Add option to QuantumCircuit.draw to omit final measurements

[kevinsung]

What should we add?

Often the last operation in a circuit is a measurement of all the qubits, and this takes up a lot of space in the drawing. I would like to add an option to omit final measurements from the drawing.

[Cryoris]

The solution proposed in #4149 which would just align all final measurements would also be nice, that way it is compact but we can still see the measurements.

[kevinsung]

The solution proposed in #4149 which would just align all final measurements would also be nice, that way it is compact but we can still see the measurements.

Ah that's also a nice idea!

[enavarro51]

@Cryoris, @kevinsung, @jakelishman I can take a look at this, at least for the mpl drawer. It does bring up a number of design questions.

• In the following circuit,

qr = QuantumRegister(2)
cr = ClassicalRegister(3)
qc = QuantumCircuit(qr, cr)
qc.x(0)
qc.h(0)
qc.measure(0, 0)
qc.x(1)
qc.h(1)
qc.measure(1, 1)
qc.x(1)
qc.measure(1, 2)
qc.h(1)
qc.draw()

since the first 2 measures are at the same depth, it seems reasonable to make these without the double vertical line as pictured in #4149. Having said that, why not make the third measure the same and remove all the double lines to the classical bits since the bit will be indicated either in the measure box or under it?

• Taking this a step further,

qr = QuantumRegister(2)
cr = ClassicalRegister(3)
qc = QuantumCircuit(qr, cr)
with qc.if_test((cr, 2)):
    qc.x(0)
with qc.if_test(expr.equal(cr, 2)):
    qc.y(0)
qc.draw()

if we were to put c6 == 2 under the If in the first red box, there would be no need for the double vertical lines here either. Which brings up the ultimate point, since the old c_if is going away and the measures can be done as above, why not do away with the entire classical bit section of the drawers?

This would free up a lot of space both vertically and horizontially as we move to 100+ qubit drawings, and it should be workable for both the mpl and text drawers.