, and thermal fluctuations. I will describe some of the emerging structure-function relationships for these reactions, which inform our understanding of energy flow in natural systems, as well as in structures of interest in nanotechnology and energy science.

April 23
Better Living Through Hyper-Mutation
Myron F. Goodman
Biological Sciences and Chemistry


DNA damage leads to mutations, and that’s almost always bad. Enzymes designed to scan double-stranded DNA to eliminate damaged DNA bases have been extensively studied. Yet, mutations are also needed to generate genetic diversity. There are enzymes designed to scan single-stranded (ss)DNA to introduce “damaged” DNA bases, for example, by converting the base cytosine to uracil. Little is known about enzymes that scan ssDNA and how these enzymes locate suitable target motifs to mutate. We will discuss our recent studies with two ssDNA scanning enzymes. AID (activation-induced cytidine deaminase) hyper-mutates the variable regions of immunoglobulin genes to make highly diverse antibodies. Apo3G hyper-mutates HIV-1 to disable the virus. I will discuss a random-walk model and single molecule FRET experiments that address how ssDNA scanning and motif targeting occur.


  • Department of Physics and Astronomy
  • University of Southern California
  • 825 Bloom Walk
  • ACB 439
  • Los Angeles, CA 90089-0484