243 lines
8.0 KiB
Plaintext
243 lines
8.0 KiB
Plaintext
---
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title: SnapshotExpectationValue
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description: API reference for qiskit.providers.aer.extensions.SnapshotExpectationValue
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in_page_toc_min_heading_level: 1
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python_api_type: class
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python_api_name: qiskit.providers.aer.extensions.SnapshotExpectationValue
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---
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# SnapshotExpectationValue
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<Class id="qiskit.providers.aer.extensions.SnapshotExpectationValue" isDedicatedPage={true} github="https://github.com/qiskit/qiskit-aer/tree/stable/0.8/qiskit/providers/aer/extensions/snapshot_expectation_value.py" signature="SnapshotExpectationValue(label, op, single_shot=False, variance=False)" modifiers="class">
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Bases: `qiskit.providers.aer.extensions.snapshot.Snapshot`
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Snapshot instruction for supported methods of Qasm simulator.
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Create an expectation value snapshot instruction.
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**Parameters**
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* **label** (*str*) – the snapshot label.
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* **op** ([*Operator*](qiskit.quantum_info.Operator "qiskit.quantum_info.Operator")) – operator to snapshot.
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* **single\_shot** (*bool*) – return list for each shot rather than average \[Default: False]
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* **variance** (*bool*) – compute variance of values \[Default: False]
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**Raises**
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**ExtensionError** – if snapshot is invalid.
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<Admonition title="Note" type="note">
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This instruction will be deprecated after the qiskit-aer 0.8 release. It has been superseded by the [`qiskit.providers.aer.library.SaveExpectationValue`](qiskit.providers.aer.library.SaveExpectationValue "qiskit.providers.aer.library.SaveExpectationValue") and [`qiskit.providers.aer.library.SaveExpectationValueVariance`](qiskit.providers.aer.library.SaveExpectationValueVariance "qiskit.providers.aer.library.SaveExpectationValueVariance") instructions.
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</Admonition>
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## Methods
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### add\_decomposition
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<Function id="qiskit.providers.aer.extensions.SnapshotExpectationValue.add_decomposition" signature="SnapshotExpectationValue.add_decomposition(decomposition)">
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Add a decomposition of the instruction to the SessionEquivalenceLibrary.
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</Function>
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### assemble
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<Function id="qiskit.providers.aer.extensions.SnapshotExpectationValue.assemble" signature="SnapshotExpectationValue.assemble()">
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Assemble a QasmQobjInstruction for snapshot\_expectation\_value.
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</Function>
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### broadcast\_arguments
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<Function id="qiskit.providers.aer.extensions.SnapshotExpectationValue.broadcast_arguments" signature="SnapshotExpectationValue.broadcast_arguments(qargs, cargs)">
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Validation of the arguments.
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**Parameters**
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* **qargs** (*List*) – List of quantum bit arguments.
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* **cargs** (*List*) – List of classical bit arguments.
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**Yields**
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*Tuple(List, List)* – A tuple with single arguments.
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**Raises**
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**CircuitError** – If the input is not valid. For example, the number of arguments does not match the gate expectation.
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</Function>
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### c\_if
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<Function id="qiskit.providers.aer.extensions.SnapshotExpectationValue.c_if" signature="SnapshotExpectationValue.c_if(classical, val)">
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Add classical condition on register or cbit classical and value val.
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</Function>
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### copy
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<Function id="qiskit.providers.aer.extensions.SnapshotExpectationValue.copy" signature="SnapshotExpectationValue.copy(name=None)">
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Copy of the instruction.
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**Parameters**
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**name** (*str*) – name to be given to the copied circuit, if None then the name stays the same.
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**Returns**
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**a copy of the current instruction, with the name**
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updated if it was provided
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**Return type**
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[qiskit.circuit.Instruction](qiskit.circuit.Instruction "qiskit.circuit.Instruction")
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</Function>
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### define\_snapshot\_register
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<Function id="qiskit.providers.aer.extensions.SnapshotExpectationValue.define_snapshot_register" signature="SnapshotExpectationValue.define_snapshot_register(circuit, label=None, qubits=None)" modifiers="static">
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Defines qubits to snapshot for all snapshot methods
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</Function>
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### inverse
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<Function id="qiskit.providers.aer.extensions.SnapshotExpectationValue.inverse" signature="SnapshotExpectationValue.inverse()">
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Special case. Return self.
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</Function>
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### is\_parameterized
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<Function id="qiskit.providers.aer.extensions.SnapshotExpectationValue.is_parameterized" signature="SnapshotExpectationValue.is_parameterized()">
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Return True .IFF. instruction is parameterized else False
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</Function>
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### mirror
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<Function id="qiskit.providers.aer.extensions.SnapshotExpectationValue.mirror" signature="SnapshotExpectationValue.mirror()">
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DEPRECATED: use instruction.reverse\_ops().
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**Returns**
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**a new instruction with sub-instructions**
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reversed.
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**Return type**
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[qiskit.circuit.Instruction](qiskit.circuit.Instruction "qiskit.circuit.Instruction")
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</Function>
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### qasm
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<Function id="qiskit.providers.aer.extensions.SnapshotExpectationValue.qasm" signature="SnapshotExpectationValue.qasm()">
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Return a default OpenQASM string for the instruction.
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Derived instructions may override this to print in a different format (e.g. measure q\[0] -> c\[0];).
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</Function>
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### repeat
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<Function id="qiskit.providers.aer.extensions.SnapshotExpectationValue.repeat" signature="SnapshotExpectationValue.repeat(n)">
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Creates an instruction with gate repeated n amount of times.
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**Parameters**
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**n** (*int*) – Number of times to repeat the instruction
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**Returns**
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Containing the definition.
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**Return type**
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[qiskit.circuit.Instruction](qiskit.circuit.Instruction "qiskit.circuit.Instruction")
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**Raises**
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**CircuitError** – If n \< 1.
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</Function>
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### reverse\_ops
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<Function id="qiskit.providers.aer.extensions.SnapshotExpectationValue.reverse_ops" signature="SnapshotExpectationValue.reverse_ops()">
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For a composite instruction, reverse the order of sub-instructions.
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This is done by recursively reversing all sub-instructions. It does not invert any gate.
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**Returns**
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**a new instruction with**
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sub-instructions reversed.
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**Return type**
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[qiskit.circuit.Instruction](qiskit.circuit.Instruction "qiskit.circuit.Instruction")
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</Function>
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### soft\_compare
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<Function id="qiskit.providers.aer.extensions.SnapshotExpectationValue.soft_compare" signature="SnapshotExpectationValue.soft_compare(other)">
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Soft comparison between gates. Their names, number of qubits, and classical bit numbers must match. The number of parameters must match. Each parameter is compared. If one is a ParameterExpression then it is not taken into account.
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**Parameters**
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**other** (*instruction*) – other instruction.
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**Returns**
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are self and other equal up to parameter expressions.
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**Return type**
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bool
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</Function>
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### validate\_parameter
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<Function id="qiskit.providers.aer.extensions.SnapshotExpectationValue.validate_parameter" signature="SnapshotExpectationValue.validate_parameter(parameter)">
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Instruction parameters has no validation or normalization.
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</Function>
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## Attributes
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### decompositions
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<Attribute id="qiskit.providers.aer.extensions.SnapshotExpectationValue.decompositions">
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Get the decompositions of the instruction from the SessionEquivalenceLibrary.
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</Attribute>
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### definition
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<Attribute id="qiskit.providers.aer.extensions.SnapshotExpectationValue.definition">
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Return definition in terms of other basic gates.
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</Attribute>
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### duration
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<Attribute id="qiskit.providers.aer.extensions.SnapshotExpectationValue.duration">
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Get the duration.
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</Attribute>
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### label
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<Attribute id="qiskit.providers.aer.extensions.SnapshotExpectationValue.label">
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Return snapshot label
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</Attribute>
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### params
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<Attribute id="qiskit.providers.aer.extensions.SnapshotExpectationValue.params">
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return instruction params.
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</Attribute>
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### snapshot\_type
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<Attribute id="qiskit.providers.aer.extensions.SnapshotExpectationValue.snapshot_type">
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Return snapshot type
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</Attribute>
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### unit
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<Attribute id="qiskit.providers.aer.extensions.SnapshotExpectationValue.unit">
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Get the time unit of duration.
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</Attribute>
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</Class>
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