Implements a cphase using the Ising gate generated from 2 Sycamore gates.

A CPHASE gate has the matrix diag([1, 1, 1, exp(1j * theta)]) and can be mapped to the Ising gate by prep and post rotations of Z-pi/4. We drop the global phase shift of theta/4.

theta exp(1j * theta )
q0 First qubit id to operate on
q1 Second qubit id to operate on

returns: a cirq program implementing cphase