qiskit.quantum_info.partial_trace¶
- partial_trace(state, qargs)[source]¶
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 or DensityMatrix) – the input state.
qargs (list) – The subsystems to trace over.
- Returns
The reduced density matrix.
- Return type
- Raises
QiskitError – if input state is invalid.