This plugin requires Python version 3.6 or above, as well as PennyLane and Qulacs. Installation of this plugin, as well as all dependencies, can be done using pip:

$ pip install pennylane-qulacs["cpu"]

Note that you need to include whether to install the CPU version (pennylane-qulacs["cpu"]) or the GPU version (pennylane-qulacs["gpu"]) of Qulacs for it to be installed correctly. Otherwise Qulacs will need to be installed independently:

pip install qulacs pennylane-qulacs

Alternatively, you can install PennyLane-Qulacs from the source code by navigating to the top directory and running:

$ python install


Qulacs supports parallelized executions via OpenMP. To set the number of threads to use during simulations you need to update the environment variable OMP_NUM_THREADS. It can be set using the UNIX command:

export OMP_NUM_THREADS = 8

where 8 can be replaced by the number of threads that you wish to use. By default Qulacs uses all available threads. To restore the default behaviour, simply remove the environment variable. It can be done using the UNIX command:


See the OpenMP documentation page for OMP_NUM_THREADS or here for more details on how to use environment variables.


PennyLane-Qulacs requires the following libraries be installed:

as well as the following Python packages:

If you currently do not have Python 3 installed, we recommend Anaconda for Python 3, a distributed version of Python packaged for scientific computation.


To test that the PennyLane-Qulacs plugin is working correctly you can run

$ make test

in the source folder.


To build the HTML documentation, go to the top-level directory and run:

$ make docs

The documentation can then be found in the doc/_build/html/ directory.