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**From**: Janos Asboth <asboth.janos AT wigner.mta.hu>**To**: fizinfo AT lists.kfki.hu**Subject**: [Fizinfo] BME Elméleti Fizika Tanszék szemináriuma, szept 6 -- Andrea Alberti**Date**: Tue, 3 Sep 2019 17:05:04 +0200**Authentication-results**: smtp1.kfki.hu (amavisd-new); dkim=pass (1024-bit key) reason="pass (just generated, assumed good)" header.d=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).

**[Fizinfo] BME Elméleti Fizika Tanszék szemináriuma, szept 6 -- Andrea Alberti**,*Janos Asboth, 09/03/2019*

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