Returns a gate with the matrix e^{-i Z rads / 2}.

def Rz(rads: Union[float, sympy.Basic]) -> ZPowGate:
    """Returns a gate with the matrix e^{-i Z rads / 2}."""
    pi = sympy.pi if protocols.is_parameterized(rads) else np.pi
    return ZPowGate(exponent=rads / pi, global_shift=-0.5)