Statevector.draw('latex') can't handle near zero numbers

Environment

• Qiskit Terra version: 0.19.1
• Python version: 3.8.10
• Operating system: win11x64

What is happening?

Performing Statevector.draw(‘latex’) on a statevector that includes numbers which are near zero, results in bad output.

How can we reproduce the issue?

A sample CSWAP-test circuit:

qc = QuantumCircuit(3)
qc.h(0)
qc.cswap(0, 1, 2)
qc.h(0)

evolution of a sample input statevector according to the CSWAP-TEST:

sv = Statevector.from_label('--0').evolve(qc)
print(sv.data)

Notice the near zero numbers at indices 1,3,5 and 7:

[ 5.00000000e-01+0.j  3.11164266e-19+0.j -5.00000000e-01+0.j
 -3.11164266e-19+0.j -5.00000000e-01+0.j -3.11164266e-19+0.j
  5.00000000e-01+0.j  3.11164266e-19+0.j]

Performing:

sv.draw('latex')

Produces:

What should happen?

Should produce:

Any suggestions?

Although a vector output and not Dirac notation, note that performing:

array_to_latex(sv)

does not suffer from the same problem. Is it possible to set up a global “snap to sigma” parameter to the whole system, such that all underlying auxiliary functions can follow? (and it would be nice to change ‘latex’ to ‘dirac’… 😃)

[frankharkins]

Can you assign me please?

[DrEntropy]

Oh that comment was meant to help whoever is going to patch the code, not for end user work around. My work around btw is to do this:

from qiskit.visualization import state_visualization
data2 = Statevector([ state_visualization._round_if_close(v) for v in data._data])
data2.draw('latex')

which is ugly but works 😃