Platform dependent numerical errors with Weyl decomposition

[ACE07-Sev]

Platform dependency of weyl.py

Description

The implementation of the weyl.py and consequently two_qubit_decomposition.py cause numerical accuracy errors on different OS platforms, leading to logical errors and failed assertions.

This issue is caused by the dependency of scipy.linalg.eig on tiny values as small as 1e^-17, and slightest inaccuracies can cause the resulting eigenvalues and eigenvectors to differ, leading to wrong results.

The goal is to resolve this implementation to enable stable platform support for Windows and Mac OS users.

Tips

• This issue is currently being discussed in pr CI/CD modification #10, and relevant qiskit issue which the implementation is based on.

[ACE07-Sev]

Some notes on the issue. There are two cases where the numerical instability occurs:

• quick.synthesis.gate_decompositions.two_qubit_decomposition.weyl.TwoQubitWeylDecomposition, in decompose_unitary where we define M2.
• quick.circuit.circuit_utils extract_single_qubits_and_diagonal.

[ACE07-Sev]

Fixed in #58 .