# Quantum Dot Physics

When electrons are confined to small spaces, they no longer apear to be pointlike particles, but instead behave as waves. Some well-known examples of electron wavefunctions are the atomic and molecular orbitals of physical chemistry. These wavefunctions are quantum states, whose behavior is described by the equations of quantum mechanics, such as SchÃ¶dinger's equation or Feynman path integrals. Recent advances in nanotechnology have given scientists the ability to fabricate, manipulate, image, and measure structures a few nanometers across. These nanostructures are composed of tens to thousands of atoms, and are able to confine electrons in quantum states. The simplest of these structures confine electrons in small spherical or circular spaces, and are known as quantum dots.

## Collaborators

- Drucker Research Group, Arizona State University
- Semiconductor Theory Group, Hariot-Watt University, Edinburgh, Scotland

## Publications

- Sutharsan Ketharanathan, Sourabh Sinha, John Shumway, and Jeff Drucker,
“
*Electron charging in epitaxial Ge quantum dots on Si(001),*” J. Appl Phys.**105**, 044312 (2009). - Lei Zhang, Jesper Pedersen, Matthew J. Gilbert, and J. Shumway,
*“Path integral study of the role of correlation in exchange coupling of spins in double quantum dots and optical lattices,”*(arXiv:0809.0038, pdf download 5 pp. 784 KB). - M. Wimmer, S. V. Nair, and J. Shumway,
*"Biexciton recombination rates in self-assembled quantum dots,"*Phys. Rev. B**73**, 165305 (2006) (pdf download 11 pp. 715 KB, cond-mat/0512603). - J. Shumway,
*"A Quantum Monte Carlo Method for Non-Parabolic Electron Bands in Semiconductor Heterostructures,"*J. Phys.: Condens. Matter**17**, 2563-2570 (2005).(pdf download 8 pp. 201 KB) - Michael R. Mckay, Jeff Drucker, and John Shumway,
*“Real-Time Coarsening Dynamics of Ge/Si(100) Nanostructures Using Elevated Temperature Scanning Tunneling Microscopy,”*in*Stability of Thin Films and Nanostructures*, edited by R.P. Vinci, R. Schwaiger, A. Karim, and V. Shenoy (Mater. Res. Soc. Symp. Proc.**854E**, Warrendale, PA , 2005), U4.6. - M. Harowitz and J. Shumway,
*"Path Integral Simulations of Charged Multiexcitons in InGaAs/GaAs Quantum Dots,"*pp.697-698 in Physics of Semiconductors: 27th International Conference on the Physics of Semiconductors, edited by José Menéndez and Chris G. Van de Walle (AIP 2005). (pdf download 2 pp. 242 KB) - Gabriel Bester, Alex Zunger, and J. Shumway
*"Broken-Symmetry and Quantum Entanglement of an exciton in InGaAs/GaAs Quantum Dot Molecules,"*Phys. Rev. B**71**, 075325 (2005). - G. Bester, J. Shumway, and A. Zunger, "
*Theory of excitonic spectra and entanglement engineering in dot molecules*," Phys. Rev. Lett.**93**, 047401 (2004). (cond-mat/0406725). - J. Shumway, A. Franceschetti, and Alex Zunger,
*"Correlation versus mean-field contributions to excitons, multi-excitons, and charging energies in semiconductor quantum dots,"*Phys. Rev. B**63**, 155316 (2001). ( cond-mat/0012050). - J. Shumway, L. R. C. Fonseca, J. P. Leburton, Richard M. Martin, and
D. M. Ceperley,
*"Electronic structure of self-assembled quantum dots: comparison between density functional theory and diffusion quantum Monte Carlo,"*Physica E**8**, 260-268 (2000). ( cond-mat/0003140).

## Resources

A major component of our research program is the development of computer algorithms for solving the equations of quantum physics. These computer simulations generate quantitative information about the dots and other quantum devices. Simulation data aids in design and interpretation of experiments, and form a link between general ideas of theoretical physics and detailed measurements of specific experiments. Our specialty is the use of stochastic algorithms, known as Quantum Monte Carlo (QMC).

Reproducibility of calculations is important to scientific integrity and progress in computational physics. We are releasing source code for some of our quantum dot simulations in an effort to cooperate with other research groups and aid begining researchers. These nanostructure modeling codes are being distributed under the GNU GPL for open source software.