Have control state of qubits visible in the circuit drawing

Feature details

When using a controlled gate with custom control values, the drawing of the circuit does not represent this. The control values correctly show up in the mpl figure. Example:

dev = qml.device('default.qubit',wires=4, shots=100)
@qml.qnode(dev)
def circ():
    for i in range(4):
        qml.Hadamard(wires=i)
    qml.MultiControlledX([0,1,2],3,'010')
    qml.MultiControlledX([0, 1, 2], 3, '111')
    qml.MultiControlledX([0, 1, 2], 3, '000')
    return qml.probs(0)

print(qml.draw(circ)())
fig, ax = qml.draw_mpl(circ)()
fig.show()

0: ──H─╭C─╭C─╭C─┤  Probs
1: ──H─├C─├C─├C─┤       
2: ──H─├C─├C─├C─┤       
3: ──H─╰X─╰X─╰X─┤

Implementation

Will have to fix different symbols for 0 and 1 control state. Maybe 0 state can be represented by an ‘O’ and keep ‘C’ for state 1.

How important would you say this feature is?

1: Not important. Would be nice to have.

Additional information

No response

[CatalinaAlbornoz]

Remember to add [unitaryhack] in the title for your PR @ankit27kh. And remember to sign up for the hack in case you haven’t already!

[albi3ro]

Hi @ankit27kh , The visual difference between C and O is slight enough that I don’t think it makes a clear distinction.

But I found the fixed-width unicode symbols ● and ○. With those, a MultiControlledX will look like:

0: ─╭●─┤  <Z>
1: ─├○─┤     
2: ─╰X─┤   

I actually really like how that looks, as it even more closely parallels the typical circuit drawing graphics. Thanks for the great idea 👍

Also, great catch on the ControlledQubitUnitary in the mpl drawer!

It would be a great task for an external contributor as well.