QmeQ is an open-source Python package for calculations of transport through quantum dot devices. The so-called Anderson-type models are used to describe the quantum dot device, where quantum dots are coupled to the leads by tunneling. QmeQ can calculate the stationary state particle and energy currents using various approximate density matrix approaches. As for now we have implemented the following first-order methods
- Pauli (classical) master equation
- Lindblad approach
- Redfield approach
- First order von Neumann (1vN) approach
which can describe the effect of Coulomb blockade. Additionally, there is a possibility to model electron-phonon interaction inside a quantum dot using the first-order approaches. QmeQ also has two second-order methods
- Second order von Neumann (2vN) approach
- Real Time Diagrammatic (RTD) approach
2vN and RTD approaches can address the effects of cotunneling and pair tunneling. Additionally, the 2vN approach can describe broadening of quantum dot states. The advantage of RTD approach is that it requires a lot less memory and computation time resources.
All the methods in QmeQ are approximate so depending on parameter regime they can fail, and a good knowledge of the method is required whether to trust the result or not. For example, Redfield, 1vN, and 2vN approaches can violate positivity of the reduced density matrix and lead to currents flowing against the bias. We still think it is important to have a package where a user can duplicate existing calculations, check applicability of different methods, or simply discover new kind of physics using different approximate master equations.
For installation instructions see INSTALL.md.
For an introduction to QmeQ see this tutorial and various examples.
QmeQ has The BSD 2-Clause License and it can be found in LICENSE.md.
Please consider citing QmeQ if the use of this project gives results which lead to scientific publication:
G. Kiršanskas, J. N. Pedersen, O. Karlström, M. Leijnse, and A. Wacker, QmeQ 1.0: An open-source Python package for calculations of transport through quantum dot devices, Comput. Phys. Commun. 221, 317 (2017).
The preprint version of the paper can be found on the arXiv.org server.