Circuits with Reset can not be transpiled with AerSimulator with a noise model

[wshanks]

Informations

• Qiskit Aer version: 0.13.0
• Python version: 3.11
• Operating system: Fedora Linux 38

What is the current behavior?

When trying to transpile a circuit with a Reset instruction with an AerSimulator backend with a noise model, the transpiler raises an exception about "reset" not being in the equivalence library.

Steps to reproduce the problem

import numpy as np
from qiskit import QuantumCircuit, transpile
from qiskit_aer import AerSimulator
from qiskit_aer.noise import NoiseModel



noise_model = NoiseModel()
# Uncomment this line for a successful transpilation
# noise_model = NoiseModel(basis_gates=["id", "rz", "sx", "cx", "reset"])
noise_model.add_readout_error(np.array([[0.9, 0.1], [0.1, 0.9]]), [0])

backend = AerSimulator(noise_model=noise_model)

qc = QuantumCircuit(1, 1)
qc.reset(0)
qc.measure(0, 0)
transpile(qc, backend)

What is the expected behavior?

Successful transpilation

Suggested solutions

This is a consequence of the conversion to BackendV2. Before the conversion, AerSimulator had no target object so this code would execute and insert reset into the list of allowed instructions. Now when the noise model is set as an option, this code sets the basis gates:

qiskit-aer/qiskit_aer/backends/aer_simulator.py

Lines 901 to 902 in 85831ee

	if key in ["method", "noise_model", "basis_gates"]:
	self._cached_basis_gates = self._basis_gates()

which takes the intersection of the default set with the basis gates of the noise model:

qiskit-aer/qiskit_aer/backends/aer_simulator.py

Lines 945 to 947 in 85831ee

	if noise_model:
	noise_gates = noise_model.basis_gates
	basis_gates = basis_gates.intersection(noise_gates)

which defaults to just a small set of gates:

qiskit-aer/qiskit_aer/noise/noise_model.py

Lines 197 to 201 in 85831ee

	if basis_gates is None:
	# Default basis gates is id, rz, sx, cx so that all standard
	# non-identity instructions can be unrolled to rz, sx, cx,
	# and identities won't be unrolled
	self._basis_gates = set(["id", "rz", "sx", "cx"])

These cached basis gates get used to set the backend configuration basis gates:

qiskit-aer/qiskit_aer/backends/aer_simulator.py

Line 868 in 85831ee

config.basis_gates = self._cached_basis_gates + config.custom_instructions

The convert_to_target() function which AerSimulator uses to generate the target object uses the configuration basis gates to set the instructions in the target and so "reset" is not included.

I am not sure if it makes sense to add reset to the default set for NoiseModel or if some other solution is preferred. My workaround for now is to use NoiseModel(basis_gates=["id", "rz", "sx", "cx", "reset"]).

[wshanks]

Closed by #1976