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name: quantum-info description: "Guides agents using Qiskit quantum-information states, operators, observables, channels, random generators, predicates, and measures." disable-model-invocation: true metadata: disco-role: operating license: Apache 2.0

Qiskit quantum-info workflows

Use this sub-skill when the task is about mathematical objects in qiskit.quantum_info: states, operators, observables, channels, random generators, matrix predicates, and fidelity or entropy measures.

Read next

• references/workflows.md for common state, operator, Pauli, random-object, and measure recipes.
• references/troubleshooting.md for dimension, measurement, optional-dependency, and numerical-tolerance failures.
• ../../references/module-map.md for route boundaries.
• ../../scripts/check_qiskit_environment.py --sections quantum-info for a source-free quantum-info smoke check.

Include here

• Statevector, DensityMatrix, StabilizerState, and state utilities.
• Operator, ScalarOp, SparsePauliOp, Pauli, Clifford, sparse Pauli types, and channel objects.
• Random generators such as random_statevector, random_unitary, random_pauli, and random_quantum_channel.
• Fidelity, entropy, purity, partial trace, commutator, and matrix-predicate workflows.

Exclude or route elsewhere

• Constructing a circuit before analysis belongs in ../circuit/SKILL.md.
• Compiling for a backend belongs in ../transpiler/SKILL.md.
• Running samplers/estimators belongs in ../primitives/SKILL.md.
• Saving objects as QASM/QPY belongs in ../serialization/SKILL.md.
• Plotting states or histograms belongs in ../visualization/SKILL.md.

Default route

Start here when the user asks about amplitudes, matrices, state evolution, observables, Pauli operators, fidelity, or why two circuits are equivalent up to global phase.

What to remember

• State and operator objects grow exponentially in qubit count; avoid full matrices for large circuits.
• Operator.from_circuit() expects a unitary-like circuit, while measured circuits are often not valid operator inputs.
• Use SparsePauliOp for estimator observables and Hamiltonian-like sums.
• Always state the tolerance and whether global phase should be ignored when comparing matrices.