62 lines
3.3 KiB
Plaintext
62 lines
3.3 KiB
Plaintext
---
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title: unitary_overlap (dev version)
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description: API reference for qiskit.circuit.library.unitary_overlap in the dev version of qiskit
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in_page_toc_min_heading_level: 1
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python_api_type: function
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python_api_name: qiskit.circuit.library.unitary_overlap
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---
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<span id="qiskit-circuit-library-unitary-overlap" />
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# qiskit.circuit.library.unitary\_overlap
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<Function id="qiskit.circuit.library.unitary_overlap" isDedicatedPage={true} github="https://github.com/Qiskit/qiskit/tree/main/qiskit/circuit/library/overlap.py#L105-L183" signature="qiskit.circuit.library.unitary_overlap(unitary1, unitary2, prefix1='p1', prefix2='p2', insert_barrier=False)">
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Circuit that returns the overlap between two unitaries $U_2^{\dag} U_1$.
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The input quantum circuits must represent unitary operations, since they must be invertible. If the inputs will have parameters, they are replaced by [`ParameterVector`](qiskit.circuit.ParameterVector "qiskit.circuit.ParameterVector")s with names “p1” (for circuit `unitary1`) and “p2” (for circuit `unitary_2`) in the output circuit.
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This circuit is usually employed in computing the fidelity:
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$$
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\left|\langle 0| U_2^{\dag} U_1|0\rangle\right|^{2}
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$$
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by computing the probability of being in the all-zeros bit-string, or equivalently, the expectation value of projector $|0\rangle\langle 0|$.
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**Reference Circuit:**
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```python
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import numpy as np
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from qiskit.circuit.library import efficient_su2, unitary_overlap
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# get two circuit to prepare states of which we compute the overlap
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circuit = efficient_su2(2, reps=1)
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unitary1 = circuit.assign_parameters(np.random.random(circuit.num_parameters))
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unitary2 = circuit.assign_parameters(np.random.random(circuit.num_parameters))
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# create the overlap circuit
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overlap = unitary_overlap(unitary1, unitary2)
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overlap.draw('mpl')
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```
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**Parameters**
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* **unitary1** ([*QuantumCircuit*](qiskit.circuit.QuantumCircuit "qiskit.circuit.quantumcircuit.QuantumCircuit")) – Unitary acting on the ket vector.
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* **unitary2** ([*QuantumCircuit*](qiskit.circuit.QuantumCircuit "qiskit.circuit.quantumcircuit.QuantumCircuit")) – Unitary whose inverse operates on the bra vector.
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* **prefix1** ([*str*](https://docs.python.org/3/library/stdtypes.html#str "(in Python v3.13)")) – The name of the parameter vector associated to `unitary1`, if it is parameterized. Defaults to `"p1"`.
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* **prefix2** ([*str*](https://docs.python.org/3/library/stdtypes.html#str "(in Python v3.13)")) – The name of the parameter vector associated to `unitary2`, if it is parameterized. Defaults to `"p2"`.
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* **insert\_barrier** ([*bool*](https://docs.python.org/3/library/functions.html#bool "(in Python v3.13)")) – Whether to insert a barrier between the two unitaries.
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**Raises**
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* [**CircuitError**](circuit#qiskit.circuit.CircuitError "qiskit.circuit.CircuitError") – Number of qubits in `unitary1` and `unitary2` does not match.
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* [**CircuitError**](circuit#qiskit.circuit.CircuitError "qiskit.circuit.CircuitError") – Inputs contain measurements and/or resets.
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**Return type**
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[*QuantumCircuit*](qiskit.circuit.QuantumCircuit "qiskit.circuit.quantumcircuit.QuantumCircuit")
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</Function>
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