More tests

src/mqt/qecc/codes/stabilizer_code.py

@@ -44,9 +44,8 @@ def __init__(
             Lx: The logical X-operators.
         """
         self._check_stabilizer_generators(generators)
-
+        self.n = get_n_qubits_from_pauli(generators[0])
         self.generators = paulis_to_binary(generators)
-        self.n = get_n_qubits_from_pauli(self.generators[0])
         self.symplectic_matrix = self.generators[:, :-1]  # discard the phase
         self.phases = self.generators[:, -1]
         self.k = self.n - mod2.rank(self.generators)
@@ -172,6 +171,7 @@ def pauli_to_binary(p: Pauli) -> npt.NDArray:
     phase = 0
     if p[0] in {"+", "-"}:
         phase = 0 if p[0] == "+" else 1
+        p = p[1:]
     x_part = np.array([int(p == "X") for p in p])
     z_part = np.array([int(p == "Z") for p in p])
     y_part = np.array([int(p == "Y") for p in p])
@@ -204,6 +204,8 @@ def get_n_qubits_from_pauli(p: Pauli) -> int:
     """Get the number of qubits from a Pauli string."""
     if isinstance(p, np.ndarray):
         return int(p.shape[0] // 2)
+    if p[0] in {"+", "-"}:
+        return len(p) - 1
     return len(p)
 
 

test/python/test_code.py

@@ -185,6 +185,18 @@ def test_five_qubit_code(five_qubit_code_stabs: list[str]) -> None:
     assert strings == five_qubit_code_stabs
 
 
+def test_stabilizer_sign() -> None:
+    """Test that (negative) signs are correctly handled in stabilizer codes."""
+    s = ["-ZZZZ", "-XXXX"]
+    code = StabilizerCode(s)
+    assert code.n == 4
+    assert code.k == 2
+
+    error = "XIII"
+    syndrome = code.get_syndrome(error)
+    assert np.array_equal(syndrome, np.array([1, 0]))
+
+
 def test_no_stabilizers() -> None:
     """Test that an error is raised if no stabilizers are provided."""
     with pytest.raises(InvalidStabilizerCodeError):
@@ -212,34 +224,40 @@ def test_invalid_pauli_strings() -> None:
 def test_no_x_logical() -> None:
     """Test that an error is raised if no X logical is provided when a Z logical is provided."""
     with pytest.raises(InvalidStabilizerCodeError):
-        StabilizerCode(["ZZZZ", "XXXX"], Lz=["XXII"])
+        StabilizerCode(["ZZZZ", "XXXX"], Lx=["XXII"])
 
 
 def test_no_z_logical() -> None:
     """Test that an error is raised if no Z logical is provided when an X logical is provided."""
     with pytest.raises(InvalidStabilizerCodeError):
-        StabilizerCode(["ZZZZ", "XXXX"], Lx=["ZZII"])
+        StabilizerCode(["ZZZZ", "XXXX"], Lz=["ZZII"])
 
 
 def test_logicals_wrong_length() -> None:
     """Test that an error is raised if the logicals have the wrong length."""
     with pytest.raises(InvalidStabilizerCodeError):
-        StabilizerCode(["ZZZZ", "XXXX"], Lx=["XX"], Lz=["ZZ"])
+        StabilizerCode(["ZZZZ", "XXXX"], Lx=["XX"], Lz=["IZZI"])
+    with pytest.raises(InvalidStabilizerCodeError):
+        StabilizerCode(["ZZZZ", "XXXX"], Lx=["IXXI"], Lz=["ZZ"])
 
 
 def test_commuting_logicals() -> None:
     """Test that an error is raised if the logicals commute."""
     with pytest.raises(InvalidStabilizerCodeError):
-        StabilizerCode(["ZZZZ", "XXXX"], Lx=["ZZII"], Lz=["XXII"])
+        StabilizerCode(["ZZZZ", "XXXX"], Lz=["ZZII"], Lx=["XXII"])
 
 
 def test_anticommuting_logicals() -> None:
     """Test that an error is raised if the logicals anticommute with the stabilizer generators."""
     with pytest.raises(InvalidStabilizerCodeError):
-        StabilizerCode(["ZZZZ", "XXXX"], Lx=["ZI II"], Lz=["XIII"])
+        StabilizerCode(["ZZZZ", "XXXX"], Lz=["ZIII"], Lx=["IXXI"])
+    with pytest.raises(InvalidStabilizerCodeError):
+        StabilizerCode(["ZZZZ", "XXXX"], Lz=["IZZI"], Lx=["XIII"])
 
 
 def test_too_many_logicals() -> None:
     """Test that an error is raised if too many logicals are provided."""
     with pytest.raises(InvalidStabilizerCodeError):
-        StabilizerCode(["ZZZZ", "XXXX"], Lx=["ZZII", "ZZII", "ZZII"], Lz=["XXII", "IIXX", "IIXX"])
+        StabilizerCode(["ZZZZ", "XXXX"], Lz=["ZZII", "ZZII", "ZZII"], Lx=["IXXI"])
+    with pytest.raises(InvalidStabilizerCodeError):
+        StabilizerCode(["ZZZZ", "XXXX"], Lz=["IZZI"], Lx=["XXII", "XXII", "XXII"])