QFASTDecompositionPass output fails QASM conversion (‘_qasm_name’ missing)

[mariagg-quantinuum]

The QFASTDecompositionPass from bqskit.passes accepts a gate specification (the gate to decompose unitaries into). The default is PauliGate(2), a universal gate.
When I try to convert the pass output to tket via bqskit_to_pytket, I get AttributeError: 'PauliGate' object has no attribute '_qasm_name'. I assume Pauli gates are not QASM-compatible?

Are there alternative gates I can use with this pass?
Gates seems to be modifiable, but when I try alternative gates for simple circuits such as:

from pytket import Circuit
from bqskit.ext import pytket_to_bqskit, bqskit_to_pytket
from bqskit.compiler import Compiler
from bqskit.passes import LEAPSynthesisPass,QFASTDecompositionPass,WalshDiagonalSynthesisPass
from tket.circuit import Tk2Circuit
from bqskit.ir.gates.parameterized import U2Gate

# tket circuit
circuit = Circuit(3).CX(0,1).CX(1,0).CX(0,1).CX(1,0).CX(0,1).CX(1,0).CX(0,2)
# tket circuit -> bqskit circuit
bqc = pytket_to_bqskit(c)

# optimisation pass
with Compiler(num_workers=1) as comp:
    out_bqc = comp.compile(bqc, [QFASTDecompositionPass(gate=U2Gate(2))])

# bqskit circuit -> tket circuit
out_tk1 = bqskit_to_pytket(out_bqc)

it takes over 3 hours and likely never compiles.

[edyounis]

Yeah, that will not finish compiling because the circuit you are trying to build is not expressible over U2Gates alone. QFAST uses a parameterized location gate to "optimize" the placement and parameters of gates. The unitary you are synthesizing still needs to be expressible in the gateset you choose. That's why the PauliGate(2) is the default. It is a universal two-qubit gate, which, on its own, is a universal gate set and can express any unitary. Depending on your goal, there are a few ways to solve your problem. Making some assumptions that you want to synthesize the input circuit into some specific gateset, I recommend checking out the QFAST example. It first uses QFAST to synthesize the circuit into PauliGates, then uses QSearch to decompose those into some other gate set, by default CNOTs and U3s. You can take a look at the documentation of QSearch, specifically the layer generator, if you want to change the gate set. If you really want the PauliGate outputs, then I recommend iterating over them (via for op in circuit) and converting them manually into whatever TKet uses to represent arbitrary unitary instructions. I think it's something called a Box or a subclass of that.

[mariagg-quantinuum]

will try this thanks!