QuantumVolume QASM circuit error

Information

• Qiskit Terra version: qiskit-terra==0.18.1
• Python version: 3.7.3
• Operating system: macOS Mojave

What is the current behavior?

The method QuantumVolume at qiskit.circuit.library.quantum_volume can be used to generate quantum volume circuits. Some of the circuits generated by this method throw an error when they are saved as a QASM file, and then read in using QuantumCircuit.from_qasm_file(path)

Steps to reproduce the problem

This circuit:

• qasm_error_circuit.txt

was generated using the qiskit.circuit.library.quantum_volume method. When I run this code:

from qiskit import QuantumCircuit

qc = QuantumCircuit.from_qasm_file("qasm_error_circuit.txt")

I get the error

    qc = QuantumCircuit.from_qasm_file("qasm_error_circuit.txt")
  File "//anaconda3/lib/python3.7/site-packages/qiskit/circuit/quantumcircuit.py", line 1900, in from_qasm_file
    return _circuit_from_qasm(qasm)
  File "//anaconda3/lib/python3.7/site-packages/qiskit/circuit/quantumcircuit.py", line 2733, in _circuit_from_qasm
    ast = qasm.parse()
  File "//anaconda3/lib/python3.7/site-packages/qiskit/qasm/qasm.py", line 54, in parse
    return qasm_p.parse(self._data)
  File "//anaconda3/lib/python3.7/site-packages/qiskit/qasm/qasmparser.py", line 1070, in parse
    self.parser.parse(data, lexer=self.lexer, debug=self.parse_deb)
  File "//anaconda3/lib/python3.7/site-packages/ply/yacc.py", line 333, in parse
    return self.parseopt_notrack(input, lexer, debug, tracking, tokenfunc)
  File "//anaconda3/lib/python3.7/site-packages/ply/yacc.py", line 1120, in parseopt_notrack
    p.callable(pslice)
  File "//anaconda3/lib/python3.7/site-packages/qiskit/qasm/qasmparser.py", line 525, in p_gate_decl_0
    self.update_symtab(program[0])
  File "//anaconda3/lib/python3.7/site-packages/qiskit/qasm/qasmparser.py", line 77, in update_symtab
    str(prev.line) + ', file', prev.file)
qiskit.qasm.exceptions.QasmError: "Duplicate declaration for gate 'su4_976' at line 88, file qasm_error_circuit.txt.\nPrevious occurrence at line 18, file qasm_error_circuit.txt"

What is the expected behavior?

Suggested solutions

Naming each su4 declaration with additional unique numbers so there are no duplicates.

[epelofske-LANL]

I suspect your environment might have gone wrong somewhere, and a Terra from the 0.17 series or earlier has ended up on the path by accident, which is before #5887 was merged to fix many of these problems.

@jakelishman Yes, that is the problem. According to pip I have qiskit-terra==0.18.1 installed, but the actual version I am using is 0.17.0:

>>> import qiskit
>>> print(qiskit.__file__)
//anaconda3/lib/python3.7/site-packages/qiskit/__init__.py
>>> print(qiskit.__version__)
0.17.0

[jakelishman]

Ah, that’s good to know! Thanks - bugs are always super scary when we can’t reproduce them, so good to know the cause in the end.

In general, conda and pip play a little weirdly together. When you’re using packages from both at once, conda list is typically a little more reliable than pip list, because conda knows how to read pip’s status, but it doesn’t really work the other way around.