The Oxford Duden German Dictionary Oxford University Press 1998 edition, translates Ausgangssperre as - "curfew" (für Soldaten - for soldiers), confinement to barracks.
No mention here is made of quarantine for which there is a German word - Quarantäne.However, in the comments following the question, @Robusto and I would appear to be in agreement that the English word quarantine does not necessarily imply compulsion. Hence there would not seem to be a single English word which means "enforced quarantine".
The word internment exists in English (German Internierung), but the OED indicates this as "for political or military purposes". It means "detention without trial". However I have never heard the word "internment" used for compulsory quarantine.
So I think the best English translation, in the circumstances, would be to resort to two words "compulsory quarantine".
Why do they not use the word Quarantäne, rather than Ausgangssperre? Is it because, as in English, it does not imply compulsion?