math mode in gate names is not working

[1ucian0]

Environment

• Qiskit Terra version: 0.23.0.dev0+67f85b0
• Python version: 3.9
• Operating system: MacOS

What is happening?

Inspired by https://quantumcomputing.stackexchange.com/a/29167/1859
According with #4669, it is possible to use $ for activate LaTeX math mode in gate names. However, that triggers an error.

How can we reproduce the issue?

Take the possible example:

from qiskit import QuantumCircuit
from qiskit.circuit.library import HGate
circ = QuantumCircuit(1)
circ.append(HGate(label="$U^a$"),[0])
circ.draw('latex')  

This triggers a pdflatex compilation error. However, circ.append(HGate(label="U^a"),[0]) works.

What should happen?

This might be a regression. I think at some point we supported math mode in names. What it should happen is that $ activates it.

Any suggestions?

No response

[jakelishman]

The PR you reference is for the MPL drawer, not the LaTeX one. From a quick scan-through, it looks like we've pretty much always been drawing LaTeX labels in math mode, except wrapped in a \mathrm. #5855 added the explicit escaping for ^ and _.

We could probably use a similar approach to #4669; escape the name components that are outside the dollar signs, and pass through the inside-dollar-sign bits to LaTeX verbatim.

(I note that in that stackexchange question, the user's gate name isn't valid LaTeX already - _ consumes one single token, but they want it to consume the entire \mathrm{rot}. They should have written $U_{\mathrm{rot}}$, most likely.)

[1ucian0]

The PR you reference is for the MPL drawer, not the LaTeX one.

ups! my bad.

(I note that in that stackexchange question, the user's gate name isn't valid LaTeX already - _ consumes one single token, but they want it to consume the entire \mathrm{rot}. They should have written $U_{\mathrm{rot}}$, most likely.)

I extended the answer with that clarification, thanks.