Copyright (c) 2017 by Alwin Zulehner, Stefan Hillmich, Alexandru Paler, and Robert Wille
Johannes Kepler University Linz, Austria
http://www.jku.at/iic/eda/ibm_qx_mapping

The software is intellectual property of the above mentioned authors. You can freely redistribute this software for non-commercial purposes as long as it includes a reference to its origin (e.g. by referring to the corresponding paper cited below).

Use at your own risk! In no event shall the authors be liable for any damages whatsoever (including without limitation damages for loss of business profits, business interruption, loss of business information, or any other pecuniary loss) arising from the use of or inability to use the software, even if the authors have been advised of the possibility of such damages.

If you have any questions feel free to contact us using [email protected]

In March 2017, IBM launched the project IBM Q with the goal to provide access to quantum computers for a broad audience. This allowed users to conduct quantum experiments on a 5-qubit and, since June 2017, also on a 16-qubit quantum computer (called IBM QX2 and IBM QX3, respectively). Later, further architectures have been added. In order to use these, the desired quantum functionality (e.g. provided in terms of a quantum circuit) has to properly be mapped so that the underlying physical constraints are satisfied – a complex task. This demands for solutions to automatically and efficiently conduct this mapping process. Here, we propose such an approach which satisfies all constraints given by the architecture and, at the same time, aims to keep the overhead in terms of additionally required quantum gates minimal. The proposed approach is generic and can easily be configured for future architectures. Experimental evaluations show that the proposed approach clearly outperforms IBM’s own mapping solution. In fact, for many quantum circuits, the proposed approach determines a mapping to the IBM architecture within less than five minutes (and within a fraction of a second in most cases), while IBM’s solution suffers from long runtimes and runs into a timeout of 1 hour in several cases. As an additional benefit, the proposed approach yields mapped circuits with smaller costs (i.e. fewer additional gates are required).

The package has been tested under Linux (Ubuntu 17.04, 64-bit) and should be compatible with any current version of g++/cmake. No additional packages are required.

To build the quantum simulator type:

mkdir build
cd build 
cmake ..
cmake --build .
cd ..
./build/ibm_qx_mapping "examples/4gt11_84.qasm" "mapped.qasm"

The mapping of a quantum circuit can be conducted as follows:

./build/ibm_qx_mapping <input_file> <output_file> maps the circuit <input_file> (given in the OpenQASM 2.0 format) to the IBM QX5 quantum processor. Note that this implementation contains only one certain aspect of the mapping procedure, namely satisfying the architectural constraints. Therefore, it assumes that the circuit is already decomposed into elementary operations. The resulting circuit is written to <output_file> and can then be executed on the IBM QX architecture. Our implementation does not perform post mapping optimization (as done e.g. in IBM's Python SDK). However, they can be easily conducted by passing the resulting circuit to IBM's SDK.

If you use out mapping algorithm for your research, we would be thankful if you referred to it by citing the following publication:

@article{zulehner2019efficient,
  title={An efficient methodology for mapping quantum circuits to the {IBM} {QX} architectures},
  author={Zulehner, Alwin and Paler, Alexandru and Wille, Robert},
  journal={{IEEE} Transactions on Computer-Aided Design of Integrated Circuits and Systems},
  volume={38},
  number={7},
  pages={1226--1236},
  year={2019}
}