qiskit.visualization.plot_state_paulivec

qiskit.visualization.plot_state_paulivec(state, title='', figsize=None, color=None, ax=None, *, filename=None)

Plot the Pauli-vector representation of a quantum state as bar graph.

The Pauli-vector of a density matrix $\rho$ is defined by the expectation of each possible tensor product of single-qubit Pauli operators (including the identity), that is

This function plots the coefficients $\mathrm{Tr}(\sigma\rho)$ as bar graph.

Parameters

• state (Statevector orDensityMatrix or ndarray) – an N-qubit quantum state.
• title (str) – a string that represents the plot title
• figsize (tuple) – Figure size in inches.
• color (list orstr) – Color of the coefficient value bars.
• ax (matplotlib.axes.Axes) – An optional Axes object to be used for the visualization output. If none is specified a new matplotlib Figure will be created and used. Additionally, if specified there will be no returned Figure since it is redundant.

Returns

The matplotlib.Figure of the visualization if the ax kwarg is not set

Return type

matplotlib.figure.Figure

Raises

• MissingOptionalLibraryError – Requires matplotlib.
• VisualizationError – if input is not a valid N-qubit state.

Examples

# You can set a color for all the bars.
 
from qiskit import QuantumCircuit
from qiskit.quantum_info import Statevector
from qiskit.visualization import plot_state_paulivec
 
qc = QuantumCircuit(2)
qc.h(0)
qc.cx(0, 1)
 
state = Statevector(qc)
plot_state_paulivec(state, color='midnightblue', title="New PauliVec plot")

# If you introduce a list with less colors than bars, the color of the bars will
# alternate following the sequence from the list.
 
import numpy as np
from qiskit.quantum_info import DensityMatrix
from qiskit import QuantumCircuit
from qiskit.visualization import plot_state_paulivec
 
qc = QuantumCircuit(2)
qc.h(0)
qc.cx(0, 1)
 
qc = QuantumCircuit(2)
qc.h([0, 1])
qc.cz(0, 1)
qc.ry(np.pi/3, 0)
qc.rx(np.pi/5, 1)
 
matrix = DensityMatrix(qc)
plot_state_paulivec(matrix, color=['crimson', 'midnightblue', 'seagreen'])