rewrite rule for U3 to clifford (#335)

Co-authored-by: E Huang <[email protected]>
Co-authored-by: John Long <[email protected]>

Author: 3 people

.pre-commit-config.yaml

@@ -14,7 +14,7 @@ repos:
     - id: isort
       name: isort (python)
 - repo: https://github.com/psf/black
-  rev: 24.10.0
+  rev: 25.1.0
   hooks:
     - id: black
 - repo: https://github.com/charliermarsh/ruff-pre-commit

src/bloqade/squin/op/__init__.py

@@ -30,6 +30,9 @@
     shift as shift,
     spin_n as spin_n,
     spin_p as spin_p,
+    sqrt_x as sqrt_x,
+    sqrt_y as sqrt_y,
+    sqrt_z as sqrt_z,
     adjoint as adjoint,
     control as control,
     identity as identity,

src/bloqade/squin/op/_wrapper.py

@@ -69,6 +69,18 @@ def y() -> types.Op: ...
 def z() -> types.Op: ...
 
 
+@wraps(stmts.SqrtX)
+def sqrt_x() -> types.Op: ...
+
+
+@wraps(stmts.SqrtY)
+def sqrt_y() -> types.Op: ...
+
+
+@wraps(stmts.S)
+def sqrt_z() -> types.Op: ...
+
+
 @wraps(stmts.H)
 def h() -> types.Op: ...
 

src/bloqade/squin/op/stmts.py

@@ -142,7 +142,12 @@ class Reset(PrimitiveOp):
 
 
 @statement
-class PauliOp(ConstantUnitary):
+class CliffordOp(ConstantUnitary):
+    pass
+
+
+@statement
+class PauliOp(CliffordOp):
     pass
 
 
@@ -173,6 +178,19 @@ class Z(PauliOp):
     pass
 
 
+@statement(dialect=dialect)
+class SqrtX(ConstantUnitary):
+    pass
+
+
+@statement(dialect=dialect)
+class SqrtY(ConstantUnitary):
+    pass
+
+
+# NOTE no SqrtZ since its equal to S
+
+
 @statement(dialect=dialect)
 class H(ConstantUnitary):
     pass

src/bloqade/squin/rewrite/U3_to_clifford.py

@@ -0,0 +1,149 @@
+# create rewrite rule name SquinMeasureToStim using kirin
+import math
+from typing import List, Tuple, Callable
+
+import numpy as np
+from kirin import ir
+from kirin.dialects import py
+from kirin.rewrite.abc import RewriteRule, RewriteResult
+
+from bloqade.squin import op, qubit
+
+
+def sdag() -> list[ir.Statement]:
+    return [_op := op.stmts.S(), op.stmts.Adjoint(op=_op.result, is_unitary=True)]
+
+
+# (theta, phi, lam)
+U3_HALF_PI_ANGLE_TO_GATES: dict[
+    tuple[int, int, int], Callable[[], Tuple[List[ir.Statement], ...]]
+] = {
+    (0, 0, 0): lambda: ([op.stmts.Identity(sites=1)],),
+    (0, 0, 1): lambda: ([op.stmts.S()],),
+    (0, 0, 2): lambda: ([op.stmts.Z()],),
+    (0, 0, 3): lambda: (sdag(),),
+    (1, 0, 0): lambda: ([op.stmts.SqrtY()],),
+    (1, 0, 1): lambda: ([op.stmts.S()], [op.stmts.SqrtY()]),
+    (1, 0, 2): lambda: ([op.stmts.H()],),
+    (1, 0, 3): lambda: (sdag(), [op.stmts.SqrtY()]),
+    (1, 1, 0): lambda: ([op.stmts.SqrtY()], [op.stmts.S()]),
+    (1, 1, 1): lambda: ([op.stmts.S()], [op.stmts.SqrtY()], [op.stmts.S()]),
+    (1, 1, 2): lambda: ([op.stmts.Z()], [op.stmts.SqrtY()], [op.stmts.S()]),
+    (1, 1, 3): lambda: (sdag(), [op.stmts.SqrtY()], [op.stmts.S()]),
+    (1, 2, 0): lambda: ([op.stmts.SqrtY()], [op.stmts.Z()]),
+    (1, 2, 1): lambda: ([op.stmts.S()], [op.stmts.SqrtY()], [op.stmts.Z()]),
+    (1, 2, 2): lambda: ([op.stmts.Z()], [op.stmts.SqrtY()], [op.stmts.Z()]),
+    (1, 2, 3): lambda: (sdag(), [op.stmts.SqrtY()], [op.stmts.Z()]),
+    (1, 3, 0): lambda: ([op.stmts.SqrtY()], sdag()),
+    (1, 3, 1): lambda: ([op.stmts.S()], [op.stmts.SqrtY()], sdag()),
+    (1, 3, 2): lambda: ([op.stmts.Z()], [op.stmts.SqrtY()], sdag()),
+    (1, 3, 3): lambda: (sdag(), [op.stmts.SqrtY()], sdag()),
+    (2, 0, 0): lambda: ([op.stmts.Y()],),
+    (2, 0, 1): lambda: ([op.stmts.S()], [op.stmts.Y()]),
+    (2, 0, 2): lambda: ([op.stmts.Z()], [op.stmts.Y()]),
+    (2, 0, 3): lambda: (sdag(), [op.stmts.Y()]),
+}
+
+
+def equivalent_u3_para(
+    theta_half_pi: int, phi_half_pi: int, lam_half_pi: int
+) -> tuple[int, int, int]:
+    """
+    1. Assume all three angles are in the range [0, 4].
+    2. U3(theta, phi, lam) = -U3(2pi-theta, phi+pi, lam+pi).
+    """
+    return ((4 - theta_half_pi) % 4, (phi_half_pi + 2) % 4, (lam_half_pi + 2) % 4)
+
+
+class SquinU3ToClifford(RewriteRule):
+    """
+    Rewrite squin U3 statements to clifford when possible.
+    """
+
+    def rewrite_Statement(self, node: ir.Statement) -> RewriteResult:
+        if isinstance(node, (qubit.Apply, qubit.Broadcast)):
+            return self.rewrite_ApplyOrBroadcast_onU3(node)
+        else:
+            return RewriteResult()
+
+    def get_constant(self, node: ir.SSAValue) -> float | None:
+        if isinstance(node.owner, py.Constant):
+            # node.value is a PyAttr, need to get the wrapped value out
+            return node.owner.value.unwrap()
+        else:
+            return None
+
+    def resolve_angle(self, angle: float) -> int | None:
+        """
+        Normalize the angle to be in the range [0, 2π).
+        """
+        # convert to 0.0~1.0, in unit of pi/2
+        angle_half_pi = angle / math.pi * 2.0
+
+        mod = angle_half_pi % 1.0
+        if not (np.isclose(mod, 0.0) or np.isclose(mod, 1.0)):
+            return None
+
+        else:
+            return round((angle / math.tau) % 1 * 4) % 4
+
+    def rewrite_ApplyOrBroadcast_onU3(
+        self, node: qubit.Apply | qubit.Broadcast
+    ) -> RewriteResult:
+        """
+        Rewrite Apply and Broadcast nodes to their clifford equivalent statements.
+        """
+        if not isinstance(node.operator.owner, op.stmts.U3):
+            return RewriteResult()
+
+        gates = self.decompose_U3_gates(node.operator.owner)
+
+        if len(gates) == 0:
+            return RewriteResult()
+
+        for stmt_list in gates:
+            for gate_stmt in stmt_list[:-1]:
+                gate_stmt.insert_before(node)
+
+            oper = stmt_list[-1]
+            oper.insert_before(node)
+            new_node = node.__class__(operator=oper.result, qubits=node.qubits)
+            new_node.insert_before(node)
+
+        node.delete()
+
+        # rewrite U3 to clifford gates
+        return RewriteResult(has_done_something=True)
+
+    def decompose_U3_gates(self, node: op.stmts.U3) -> Tuple[List[ir.Statement], ...]:
+        """
+        Rewrite U3 statements to clifford gates if possible.
+        """
+        theta = self.get_constant(node.theta)
+        phi = self.get_constant(node.phi)
+        lam = self.get_constant(node.lam)
+
+        if theta is None or phi is None or lam is None:
+            return ()
+
+        theta_half_pi: int | None = self.resolve_angle(theta)
+        phi_half_pi: int | None = self.resolve_angle(phi)
+        lam_half_pi: int | None = self.resolve_angle(lam)
+
+        if theta_half_pi is None or phi_half_pi is None or lam_half_pi is None:
+            return ()
+
+        angles_key = (theta_half_pi, phi_half_pi, lam_half_pi)
+        if angles_key not in U3_HALF_PI_ANGLE_TO_GATES:
+            angles_key = equivalent_u3_para(*angles_key)
+            if angles_key not in U3_HALF_PI_ANGLE_TO_GATES:
+                return ()
+
+        gates_stmts = U3_HALF_PI_ANGLE_TO_GATES.get(angles_key)
+
+        # no consistent gates, then:
+        assert (
+            gates_stmts is not None
+        ), "internal error, U3 gates not found for angles: {}".format(angles_key)
+
+        return gates_stmts()

src/bloqade/stim/dialects/gate/stmts/__init__.py

@@ -1,4 +1,10 @@
 from .pp import SPP as SPP
+from .base import (
+    Gate as Gate,
+    TwoQubitGate as TwoQubitGate,
+    SingleQubitGate as SingleQubitGate,
+    ControlledTwoQubitGate as ControlledTwoQubitGate,
+)
 from .control_2q import CX as CX, CY as CY, CZ as CZ
 from .clifford_1q import (
     H as H,

src/bloqade/stim/rewrite/qubit_to_stim.py

@@ -3,6 +3,7 @@
 
 from bloqade.squin import op, qubit
 from bloqade.squin.rewrite import AddressAttribute
+from bloqade.stim.dialects import gate
 from bloqade.stim.rewrite.util import (
     SQUIN_STIM_GATE_MAPPING,
     rewrite_Control,
@@ -34,6 +35,15 @@ def rewrite_Apply_and_Broadcast(
         if isinstance(applied_op, op.stmts.Control):
             return rewrite_Control(stmt)
 
+        # check if its adjoint, assume its canonicalized so no nested adjoints.
+        is_conj = False
+        if isinstance(applied_op, op.stmts.Adjoint):
+            if not applied_op.is_unitary:
+                return RewriteResult()
+
+            is_conj = True
+            applied_op = applied_op.op.owner
+
         # need to handle Control through separate means
         # but we can handle X, Y, Z, H, and S here just fine
         stim_1q_op = SQUIN_STIM_GATE_MAPPING.get(type(applied_op))
@@ -54,7 +64,10 @@ def rewrite_Apply_and_Broadcast(
         if qubit_idx_ssas is None:
             return RewriteResult()
 
-        stim_1q_stmt = stim_1q_op(targets=tuple(qubit_idx_ssas))
+        if isinstance(stim_1q_op, gate.stmts.Gate):
+            stim_1q_stmt = stim_1q_op(targets=tuple(qubit_idx_ssas), dagger=is_conj)
+        else:
+            stim_1q_stmt = stim_1q_op(targets=tuple(qubit_idx_ssas))
         stmt.replace_by(stim_1q_stmt)
 
         return RewriteResult(has_done_something=True)

src/bloqade/stim/rewrite/util.py

@@ -13,6 +13,8 @@
     op.stmts.Z: gate.Z,
     op.stmts.H: gate.H,
     op.stmts.S: gate.S,
+    op.stmts.SqrtX: gate.SqrtX,
+    op.stmts.SqrtY: gate.SqrtY,
     op.stmts.Identity: gate.Identity,
     op.stmts.Reset: collapse.RZ,
 }