# This code is part of Qiskit. # # (C) Copyright IBM 2018-2023. # # This code is licensed under the Apache License, Version 2.0. You may # obtain a copy of this license in the LICENSE.txt file in the root directory # of this source tree or at http://www.apache.org/licenses/LICENSE-2.0. # # Any modifications or derivative works of this code must retain this # copyright notice, and modified files need to carry a notice indicating # that they have been altered from the originals. """ Quantum error class for Aer noise model """ import numbers from typing import Iterable import numpy as np from qiskit.circuit import QuantumCircuit, Instruction, Reset from qiskit.circuit.exceptions import CircuitError from qiskit.circuit.library.generalized_gates import PauliGate, UnitaryGate from qiskit.circuit.library.standard_gates import IGate, XGate, YGate, ZGate from qiskit.exceptions import QiskitError from qiskit.quantum_info import Kraus, SuperOp, Clifford, Pauli from qiskit.quantum_info.operators.base_operator import BaseOperator 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 .base_quantum_error import BaseQuantumError from ..noiseerror import NoiseError class QuantumError(BaseQuantumError, TolerancesMixin): """ Quantum error class for Aer noise model .. warning:: The init interface for this class is not finalized and may change in future releases. For maximum backwards compatibility use the QuantumError generating functions in the `noise.errors` module. """ def __init__(self, noise_ops): """ Create a quantum error for a noise model. Noise ops may either be specified as a :obj:`~qiskit.quantum_info.operators.channel.quantum_channel.QuantumChannel` for a general CPTP map, or as a list of ``(circuit, p)`` pairs where ``circuit`` is a circuit-like object for the noise, and ``p`` is the probability of the noise event. Any type of input will be converted to the probabilistic mixture of circuit format. **Example** An example noise_ops for a bit-flip error with error probability ``p = 0.1`` is: .. code-block:: python noise_ops = [(IGate(), 0.9), (XGate(), 0.1)] or specifying explicit qubit arguments, .. code-block:: python noise_ops = [((IGate(), [0]), 0.9), ((XGate(), [0]), 0.1)] The same error represented as a Kraus channel can be input as: .. code-block:: python noise_ops = Kraus([np.sqrt(0.9) * np.array([[1, 0], [0, 1]]), np.sqrt(0.1) * np.array([[0, 1], [1, 0]])]) Args: noise_ops (QuantumChannel or Iterable): Either a quantum channel or a list of ``(circuit, p)`` pairs, which represents a quantum error, where ``circuit`` is a circuit-like object for the noise, and ``p`` is the probability of the noise event. Circuit-like types include ``QuantumCircuit``, ``(Instruction, qargs)`` and a list of ``(Instruction, qargs)``. Note that ``qargs`` should be a list of integers and can be omitted (default qubits are used in that case). See also examples above. Raises: NoiseError: If input noise_ops is invalid, e.g. it's not a CPTP map. """ # Shallow copy constructor if isinstance(noise_ops, QuantumError): self._circs = noise_ops.circuits self._probs = noise_ops.probabilities super().__init__(num_qubits=noise_ops.num_qubits) return # Single circuit case if not isinstance(noise_ops, Iterable) or ( isinstance(noise_ops, tuple) and isinstance(noise_ops[0], Instruction) ): noise_ops = [(noise_ops, 1.0)] # Convert zipped object to list (to enable multiple iteration over it) if not isinstance(noise_ops, list): noise_ops = list(noise_ops) # Input checks for pair in noise_ops: if not isinstance(pair, tuple) or len(pair) != 2: raise NoiseError(f"Invalid type of input is found around '{pair}'") _, p = pair # pylint: disable=invalid-name if not isinstance(p, numbers.Real): raise NoiseError(f"Invalid type of probability: {p}") if p < -1 * QuantumError.atol: raise NoiseError(f"Negative probability is invalid: {p}") # Remove zero probability circuits noise_ops = [(op, prob) for op, prob in noise_ops if prob > 0] if len(noise_ops) == 0: raise NoiseError( "noise_ops must contain at least one operator with non-zero probability" ) ops, probs = zip(*noise_ops) # unzip # Initialize internal variables with error checking total_probs = sum(probs) if not np.isclose(total_probs - 1, 0, atol=QuantumError.atol): raise NoiseError(f"Probabilities are not normalized: {total_probs} != 1") # Rescale probabilities if their sum is ok to avoid accumulation of rounding errors self._probs = list(np.array(probs) / total_probs) # Convert instructions to circuits circs = [self._to_circuit(op) for op in ops] num_qubits = max(qc.num_qubits for qc in circs) self._circs = [self._enlarge_qreg(qc, num_qubits) for qc in circs] # Check validity of circuits for circ in self._circs: if circ.clbits: raise NoiseError("Circuit with classical register cannot be a channel") if circ.num_qubits != num_qubits: raise NoiseError("Number of qubits used in noise ops must be the same") super().__init__(num_qubits=num_qubits) # pylint: disable=too-many-return-statements @classmethod def _to_circuit(cls, op): if isinstance(op, QuantumCircuit): return op if isinstance(op, tuple): inst, qubits = op circ = QuantumCircuit(max(qubits) + 1) circ.append(inst, qargs=qubits) return circ if isinstance(op, Instruction): if op.num_clbits > 0: raise NoiseError( f"Unable to convert instruction with clbits: {op.__class__.__name__}" ) circ = QuantumCircuit(op.num_qubits) circ.append(op, qargs=list(range(op.num_qubits))) return circ if isinstance(op, QuantumChannel): if not op.is_cptp(atol=cls.atol): raise NoiseError("Input quantum channel is not CPTP.") try: return cls._to_circuit(Kraus(op).to_instruction()) except QiskitError as err: raise NoiseError( f"Fail to convert {op.__class__.__name__} to Instruction." ) from err if isinstance(op, BaseOperator): if hasattr(op, "to_instruction"): try: return cls._to_circuit(op.to_instruction()) except QiskitError as err: raise NoiseError( f"Fail to convert {op.__class__.__name__} to Instruction." ) from err else: raise NoiseError( f"Unacceptable Operator, not implementing to_instruction: " f"{op.__class__.__name__}" ) if isinstance(op, list): if all(isinstance(aop, tuple) for aop in op): num_qubits = max(max(qubits) for _, qubits in op) + 1 circ = QuantumCircuit(num_qubits) for inst, qubits in op: try: circ.append(inst, qargs=qubits) except CircuitError as err: raise NoiseError( f"Invalid operation type: {inst.__class__.__name__}," f" not appendable to circuit." ) from err return circ else: raise NoiseError(f"Invalid type of op list: {op}") raise NoiseError(f"Invalid noise op type {op.__class__.__name__}: {op}") def __repr__(self): """Display QuantumError.""" return ( f"<{self._repr_name()}, num_qubits={self.num_qubits}," f" size={self.size}, probabilities={self.probabilities}>" ) def __str__(self): """Print error information.""" output = f"QuantumError on {self.num_qubits} qubits. Noise circuits:" for j, pair in enumerate(zip(self.probabilities, self.circuits)): output += f"\n P({j}) = {pair[0]}, Circuit = \n{pair[1]}" return output def __eq__(self, other): """Test if two QuantumErrors are equal as SuperOps""" if not isinstance(other, BaseQuantumError): return False return self.to_quantumchannel() == other.to_quantumchannel() @property def size(self): """Return the number of error circuit.""" return len(self.circuits) @property def circuits(self): """Return the list of error circuits.""" return self._circs @property def probabilities(self): """Return the list of error probabilities.""" return self._probs def ideal(self): """Return True if this error object is composed only of identity operations. Note that the identity check is best effort and up to global phase.""" for circ in self.circuits: try: # Circuit-level identity check for clifford Circuits clifford = Clifford(circ) if clifford != Clifford(np.eye(2 * circ.num_qubits, dtype=bool)): return False except QiskitError: pass # Component-wise check for non-Clifford circuits for instruction in circ: op = instruction.operation if isinstance(op, IGate): continue if isinstance(op, PauliGate): if op.params[0].replace("I", ""): return False else: # Convert to Kraus and check if identity kmats = Kraus(op).data if len(kmats) > 1: return False if not is_identity_matrix( kmats[0], ignore_phase=True, atol=self.atol, rtol=self.rtol ): return False return True def to_quantumchannel(self): """Convert the QuantumError to a SuperOp quantum channel. Required to enable SuperOp(QuantumError).""" # Initialize as an empty superoperator of the correct size dim = 2**self.num_qubits ret = SuperOp(np.zeros([dim * dim, dim * dim])) for circ, prob in zip(self.circuits, self.probabilities): component = prob * SuperOp(circ) ret = ret + component return ret def error_term(self, position): """ Return a single term from the error. Args: position (int): the position of the error term. Returns: tuple: A pair `(circuit, p)` for error term at `position` < size where `p` is the probability of the error term, and `circuit` is the list of qobj instructions for the error term. Raises: NoiseError: If the position is greater than the size of the quantum error. """ if position < self.size: return self.circuits[position], self.probabilities[position] else: raise NoiseError( f"Position {position} is greater than the number of error outcomes {self.size}" ) def to_dict(self): """Return the current error as a dictionary.""" # Assemble noise circuits instructions = [] for circ in self._circs: circ_inst = [] for inst in circ.data: inst_dict = {} inst_dict["name"] = inst.operation.name inst_dict["qubits"] = [circ.find_bit(q).index for q in inst.qubits] if inst.operation.params: inst_dict["params"] = inst.operation.params if inst.operation.label: inst_dict["label"] = inst.operation.label condition = getattr(inst.operation, "condition", None) if condition: inst_dict["condition"] = condition circ_inst.append(inst_dict) instructions.append(circ_inst) # Construct error dict error = { "type": "qerror", "id": self.id, "operations": [], "instructions": instructions, "probabilities": list(self.probabilities), } 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("error 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 == "reset": noise_elem.append((Reset(), inst_qubits)) elif inst_name == "measure": raise NoiseError("instruction 'measure' not supported") elif inst_name == "pauli": if "params" not in elem: raise NoiseError("pauli does not have a parameter value") noise_elem.append((Pauli(elem["params"][0]), inst_qubits)) elif inst_name == "kraus": if "params" not in elem: raise NoiseError("kraus does not have a parameter value") noise_elem.append((Kraus(elem["params"]), inst_qubits)) elif inst_name == "unitary": if "params" not in elem: raise NoiseError("unitary does not have a parameter value") noise_elem.append((UnitaryGate(elem["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) if qargs is not None: if self.num_qubits < other.num_qubits: raise QiskitError( "Number of qubits of this error must be less than" " that of the error to be composed if using 'qargs' argument." ) if len(qargs) != other.num_qubits: raise QiskitError( "Number of items in 'qargs' argument must be the same as" " number of qubits of the error to be composed." ) if front: raise QiskitError( "QuantumError.compose does not support 'qargs' when 'front=True'." ) circs = [ self._compose_circ(lqc, rqc, qubits=qargs, front=front) for lqc in self.circuits for rqc in other.circuits ] probs = [lpr * rpr for lpr in self.probabilities for rpr in other.probabilities] return QuantumError(zip(circs, probs)) @staticmethod def _enlarge_qreg(qc: QuantumCircuit, num_qubits: int): if qc.num_qubits < num_qubits: enlarged = QuantumCircuit(num_qubits) return enlarged.compose(qc) return qc @staticmethod def _compose_circ(lqc: QuantumCircuit, rqc: QuantumCircuit, qubits, front): if qubits is None: if front: lqc, rqc = rqc, lqc if lqc.num_qubits < rqc.num_qubits: lqc = QuantumError._enlarge_qreg(lqc, rqc.num_qubits) return lqc.compose(rqc) return lqc.compose(rqc, qubits=qubits, front=front) def tensor(self, other): if not isinstance(other, QuantumError): other = QuantumError(other) circs = [lqc.tensor(rqc) for lqc in self.circuits for rqc in other.circuits] probs = [lpr * rpr for lpr in self.probabilities for rpr in other.probabilities] return QuantumError(zip(circs, probs)) def expand(self, other): return other.tensor(self)