Merge pull request #176 from GenericP3rson/qft_layer

QFT Layer and Algorithm

Author: Hanrui-Wang

torchquantum/algorithm/__init__.py

@@ -23,4 +23,5 @@
 """
 
 from .vqe import *
-from .hamiltonian import *
+from .hamiltonian import *
+from .qft import *

torchquantum/algorithm/qft.py

@@ -0,0 +1,35 @@
+import torchquantum as tq
+from typing import Iterable
+
+__all__ = ["QFT"]
+
+
+class QFT(object):
+    def __init__(
+        self, n_wires: int = None, wires: Iterable = None, do_swaps=True
+    ) -> None:
+        """Init function for QFT class
+
+        Args:
+            n_wires (int): Number of wires for the QFT as an integer
+            wires (Iterable): Wires to perform the QFT as an Iterable
+            add_swaps (bool): Whether or not to add the final swaps in a boolean format
+            inverse (bool): Whether to create an inverse QFT layer in a boolean format
+        """
+        super().__init__()
+
+        self.n_wires = n_wires
+        self.wires = wires
+        self.do_swaps = do_swaps
+
+    def construct_qft_circuit(self) -> tq.QuantumModule:
+        """Construct the QFT circuit."""
+        return tq.layer.QFTLayer(
+            n_wires=self.n_wires, wires=self.wires, do_swaps=self.do_swaps
+        )
+
+    def construct_inverse_qft_circuit(self) -> tq.QuantumModule:
+        """Construct the inverse of a QFT circuit."""
+        return tq.layer.QFTLayer(
+            n_wires=self.n_wires, wires=self.wires, do_swaps=self.do_swaps, inverse=True
+        )

torchquantum/layer/layers.py

@@ -22,6 +22,7 @@
 SOFTWARE.
 """
 
+import torch
 import torch.nn as nn
 import torchquantum as tq
 import torchquantum.functional as tqf
@@ -49,6 +50,7 @@
     "CXCXCXLayer",
     "SWAPSWAPLayer",
     "RXYZCXLayer0",
+    "QFTLayer",
 ]
 
 
@@ -1467,6 +1469,113 @@ def build_layers(self):
         return layers_all
 
 
+class QFTLayer(tq.QuantumModule):
+    def __init__(
+        self,
+        n_wires: int = None,
+        wires: Iterable = None,
+        do_swaps: bool = True,
+        inverse: bool = False,
+    ):
+        """
+        Constructs a Quantum Fourier Transform (QFT) layer
+
+        Args:
+            n_wires (int): Number of wires for the QFT as an integer
+            wires (Iterable): Wires to perform the QFT as an Iterable
+            do_swaps (bool): Whether or not to add the final swaps in a boolean format
+            inverse (bool): Whether to create an inverse QFT layer in a boolean format
+        """
+        super().__init__()
+
+        assert n_wires is not None or wires is not None
+
+        if n_wires is None:
+            self.n_wires = len(wires)
+
+        if wires is None:
+            wires = range(n_wires)
+
+        self.n_wires = n_wires
+        self.wires = wires
+        self.do_swaps = do_swaps
+
+        if inverse:
+            self.gates_all = self.build_inverse_circuit()
+        else:
+            self.gates_all = self.build_circuit()
+
+    def build_circuit(self):
+        """Construct a QFT circuit."""
+
+        operation_list = []
+
+        # add the H and CU1 gates
+        for top_wire in range(self.n_wires):
+            operation_list.append({"name": "hadamard", "wires": self.wires[top_wire]})
+            for wire in range(top_wire + 1, self.n_wires):
+                lam = torch.pi / (2 ** (wire - top_wire))
+                operation_list.append(
+                    {
+                        "name": "cu1",
+                        "params": lam,
+                        "wires": [self.wires[wire], self.wires[top_wire]],
+                    }
+                )
+
+        # add swaps if specified
+        if self.do_swaps:
+            for wire in range(self.n_wires // 2):
+                operation_list.append(
+                    {
+                        "name": "swap",
+                        "wires": [
+                            self.wires[wire],
+                            self.wires[self.n_wires - wire - 1],
+                        ],
+                    }
+                )
+
+        return tq.QuantumModule.from_op_history(operation_list)
+
+    def build_inverse_circuit(self):
+        """Construct the inverse of a QFT circuit."""
+
+        operation_list = []
+
+        # add swaps if specified
+        if self.do_swaps:
+            for wire in range(self.n_wires // 2):
+                operation_list.append(
+                    {
+                        "name": "swap",
+                        "wires": [
+                            self.wires[wire],
+                            self.wires[self.n_wires - wire - 1],
+                        ],
+                    }
+                )
+
+        # add the CU1 and H gates
+        for top_wire in range(self.n_wires)[::-1]:
+            for wire in range(top_wire + 1, self.n_wires)[::-1]:
+                lam = -torch.pi / (2 ** (wire - top_wire))
+                operation_list.append(
+                    {
+                        "name": "cu1",
+                        "params": lam,
+                        "wires": [self.wires[wire], self.wires[top_wire]],
+                    }
+                )
+            operation_list.append({"name": "hadamard", "wires": self.wires[top_wire]})
+
+        return tq.QuantumModule.from_op_history(operation_list)
+
+    @tq.static_support
+    def forward(self, q_device: tq.QuantumDevice):
+        self.gates_all(q_device)
+
+
 layer_name_dict = {
     "u3cu3_0": U3CU3Layer0,
     "cu3_0": CU3Layer0,