Limitation

Functions dedicated to Qiskit Aer Simulator

QulacsBackend does not support functions specific to the Aer simulator (Reference: Aer API reference)

For example, if you use QulacsBackend to evaluate a circuit that executes the Aer custom instruction circuit.save_statevector(), an error is output.

Some classes that are not listed in Aer API reference are for Aer only.

For example, qiskit.opflow.AerPauliExpectation is for Aer only. If you want to get the expected value with QulacsBackend, use qiskit.opflow.PauliExpectation instead.

(A class name that includes the string Aer may be Aer-specific.)

Noise simulation

QulacsBackend does not support noise simulation.

The simulation using NoiseModel of Aer and the simulation of the circuit including quantum error instruction (qiskit.quantum_info.Kraus, etc.) are not possible.

Number of qubits available when including intermediate measurements

If a quantum circuit includes operations that involve measurements in the middle (excluding the measurement operation performed at the end of the circuit), the maximum number of available qubits on the system is reduced by one qubit. (mpiQulacs functional limitation.)