Demonstration of quantum brachistochrones between distant states of an atom

TL;DR

This paper demonstrates the fastest possible coherent transport of an atomic wave packet over a large distance, revealing a quantum speed limit and providing insights into quantum state dynamics with implications for quantum technologies.

Contribution

It experimentally shows quantum brachistochrone dynamics for atomic wave packets and identifies a fundamental quantum speed limit using a geometric approach.

Findings

Identified a minimum duration for coherent atomic transport

Measured quantum speed limit for matter wave splitting and recombination

Provided a geometric interpretation of quantum state evolution

Abstract

Transforming an initial quantum state into a target state through the fastest possible route---a quantum brachistochrone---is a fundamental challenge for many technologies based on quantum mechanics. Here, we demonstrate fast coherent transport of an atomic wave packet over a distance of 15 times its size---a paradigmatic case of quantum processes where the target state cannot be reached through a local transformation. Our measurements of the transport fidelity reveal the existence of a minimum duration---a quantum speed limit---for the coherent splitting and recombination of matter waves. We obtain physical insight into this limit by relying on a geometric interpretation of quantum state dynamics. These results shed light upon a fundamental limit of quantum state dynamics and are expected to find relevant applications in quantum sensing and quantum computing.