I will report on the experimental realization of fast, high-fidelity transport of atomic wave packets in deep optical lattices. The goal here is to transport atoms by one or more lattice sites in the shortest time allowed by quantum mechanics, under the constraint that no motional excitation is created after transport, and the optical lattice depth does not exceed a maximum value given by the available resources (e.g., finite laser power). To achieve fast atom transport, we use quantum optimal control, which allows several motional excitations to be created during the transport process, and yet refocus them back into the motional ground state with a fidelity at around 99%. Optimizing the process for various transport times, we clearly observe a minimum time below which transport operations unavoidably create motional excitations. This time defines the quantum speed limit for the transport operation. From the experimental data, we deduce that such a minimal transport time is essentially determined by the harmonic period of the trapping potential. Theoretically, such a time can be estimated using the energy uncertainty and the Fubini-Study metric quantifying the path length connecting the initial and final states. I will show that the fast atom transport in spin-dependent optical lattices allows us to outrun decoherence, and thus to improve coherence of Mach-Zehnder atom interferometers and of quantum-walk experiments, where atoms are delocalized in space through a multiplicity of quantum paths. Finally, I will conclude with an outlook towards two-dimensional quantum-walk experiments for the study of anomalous Floquet Chern topological insulators using pseudo spin-1/2 particles [1].

[1] Sajid et al., “Creating anomalous Floquet Chern insulators with magnetic quantum walks”
Phys. Rev. B 99, 214303 (2019).