254 lines
8.5 KiB
Plaintext
254 lines
8.5 KiB
Plaintext
---
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title: SaveExpectationValueVariance
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description: API reference for qiskit_aer.library.SaveExpectationValueVariance
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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_aer.library.SaveExpectationValueVariance
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---
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# SaveExpectationValueVariance
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<Class id="qiskit_aer.library.SaveExpectationValueVariance" isDedicatedPage={true} github="https://github.com/qiskit/qiskit-aer/tree/stable/0.12/qiskit_aer/library/save_instructions/save_expectation_value.py" signature="SaveExpectationValueVariance(operator, label='expectation_value_variance', unnormalized=False, pershot=False, conditional=False)" modifiers="class">
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Bases: `qiskit_aer.library.save_instructions.save_data.SaveAverageData`
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Save expectation value and variance of an operator.
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Instruction to save the expectation value and variance of a Hermitian operator.
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The expectation value of a Hermitian operator $H$ for a simulator in quantum state :math\`rho\`is given by $\langle H\rangle = \mbox{Tr}[H.\rho]$. The variance is given by $\sigma^2 = \langle H^2 \rangle - \langle H \rangle>^2$.
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**Parameters**
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* **operator** ([*Pauli*](qiskit.quantum_info.Pauli "qiskit.quantum_info.Pauli") *or*[*SparsePauliOp*](qiskit.quantum_info.SparsePauliOp "qiskit.quantum_info.SparsePauliOp") *or*[*Operator*](qiskit.quantum_info.Operator "qiskit.quantum_info.Operator")) – a Hermitian operator.
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* **label** (*str*) – the key for retrieving saved data from results.
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* **unnormalized** (*bool*) – If True return save the unnormalized accumulated or conditional accumulated expectation value over all shot \[Default: False].
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* **pershot** (*bool*) – if True save a list of expectation values for each shot of the simulation rather than the average over all shots \[Default: False].
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* **conditional** (*bool*) – if True save the average or pershot data conditional on the current classical register values \[Default: False].
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**Raises**
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**ExtensionError** – if the input operator is invalid or not Hermitian.
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<Admonition title="Note" type="note">
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This instruction can be directly appended to a circuit using the [`save_expectation_value()`](qiskit_aer.library.save_expectation_value "qiskit_aer.library.save_expectation_value") circuit method.
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</Admonition>
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## Methods
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### add\_decomposition
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<Function id="qiskit_aer.library.SaveExpectationValueVariance.add_decomposition" signature="SaveExpectationValueVariance.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_aer.library.SaveExpectationValueVariance.assemble" signature="SaveExpectationValueVariance.assemble()">
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Return the QasmQobjInstruction for the intructions.
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</Function>
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### broadcast\_arguments
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<Function id="qiskit_aer.library.SaveExpectationValueVariance.broadcast_arguments" signature="SaveExpectationValueVariance.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_aer.library.SaveExpectationValueVariance.c_if" signature="SaveExpectationValueVariance.c_if(classical, val)">
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Set a classical equality condition on this instruction between the register or cbit `classical` and value `val`.
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<Admonition title="Note" type="note">
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This is a setter method, not an additive one. Calling this multiple times will silently override any previously set condition; it does not stack.
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</Admonition>
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</Function>
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### copy
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<Function id="qiskit_aer.library.SaveExpectationValueVariance.copy" signature="SaveExpectationValueVariance.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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### inverse
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<Function id="qiskit_aer.library.SaveExpectationValueVariance.inverse" signature="SaveExpectationValueVariance.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_aer.library.SaveExpectationValueVariance.is_parameterized" signature="SaveExpectationValueVariance.is_parameterized()">
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Return True .IFF. instruction is parameterized else False
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</Function>
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### qasm
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<Function id="qiskit_aer.library.SaveExpectationValueVariance.qasm" signature="SaveExpectationValueVariance.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_aer.library.SaveExpectationValueVariance.repeat" signature="SaveExpectationValueVariance.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_aer.library.SaveExpectationValueVariance.reverse_ops" signature="SaveExpectationValueVariance.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_aer.library.SaveExpectationValueVariance.soft_compare" signature="SaveExpectationValueVariance.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_aer.library.SaveExpectationValueVariance.validate_parameter" signature="SaveExpectationValueVariance.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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### condition\_bits
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<Attribute id="qiskit_aer.library.SaveExpectationValueVariance.condition_bits">
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Get Clbits in condition.
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**Return type**
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`List`\[[`Clbit`](qiskit.circuit.Clbit "qiskit.circuit.classicalregister.Clbit")]
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</Attribute>
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### decompositions
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<Attribute id="qiskit_aer.library.SaveExpectationValueVariance.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_aer.library.SaveExpectationValueVariance.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_aer.library.SaveExpectationValueVariance.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_aer.library.SaveExpectationValueVariance.label">
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Return instruction label
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**Return type**
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`str`
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</Attribute>
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### name
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<Attribute id="qiskit_aer.library.SaveExpectationValueVariance.name">
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Return the name.
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</Attribute>
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### num\_clbits
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<Attribute id="qiskit_aer.library.SaveExpectationValueVariance.num_clbits">
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Return the number of clbits.
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</Attribute>
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### num\_qubits
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<Attribute id="qiskit_aer.library.SaveExpectationValueVariance.num_qubits">
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Return the number of qubits.
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</Attribute>
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### params
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<Attribute id="qiskit_aer.library.SaveExpectationValueVariance.params">
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return instruction params.
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</Attribute>
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### unit
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<Attribute id="qiskit_aer.library.SaveExpectationValueVariance.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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