LRE error with qiskit circuit

[purva-thakre]

When attempting to get the sample matrrix of a qiskit circuit, the process fails with AttributeError: 'QuantumCircuit' object has no attribute 'are_all_measurements_terminal'. This error should not be raised as the circuit of interest does not contain any measurements.

The error points to the following line where the scale factor vectors are generated and used by the sample matrix function:

mitiq/mitiq/lre/inference/multivariate_richardson.py

Lines 97 to 99 in be6a76c

	scale_factor_vectors = get_scale_factor_vectors(
	input_circuit, degree, fold_multiplier, num_chunks
	)

The function to generate the scale factor vectors relies on

mitiq/mitiq/lre/multivariate_scaling/layerwise_folding.py

Line 39 in be6a76c

_pop_measurements(circuit)

Code

ghz_circuit = generate_ghz_circuit(4, "qiskit")
circuit = ghz_circuit.compose(ghz_circuit.inverse())
print(circuit)

     ┌───┐                              ┌───┐
q_0: ┤ H ├──■────────────────────────■──┤ H ├
     └───┘┌─┴─┐                    ┌─┴─┐└───┘
q_1: ─────┤ X ├──■──────────────■──┤ X ├─────
          └───┘┌─┴─┐          ┌─┴─┐└───┘     
q_2: ──────────┤ X ├──■────■──┤ X ├──────────
               └───┘┌─┴─┐┌─┴─┐└───┘          
q_3: ───────────────┤ X ├┤ X ├───────────────
                    └───┘└───┘               


sample_matrix(circuit, 2, 2)

[purva-thakre]

Compatibility of LRE with non-Cirq frontends was ensured in #2547. To resolve this issue, we should add the corresponding unit tests in mitiq/lre/tests/test_multivariate_richardson.py which were skipped in the linked PR.

This is definitely related to #2542 (comment)

[natestemen]

This is definitely related to #2542 (comment)

Ahhh 🙈 sorry! Since I worked on this previously, would it be easiest if I take it?