Merge two Y**0.5 gate into a single Y gate

Question

How can I merge two consecutive cirq.Y**0.5 gates into a single cirq.Y gate with a transformer?

I can use cirq.merge_k_qubit_unitaries to merge the two gate but the result is not a cirq.EigenGate anymore. I want to keep the EigenGate type after the transformation.

Answer 1

A flexible way is to use the cirq.merge_operations transformer which lets you pass in your own merge function that decides what operations to merge and how. For example:

def merge_func(op1: cirq.Operation, op2: cirq.Operation) -> Optional[cirq.Operation]:
    if not isinstance(op1, cirq.GateOperation):
        return None
    if not isinstance(op2, cirq.GateOperation):
        return None
    if not isinstance(op1.gate, cirq.YPowGate):
        return None
    if not isinstance(op2.gate, cirq.YPowGate):
        return None

    return cirq.Y(*op1.qubits)**(op1.gate.exponent + op2.gate.exponent)

circuit = cirq.merge_operations(circuit, merge_func)