Fast momentum-selective transport of Bose–Einstein condensates via controlled nonadiabatic dynamics in optical lattices

We present a detailed numerical study of a protocol for momentum-selective transport of a Bose–Einstein condensate in a one-dimensional optical lattice, achieving narrow momentum distributions through controlled nonadiabatic dynamics. The protocol consists of nonadiabatic loading into the lattice, coherent acceleration using a symmetric trapezoidal acceleration profile, and nonadiabatic release into free space. Using the time-dependent Gross–Pitaevskii equation, we simulate the full sequence and analyze the role of nonadiabatic excitations on the final momentum distribution. We identify the intrasite breathing dynamics as the dominant mechanism governing spectral purity under fast loading conditions. By tracking the condensate's spatial width during the evolution, we demonstrate a direct correlation with the final momentum spread. A variational model based on a Gaussian ansatz quantitatively reproduces the observed dynamics and provides physical insight into the breathing mechanism. Our results reveal the existence of “magic” times, i.e., specific loading or acceleration durations synchronized with the breathing oscillation period, where quasimonochromatic momentum distributions can be achieved even with loading times as short as 100 μs. In the tight-binding regime, this approach offers speedup factors of 3 to 6 compared to adiabatic protocols while maintaining high transfer fidelities, providing a practical route to coherent transport for quantum sensors operating under stringent timing constraints.