Frequently Asked Questions

Q: How should I cite Qiskit in my research?

A: Please cite Qiskit by using the included BibTeX file.

Q: Why do I receive the error message AttributeError: QuantumCircuit object has no attribute save_state when using ``save_*``method on a circuit?

A: The save_* instructions are part of Qiskit Aer project, a high performance simulator for quantum circuits. These instructions do not exist outside of Qiskit Aer and are added dynamically to the QuantumCircuit class by Qiskit Aer on import. If you would like to use these instructions you must first ensure that you have imported qiskit_aer in your program before trying to call these methods. You can refer to qiskit_aer.library for the details of these custom instructions included with Qiskit Aer.

Q: Why do my results from real devices differ from my results from the simulator?

A: The simulator runs jobs as though is was in an ideal environment; one without noise or decoherence. However, when jobs are run on the real devices there is noise from the environment and decoherence, which causes the qubits to behave differently than what is intended.

Q: Why do I receive the error message, No Module 'qiskit' when using Jupyter Notebook?

A: If you used pip install qiskit and set up your virtual environment in Anaconda, then you may experience this error when you run a tutorial in Jupyter Notebook. If you have not installed Qiskit or set up your virtual environment, you can follow the Installation steps.

The error is caused when trying to import the Qiskit package in an environment where Qiskit is not installed. If you launched Jupyter Notebook from the Anaconda-Navigator, it is possible that Jupyter Notebook is running in the base (root) environment, instead of in your virtual environment. Choose a virtual environment in the Anaconda-Navigator from the Applications on dropdown menu. In this menu, you can see all of the virtual environments within Anaconda, and you can select the environment where you have Qiskit installed to launch Jupyter Notebook.

Q: Why am I getting a compilation error while installing ``qiskit``?

A: Qiskit depends on a number of other open source Python packages, which are automatically installed when doing pip install qiskit. Depending on your system’s platform and Python version, it is possible that a particular package does not provide pre-built binaries for your system. You can refer to Platform Support for a list of platforms supported by Qiskit, some of which may need an extra compiler. In cases where there are no precompiled binaries available pip will attempt to compile the package from source, which in turn might require some extra dependencies that need to be installed manually.

If the output of pip install qiskit contains similar lines to:

Failed building wheel for SOME_PACKAGE
build/temp.linux-x86_64-3.5/_openssl.c:498:30: fatal error
compilation terminated.
error: command 'x86_64-linux-gnu-gcc' failed with exit status 1

please check the documentation of the package that failed to install (in the example code, SOME_PACKAGE) for information on how to install the libraries needed for compiling from source.