Accumulates two qubit phase gates into the scratch shards.

def _two_qubit_accumulate_into_scratch(args: Dict[str, Any]):
    """Accumulates two qubit phase gates into the scratch shards."""
    index0, index1 = args['indices']
    half_turns = args['half_turns']
    scratch = _scratch_shard(args)

    projector = _one_projector(args, index0) * _one_projector(args, index1)
    # Exp11 = exp(-i pi |11><11| half_turns), but we accumulate phases as
    # pi / 2.
    scratch += 2 * half_turns * projector