Fix bugs in fermion module causing open-shell systems to have their s…

…pin-up/down determinants flipped before solving
Qiskit · Oct 7, 2024 · 2b55023 · 2b55023
1 parent 45c89c2
commit 2b55023
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diff --git a/qiskit_addon_sqd/fermion.py b/qiskit_addon_sqd/fermion.py
@@ -96,7 +96,6 @@ def solve_fermion(
     else:
         # This will become the default code path after the deprecation period.
         ci_strs = bitstring_matrix_to_ci_strs(bitstring_matrix, open_shell=open_shell)
-        ci_strs = ci_strs[::-1]
     ci_strs = _check_ci_strs(ci_strs)
 
     num_up = format(ci_strs[0][0], "b").count("1")
@@ -201,7 +200,6 @@ def optimize_orbitals(
     else:
         # Flip the output so the alpha CI strs are on the left with [::-1]
         ci_strs = bitstring_matrix_to_ci_strs(bitstring_matrix, open_shell=open_shell)
-        ci_strs = ci_strs[::-1]
     ci_strs = _check_ci_strs(ci_strs)
 
     num_up = format(ci_strs[0][0], "b").count("1")

diff --git a/releasenotes/notes/fermion-bug-2b2ed34f979b1321.yaml b/releasenotes/notes/fermion-bug-2b2ed34f979b1321.yaml
@@ -0,0 +1,3 @@
+fixes:
+  - |
+    Fixes a bug in :func:`qiskit_addon_sqd.fermion.solve_fermion` and :func:`qiskit_addon_sqd.fermion.optimize_orbitals` which causes the determinants for spin-up and spin-down to be incorrectly flipped before solving.