MeasureX.as_cirq_op fails ValueError

[NoureldinYosri]

Trying to convert a MeasureX to a Cirq op fails

>> qm = cirq.GreedyQubitManager(prefix='anc_')
>> MeasureX().as_cirq_op(qm, q=np.array(qm.qalloc(1)))
ValueError: Wrong number of qubits for <BloqAsCirqGate(MeasureX)>. Expected 1 qubits but got <(cirq.NamedQubit('anc__0'), cirq.NamedQubit('anc__0'))>.

[mpharrigan]

What's the expected result here?

[mpharrigan]

BloqAsCirqGate notes that it doesn't support "left and right registers with the same name" which corresponds to casting or reshaping operations; which is essentially what the MeasureX bloq is doing: it's converting a quantum bit to a classical bit. We can:

• override as_cirq_op for the measure bloqs with a cirq measure gate; but then the signature of the cirq gate won't match qualtran. In particular, if you do anything to the classical bit in your qualtran circuit it will fail if you try to convert to cirq
• override as_cirq_op for the measure bloqs with a split-like identity gate; which isn't really right, but would match the structure of the circuit that's requested

We could also have BloqAsCirqGate ignore registers with non-quantum types; which would cause this to turn into a de-allocating gate; I think you'd run in to the same problems as the first bullet; just in a more automated fashion

[mpharrigan]

details: bloq as cirq gate looks at the Side of a register and allocates or de-allocates as necessary but then puts all left, right, and thru qubits into the call to the gate. So it's trying to call Measure on the one qubit twice: once in its allocated form and once as its de-allocated form. Usually BloqAsCirqGate will notice this and tell you what's wrong; but not in all cases.

[NoureldinYosri]

@mpharrigan I am trying to get a cirq representation for a bloq that uses measurement based uncomputation in its decomposition which fails because of measurement Bloqs ... my main goal is to get a nice visualization of the circuit structure without the splitting/merging of wires