This is along the same lines as the earlier question: When was the first use of the word Entanglement?
I was surprised to discover that when searching for "chimera" in both of Vicky Choi's minor-embedding papers:
https://arxiv.org/abs/0804.4884,
https://arxiv.org/abs/1001.3116,
no results came up!
This means that finding the first "chimera" paper is harder than I imagined and I don't know where to look anymore. When and where can I find the first use of the term?