Preparing a twin-Fock state of spinor atomic condensate

An even number $N$ of bosonic particles equally partitioned into two modes represents a twin-Fock state (TFS), which is manifestly entangled and can be used to approach Heisenberg limited sensing precision $1/N$. Small $N$ TFSs are routinely produced from parametric down conversion, for instance, the paired photons at $N=2$. Large $N$ TFSs, however, remain elusive although their presence have been inferred in spinor atomic condensates undergoing spin exchange collisions [1-4]. Such spin mixing process has been intensively studied in recent years, whereby a N-atom polar or non-magnetic condensate evolves into a mixture of TFSs with the number of paired atoms covering a broad range from $0$ to $N/2$. The present work reports our experimental observation of $N \simeq 20000$ condensed atoms almost completely and deterministically converted into a single component TFS at $\sim 10000$ pairs through adiabatic means.\\\\ 1. E. M. Bookjans, et al, Phys. Rev. Lett. \textbf{107}, 210406 (2011).\\ 2. C. Gross, et al, Nature \textbf{480}, 219 (2011).\\ 3. B. L\"ucke, et al., Science \textbf{334}, 773(2011).\\ 4. B. L\"ucke, et al, Phys. Rev. Lett. \textbf{112}, 155304 (2014).