I've just submitted my latest paper with Tim Ralph to Physical Review A, entitled Error models for mode-mismatch in linear optics quantum computing. Previously I've done a lot of work into the effects of mode-mismatch in linear optics quantum computing (LOQC) (see previous physics posts for explanations of both these terms). This paper focusses on a basic building block of LOQC, called the parity gate, which is fundamental to many recent LOQC proposals, most notably the cluster- and parity-state approaches. Both these approaches are very promising and have completely changed the nature of the LOQC playing field. It is important to understand how errors are introduced in these models, of which mode-mismatch is one of the most dominant.