standard interface for setting default qubits to conjugate

qldpc/codes/common.py

@@ -643,10 +643,10 @@ def from_stabilizers(cls, *stabilizers: str, field: int | None = None) -> QuditC
 
  return QuditCode(matrix.reshape(num_checks, 2 * num_qudits), field)
 
- def conjugated(self, qudits: slice | Sequence[int]) -> QuditCode:
- """Apply local Fourier (Hadamard) transforms to the given qudits.
-
- This is equivalent to swapping X-type and Z-type operators."""
+ def conjugated(self, qudits: slice | Sequence[int] | None = None) -> QuditCode:
+ """Apply local Fourier transforms to data qudits, swapping X-type and Z-type operators."""
+ if qudits is None:
+  qudits = self._default_conjugate if hasattr(self, "_default_conjugate") else ()
  num_checks = len(self.matrix)
  matrix = np.reshape(self.matrix.copy(), (num_checks, 2, -1))
  matrix[:, :, qudits] = np.roll(matrix[:, :, qudits], 1, axis=1)

qldpc/codes/common_test.py

@@ -191,6 +191,7 @@ def test_deformations(num_qudits: int = 5, num_checks: int = 3, field: int = 3)
  """Apply Pauli deformations to a qudit code."""
  qudits = tuple(qubit for qubit in range(num_qudits) if np.random.randint(2))
  code = get_random_qudit_code(num_qudits, num_checks, field).conjugated(qudits)
+ assert np.array_equal(code.matrix, code.conjugated().matrix)
 
  matrix = np.reshape(code.matrix, (num_checks, 2, num_qudits))
  for node_check, node_qubit, data in code.graph.edges(data=True):

qldpc/codes/quantum.py

@@ -518,6 +518,9 @@ def __init__(
  [code_b.num_bits, code_b.num_checks],
  )
 
+ # if Hadamard-transforming qudits, conjugate those in the (1, 1) sector by default
+ self._default_conjugate = slice(self.sector_size[0, 0], None)
+
  CSSCode.__init__(
  self, matrix_x.astype(int), matrix_z.astype(int), field, skip_validation=True
  )
@@ -627,11 +630,6 @@ def get_product_node_map(
 
  return node_map
 
- def conjugated(self, qudits: slice | Sequence[int] | None = None) -> QuditCode:
- """Hadamard-transform to the qudits in sector (1, 1)."""
- qudits = qudits if qudits is not None else slice(self.sector_size[0, 0], None)
- return QuditCode.conjugated(self, qudits)
-
 
 class LPCode(CSSCode):
  """Lifted product (LP) code.
@@ -680,6 +678,9 @@ def __init__(
  protograph_b.shape[::-1],
  )
 
+ # if Hadamard-transforming qudits, conjugate those in the (1, 1) sector by default
+ self._default_conjugate = slice(self.sector_size[0, 0], None)
+
  CSSCode.__init__(
  self,
  abstract.Protograph(matrix_x.astype(object)).lift(),
@@ -688,11 +689,6 @@ def __init__(
  skip_validation=True,
  )
 
- def conjugated(self, qudits: slice | Sequence[int] | None = None) -> QuditCode:
- """Hadamard-transform to the qudits in sector (1, 1)."""
- qudits = qudits if qudits is not None else slice(self.sector_size[0, 0], None)
- return QuditCode.conjugated(self, qudits)
-
 
 ################################################################################
 # quantum Tanner code
@@ -959,7 +955,7 @@ def __init__(
  if rotated:
  # rotated surface code
  matrix_x, matrix_z = SurfaceCode.get_rotated_checks(rows, cols)
- self._qudits_to_conjugate: list[int] | slice = [
+ self._default_conjugate: list[int] | slice = [
  idx
  for idx, (row, col) in enumerate(np.ndindex(self.rows, self.cols))
  if (row + col) % 2
@@ -972,7 +968,7 @@ def __init__(
  code_ab = HGPCode(code_a, code_b, field)
  matrix_x = code_ab.matrix_x
  matrix_z = code_ab.matrix_z
- self._qudits_to_conjugate = slice(code_ab.sector_size[0, 0], None)
+ self._default_conjugate = slice(code_ab.sector_size[0, 0], None)
 
  CSSCode.__init__(self, matrix_x, matrix_z, field=field, skip_validation=True)
 
@@ -1038,11 +1034,6 @@ def get_check(
 
  return np.array(checks_x), np.array(checks_z)
 
- def conjugated(self, qudits: slice | Sequence[int] | None = None) -> QuditCode:
- """Hadamard-transform qudits in a checkerboard pattern."""
- qudits = qudits if qudits is not None else self._qudits_to_conjugate
- return QuditCode.conjugated(self, qudits)
-
 
 class ToricCode(CSSCode):
  """Surface code with periodic bounary conditions, encoding two logical qudits.
@@ -1073,7 +1064,7 @@ def __init__(
 
  # rotated toric code
  matrix_x, matrix_z = ToricCode.get_rotated_checks(rows, cols)
- self._qudits_to_conjugate: list[int] | slice = [
+ self._default_conjugate: list[int] | slice = [
  idx
  for idx, (row, col) in enumerate(np.ndindex(self.rows, self.cols))
  if (row + col) % 2
@@ -1086,7 +1077,7 @@ def __init__(
  code_ab = HGPCode(code_a, code_b, field)
  matrix_x = code_ab.matrix_x
  matrix_z = code_ab.matrix_z
- self._qudits_to_conjugate = slice(code_ab.sector_size[0, 0], None)
+ self._default_conjugate = slice(code_ab.sector_size[0, 0], None)
 
  CSSCode.__init__(self, matrix_x, matrix_z, field=field, skip_validation=True)
 
@@ -1122,11 +1113,6 @@ def get_check(
 
  return np.array(checks_x), np.array(checks_z)
 
- def conjugated(self, qudits: slice | Sequence[int] | None = None) -> QuditCode:
- """Hadamard-transform qudits in a checkerboard pattern."""
- qudits = qudits if qudits is not None else self._qudits_to_conjugate
- return QuditCode.conjugated(self, qudits)
-
 
 class GeneralizedSurfaceCode(CSSCode):
  """Surface or toric code defined on a multi-dimensional hypercubic lattice.