qp stands for "quantum polariton". This is a nickname I chosed to refer to a Fock state $\ket{1}$ of the polariton field, that can be used as a qubit, so that you can speak of qp-qp interaction (not the same as polariton-polariton interaction, that can be messy and is basically unknown) or qp teleportation or qp-photon entanglement. Ah, actually, we did observe the first qp ever created (to the best of my knowledge) through a qp-photon scheme.
Note how, beyond fun, there's genuine convenience. A flying qp is more than a flying qubit. For instance, you can control its speed.
qp is also a beautiful digraph, like a letter turning its back to a mirror. Its ligature is particularly attractive: not so much the Unicode U+0239 that it produces on my screen: ȹ but the properly kerned one: $q\kern-.1cm p$.
I also use this acronym as the title of my current main line of research. The qp project, in particular, is my application to the European Research Council to challenge me into building the best nonlinear CNOT gate on the market!