They already exist

    import numpy as np
    from qiskit import QuantumCircuit

    # 1. A quantum circuit for preparing the quantum state |000> + i |111> / √2
    qc = QuantumCircuit(3)
    # generate superposition
    qc.h(0)  
    # add quantum phase   
    qc.p(np.pi / 2, 0)  
    # 0th-qubit-Controlled-NOT gate on 1st qubit
    qc.cx(0, 1)   
    # 0th-qubit-Controlled-NOT gate on 2nd qubit 
    qc.cx(0, 2)