Optimizing number squeezing when splitting a mesoscopic condensate

We optimize number squeezing when splitting a mesoscopic Bose-Einstein condensate. Applying optimal control theory to a realistic description of the condensate allowed us to identify a form of the splitting ramp, which drastically outperforms the adiabatic splitting. The results can be interpreted in terms of a generic two-mode model mapped onto a parametric harmonic oscillator. This optimal route to squeezing paves the way to a much longer phase coherence and atom interferometry close to the Heisenberg limit.