def from_label(cls, label):
r"""Return a tensor product of Pauli X,Y,Z eigenstates.
.. list-table:: Single-qubit state labels
:header-rows: 1
* - Label
- Statevector
* - ``"0"``
- :math:`\begin{pmatrix} 1 & 0 \\ 0 & 0 \end{pmatrix}`
* - ``"1"``
- :math:`\begin{pmatrix} 0 & 0 \\ 0 & 1 \end{pmatrix}`
* - ``"+"``
- :math:`\frac{1}{2}\begin{pmatrix} 1 & 1 \\ 1 & 1 \end{pmatrix}`
* - ``"-"``
- :math:`\frac{1}{2}\begin{pmatrix} 1 & -1 \\ -1 & 1 \end{pmatrix}`
* - ``"r"``
- :math:`\frac{1}{2}\begin{pmatrix} 1 & -i \\ i & 1 \end{pmatrix}`
* - ``"l"``
- :math:`\frac{1}{2}\begin{pmatrix} 1 & i \\ -i & 1 \end{pmatrix}`
Args:
label (string): a eigenstate string ket label (see table for
allowed values).
Returns:
Statevector: The N-qubit basis state density matrix.
Raises:
QiskitError: if the label contains invalid characters, or the length
of the label is larger than an explicitly specified num_qubits.
"""
from qiskit.quantum_info.states.statevector import Statevector
return DensityMatrix(Statevector.from_label(label))
def test_from_labels(self):
"""Initialize from labels."""
desired_sv = Statevector.from_label('01+-lr')
qc = QuantumCircuit(6)
qc.initialize('01+-lr', range(6))
job = execute(qc, BasicAer.get_backend('statevector_simulator'))
result = job.result()
statevector = result.get_statevector()
fidelity = state_fidelity(statevector, desired_sv)
self.assertGreater(
fidelity, self._desired_fidelity,
"Initializer has low fidelity {:.2g}.".format(fidelity))
def from_label(cls, label):
"""Return a tensor product of Pauli X,Y,Z eigenstates.
Args:
label (string): a eigenstate string ket label 0,1,+,-,r,l.
Returns:
Statevector: The N-qubit basis state density matrix.
Raises:
QiskitError: if the label contains invalid characters, or the length
of the label is larger than an explicitly specified num_qubits.
Additional Information:
The labels correspond to the single-qubit states:
'0': [[1, 0], [0, 0]]
'1': [[0, 0], [0, 1]]
'+': [[0.5, 0.5], [0.5 , 0.5]]
'-': [[0.5, -0.5], [-0.5 , 0.5]]
'r': [[0.5, -0.5j], [0.5j , 0.5]]
'l': [[0.5, 0.5j], [-0.5j , 0.5]]
"""
return DensityMatrix(Statevector.from_label(label))