38 lines
1.0 KiB
Plaintext
38 lines
1.0 KiB
Plaintext
---
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title: entropy
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description: API reference for qiskit.quantum_info.entropy
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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.quantum_info.entropy
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---
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# qiskit.quantum\_info.entropy
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<Function id="qiskit.quantum_info.entropy" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.18/qiskit/quantum_info/states/measures.py" signature="entropy(state, base=2)">
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Calculate the von-Neumann entropy of a quantum state.
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The entropy $S$ is given by
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$$
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S(\rho) = - Tr[\rho \log(\rho)]
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$$
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**Parameters**
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* **state** ([*Statevector*](qiskit.quantum_info.Statevector "qiskit.quantum_info.Statevector") *or*[*DensityMatrix*](qiskit.quantum_info.DensityMatrix "qiskit.quantum_info.DensityMatrix")) – a quantum state.
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* **base** (*int*) – the base of the logarithm \[Default: 2].
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**Returns**
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The von-Neumann entropy S(rho).
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**Return type**
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float
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**Raises**
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**QiskitError** – if the input state is not a valid QuantumState.
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</Function>
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