# This code is part of Qiskit.
#
# (C) Copyright IBM 2018, 2019.
#
# 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.
"""
Simulator command to snapshot internal simulator representation.
"""
import warnings
from qiskit import QuantumCircuit
from qiskit.circuit.quantumregister import QuantumRegister
from qiskit.circuit import Instruction
from qiskit.extensions.exceptions import ExtensionError
[docs]class Snapshot(Instruction):
"""Simulator snapshot instruction."""
def __init__(self,
label,
snapshot_type='statevector',
num_qubits=0,
num_clbits=0,
params=None):
"""Create new snapshot instruction.
Args:
label (str): the snapshot label for result data.
snapshot_type (str): the type of the snapshot.
num_qubits (int): the number of qubits for the snapshot type [Default: 0].
num_clbits (int): the number of classical bits for the snapshot type [Default: 0].
params (list or None): the parameters for snapshot_type [Default: None].
Raises:
ExtensionError: if snapshot label is invalid.
"""
if not isinstance(label, str):
raise ExtensionError('Snapshot label must be a string.')
self._label = label
self._snapshot_type = snapshot_type
if params is None:
params = []
super().__init__('snapshot', num_qubits, num_clbits, params)
[docs] def assemble(self):
"""Assemble a QasmQobjInstruction"""
instruction = super().assemble()
instruction.label = self._label
instruction.snapshot_type = self._snapshot_type
return instruction
[docs] def inverse(self):
"""Special case. Return self."""
return Snapshot(self.num_qubits, self.num_clbits, self.params[0],
self.params[1])
[docs] @staticmethod
def define_snapshot_register(circuit,
label,
qubits=None):
"""Defines qubits to snapshot for all snapshot methods"""
# Convert label to string for backwards compatibility
if not isinstance(label, str):
warnings.warn(
"Snapshot label should be a string, "
"implicit conversion is deprecated.", DeprecationWarning)
label = str(label)
# If no qubits are specified we add all qubits so it acts as a barrier
# This is needed for full register snapshots like statevector
if isinstance(qubits, QuantumRegister):
qubits = qubits[:]
if not qubits:
tuples = []
if isinstance(circuit, QuantumCircuit):
for register in circuit.qregs:
tuples.append(register)
if not tuples:
raise ExtensionError('no qubits for snapshot')
qubits = []
for tuple_element in tuples:
if isinstance(tuple_element, QuantumRegister):
for j in range(tuple_element.size):
qubits.append(tuple_element[j])
else:
qubits.append(tuple_element)
return qubits
@property
def snapshot_type(self):
"""Return snapshot type"""
return self._snapshot_type
@property
def label(self):
"""Return snapshot label"""
return self._label
@label.setter
def label(self, name):
"""Set snapshot label to name
Args:
name (str or None): label to assign unitary
Raises:
TypeError: name is not string or None.
"""
if isinstance(name, str):
self._label = name
else:
raise TypeError('label expects a string')
def snapshot(self,
label,
snapshot_type='statevector',
qubits=None,
params=None):
"""Take a statevector snapshot of the internal simulator representation.
Works on all qubits, and prevents reordering (like barrier).
Args:
label (str): a snapshot label to report the result
snapshot_type (str): the type of the snapshot.
qubits (list or None): the qubits to apply snapshot to [Default: None].
params (list or None): the parameters for snapshot_type [Default: None].
Returns:
QuantumCircuit: with attached command
Raises:
ExtensionError: malformed command
"""
snapshot_register = Snapshot.define_snapshot_register(self, label, qubits)
return self.append(
Snapshot(
label,
snapshot_type=snapshot_type,
num_qubits=len(snapshot_register),
params=params), snapshot_register)
# Add to QuantumCircuit class
QuantumCircuit.snapshot = snapshot