qiskit.quantum_info.partial_trace
partial_trace(state, qargs)
Return reduced density matrix by tracing out part of quantum state.
If all subsystems are traced over this returns the trace() of the input state.
Parameters
- state (Statevector orDensityMatrix) – the input state.
- qargs (list) – The subsystems to trace over.
Returns
The reduced density matrix.
Return type
Raises
QiskitError – if input state is invalid.
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