By "this ability" or "this power", becoming a vampire lord is meant. Also Serana's mother Valerica can grant it after Serana's is cured by visiting her in the soul cairn ( after you tell her she's freed she will be on the balcony of Volkihar castle), however you need to be a vampire lord to re-enter the soul cairn.
Once you have defeated Harkon and left Volkihar Cathedral, if you are not a vampire yourself †, you can ask Serana if she's ever considered being cured. If Serana chooses to become human, she will no longer be able to provide you with bloodcursed arrows, nor will she be able to turn you into a vampire.
Definition of amp (Entry 2 of 3) transitive verb. 1 informal : to make (someone) more excited or energetic : excite, energize Players either get amped by the electricity of the event or founder in the ambient chaos.—
Summary of Key PointsAMPDefinition:AmplifierType:Slang Word (Jargon)Guessability:2: Quite easy to guessTypical Users:Adults and Teenagers
Summary of Key PointsAMPDefinition:AmplifierType:Slang Word (Jargon)Guessability:2: Quite easy to guessTypical Users:Adults and Teenagers