A Note on Non-Additive Quantum Codes

A method to combine two quantum error-correcting codes is presented. Even when starting with additive codes, the resulting code might be non-additive. Furthermore, the notion of the erasure space is introduced which gives a full characterisation of the erasure-correcting capabilities of the codes. For the special case that the two codes are unitary images of each other, the erasure space and the pure erasure space of the resulting code can be calculated.