# cirq.bloch_vector_from_state_vector¶

cirq.bloch_vector_from_state_vector(state: Sequence, index: int, qid_shape: Optional[Tuple[int, …]] = None) → numpy.ndarray[source]

Returns the bloch vector of a qubit.

Calculates the bloch vector of the qubit at index
in the wavefunction given by state, assuming state follows
the standard Kronecker convention of numpy.kron.
Parameters
• state – A sequence representing a wave function in which the ordering mapping to qubits follows the standard Kronecker convention of numpy.kron.

• index – index of qubit who’s bloch vector we want to find. follows the standard Kronecker convention of numpy.kron.

Returns

A length 3 numpy array representing the qubit’s bloch vector.

Raises
• ValueError – if the size of state is not a power of 2.

• ValueError – if the size of the state represents more than 25 qubits.

• IndexError – if index is out of range for the number of qubits corresponding to the state.