Source code for qiskit_aer.library.set_instructions.set_density_matrix

# This code is part of Qiskit.
#
# (C) Copyright IBM 2018, 2021.
#
# 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.
#
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"""
Instruction to set the density matrix simulator state to a matrix.
"""

from qiskit.circuit import QuantumCircuit, Instruction
from qiskit.quantum_info import DensityMatrix
from ..default_qubits import default_qubits


[docs]class SetDensityMatrix(Instruction): """Set density matrix state of the simulator""" _directive = True def __init__(self, state): """Create new instruction to set the density matrix state of the simulator. Args: state (DensityMatrix): a density matrix. Raises: ValueError: if the input density matrix is not valid. .. note:: This set instruction must always be performed on the full width of qubits in a circuit, otherwise an exception will be raised during simulation. """ if not isinstance(state, DensityMatrix): state = DensityMatrix(state) if not state.num_qubits or not state.is_valid(): raise ValueError("The input state is not valid") super().__init__("set_density_matrix", state.num_qubits, 0, [state.data])
[docs]def set_density_matrix(self, state): """Set the density matrix state of the simulator. Args: state (DensityMatrix): a density matrix. Returns: QuantumCircuit: with attached instruction. Raises: ValueError: If the density matrix is the incorrect size for the current circuit. .. note: This instruction is always defined across all qubits in a circuit. """ qubits = default_qubits(self) if not isinstance(state, DensityMatrix): state = DensityMatrix(state) if not state.num_qubits or state.num_qubits != len(qubits): raise ValueError( "The size of the density matrix for the set state" " instruction must be equal to the number of qubits" f" in the circuit (state.num_qubits ({state.num_qubits})" f" != QuantumCircuit.num_qubits ({self.num_qubits}))." ) return self.append(SetDensityMatrix(state), qubits)
QuantumCircuit.set_density_matrix = set_density_matrix