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?