50 lines
1.8 KiB
Plaintext
50 lines
1.8 KiB
Plaintext
---
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title: diamond_norm (v0.29)
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description: API reference for qiskit.quantum_info.diamond_norm in qiskit v0.29
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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.diamond_norm
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---
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<span id="qiskit-quantum-info-diamond-norm" />
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# qiskit.quantum\_info.diamond\_norm
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<Function id="qiskit.quantum_info.diamond_norm" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.18/qiskit/quantum_info/operators/measures.py" signature="diamond_norm(choi, **kwargs)">
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Return the diamond norm of the input quantum channel object.
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This function computes the completely-bounded trace-norm (often referred to as the diamond-norm) of the input quantum channel object using the semidefinite-program from reference \[1].
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**Parameters**
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* **choi** ([*Choi*](qiskit.quantum_info.Choi "qiskit.quantum_info.Choi") *or QuantumChannel*) – a quantum channel object or Choi-matrix array.
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* **kwargs** – optional arguments to pass to CVXPY solver.
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**Returns**
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**The completely-bounded trace norm**
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$\|\mathcal{E}\|_{\diamond}$.
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**Return type**
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float
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**Raises**
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**QiskitError** – if CVXPY package cannot be found.
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## Additional Information:
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The input to this function is typically *not* a CPTP quantum channel, but rather the *difference* between two quantum channels $\|\Delta\mathcal{E}\|_\diamond$ where $\Delta\mathcal{E} = \mathcal{E}_1 - \mathcal{E}_2$.
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## Reference:
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J. Watrous. “Simpler semidefinite programs for completely bounded norms”, arXiv:1207.5726 \[quant-ph] (2012).
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<Admonition title="Note" type="note">
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This function requires the optional CVXPY package to be installed. Any additional kwargs will be passed to the `cvxpy.solve` function. See the CVXPY documentation for information on available SDP solvers.
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</Admonition>
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</Function>
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