# Colloquium Spring 2006

** **

** January 9**

** Observable Entanglement Signatures and Nonlinear Response**

Alexandre Zagoskin

Condensed MAtter Theory Research Group, Physics and Astronomy, University of British Columbia

** January 16**

** Martin Luther King, Jr. Day, University Holilday**

**January 17**

- 4:15 in SLH 102 (Note Special Day)

** Tetrapyrroles: From Quantum Interference to Cancer Therapy**

Aleksander Rebane

Physics, Montana State University

**Abstract**

Tetrapyrroles are organic dyes that are used for an amazing variety of different purposes ranging from optical storage to medicine. Their enormous versatility lies in their special atomic-like optical transitions, which are only weakly coupled to vibrational motion. On the other hand, because tetrapyrroles are closely related to hemoglobin and chlorophyll, they are also inherently compatibility with living organisms. In my talk I will discuss selected applications that include ultrafast time-space holography, nonlinear multi-photon absorption, and photodynamic therapy of cancer. Much of the progress is due to the organic synthesis of novel functionalized compounds, which, in turn, relies on detailed spectroscopic studies of the underlying photophysics. I will conclude with an outlook of potential applications in biomedicine and information technology.

**January 23**

** Lattice Quantum Chromodynamics**

Keh-Fei Liu

High Energy and Particle Theory, Physics and Astronomy, University of Kentucky

**Abstract**

I will give a brief introduction of Lattice Quantum Chromodynamics (LQCD) as a practical tool to solving the strong interaction theory of quarks and gluons. A few examples of the recent developments in topological vacuum, multiquark hadrons and finite density will be given to show what numerical simulation can add to our understanding of physics in conjunction with experiments and phenomenology.

**January 30**

-Event Postponed to March 20th

** On the inevitable relativity of quantum entanglement: What do we know?**

Lorenza Viola

Condensed Matter, Department of Physics and Astronomy, Dartmouth College

**Abstract**

Quantum entanglement is one of the most basic and yet most elusive properties of quantum mechanics. In particular, characterizing and quantifying entanglement both plays an increasingly prominent role within quantum information science and provides a novel paradigm for understanding quantum correlations in complex systems. Physically, the property of a state being entangled or not is by no means unambiguously defined. Rather, it depends strongly on the way we decide to regard the whole as being composed of its part or, more generally, the way in which we are able to operationally characterize the system. In this colloquium, I will discuss in more detail the significance of such relativity and argue that a definition of entanglement directly based on quantum observables is able to capture the essence of entanglement in full generality. This path naturally leads to a notion of "generalized entanglement" which offers a unifying and flexible setting for analyzing quantum correlations. Time permitting, I will describe some recent applications to the study of quantum phase transitions and the dynamics of chaotic quantum systems.

** February 6**

** Physical Resources, Entanglement, and the Power of Quantum Computation**

Carlton Caves

Physics and Astronomy, University of New Mexico

**Abstract**

Requiring that a quantum computer not need an exponentially growing amount of any physical resource places stringent constraints on the systems that can act as quantum computers. In particular, a quantum computer must be made up of subsystems, usually qubits, thus ruling out implementing a quantum computer in a single atom or by using the interference of classical waves. Furthermore, if a quantum computer made up of subsystems performs some computation exponentially faster than any classical computer, there must be global entanglement among all the subsystems at some point during the computation. Having thus led up to the conclusion that quantum entanglement is the essential ingredient for quantum computation, I will discuss why this conclusion isn't ironclad.

** February 13**

** Novel one, two, three and four-dimensional phases of matter**

Milton Cole

Condensed Matter, Physics, Penn State

**Abstract**

In this talk I will describe some remarkable phases and phase transitions that we have predicted for both classical and quantum systems. First, I will explain what is meant by the term "dimension" in the context of phase transitions. Briefly stated, this refers to the number of space dimensions of a system that go to infinity. The dimensionality determines the kind of phases that are possible, the nature of the phase transitions, and the low and high temperature thermodynamic properties of a system. I will discuss several problems that we have studied in which one, two, three and/or four-dimensional behavior has been predicted to occur. Experimental evidence in support of these calculations will be described.

**February 20**

** President's Day, University Holiday**

** February 27**

** Cosmological Insights on Particle Physics**

Elena Pierpaoli

Theoretical Astrophysics and Relativity Group, Division of Physics, Mathematics, and Astronomy, Caltech

**Abstract**

The resuls of the last decade on the Cosmic Microwave Background (CMB) and the large scale structure have set major milestones in our understanding of the Universe. We now know the main cosmological parameters with very high precision and we are able to constrian particle physics with cosmology. I will review the theoretical interplay between particle physics and cosmology paying particular attention to neutrinos. I will show four different examples of interpaly between particle physics and cosmology, and show that cosmology now provides the tighest upper limit for the neutrino mass. I will discuss how large scale structure, clusters of galaxies in particular, complement the cosmic microwave background experiments in determining cosmological parameters.

** March 6**

** Rocket Science, Cancer, and the Movies: Diverse and Interdisciplinary Directions in Applied Physics**

Martin Gundersen

University of Southern California

**Abstract**

The talk will review interdisciplinary applied physics research that is investigating transient energetic systems. An introduction to pulsed power used to generate large amplitude electric fields for times of the order nanoseconds will first be given. As interdisciplinary examples, studies of a cancer therapy (working collaboratively with medical researchers at USC and Cedars-Sinai), and the ignition of fuels (in collaboration with several laboratories for rocket and jet engine research) will be presented. In the area of cancer research, studies of nanosecond pulsed electric fields for the induction of apoptosis (programmed cell death) in cancer cells in vitro and tumors in vivo will be described, and promising results for a potential therapy for pancreatic cancer will be reported. Studies of rocket engine ignition will be reported that include enabling results for the ignition of pulse detonation engines. Finally, a project to encourage improved portrayals of science in film for the purpose of stimulating interest in science and engineering, involving recent workshops held at the American Film Institute, will be described.

** March 13**

Spring Recess

** March 20**

-Event Postponed to March 20th

** On the inevitable relativity of quantum entanglement: What do we know?**

Lorenza Viola

Condensed Matter, Department of Physics and Astronomy, Dartmouth College

**Abstract**

Quantum entanglement is one of the most basic and yet most elusive properties of quantum mechanics. In particular, characterizing and quantifying entanglement both plays an increasingly prominent role within quantum information science and provides a novel paradigm for understanding quantum correlations in complex systems. Physically, the property of a state being entangled or not is by no means unambiguously defined. Rather, it depends strongly on the way we decide to regard the whole as being composed of its part or, more generally, the way in which we are able to operationally characterize the system. In this colloquium, I will discuss in more detail the significance of such relativity and argue that a definition of entanglement directly based on quantum observables is able to capture the essence of entanglement in full generality. This path naturally leads to a notion of "generalized entanglement" which offers a unifying and flexible setting for analyzing quantum correlations. Time permitting, I will describe some recent applications to the study of quantum phase transitions and the dynamics of chaotic quantum systems.

**March 27**

** Lost in Translation: Writing about Science for the General Public**

KC Cole

Annenberg School for Communication, USC

**Abstract**

Writing, like science, is primarily a matter of noticing what goes on in the world and communicating these insights to others. Both require a certain amount of translation, and in the process, distortion. Writing about science is thus doubly cursed, and makes some surprising demands on the writer. Among the (only partly tongue-in-cheek) requirements to be discussed are: Lie; cheat; steal; dare to be stupid; don't trust your sources (or your editors); waste peoples��� time; quote out of context; make arbitrary calls; don't expect anyone to understand you; don't expect anyone to believe you; prepare to make mistakes; avoid "hardening of the categories"; debase yourself, but never your readers; eschew objectivity; emote.

** April 3**

** Exchange Interactions in Molecular Magnets -- Understanding Mn_12**

Bruce Normand

Ecole Polytechnique Fédérale de Lausanne

**Abstract**

Despite extensive recent interest in nanomagnetic systems, the microscopic nature of their magnetic properties remains in general poorly understood. This colloquium traces the multidisciplinary detective story integrating chemical synthesis, physical experiment and computational theory to deduce the underlying interactions in the prototypical molecular magnet Mn_12-acetate.

**April 10**

** Development of quantum bits based on the Single Cooper Pair Box**

Pierre Echternach

Jet Propulsion Laboratory

**Abstract**

The Single Cooper Pair Box is a promising approach for implementation of a quantum bit. Progress in developing a regular and a differential Single Cooper Pair Box will be described. A simple method for measuring the quantum capacitance (QC) of a Single Cooper-Pair Box charge qubit using a Radio-Frequency Single Electron Transistor will be discussed. Measurement of the QC, which is proportional to the second derivative of the energy bands, can in principle be used for state readout at the degeneracy point, where decoherence due to fluctuating charges is at a minimum. The QC is measured by examining the response of the qubit to a small-amplitude AC excitation. Using this technique, an independent measurement of the qubit relaxation time can made.

** April 17**

** Micro- and Nanodevice Enabled Studies of Spin, Mechanical, and Spin-Mechanical Systems**

Hong Tang

Department of Physics & Kavli Nanoscience Institute, California Institute of Technology

**Abstract**

Recent developments in lithographic techniques make it possible to prepare novel micro- to nanoscale devices to investigate spin-coupled mesoscopic phenomena in magnetic systems. We have studied properties of individual magnetic domain walls (a local twist of spin) in multiterminal GaMnAs devices. Employing "giant Planar Hall effect", which we discovered in GaMnAs, we have been able to manipulate and electrically measure single magnetic domain walls such devices. This work has consistently revealed negative domain wall resistivity, apparently of quantum mechanical origin. In the second part of my talk, I will give an overview of our recent work on nanoelectromechanical systems. I will present several emerging applications of nanoscale mechanical devices, ranging from study of quantum phenomena in mechanical systems, to developing devices to weigh individual molecules, to electromechanical "nose" applications. I will conclude by discussing some interesting studies that merge these two exciting areas -based upon GaMnAs nanomechanical resonators, which represent a new class of hybrid spin-mechanical systems.

** April 24 **

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

- Phone: (213) 740 - 0848
- Email: physics@dornsife.usc.edu