ELFT HÍRADÓ

[Janos Asboth <asboth.janos AT wigner.mta.hu>]

                   M E G H Í V Ó - I N V I T A T I O N

     Seminar Series of the Department of Theoretical Physics at the
            Budapest University of Technology and Economics


                             Andrea Alberti
           (Institut für Angewandte Physik, Universitaet Bonn)

            Controlling atomic wave packets at the quantum speed limit

Időpont: 2019. szeptember 6. péntek, 10:15
Helyszín: BME Fizikai Intézet, Elméleti Fizika Tanszék,
Budafoki út 8. F-épület, III lépcsőház, szemináriumi szoba

     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).