https://unipd.zoom.us/j/367589168
Abstract:
Transforming an initial quantum state into a target state through the fastest possible route—a quantum brachistochrone—is a fundamental challenge for many quantum technologies. In two-level systems, the quantum brachistochrone solutions are long known. These solutions, however, are not applicable to larger systems, especially when the target state cannot be reached through a local transformation.
In this seminar, I present an experimental demonstration of coherent transport of an atomic wave packet in the shortest possible time [1]. Ours is a paradigmatic case of quantum process that cannot be reduced to a two-level system, and represents the first observation of quantum speed limit for a multilevel system, where the transition from a quantum-controllable to a quantum-noncontrollable process is sharply resolved by fidelity measurements. I will show how a geometric interpretation of quantum state dynamics gives us insight into the quantum speed limit of the process.
In a second series of experiments [2], we have tested for the first time in a multi-level system two well-known quantum speed limits, the Mandelstam–Tamm and the Margolus–Levitin bounds. We use a novel measurement technique to measure the Fubini-Study distance of quantum states in Hilbert space, and thus to quantify the distance of the evolved state from the geodesic quantum path.
Our results, establishing quantum speed limits beyond the simple two-level system, are important to understand the ultimate performance of quantum computing devices and related advanced quantum technologies.
[1] M. R. Lam, N. Peter, T. Groh, W. Alt, C. Robens, D. Meschede, A. Negretti, S. Montangero, T. Calarco, and A. Alberti, “Demonstration of Quantum Brachistochrones between Distant States of an Atom,” Phys. Rev. X 11, 011035 (2021)
[2] G. Ness, M. R. Lam, W. Alt, D. Meschede, Y. Sagi, and A. Alberti, “Observing quantum-speed-limit crossover with matter wave interferometry,” (2021), arXiv:2104.05638 [quant-ph]
