Influence of preserve_param_uuid parameter in qiskit_to_tk

[nquetschlich]

Hi there,

I am currently playing around with parameterized circuit compilation using both qiskit and TKET. In that regard, I noticed in qiskit_to_tk setting the parameter preserve_param_uuid=True very much affects the size of the output circuit, as shown in this example:

from pytket.extensions.qiskit import qiskit_to_tk, tk_to_qiskit 
from pytket.passes import CliffordSimp
from qiskit import QuantumCircuit

from qiskit.transpiler.passes import BasisTranslator
from qiskit.transpiler import PassManager
from qiskit.circuit import Parameter
from qiskit.circuit.equivalence_library import StandardEquivalenceLibrary

def generate_circuit(n_qubits:int) -> QuantumCircuit:

    circuit = QuantumCircuit(n_qubits, n_qubits)
    param_counter = 0

    for j in range(n_qubits):
        circuit.rz(Parameter(f"x_{param_counter}"), j)
        param_counter += 1
        circuit.rx(Parameter(f"x_{param_counter}"), j )
        param_counter += 1
        circuit.rz(Parameter(f"x_{param_counter}"), j )
        param_counter += 1

    circuit.rxx(Parameter(f"x_{param_counter}"), 0,1)
    param_counter += 1

    return circuit

qc = generate_circuit(2)
print(qc.draw())
pm = PassManager(BasisTranslator(StandardEquivalenceLibrary, target_basis=["sx", "rz", "cx", "x"]))
qc = pm.run(qc)
print("Gate Counts before:", qc.count_ops())

tket_qc = qiskit_to_tk(qc, preserve_param_uuid=True)
CliffordSimp().apply(tket_qc)
qc_param_true = tk_to_qiskit(tket_qc)
print("Gate Counts after using preserve_param_uuid=True:", qc_param_true.count_ops())

tket_qc = qiskit_to_tk(qc, preserve_param_uuid=False)
CliffordSimp().apply(tket_qc)
qc_param_false = tk_to_qiskit(tket_qc)
print("Gate Counts after using preserve_param_uuid=False:", qc_param_false.count_ops())

The code prints:

Gate Counts before: OrderedDict([('rz', 19), ('sx', 8), ('cx', 2)])
Gate Counts after using preserve_param_uuid=True: OrderedDict([('u', 183), ('cx', 2)])
Gate Counts after using preserve_param_uuid=False: OrderedDict([('u', 5), ('cx', 2)])

Showing a large difference in u gates. However, if we do not compile to the native gateset before using qiskit, this is not the case. Since this behavior is not intuitive to me, I was hoping for some clarification from your side.

[cqc-alec]

See #264 .