# Quantum++

## Version 6.0 - 14 April 2025

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---

## About

**Quantum++** is a modern C++ general purpose quantum computing library,
composed solely of template header files. **Quantum++** is written in standard
C++17 and has very low external dependencies, using only the
[Eigen 3](https://eigen.tuxfamily.org) linear algebra header-only template
library and, if available, the [OpenMP](https://www.openmp.org/)
multiprocessing library.

**Quantum++** is not restricted to qubit systems or specific quantum
information processing tasks, being capable of simulating arbitrary quantum
processes. The main design factors taken in consideration were the ease of use,
high portability, and high performance. The library's simulation capabilities
are only restricted by the amount of available physical memory.

To report any bugs or ask for additional features/enhancements, please
[submit an issue](https://github.com/softwareQinc/qpp/issues) with an
appropriate label.

If you are interested in contributing to this project, feel free to contact us.
Alternatively, fork the repository, create a custom branch, add your
contribution, then finally create a pull request. If we accept the pull
request, we will merge your custom branch with the latest main/development
branch. The latter will eventually be merged into a future release version. To
contribute, it is preferable to have a solid knowledge of modern C++
(preferably C++17 or later), including templates and the standard library, a
basic knowledge of quantum computing and linear algebra, and working experience
with [Eigen 3](https://eigen.tuxfamily.org).

For additional [Eigen 3](https://eigen.tuxfamily.org) documentation
see <https://eigen.tuxfamily.org/dox/>. For a simple
[Eigen 3](https://eigen.tuxfamily.org) quick ASCII reference see
<https://eigen.tuxfamily.org/dox/AsciiQuickReference.txt>.

Copyright (c) 2017 - 2025 softwareQ Inc. All rights reserved.

---

## License

[Quantum++](https://github.com/softwareQinc/qpp) is distributed under the MIT
license. Please see the
[`LICENSE.txt`](https://github.com/softwareQinc/qpp/blob/main/LICENSE.txt)
file for more details.

---

## Installation instructions and further documentation

Please see the installation guide
[`INSTALL.md`](https://github.com/softwareQinc/qpp/blob/main/INSTALL.md) and
the comprehensive [Wiki](https://github.com/softwareQinc/qpp/wiki) for further
documentation and detailed examples.

To generate the full official API documentation in both LaTeX and HTML formats
run
[`doxygen`](https://www.doxygen.nl) on
the [`Doxyfile`](https://github.com/softwareQinc/qpp/blob/main/Doxyfile) file.
The tool `dot` from the [`Graphviz`](https://www.graphviz.org) package must be
installed (`sudo apt-get install graphviz` on Ubuntu/Debian Linux,
or `brew install graphviz` on macOS). Running `doxygen` will generate the
documentation directory `doc` containing both the HTML and LaTeX documentation.

The HTML documentation file will be accessible by opening `doc/html/index.html`
with the browser of your choice. To generate a PDF file of the documentation,
run

```shell
latexmk -pdf refman.tex
```

from the `doc/latex` directory or compile the file `doc/latex/refman.tex` with
your LaTeX compiler. This will create the `doc/latex/refman.pdf` documentation
file. Consult your favourite LaTeX manual for how to compile/build LaTeX files
under your specific operating system.

---

## Python 3 wrapper

[**pyqpp**](https://github.com/softwareQinc/qpp/blob/main/pyqpp) is a Python 3
wrapper for **Quantum++**. **pyqpp** requires the same dependencies as
**Quantum++**, and can be installed using `pip`

```shell
pip install git+https://github.com/softwareQinc/qpp
```

For more details, please see
[pyqpp/README.md](https://github.com/softwareQinc/qpp/blob/main/pyqpp/README.md).
