Quantum mechanics is at the heart of our technology and economy - the laser and the transistor are quantum devices - but its full potential is far from being realized. Recent technological advances in optics, nanoscience and engineering allow experimentalists to create artificial structures or put microscopic and mesoscopic systems under new manipulable conditions in which quantum phenomena play a fundamental role.

Quantum technologies exploit these effects with practical purposes. The objective of Quantum Science is to discover, study, and control quantum efects at a fundamental level. These are two sides of a virtuous circle: new technologies lead to the discovery and study of new phenomena that will lead to new technologies.

Our group's aim is  to control and understand quantum phenomena in a multidisciplinary intersection of  Quantum Information, Quantum optics and cold atoms, Quantum Control, Spintronics, Quantum metrology, Atom interferometry, Superconducting qubits and Circuit QED and Foundations of Quantum Mechanics.



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Andrea Alberti (Bonn University) (Seminar)

When end where

31/10/2018, 10:30


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)