QubitPauliString.state_expectation does not work for named qubits

[CalMacCQ]

I'd expect to be able to calculate $\langle X\rangle$ on a qubit named "p" as follows with QubitPauliString.state_expectation.

from pytket import Circuit, Qubit
from pytket.pauli import Pauli, QubitPauliString

circ = Circuit()
qubit_p = Qubit("p", 0)
circ.add_qubit(qubit_p)

pauli_x = QubitPauliString(circ.qubits, [Pauli.X])
print(pauli_x.state_expectation(circ.get_statevector()))

However this gives

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
Cell In[16], line 9
      6 circ.add_qubit(qubit_p)
      8 pauli_x = QubitPauliString(circ.qubits, [Pauli.X])
----> 9 print(pauli_x.state_expectation(circ.get_statevector()))

RuntimeError: Qubit list given to to_sparse_matrix doesn't contain p[0]

If I simply substitute "p" for the default qubit name "q" everything works fine.

[cqc-alec]

@willsimmons1465 I'm interested in your opinion on this. It feels like it should work with non-default qubits, but should it? If one digs into the code path there are explicit requirements that the qubit register be the default: e.g. here.

[github-actions]

This issue has been automatically marked as stale.