Qiskit/qiskit-metapackage

qc.draw() fails for 3-qubit dynamic circuit

balewski opened this issue · 1 comments

balewski commented

Informations

  • Qiskit version:

  • $ pip list |grep qiskit
    pytket-qiskit 0.34.0
    qiskit 0.41.0
    qiskit-aer 0.11.2
    qiskit-experiments 0.4.0
    qiskit-ibm-experiment 0.2.8
    qiskit-ibm-provider 0.2.1
    qiskit-ibm-runtime 0.8.0
    qiskit-terra 0.23.1

  • Python version:
    $ python3 -V
    Python 3.10.6

  • Operating system:
    Ubuntu 22

What is the current behavior?

Printing of dynamic circuit with 3 conditional gates crashes with the error:

Traceback (most recent call last):
File "/quantumMind/Qiskit/issues/./issue10_dynTwo.py", line 32, in
print(qc.draw(output="text", idle_wires=False))
File "/usr/local/lib/python3.10/dist-packages/qiskit/visualization/circuit/text.py", line 707, in str
return self.single_string()
File "/usr/local/lib/python3.10/dist-packages/qiskit/visualization/circuit/text.py", line 728, in single_string
return "\n".join(self.lines()).encode(self.encoding).decode(self.encoding)
File "/usr/local/lib/python3.10/dist-packages/qiskit/visualization/circuit/text.py", line 771, in lines
layers = self.build_layers()
File "/usr/local/lib/python3.10/dist-packages/qiskit/visualization/circuit/text.py", line 1201, in build_layers
layer.connect_with("│")
File "/usr/local/lib/python3.10/dist-packages/qiskit/visualization/circuit/text.py", line 1525, in connect_with
affected_bit.connect(wire_char, ["bot"])
AttributeError: 'NoneType' object has no attribute 'connect'

Steps to reproduce the problem

Execute this program. Note, if nq=3 is changed to nq=2 program runs correctly

import qiskit as qk
import qiskit.qasm3
import sys
#...!...!....................
def circMcbXM(nq):
    crPre = qk.ClassicalRegister(nq, name="pre")
    crPost = qk.ClassicalRegister(nq, name="post")
    qr = qk.QuantumRegister(nq, name="q")
    qc= qk.QuantumCircuit(qr, crPre,crPost,name='McbXM')
    for i in range(nq):
        qc.h(i)
        qc.measure(i,crPre[i])
        with qc.if_test((crPre[i], i)):
            qc.x(i)  # conditionla state flip
        qc.measure(i, crPost[i])
    return qc

# -------Create a Quantum Circuit 
nq=3
qc=circMcbXM(nq)
print('created circ for nq=',nq)

print('M: dump QASM3 idela circ:\n')
qiskit.qasm3.dump(qc,sys.stdout)
print('\n  --- end ---\n')
print(qc.draw(output="text", idle_wires=False))

What is the expected behavior?

circuit should be printed

Suggested solutions

balewski commented

the circuit is invalid because for the 3rd qubit the condition : with qc.if_test((crPre[i], i) has i=2
After the line is changed to
with qc.if_test((crPre[i], 0)
All works.

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