Quantum non-Gaussian coherences of an oscillating atom

TL;DR

This paper demonstrates the experimental observation of quantum non-Gaussian coherences in a single calcium ion's mechanical vibrations, establishing their robustness and significance for quantum technologies.

Contribution

It derives bounds for quantum coherences and experimentally observes non-Gaussian coherences in atomic oscillations, advancing understanding of quantum coherence in harmonic oscillators.

Findings

Observation of quantum non-Gaussian coherences up to six phonons

Coherence robustness for over 20 ms against dephasing

Establishment of thresholds for genuine quantum non-Gaussian states

Abstract

Quantum coherence between energy eigenstates of harmonic oscillators is essential for quantum physics. Even the most elementary binary superpositions of the ground and the higher eigenstate are highly required for quantum sensing, thermodynamics, and computing. We derive upper bounds for quantum coherences achieved by classical and Gaussian states and operations and, subsequently, obtain a hierarchy of the thresholds for the off-diagonal elements necessary to reach genuine quantum non-Gaussian coherences. We experimentally demonstrate unambiguous observation of quantum non-Gaussian coherences in mechanical vibrations of a single calcium ion up to the superposition of zero and six phonons. The analysis of the robustness with respect to pure dephasing in a motional Ramsey experiment demonstrates the feasibility of their storage for up to more than 20 ms for superpositions with a large energy difference of participating number states. The presented observations prove that atomic oscillations go deeply into a diverse area of discrete quantum non-Gaussian coherent phenomena critical for their applications.