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Upgrade Guide

This document describes breaking changes and how to upgrade. For a complete list of changes including minor and patch releases, please refer to the changelog.

Unreleased

2.2.0

Python wheels

This release contains two changes to the distributed wheels.

First, we have removed all wheels for Python 3.13t. Free-threading Python was introduced as an experimental feature in Python 3.13. It became stable in Python 3.14.

Second, for Python 3.12+, we are now providing Stable ABI wheels instead of separate version-specific wheels. This was enabled by migrating our Python bindings from pybind11 to nanobind.

Both of these changes were made in the interest of conserving PyPI space and reducing CI/CD build times. The full list of wheels now reads:

  • 3.10
  • 3.11
  • 3.12+ Stable ABI
  • 3.14t

2.1.0

End of support for Python 3.9

Starting with this release, MQT DDSIM no longer supports Python 3.9. This is in line with the scheduled end of life of the version. As a result, MQT DDSIM is no longer tested under Python 3.9 and no longer ships Python 3.9 wheels.

2.0.0

This major release introduces several breaking changes, including the removal of deprecated features. The following paragraphs describe the most important changes and how to adapt your code accordingly. We intend to provide a more comprehensive migration guide for future releases.

The major change in this major release is the move to the MQT Core Python package. This move allows us to make qiskit a fully optional dependency and entirely rely on the MQT Core IR for representing circuits. Additionally, the mqt-core Python package now ships all its C++ libraries as shared libraries so that these need not be fetched or built as part of the build process. This was tricky to achieve cross-platform, and you can find some more backstory in the corresponding PR #336. The problem was simplified by the latest pybind11 release (v3) that greatly increased binary compatibility. It is not necessary to build MQT Core from source, and a simple uv sync is enough to successfully run pytest. We expect the MQT Core integration to mature over the next few releases. If you encounter any issues, please let us know.

Support for the tensor network strategy in the path simulator has been removed. If you still depend on that method, please use the last version of MQT DDSIM that supports them, which is 1.24.0.

MQT Core itself dropped support for several parsers in v3.0.0, including the .real, .qc, .tfc, and GRCS parsers. The .real parser lives on as part of the MQT SyReC project. All others have been removed without replacement. Consequently, these input formats are no longer supported in MQT DDSIM.

MQT DDSIM has moved to the munich-quantum-toolkit GitHub organization under https://github.com/munich-quantum-toolkit/ddsim. While most links should be automatically redirected, please update any links in your code to point to the new location. All links in the documentation have been updated accordingly.

MQT DDSIM now requires CMake 3.24 or higher. Most modern operating systems should have this version available in their package manager. Alternatively, CMake can be conveniently installed from PyPI using the cmake package.

MQT DDSIM now supports Qiskit 2.0. As a result, the return values of the Estimator and Sampler have been changed to align with Qiskit's implementations.

To developers of MQT DDSIM, it is worth mentioning that all Python code (except tests) has been moved to the top-level python directory. Furthermore, the C++ code for the Python bindings has been moved to the top-level bindings directory.

Furthermore, many Python modules and classes have been renamed. In particular,

  • HybridCircuitSimulator has been renamed to HybridSimulator,
  • HybridMode has been renamed to HybridSimulatorMode,
  • PathCircuitSimulator has been renamed to PathSimulator, and
  • ConstructionMode has been renamed to UnitarySimulatorMode.
  • Some of the Qiskit backends have been renammed. For the new names, see DDSIMProvider.get_backend().

The UnitarySimulatorMode, HybridSimulatorMode, and PathSimulatorMode enums are now exposed via pybind11's new py::native_enum, which makes them compatible with Python's enum.Enum class (PEP 435). As a result, the enums can no longer be initialized using a string. Instead of PathSimulatorMode("sequential") or "sequential", use PathSimulatorMode.sequential.

Finally, the minimum required C++ version has been raised from C++17 to C++20. The default compilers of our test systems support all relevant features of the standard.