Transpiling a circuit with Tket, taking topology into account

Question

There is a simple circuit with one CNOT like the following:

• Topology 0 → 1 (directed connection)
• CNOT 1 → 0

Note that CNOT is placed opposite to the connection.

If this is transpiled correctly, it should look like the following circuit.

1. HH
2. CNOT 0 → 1
3. HH

What is the proper Tket transpilation pass(es) required to perform this transpilation?

I wrote the following code but did not get the desired result.

from pytket import Circuit
from pytket.circuit import Node
from pytket.architecture import Architecture
from pytket.placement import place_with_map
from pytket.passes import RoutingPass
nodes = [Node("node" + str(i), i) for i in range(2)]
arch = Architecture([(nodes[1], nodes[0])])
circuit = Circuit(2)
circuit.CX(0, 1)  # needs transpilation here
initial_mapping = {circuit.qubits[i]: nodes[i] for i in range(len(nodes))}
place_with_map(circuit, initial_mapping)
transpile
RoutingPass(arch).apply(circuit)

Answer 1

DecomposeSwapsToCXs looks like it does the trick.

from pytket import Circuit
from pytket.circuit import Node
from pytket.architecture import Architecture
from pytket.placement import place_with_map
from pytket.passes import DecomposeSwapsToCXs
from pytket.circuit.display import render_circuit_jupyter
circuit = Circuit(2)
circuit.CX(0, 1)  # needs transpilation here
print("Original circuit:")
render_circuit_jupyter(circuit)
nodes = [Node("node" + str(i), i) for i in range(circuit.n_qubits)]
arch = Architecture([(nodes[1], nodes[0])])
initial_mapping = {circuit.qubits[i]: nodes[i] for i in range(circuit.n_qubits)}
place_with_map(circuit, initial_mapping)
DecomposeSwapsToCXs(arch, True).apply(circuit)
print("\nTranspiled circuit after applying DecomposeSwapsToCXs:")
render_circuit_jupyter(circuit)