arbitrary order in circuit drawers

What should we add?

Circuit drawers currently have reverse_bits, as an option to modify the order in which wires are represented. @ajavadia suggests a generalized version of that feature: wire_order. This parameter might define the order of the wires draw(..., wire_order=[3,0,2,1]) and can eventually replace reverse_bits with draw(..., wire_order='reverse'.

[enavarro51]

A couple of more questions,

If a user uses both reverse_bits and wire_order, do we

• raise
• prioritize one or the other
• do wire_order and then reverse it

If the the wire_order list is not the right length or does not have a unique integer for each bit, do we

• raise using the same error message for each
• raise with separate explanations
• warn and continue without using wire_order

[ajavadia]

But what I’m saying is that QuantumCircuit.reverse_bits() is not just a change in visualization, it actually changes the circuit. So I think we need both the circuit option and the visualization option.

In [5]: qc.draw()
Out[5]:
     ┌───┐
q_0: ┤ H ├
     └───┘
q_1: ─────

q_2: ─────


In [6]: qc.draw(reverse_bits=True)    # same circuit, just drawn differently (top-to-bottom instead of bottom-to-top)
Out[6]:

q_2: ─────

q_1: ─────
     ┌───┐
q_0: ┤ H ├
     └───┘

In [7]: qc.reverse_bits().draw()   # a different circuit: H is now applied to a different qubit
Out[7]:

q_0: ─────

q_1: ─────
     ┌───┐
q_2: ┤ H ├
     └───┘

and so we need to add a generalization of these in the form of QuantumCiruit.permute_bits([....]) and QuantumCircuit.draw(permute_bits=[...])