latex drawer support for cregbundle

[1ucian0]

In the spirit of #2797 it would be great if latex drawer add support for cregbundle.

Take the following example:

from qiskit import *
qr = QuantumRegister(3, 'q')
cr = ClassicalRegister(3, 'c')
circuit = QuantumCircuit(qr, cr)
circuit.measure(qr, cr)
circuit.draw('latex')

I suggest something like this:

circuit.draw('latex', cregbundle=True)

The latex code for that figure is:

\begin{equation*}
    \Qcircuit @C=1.0em @R=1.0em @!R {
	 	\lstick{ {q}_{0} :  } & \qw & \meter & \qw & \qw & \qw & \qw\\
	 	\lstick{ {q}_{1} :  } & \qw & \qw & \meter & \qw & \qw & \qw\\
	 	\lstick{ {q}_{2} :  } & \qw & \qw & \qw & \meter & \qw & \qw\\
	 	\lstick{c:} & {/_{_3}} \cw & \dstick{0} \cw \cwx[-3] & \dstick{1} \cw \cwx[-2] & \dstick{2} \cw \cwx[-1] & \cw & \cw\\
	 }
\end{equation*}

[rao107]

Hello! I haven't contributed to any open-source software but I want to try my hand at this.

[1ucian0]

Sure! Go ahead. Let me know if I can help!

[1ucian0]

It seems there is a small bug:

cr1 = ClassicalRegister(2, 'c1')
cr2 = ClassicalRegister(2, 'c2')
qr = QuantumRegister(2, 'q')
circuit = QuantumCircuit(qr, cr1, cr2)
circuit.measure(qr[0], cr1[0])
circuit.measure(qr[0], cr1[1])
circuit.measure(qr[0], cr2[0])
circuit.measure(qr[0], cr2[1])

with circuit.draw('latex', cregbundle=False):

with circuit.draw('latex', cregbundle=True):

The expected result is to have two registers in the last image.

A side note (if it's not easy to fix, no worries. We can leave it for later). Would it be possible avoid moving the gates right? Consider this:

circuit = QuantumCircuit(1, 1)
circuit.h(0)
circuit.measure(0, 0)
circuit.draw('latex', cregbundle=False)

circuit = QuantumCircuit(1, 1)
circuit.h(0)
circuit.measure(0, 0)
circuit.draw('latex', cregbundle=True)

[rao107]

Oh wow, I never realized that multiple classical registers could be in the same circuit! That's pretty interesting. I'm working on squashing that bug now.

Relating to the side note: I'll certainly try my best to fix the formatting and avoid moving the gates to the right but, even from a brief look, the problem looks more complicated than I can handle. It's not going to stop me from trying though!

Unrelated to the bugs brought up, I found another bug where the number on the bundle would bug out:

circuit = QuantumCircuit(1, 10)
circuit.measure(0,0)
circuit.draw('latex', cregbundle=True)

But I then I fixed it:

I just wanted to let you know that I know about this and I've already dealt with it in case you also find the same bug as well.