## Overview

### News from our Group

- New publication:
“
*Tuning biexciton binding and anti-binding in core/shell quantum dots*,” Peter G. McDonald, Edward J. Tyrrell, John Shumway, Jason M. Smith, and Ian Galbraith, Phys. Rev. B**86**, 125310, (2012). - New publication:
“
*Chemical recognition and binding kinetics in a functionalized tunnel junction*,” S. Chang, S. Huang, H. Liu, P. Zhang, F. Liang, R. Akahori, S. Li, B. Gyarfas, J. Shumway, B. Ashcroft, J. He, and S. Lindsay, Nanotechnology23 , 235101 (2012). - New publication:
“
*Effects of Fermion Flavor on Exciton Condensation in Double Layer Systems*,” J. Shumway and M. J. Gilbert, Phys. Rev. B**85**, 033103, (2012). is live on nanoHUB with new documentation.*pi-qmc*

## Research

### Path Integral Quantum Monte Carlo

Path integrals allow us to solve physics problems by summing over many trajectories. This approach is well suited for problems involving quantum and thermal fluctuations, and it has a smooth crossover to classical physics. The path integrals may be efficiently evaluated with Monte Carlo sampling on modern PC's and high-performance computing clusters.

### Quantum Dots

The term “quantum dot” can refer to any structure that exhibits three-dimensional quantum confinement of electrons. We focus our studies on self-assembled heteroepitaxial dots, especially InGaAs/GaAs and Ge/Si. With NSF-CAREER funding we have developed efficient path integral simulations for quantum dots that allow us to calculate equilibrium dot occupation, exciton recombination rates, polarizabilities, and other properties of realistic quantum dot models.

### Nanoelectronics

At the nanometer length scale, electronic currents exhibit quantum effects such as quantized conductance and ballistic transport. Through the SRC-NRI SouthWest Institute for Nanoelectronics (SWAN) we are developing new path-integral simulation techniques to evaluate novel nanoscale switching devices. Our theoretical approach utilizes current-current fluctuations in the framework of Kubo's linear response theory.

### Ultracold Trapped Atoms

One of the biggest advances in condensed matter physics in recent years is new experimental connections to atomic physics. By cooling atoms to nanokelvin temperatures on atomic lattice, scientists have created new realizations of common condensed matter models. We use path integral methods to study properties of bosonic and fermionic atoms in optical lattices.

### Warm Dense Matter

At high temperatures and high densities—as found in gas giant planets or in fusion experiments—we must often resort to computer simulations to learn about material properties. In collaboration with Lawrence Livermore National Laboratory and ASU's School of Earth and Space Exploration, we are studying properties of hot, dense hydrogen and helium and other materials.

## Resources

### Simulation Tools

As part of our the broader impact of our NSF-CAREER research grant, we develop and distribute open-source simulation tools for modeling quantum dots. These tools are object-oriented and make heavy use of structure XML and HDF5 data formats. We regularly run these simulations on Mac OSX and Linux PC's and high-performance computing centers, including ASU's Fulton HPC and the NSF Teragrid.

### Classroom Tutorials

As further outreach, we have ported key parts of our object-oriented path integral simulation code to Java. This classroom demo performs live simulations of sixteen bosons to demonstrate Feynman's path integral model of Bose condensation. At ASU we have used this tutorial to supplement lectures on path integrals in our senior level quantum mechanics and graduate statistical mechanics courses.