CSWAP and CMultiSWAP

cirq_qubitization/bloq_algos/controlled_swap_bloq.py

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+from functools import cached_property
+from typing import Dict
+
+import numpy as np
+from attrs import frozen
+from numpy.typing import NDArray
+
+from cirq_qubitization import TComplexity
+from cirq_qubitization.quantum_graph.bloq import Bloq
+from cirq_qubitization.quantum_graph.composite_bloq import CompositeBloq, Soquet, SoquetT
+from cirq_qubitization.quantum_graph.fancy_registers import FancyRegister, FancyRegisters
+
+
+@frozen
+class CSWAP(Bloq):
+    """A controlled swap between two-qubits
+
+    Args:
+        cv1: Whether the control bit is a positive (1) control.
+             Alternatively, control bit can be negatively (0) controlled.
+
+    Registers:
+     - ctrl: A two-bit control register.
+     - x: first bit to swap
+     - y: second bit to swap
+    """
+
+    cv1: int = 1
+
+    @cached_property
+    def registers(self) -> FancyRegisters:
+        return FancyRegisters(
+            [
+                FancyRegister('ctrl', 1, wireshape=(1,)),
+                FancyRegister('x', 1, wireshape=(1,)),
+                FancyRegister('y', 1, wireshape=(1,)),
+            ]
+        )
+
+    def t_complexity(self) -> 'TComplexity':
+        """The `TComplexity` for this bloq.
+
+        C-swap is decomposed into two CNOT + 1 Toffoli.
+        Each Toffoli is 7 T-gates, 8 Cliffords, and 0 rotations
+        """
+        num_toffoli = 1
+        return TComplexity(t=num_toffoli * 7, clifford=2 + 8 * num_toffoli, rotations=0)
+
+
+@frozen
+class CMultiSWAP(Bloq):
+    """A controlled n-bit swap between two registers
+
+    Args:
+        cv1: Whether the control bit is a positive (1) control.
+             Alternatively, control bit can be negatively (0) controlled.
+        reg_length: Length of the registers
+
+    Registers:
+     - ctrl: A two-bit control register.
+     - reg_x: The first register of size n-bits
+     - reg_y: The second register of size n-bits
+    """
+
+    reg_length: int = None
+    cv1: int = 1
+
+    @cached_property
+    def registers(self) -> FancyRegisters:
+        return FancyRegisters(
+            [
+                FancyRegister('ctrl', 1, wireshape=(1,)),
+                FancyRegister('reg_x', self.reg_length, wireshape=(1,)),
+                FancyRegister('reg_y', self.reg_length, wireshape=(1,)),
+            ]
+        )
+
+    def pretty_name(self) -> str:
+        return "CSWAP"
+
+    def build_composite_bloq(
+        self, bb: 'CompositeBloqBuilder', *, cntrl_and_targets: NDArray[Soquet]
+    ) -> Dict[str, 'SoquetT']:
+        """Decomposes multi-cswap `CnSWAP` in-terms of an `CSWAP`"""
+        ctrl = (cntrl_and_targets[0],)
+        reg_x = cntrl_and_targets[1 : self.reg_length + 1]
+        reg_y = cntrl_and_targets[self.reg_length + 1 :]
+        returned_x = []
+        returned_y = []
+        for n_idx in range(self.reg_length):
+            # overwrite control with same control
+            ctrl, out_reg_x, out_reg_y = bb.add(
+                CSWAP(cv1=self.cv1), ctrl=ctrl, x=reg_x[n_idx], y=reg_y[n_idx]
+            )
+            returned_x.append(out_reg_x)
+            returned_y.append(out_reg_y)
+        return {
+            'ctrl': np.asarray([ctrl]),
+            'reg_x': np.asarray(returned_x),
+            'reg_y': np.asarray(returned_y),
+        }