We consider the late time one-loop quantum backreaction from inflationary fluctuations of a non-minimally coupled , massless scalar field .
The scalar is assumed to be a spectator field in an inflationary model with a constant principal slow roll \epsilon parameter .
We regulate the infrared by matching onto a pre-inflationary radiation era .
We find a large late time backreaction when the nonminimal coupling \xi is negative ( in which case the scalar exhibits a negative mass term during inflation ) .
The one-loop quantum backreaction becomes significant today for moderately small non-minimal couplings , \xi \sim - 1 / 20 , and it changes sign ( from negative to positive ) at a recent epoch when inflation lasts not much longer than what is minimally required , N \gtrsim 66 .
Since currently we do not have a way of treating the classical fluid and the quantum backreaction in a self-consistent manner , we can not say decidely whether the backreaction from inflationary quantum fluctuations of a non-minimally coupled scalar can mimic dark energy .