Andrea Alberti (Bonn University)
When and where
31/10/2018, 10:30 - 00:00
Description
WHEN: 2018/10/31 , 10:30
WHERE: seminar room of Theoretical Physics Dept.
I will report on the experimental demonstration of fast, high-fidelity
transport of atomic wave packets in spin-dependent optical lattices.
The basic idea is to transport a cesium atom from a given lattice site
to a neighboring one in the shortest time allowed by quantum
mechanics, under only two conditions: (1) the wave packet, which is
initially prepared in the motional ground state of the initial
trapping potential, must end up in the ground state of the final
trapping potential, (2) during the process, the depth of the optical
lattice potential cannot exceed a certain value fixed by some natural
constraints (e.g., finite laser power).
Our transport experiments are carried out using
polarization-synthesized optical lattices, which relying on a fast
polarization synthesizer [1], enabling full and independent control of
the potential for the spin-up and spin-down states. The sub-nanometer
precision and high bandwidth of our system allows us to test quantum
optimal control to speed up the transport dynamics. To achieve such a
speed-up, optimal transport ramps allow several motional excitations
to be created during the transport process, before these are refocused
back into the ground state at the end. Optimizing the process for
various transport times, we clearly observe a minimum time below which
transport operations unavoidably create motional excitations of the
atoms in the final trapping potential. This time defines the quantum
speed limit of the target transformation.
Beyond their fundamental interest, quantum manipulations at the
quantum speed limit are expected to find numerous applications for
quantum computing and quantum sensing. In this respect, I will show a
first application of quantum optimal control to enhance the contrast
of an atomic Mach-Zehnder interferometer, enabling the measurement of
external forces with high precision.
[1] C. Robens, S. Brakhane, W. Alt, D. Meschede, J. Zopes and A.
Alberti, “Fast, High-Precision Optical Polarization Synthesizer for
Ultracold-Atom Experiments,” Phys. Rev. Appl. 9, 034016 (2018)