Spring 2013 - The Hamilton Colloquium Series
4:30 PM Jadwin A10
February 7, 2013
University of California, Irvine
"A Condensed Matter Physicist Looks at Cancer, Tumor Location, and the Tumor Microenvironment"
We will discuss what physics can bring to cancer biology, and the types of questions that physicists can ask such as ``Why does a tumor grow where it does?'' and ``How does the microenvironment of a tumor affect its growth?'' Cancer cells do not act alone. They get their cues from the their environment which consists of the extracellular matrix and the cells (fibroblasts) that form it. These cues can be both chemical and mechanical in nature.
Host: Bob Austin
February 14, 2013
Duncan Haldane, Princeton University
"The Entanglement Spectrum: A new tool for studying quantum states of matter"
Until recently, the von Neumann entropy and its generalizations (Renyi) were the principal quantitative characterizations of entanglement. A richer characterization, first developed here at Princeton, is becoming the tool of choice for investigating topological (and conventional) order in quantum ground states of condensed matter systems. A Schmidt decomposition that partitions the ground state between two sets of degrees of freedom can be presented as the spectrum of the reduced density matrix, characterized by symmetry quantum numbers, analogous to the spectrum of elementary excitations of a Hamiltonian. From this spectrum, a rich amount of information about the ground state, both topological and geometrical, can be extracted.
Host: Phuan Ong
February 21, 2013
Roderich Moessner, Max-Planck Institute for the Physics of Complex Systems, Dresden
"Magnetic Monopoles in Spin Ice"
Magnetic monopoles were first proposed to exist by Dirac many decades ago as the natural counterparts of electrically charged particles such as the electron. Despite much searching, no elementary monopoles have ever been observed, even though many theories of high-energy physics suggest that they should be present. Here, we present an alternative route for the observation of monopoles as a low- rather than a high-energy phenomenon. It involves a process known as fractionalization, which is a striking emergent phenomenon, in which an 'elementary' particle breaks up into two independent entities. A celebrated example of this is spin-charge separation, in which an electron's magnetic spin and electric (charge) properties appear to become independent degrees of freedom. The spin ice materials Dy_2Ti_2O_7 and Ho_2Ti_2O_7 provide a rare instance of fractionalization in three dimensions: their atomic magnetic dipole moments fractionalize, resulting in elementary excitations which can be thought of as magnetic monopoles.
This colloquium presents a self-contained introduction to theoretical concepts and experimental phenomena in the physics of spin ice. It focuses on the unique signatures of the peculiar nature of its ground state and its excitations. These include unusual neutron scattering structure factors, rich non-equilibrium physics, as well as a response to external magnetic fields that promotes spin ice as a magnetic Coulomb liquid, a magnetic analogue of an electrolyte. Finally, this talk addresses open questions and future perspectives for detecting individual monopoles, among them a (thought) experiment inspired by high energy physics.
Host: Shivaji Sondhi
February 28, 2013
Abhay Pasupathy, Columbia University
"What drives electronic nematicity in the iron-based superconductors?"
The iron arsenides are a recently discovered class of unconventional superconducting materials. This class of materials consists of various families (cryptically called 111, 122, 1111, etc.) each of which has a "parent" compound. These parent compounds (e.g. NaFeAs) are typically not superconducting, but display a spin-density wave phase at low temperature. Superconductivity emerges in these materials when the chemical composition of the parent is tuned. We believe that electronic interactions are responsible for both the magnetic and superconducting states, and identifying the details of these interactions is a key experimental goal. Along these lines, recent experiments have shown that the electronic structure of these materials spontaneously breaks the underlying lattice symmetry at high temperature, forming an electronic nematic state. I will present recent scanning tunneling microscopy experiments probing the nature of this nematic state at the atomic scale, and discuss its relationship to superconductivity in these materials.
Host: Ali Yazdani
March 7, 2013
Ignacio Cirac, PCTS lecturer, Max-Planck Institute for Quantum Optics, Garching
"Dissipation as a New Tool in Quantum Information Science"
Quantum entanglement, the most striking feature of quantum mechanics, is also the basic ingredient in most applications in the field of quantum information. Unfortunately, it is very fragile: in all experiments so far the coupling of the systems to the environment has lead to dissipation which either destroys entanglement or prevents its generation. Here we propose, analyze, and demonstrate a new method to entangle two distant macroscopic atomic ensembles by purely dissipative means. This counterintuitive effect is achieved by engineering the coupling of our systems to the environment, and leads to a more robust and therefore longer lived entanglement. Apart from that, we show that engineered dissipation can be used in quantum computation and communication, as well as to create passive quantum memories.
Host: Igor Klebanov
March 14, 2013
William Young, Scripps Institution of Oceanography, University of California, San Diego
"Two Dimensional Turbulence"
In the first part of this talk I will review basic results about two-dimensional turbulence emphasizing the absence of a dissipative anomaly in D=2, and the energy-conserving long-time behavior of solutions of the inviscid equations of motion. Arguments dating back to Onsager predict the formation of an ensemble of vortices separated by potential flow. Close encounters between like-signed vortices lead to irreversible merger into larger vortices. A simple scaling argument predicts relations between different quantities, such as the decay of the vortex density and the expansion in radius of a typical vortex. In the second part of the talk I will turn to forced two-dimensional turbulence and the problem of vortex condensation into the gravest mode of a finite box. I will show that for most forcing functions the amplitude of the condensate in the inviscid limit is independent of viscosity. This non-singular inviscid limit is compatible with the energy power integral because the flow adjusts so that the work done on the two-dimensional fluid by a prescribed force is linearly proportional to viscosity in the inviscid limit.
Host: Igor Klebanov
March 28, 2013
Alain Aspect, Institut d'Optique, Palaiseau
"From Einstein's intuition to quantum bits: a new quantum age?"
In 1935, with co-authors Podolsky and Rosen, Einstein discovered a weird quantum situation, where particles in a pair are so strongly correlated that Schrödinger called them “entangled.” By analyzing that situation, Einstein concluded that the quantum formalism was incomplete. Niels Bohr immediately opposed that conclusion, and the debate lasted until the death of these two giants of physics.
In 1964, John Bell produced the famous inequalities that have allowed experimentalists to settle the debate, and to show directly that the revolutionary concept of entanglement is indeed a reality.
Based on that concept, a new field of research has emerged, quantum information, where one uses quantum bits, the so-called “qubits.” In contrast to classical bits, which are either in state 0 or state 1, qubits can be simultaneously in state 0 and state 1. Entanglement between qubits enables conceptually new methods for processing and transmitting information. Large scale practical implementation of such concepts might revolutionize our society, as did the laser, the transistor and integrated circuits, some of the most striking fruits of the first quantum revolution, which began with the 20th century.
April 4, 2013
Amir Yacoby, Harvard University
“Quantum Information Processing and Metrology Using Few Electron Spins in Solids”
April 11, 2013
Frank Jenko, Max-Planck Institute für Plasmaphysik-Garching
"Exploring the Mysteries of Plasma Turbulence"
Plasma turbulence is a ubiquitous phenomenon, influencing the dynamics in most of the visible universe and playing a crucial role in countless experiments of basic and applied plasma science. Its comprehension and control is a prerequisite to the realization of fusion energy. At the same time, it constitutes a fascinating example of spatiotemporal chaos caused by the nonlinear coupling of many degrees of freedom in open systems. In recent years, new theoretical ideas, advanced computational methods, and improved measurement techniques have led to significant progress. Nevertheless, various fundamental aspects of turbulence in laboratory and astrophysical plasmas are still not well understood. The aim of this talk is to review the state of the art and outline future challenges in this active area of research.
Host: Matthew Kunz
8 p.m., April 25, 2013
38th Annual Donald Hamilton Lecture
Joe Incandela, University of California-Santa Barbara and CERN
"The Search for the Higgs Boson: Discovery at the LHC"
May 2, 2013
Eliot Quataert, University of California-Berkeley
"The Physics of Galaxy Cluster Plasmas"
Hamilton Colloquium Series