CRJ-900 Captain reported encountering severe wake turbulence on descent into ATL in trail of an A350.

Narrative

Encountered momentary severe turbulence associated with wake descending through 11;000 into Atlanta.Cause: During descent into Atlanta; around 11;000 ft msl; we encountered momentary severe turbulence; almost certainly associated with wake. I queried ATC as to what we were following and found we were in trail of a heavy A350. I informed ATC that we hit their wake. At the time of the encounter we had a direct headwind; but the wind shifted to a crosswind by 10;000; so I did not request a vector. From that point ATC increased our separation with a longer final and slower airspeed. No further wake was encountered. I called the flight attendants after the encounter and they indicated there were no injuries. After the flight; both flight attendants indicated that they had lost their footing or been momentarily thrown from their feet during the encounter. The forward flight attendant said she hit the wall and was hurting from the impact; but was not injured and needed no medical intervention.