A transpilation pass that ensures there is a state preparation at the
beginning of the circuit.
If there isn't, a Reset is added (i.e. prepare the zero state in the Z basis).
The reason for this pass is that Qiskit runs the RemoveResetInZeroState
pass as part of the default transpilation passes, in most cases (precisely
for optimization_level >=1, the default being 1).
The community seems to agree that this behavior is a bad decision and
should be removed. https://github.com/Qiskit/qiskit-terra/issues/6943
The rationale for this behavior was that IBM backends always reset the
qubits to zero between shots. This behavior cannot be assumed to be true
for all backends, including Alice & Bob's.
Once this issue is resolved, this transpilation pass should be removed from
the Alice & Bob provider.
This transpilation pass cannot be added to the transpilation stage plugin
of the Alice & Bob provider, because the RemoveResetInZeroState runs
in the optimization stage, which happens after the transpilation stage.
For this reason, this pass is run manually right before the compilation
from Qiskit to QIR.
From the docstring of
EnsurePreparationPass:A transpilation pass that ensures there is a state preparation at the beginning of the circuit.
If there isn't, a Reset is added (i.e. prepare the zero state in the Z basis).
The reason for this pass is that Qiskit runs the
RemoveResetInZeroStatepass as part of the default transpilation passes, in most cases (precisely for optimization_level >=1, the default being 1).The community seems to agree that this behavior is a bad decision and should be removed. https://github.com/Qiskit/qiskit-terra/issues/6943 The rationale for this behavior was that IBM backends always reset the qubits to zero between shots. This behavior cannot be assumed to be true for all backends, including Alice & Bob's. Once this issue is resolved, this transpilation pass should be removed from the Alice & Bob provider.
This transpilation pass cannot be added to the transpilation stage plugin of the Alice & Bob provider, because the
RemoveResetInZeroStateruns in the optimization stage, which happens after the transpilation stage.For this reason, this pass is run manually right before the compilation from Qiskit to QIR.