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Professor Erik Sorensen  
Area: Condensed Matter Physics (Theoretical)
Erik Sorensen
Location: ABB 322
Phone: 905-525-9140 ext 27586
Fax: (905)546-1252
  1. Letter to Grad Students

December 2009

Erik Sorensen
Department of Physics & Astronomy
McMaster University

Dear Prospective Graduate Student,

My research is centered in condensed matter theory and computational physics. In general I have in the last few years been working within the area of strongly correlated systems, with an emphasis on understanding the critical properties of such systems. I have worked on a number of problems related to low-dimensional magnetism in particular one-dimensional S=1 and S=1/2 quantum spin chains, investigating the different phases and excitations. I am quite interested in quantum phase transitions; notably I have been working on the transitions occurring in the quantum Hall effect and transitions in low-dimensional magnets. I have also done some work on superconductivity, looking at the superconductor to insulator transition. Recently, I have become interested in quantum entanglement and quantum information and the relations these concepts have to strongly correlated systems. Another recent topic is the experimental realization of optical lattices that have been used for trapping cold atoms. I have a strong interest in computational physics and numerical methods in general (as well as in analytical techniques) and a considerable part of my research tends to use what one might call advanced numerical techniques such as densitry matrix renormalization group methods and quantum Monte Carlo. Some of these methods are well suited for parallel computers such as the SHARCnet facility that we will be using.

My most recent Ph D students were Fei Lin, now pursuing a postdoc at University of Illinois Urbana Champaign, and Fabien Alet, who recently got a CNRS position in France. Fei's Ph D work concerned strong correlation effects in fullerene molecules. Using large scale quantum Monte Carlo simulations he managed to determine the spectral functions for a single C60 molecule. Using this information, combined with cluster perturbation theory, one can gain significant insight into the physics of the molecular solids that C60 molecules form. These molecular solids are known to become superconducting at surprisingly high temperatures and Fei managed to clarify many aspects of a proposed purely electronic mechanism for the superconducting transition. Fabien Alet, used continuous time quantum Monte Carlo methods to study low dimensional magnetism and quantum impurities. Some of his results on low temperature susceptibility and on-site magnetization can be directly measured in NMR experiments. However, most of his thesis work was spent studying and developing efficient methods for doing quantum Monte Carlo simulations using worm algorithms. He succesfully developed a new Monte Carlo algorithm that we subsequently applied to study quantum phase transitions in bosonic systems with an unprecedented detail. My most recent M. Sc student was Peter Hitchcock, who moved to Cornell university for his Ph D. Peter did his Masters thesis on the persistent current in small mesoscopic rings with an impurity in them. He studied this problem using an almost exact Hirsch-Fye quantum Monte Carlo algorithm. For samples of recent papers I have written with students and postdocs, please see my web-page under "Recent Publications".

Advanced numerical methods are crucial for the study of many modern problems in physics and is extensively used in R\&D and in other areas of industry making use of C++ / F90. In my opinion, graduate students in the area of computational physics should have excellent job possibilities.

Erik Sorensen