Gates in qutip-qutip

[ajgpitch]

Problem Description

Now that qutip-qip has moved to another package, gates are not available in the main repo. This is inconvenient for examples such as the control optimization ones, where one would need to install the qutip-qip package just to access say the Hadamard or CNOT for instance.

Proposed Solution

The easiest solution would be just to copy the gates.py file from the QIP package into the main repo. Perhaps might confuse imports in qip? Also, I think that file has func defs that refer to 'controls' that might not make sense in this repo

Alternate Solutions

Have a file called operations.py. Just have a subset of the gates (operations), the most typical named unitaries - sounds less QIP like and would avoid import confusion. I think also hadamard_transform could be shortened to hadamard, but also include the original name.

Additional Context

No response

[BoxiLi]

We have kept many gates in qutip/core/gates. Not all of them but surely for cnot, hadamard etc.

[BoxiLi]

It is actually very similar to your solution. We should add this to the migration guide.

[ajgpitch]

Thanks @BoxiLi
Okay, embarrassingly, I was still in my update-4,x branch, so hence didn't find the file.

Still, I did try a lot of stuff like from qutip import hadamard_transform (in other envs) that didn't work, before I found (with some help) that from qutip import gates is a good option. It seems like there was a deliberate choice not to expose the function names individually.

A search for "hadamard_transform" or "gates" does not return anything helpful. Does it need pointing at in the docs build?

[BoxiLi]

That seems true, gates are missing from the documentation. This could be a Good first issue. To add them back to the documentation.