pyqpp - Python 3 bindings for Quantum++

---

Installation instructions

pyqpp shares the same dependencies as Quantum++ and can be installed via pip

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

---

Overview

pyqpp is a modern Python 3 interface to the Quantum++ C++ library. It provides Python users with complete access to the full Quantum++ API, including quantum computing primitives, circuit construction and manipulation tools, high-performance circuit simulation engines, and the full suite of utility functions. The interface is implemented using pybind11, offering a clean, intuitive, and high-performance Pythonic experience while preserving the power and efficiency of the underlying C++ implementation.

The bindings are easy to extend; see the Custom Bindings section for guidance.

Illustrative examples are provided in examples.

---

OpenQASM circuits

Use pyqpp.qasm.read_from_file() to obtain the qpp::QCircuit representation of an OpenQASM 2.0 file.

---

Custom bindings

To wrap a custom function, use pybind11::module::def, such as

template<typename Func, typename ...Extra>
module &def(const char *name_, Func &&f, const Extra&... extra)

Here Func can be a plain C++ function, a function pointer, or a lambda function. For example, consider the qpp::randU() function

cmat randU(idx D = 2);

which is wrapped as

PYBIND11_MODULE(pyqpp, m) {
    ...

    m.def("randU", &qpp::randU, "Generates a random unitary matrix",
          py::arg("D") = 2);

    ...
}

---

Template functions

We cannot wrap templated functions; instead, we must explicitly instantiate them. For example, consider the qpp::norm() function

template <typename Derived>
double norm(const Eigen::MatrixBase<Derived>& A);

One way to wrap this is

PYBIND11_MODULE(pyqpp, m) {
    ...

    m.def("norm", [](const cmat& A) { return qpp::norm(A); }, "Frobenius norm");
    m.def("norm", [](const ket& A) { return qpp::norm(A); }, "Frobenius norm");

    ...
}

This creates the overloaded pyqpp.norm() function, which can accept qpp::ket or qpp::cmat types. To avoid repetition of boilerplate code, we can templatize the binding

template<typename T>
void def_norm(pybind11::module &m) {
    m.def("norm", [](const T& A) { return qpp::norm(A); }, "Frobenius norm");
}

PYBIND11_MODULE(pyqpp, m) {
    ...

    def_norm<cmat>(m);
    def_norm<ket>(m);

    ...
}