ELFT HÍRADÓ

[juhasz.robert AT wigner.mta.hu]

WIGNER SZFI Seminar

Controlling atomic wave packets at the quantum speed limit
Andrea Alberti

Institut für Angewandte Physik, Universitaet Bonn, Germany (host: Asbóth
János)

Tuesday, 3 September 2019 10:00, KFKI Campus, Bldg. 1, 2nd floor, Conference
Room

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).

Everyone is welcome to attend.

Róbert Juhász
szfi-seminar AT wigner.mta.hu