Implementation and test of QuantumError.from_dict. (Qiskit#1942)

* Implementation and test of QuantumError.from_dict.

* Made code lint warning free.

---------

Co-authored-by: Jun Doi <[email protected]>

qiskit_aer/noise/errors/quantum_error.py

@@ -19,17 +19,18 @@
 
 import numpy as np
 
-from qiskit.circuit import QuantumCircuit, Instruction, QuantumRegister
+from qiskit.circuit import QuantumCircuit, Instruction, QuantumRegister, Reset
 from qiskit.circuit.exceptions import CircuitError
 from qiskit.circuit.library.generalized_gates import PauliGate
-from qiskit.circuit.library.standard_gates import IGate
+from qiskit.circuit.library.standard_gates import IGate, XGate, YGate, ZGate
 from qiskit.exceptions import QiskitError
 from qiskit.quantum_info.operators.base_operator import BaseOperator
 from qiskit.quantum_info.operators.channel import Kraus, SuperOp
 from qiskit.quantum_info.operators.channel.quantum_channel import QuantumChannel
 from qiskit.quantum_info.operators.mixins import TolerancesMixin
 from qiskit.quantum_info.operators.predicates import is_identity_matrix
 from qiskit.quantum_info.operators.symplectic import Clifford
+from qiskit.extensions import UnitaryGate
 from ..noiseerror import NoiseError
 
 
@@ -345,6 +346,63 @@ def to_dict(self):
         }
         return error
 
+    @staticmethod
+    def from_dict(error):
+        """Implement current error from a dictionary."""
+        # check if dictionary
+        if not isinstance(error, dict):
+            raise NoiseError("error is not a dictionary")
+        # check expected keys "type, id, operations, instructions, probabilities"
+        if (
+            ("type" not in error)
+            or ("id" not in error)
+            or ("operations" not in error)
+            or ("instructions" not in error)
+            or ("probabilities" not in error)
+        ):
+            raise NoiseError("erorr dictionary not containing expected keys")
+        error_instructions = error["instructions"]
+        error_probabilities = error["probabilities"]
+
+        if len(error_instructions) != len(error_probabilities):
+            raise NoiseError("probabilities not matching with instructions")
+        # parse instructions and turn to noise_ops
+        noise_ops = []
+        for idx, inst in enumerate(error_instructions):
+            noise_elem = []
+            for elem in inst:
+                inst_name = elem["name"]
+                inst_qubits = elem["qubits"]
+
+                if inst_name == "x":
+                    noise_elem.append((XGate(), inst_qubits))
+                elif inst_name == "id":
+                    noise_elem.append((IGate(), inst_qubits))
+                elif inst_name == "y":
+                    noise_elem.append((YGate(), inst_qubits))
+                elif inst_name == "z":
+                    noise_elem.append((ZGate(), inst_qubits))
+                elif inst_name == "kraus":
+                    if "params" not in inst[0]:
+                        raise NoiseError("kraus does not have a parameter value")
+                    noise_elem.append((Kraus(inst[0]["params"]), inst_qubits))
+                elif inst_name == "reset":
+                    noise_elem.append((Reset(), inst_qubits))
+                elif inst_name == "measure":
+                    raise NoiseError("instruction 'measure' not supported")
+                elif inst_name == "unitary":
+                    if "params" not in inst[0]:
+                        raise NoiseError("unitary does not have a parameter value")
+                    noise_elem.append((UnitaryGate(inst[0]["params"][0]), inst_qubits))
+                else:
+                    raise NoiseError("error gate for instruction not recognized")
+
+            noise_ops.append((noise_elem, error_probabilities[idx]))
+
+        error_obj = QuantumError(noise_ops)
+
+        return error_obj
+
     def compose(self, other, qargs=None, front=False):
         if not isinstance(other, QuantumError):
             other = QuantumError(other)

releasenotes/notes/quantum_error_from_dict-8188a864109edd67.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    Implements from_dict() method for QuantumError. This takes a dictionary
+    and checks if style is the one from to_dict() method. If any mismatches
+    are determined then NoiseError is raised. Else dict is parsed and a new
+    QuantumError with noise_ops created.

test/terra/noise/test_quantum_error.py

@@ -22,7 +22,7 @@
 from qiskit.circuit.library.standard_gates import IGate, XGate, YGate, ZGate
 from qiskit.extensions import UnitaryGate
 from qiskit.quantum_info.operators import SuperOp, Kraus, Pauli
-from qiskit_aer.noise import QuantumError
+from qiskit_aer.noise import QuantumError, pauli_error, reset_error
 from qiskit_aer.noise.noiseerror import NoiseError
 
 
@@ -255,6 +255,151 @@ def test_tensor_with_different_type_of_operator(self):
         )
         self.assertEqual(actual, expected)
 
+    def test_from_dict_pauli(self):
+        """Test from_dict method for pauli errors."""
+        p_error_rate = 0.05
+        error_quantum = pauli_error([("X", p_error_rate), ("I", 1 - p_error_rate)])
+
+        error_dict = error_quantum.to_dict()
+        error_quantum2 = QuantumError.from_dict(error=error_dict)
+        self.assertEqual(error_quantum, error_quantum2)
+
+    def test_from_dict_kraus(self):
+        """Test from_dict method for kraus channels."""
+        noise_ops = Kraus(
+            [np.sqrt(0.9) * np.array([[1, 0], [0, 1]]), np.sqrt(0.1) * np.array([[0, 1], [1, 0]])]
+        )
+
+        error_quantum = QuantumError(noise_ops)
+        error_dict = error_quantum.to_dict()
+
+        error_kraus = QuantumError.from_dict(error_dict)
+        self.assertEqual(error_quantum, error_kraus)
+
+    def test_from_dict_reset(self):
+        """Test from_dict method for reset errors."""
+        error_quantum = reset_error(0.98, 0.02)
+
+        error_dict = error_quantum.to_dict()
+
+        error_reset = QuantumError.from_dict(error_dict)
+        self.assertEqual(error_quantum, error_reset)
+
+    def test_from_dict_unitarygate(self):
+        """Test from_dict method for unitarygate errors."""
+        error_quantum = QuantumError(UnitaryGate(np.eye(2)))
+
+        error_dict = error_quantum.to_dict()
+
+        error_unitary = QuantumError.from_dict(error_dict)
+        self.assertEqual(error_quantum, error_unitary)
+
+    def test_from_dict_raise_if_error_is_measure(self):
+        """Test exception is raised by from_dict method for measure errors."""
+        error_quantum = QuantumError(UnitaryGate(np.eye(2)))
+
+        error_dict = error_quantum.to_dict()
+
+        # exchange instruction "unitary" with "measure" to provoke exception
+        error_dict["instructions"][0][0]["name"] = "measure"
+        with self.assertRaises(NoiseError):
+            error_unitary = QuantumError.from_dict(error_dict)
+
+    def test_from_dict_raise_if_parameter_is_non_dict(self):
+        """Test exception is raised by from_dict if parameter is not a dict"""
+        dict_param = []
+        with self.assertRaises(NoiseError):
+            QuantumError.from_dict(dict_param)
+
+    def test_from_dict_raise_if_parameter_is_not_well_formed(self):
+        """Test exception is raised by from_dict if parameter is not well formed"""
+        error_quantum = QuantumError(UnitaryGate(np.eye(2)))
+
+        # remove 'type'
+        error_dict_type = error_quantum.to_dict()
+        error_dict_type.pop("type")
+        with self.assertRaises(NoiseError):
+            error_unitary = QuantumError.from_dict(error_dict_type)
+
+        # remove 'id'
+        error_dict_id = error_quantum.to_dict()
+        error_dict_id.pop("id")
+        with self.assertRaises(NoiseError):
+            error_unitary = QuantumError.from_dict(error_dict_id)
+
+        # remove 'operations'
+        error_dict_operations = error_quantum.to_dict()
+        error_dict_operations.pop("operations")
+        with self.assertRaises(NoiseError):
+            error_unitary = QuantumError.from_dict(error_dict_operations)
+
+        # remove 'instructions'
+        error_dict_instructions = error_quantum.to_dict()
+        error_dict_instructions.pop("instructions")
+        with self.assertRaises(NoiseError):
+            error_unitary = QuantumError.from_dict(error_dict_instructions)
+
+        # remove 'probabilities'
+        error_dict_probabilities = error_quantum.to_dict()
+        error_dict_probabilities.pop("probabilities")
+        with self.assertRaises(NoiseError):
+            error_unitary = QuantumError.from_dict(error_dict_probabilities)
+
+    def test_from_dict_raise_if_len_probabilites_is_not_len_instructions(self):
+        """Test exception is raised by from_dict if length of probabilities does not meet length of instructions"""
+        # test more probabilities than instructions
+        error_quantum = QuantumError(UnitaryGate(np.eye(2)))
+
+        error_dict = error_quantum.to_dict()
+
+        # add another probabilities not matching no instructions
+        error_dict["probabilities"].append(0.8)
+        with self.assertRaises(NoiseError):
+            error_unitary = QuantumError.from_dict(error_dict)
+
+        # test less probabilities than instructions
+        error_dict2 = error_quantum.to_dict()
+
+        # remove another probabilities not matching no instructions
+        error_dict2["probabilities"].remove(1.0)
+        with self.assertRaises(NoiseError):
+            error_unitary = QuantumError.from_dict(error_dict2)
+
+    def test_from_dict_raise_if_kraus_has_no_params(self):
+        """Test exception is raised by from_dict if kraus has not attribute params"""
+        noise_ops = Kraus(
+            [np.sqrt(0.9) * np.array([[1, 0], [0, 1]]), np.sqrt(0.1) * np.array([[0, 1], [1, 0]])]
+        )
+
+        error_quantum = QuantumError(noise_ops)
+        error_dict = error_quantum.to_dict()
+
+        # remove params to provoke exception
+        error_dict["instructions"][0][0].pop("params")
+        with self.assertRaises(NoiseError):
+            error_kraus = QuantumError.from_dict(error_dict)
+
+    def test_from_dict_raise_if_unitary_has_no_params(self):
+        error_quantum = QuantumError(UnitaryGate(np.eye(2)))
+
+        error_dict = error_quantum.to_dict()
+
+        # remove params to provoke exception
+        error_dict["instructions"][0][0].pop("params")
+        with self.assertRaises(NoiseError):
+            error_unitary = QuantumError.from_dict(error_dict)
+
+    def test_from_dict_raise_if_instruction_not_supported(self):
+        """Test exception is raised by from_dict if instruction is not supported"""
+        error_quantum = QuantumError(UnitaryGate(np.eye(2)))
+
+        error_dict = error_quantum.to_dict()
+
+        # exchange instruction "unitary" with "blubb" to provoke exception
+        error_dict["instructions"][0][0]["name"] = "blubb"
+        with self.assertRaises(NoiseError):
+            error_unitary = QuantumError.from_dict(error_dict)
+
 
 if __name__ == "__main__":
     unittest.main()