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SparsePauliOp incorrectly sets non-zero imaginary component #13522

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kaelynj opened this issue Dec 3, 2024 · 2 comments · May be fixed by #13580
Open

SparsePauliOp incorrectly sets non-zero imaginary component #13522

kaelynj opened this issue Dec 3, 2024 · 2 comments · May be fixed by #13580
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@trigpolynom
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bug Something isn't working mod: quantum info Related to the Quantum Info module (States & Operators)

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@kaelynj
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kaelynj commented Dec 3, 2024

Environment

  • Qiskit version: 1.3.0
  • Python version: 3.11.7
  • Operating system: Fedora 40

What is happening?

When a SparsePauliOp object is instantiated with a long string of Y's (greater than 100), the imaginary component of the coefficients is non-zero (but trivially small, ~1e-15). This results in errors when submitting jobs using qiskit-ibm-runtime which throws an error when using the SparsePauliOp as the expectation value to estimate.

How can we reproduce the issue?

from qiskit.quantum_info import SparsePauliOp
# produces non-zero imaginary component
yyy = SparsePauliOp('Y'*100)
print(yyy.coeffs)
# correctly contains no imaginary component
yy = SparsePauliOp('Y'*99)
print(yy.coeffs)

What should happen?

A high-weight SparsePauliOp, when no coefficients are specified, should possess coeffcients = [1.0, 0.0]

Any suggestions?

No response
@kaelynj kaelynj added the bug Something isn't working label Dec 3, 2024
@kaelynj kaelynj changed the title Non-zero imaginary component Incorrectly set non-zero imaginary component in SparsePauliOp Dec 3, 2024
@kaelynj kaelynj changed the title Incorrectly set non-zero imaginary component in SparsePauliOp SparsePauliOp incorrectly sets non-zero imaginary component Dec 3, 2024
@trigpolynom
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I'd like to take this on if that is okay

@ShellyGarion ShellyGarion added the mod: quantum info Related to the Quantum Info module (States & Operators) label Dec 15, 2024
@trigpolynom trigpolynom linked a pull request Dec 18, 2024 that will close this issue
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@trigpolynom
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trigpolynom commented Dec 18, 2024 •
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Got a draft PR #13580. Mind taking a look at the approach to the fix? @kaelynj @ShellyGarion @Cryoris

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bug Something isn't working mod: quantum info Related to the Quantum Info module (States & Operators)
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Fix SparsePauliOp initialization with dense Y labels trigpolynom/qiskit
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@kaelynj @ShellyGarion @trigpolynom