Incoherence in notation for RZX gate

[bowangle]

URL to the relevant documentation

https://docs.quantum.ibm.com/api/qiskit/qiskit.circuit.library.RZXGate

In examples section, third equation

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• [X] typo
• [ ] code bug
• [ ] out-of-date content
• [ ] broken link
• [ ] other

Describe the fix.

If we follow the notation introduce for RZX(θ) q0,q1=exp(−i θ/2 X⊗Z) which are the default notation, it would mean that in the "examples" section, we should have RZX(θ=π)=−iX⊗Z instead of −iZ⊗X. It's not coherent with the fact that in the note section, we use big-endian convention for the tensor notation. Or else we have to tell in which way we apply the gate by adding the q1,q0 index like this: RZX(θ=π)q1,q0=−iZ⊗X.

[Eric-Arellano]

Thanks! This is an issue in the API docs, so it needs to be fixed in qiskit/qiskit. I'm transferring it there.