报告摘要：  The sensitivity for estimating an unknown parameter from repeated
(ensemble) measurement is typically constrained by the standard
quantum limit (SQL) 1/N1/2, where N is the number of ensembles
involved. When applied to atomic clock (frequency metrology), the
clock frequency is the parameter corresponding to a chosen atomic
transition, and N is the total number of atoms. It is widely known
that quantum correlation or entanglement between different atoms
(ensembles) can enhance parameter estimation beyond the SQL. The
required atomic correlation or entanglement can be generated from
controlled interactions when quantum coherence can be sustained, as
conveniently afforded in atomic quantum gases. This talk will discuss
some of our recent results enabling parameter estimation beyond the
SQL in two-component as well as in spin-1 atomic Bose-Einstein
condensates.