from qiskit.visualization import plot_bloch_vector %matplotlib inline plot_bloch_vector([0,1,0], title="New Bloch Sphere")
UPDATE: Qiskit Terra 0.16 (release Oct 2020) fixes this issue.
I just merged PR 4893, fixing this issue in
coming Qiskit Terra 0.16. This closes 4905 and 4893 (reporting this very same problem) by setting the correct aspecting ration when Matplotlib installed is 3.3.0 or above. This issue was introduced by Matplotlib 3.3 as part of a fix.
TL;DR: Problem introduce by MPL 3.3.0 that will be fixed in Qiskit Terra 0.16. In the meanwhile, you can downgrade to MPL 3.2 as a workaround.