Local probe of single phonon dynamics in warm ion crystals

TL;DR

This paper demonstrates a method to locally probe and analyze phonon dynamics and quantum discord in large chains of trapped ions, enabling insights into coherence and many-body physics with minimal measurement resources.

Contribution

It introduces a technique to extract autocorrelation functions and quantum discord from a small part of a large ion chain, advancing scalable quantum system characterization.

Findings

Successful tracing of a single phonon excitation in chains of up to 42 ions.

Observation of excitation spreading and partial refocusing amidst thermal background.

Reflection of quantum discord dynamics between electronic and vibrational states.

Abstract

The detailed characterization of non-trivial coherence properties of composite quantum systems of increasing size is an indispensable prerequisite for scalable quantum computation, as well as for understanding of nonequilibrium many-body physics. Here we show how autocorrelation functions in an interacting system of phonons as well as the quantum discord between distinct degrees of freedoms can be extracted from a small controllable part of the system. As a benchmark, we show this in chains of up to 42 trapped ions, by tracing a single phonon excitation through interferometric measurements of only a single ion in the chain. We observe the spreading and partial refocusing of the excitation in the chain, even on a background of thermal excitations. We further show how this local observable reflects the dynamical evolution of quantum discord between the electronic state and the vibrational degrees of freedom of the probe ion.