Distinguishing multi-spin interactions from lower-order effects

TL;DR

This paper introduces two robust methods to experimentally verify and distinguish multi-spin interactions from lower-order effects in quantum spin systems, facilitating advanced quantum engineering and characterization.

Contribution

It presents static and dynamic detection techniques for identifying n-local multi-spin couplings, including generalizations and analysis of their effectiveness for larger systems.

Findings

Standard measurement distinguishes up to five spins from lower-order effects.

Dynamic detection method is asymptotically optimal for larger system sizes.

Methods are robust across various coupling strengths and qubit types.

Abstract

Multi-spin interactions can be engineered with artificial quantum spins. However, it is challenging to verify such interactions experimentally. Here we describe two methods to characterize the $n$-local coupling of $n$ spins. First, we analyze the variation of the transition energy of the static system as a function of local spin fields. Standard measurement techniques are employed to distinguish $n$-local interactions between up to five spins from lower-order contributions in the presence of noise and spurious fields and couplings. Second, we show a detection technique that relies on time dependent driving of the coupling term. Generalizations to larger system sizes are analyzed for both static and dynamic detection methods, and we find that the dynamic method is asymptotically optimal when increasing the system size. The proposed methods enable robust exploration of multi-spin interactions across a broad range of both coupling strengths and qubit modalities.