Aubretia is as tough as old boots and i'm surprised it's dying back.
As it's newly planted have you maintained regular watering of it, or was weedkiller used in that area - could it be taking up the residue ?

Yes we bought some too, and it looked as if it was dying back. Then when I looked more closely I saw that it was spouting tiny new leaves all over the place, although it still looks dead from a distance. I think it's just part of the post-flowering cycle.

I remember my dad used to cut his aubretia back every year after it had flowered and I suspect this isn't unrelated. Try pruning it right back and look for new growth on strong, less straggly stems.