Emitting circuit with multiple call to stdlib.cx errors

[david-pl]

Courtesy of @jon-wurtz

from bloqade import squin
from bloqade.cirq_utils import emit_circuit

@squin.kernel
def steane_zero_prep():
    qbs = squin.qubit.new(7)
    squin.gate.h(qbs[1])
    squin.gate.h(qbs[2])
    squin.gate.h(qbs[3])
    squin.gate.cx(qbs[1], qbs[0])
    squin.gate.cx(qbs[3], qbs[5])
    squin.gate.cx(qbs[2], qbs[6])
    squin.gate.cx(qbs[1], qbs[4])
    squin.gate.cx(qbs[2], qbs[0])
    squin.gate.cx(qbs[3], qbs[6])
    squin.gate.cx(qbs[1], qbs[5])
    squin.gate.cx(qbs[6], qbs[4])

circuit = emit_circuit(steane_zero_prep)

This errors with InterpreterError: SSAValue <ResultValue[ControlOp[XOp]] op, uses: 1> not found.

[david-pl]

In light of the upcoming squin refactor, where we use stdlib extensively, I looked into this. The problem is that squin.gate.cx internally calls squin.op.cx, which is a kernel that returns an operator. Since the cirq emit doesn't deal too well with return values, this gets lost somewhere and is thus missing from the frame.

Instead of fixing this, I'll leave it until the refactor is complete, where we can no longer have operators without any qubits. So this will just be fixed by the refactor.

[david-pl]

This is fixed via the refactor in #520. Just remember to remove the .gate:

from bloqade import squin
from bloqade.cirq_utils import emit_circuit

@squin.kernel
def steane_zero_prep():
    qbs = squin.qubit.new(7)
    squin.h(qbs[1])
    squin.h(qbs[2])
    squin.h(qbs[3])
    squin.cx(qbs[1], qbs[0])
    squin.cx(qbs[3], qbs[5])
    squin.cx(qbs[2], qbs[6])
    squin.cx(qbs[1], qbs[4])
    squin.cx(qbs[2], qbs[0])
    squin.cx(qbs[3], qbs[6])
    squin.cx(qbs[1], qbs[5])
    squin.cx(qbs[6], qbs[4])

circuit = emit_circuit(steane_zero_prep)
print(circuit)