Module 'qutip.qip.circuit' has no attribute 'gate_expand_1toN' and 'gate_expand_2toN'

[MrSago]

File "...\learn-qc-with-python-and-qsharp\ch05\simulator.py", line 88, in _apply
    matrix = qt.circuit.gate_expand_1toN(
AttributeError: module 'qutip.qip.circuit' has no attribute 'gate_expand_1toN'


File "...\learn-qc-with-python-and-qsharp\ch06\simulator.py", line 124, in _apply
  matrix = qt.circuit.gate_expand_2toN(unitary,
AttributeError: module 'qutip.qip.circuit' has no attribute 'gate_expand_2toN'

[nadimragab]

Please use qt.gate_expand_1toN instead of qt.circuit.gate_expand_1toN because gate_expand_1toN, refer to https://qutip.org/docs/latest/modules/qutip/qip/operations/gates.html for more details

[sufyanAbbasi]

I'd also recommend locking your qutip install to 4.7.6, i.e. pip install qutip==4.7.6, as qutip version 5 doesn't have that method anymore. Unfortunately, I'm not sure what the version 5 equivalent is.

[Florian-Heringa]

In version 5.1.0 you can use the qutip.expand_operator() function. This is a generalised version of the gate_expand_ntoN() functions so the input is a bit different. In this case I got it to work by doing this: matrix = qt.expand_operator(unitary, [2] * self.capacity, ids[0]) in the _apply() method of the Simulator. Similar for the measure() method of the SimulatedQubit: qt.expand_operator(qt.basis(2, outcome) * qt.basis(2, outcome).dag(), [2] *self.parent.capacity, self.qubit_id).

This works since the function expects the dimensionality of the composite systems, in this case simple qubits, which have 2 states. So multiplying this by the amount of qubits gives the total dimensionality specification. In the old version this was handled on a case-by-case basis so this was not necessary.