Hi, I’m trying to implement QCNN in Pennylane and ran into a problem.
Given a circuit with n qubits, QCNN requires us to measure n/2 of the wires at first pooling layer, n/4 wires at second pooling layer and so on. The output of these measurements are used as parameters in rotation gates applied to the n/2 remaining wires after first pooling layer, n/4 remaining wires after the second pooling layer etc.
Now suppose we have 4 qubits. I tried to perform a measurement on the 0th and 2nd qubits, and then add RY gates to the 1st and 3rd qubits. Unfortunately, I got the error:
ValueError: Quantum operation RY(tensor(0.95956891, requires_grad=True), wires=) must occur prior to any measurements.
Given this discussion (Ancillary Subsystem Measurement then Trace Out) a few months ago and my findings, it appears that such operation is not supported, therefore QCNN is impossible to be implemented in Pennylane. Am I correct? Are there any plans to add support for mid-circuit measurement in the near future?