[Seminar] WIGNER SZFI Seminar, 3 Sept -Andrea Alberti

[juhasz]

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