Optimal Quantum Overlapping Tomography

TL;DR

This paper introduces an optimal framework for quantum overlapping tomography that minimizes measurement costs and is experimentally feasible, advancing the characterization of complex quantum systems.

Contribution

It presents a unified, efficient measurement scheme for quantum overlapping tomography based on clique cover models, applicable to various RDM topologies and validated experimentally.

Findings

Achieved significant reduction in measurement costs for RDM reconstruction

Validated the measurement schemes on nuclear spin and superconducting quantum processors

Demonstrated robustness of the approach with noisy data

Abstract

Partial tomography, which focuses on reconstructing reduced density matrices (RDMs), has emerged as a promising approach for characterizing complex quantum systems, particularly when full state tomography is impractical. Recently, overlapping tomography has been proposed as an efficient method for determining all $k$-qubit RDMs using logarithmic polynomial measurements, though it has not yet reached the ultimate limit. Here, we introduce a unified framework for optimal quantum overlapping tomography by mapping the problem to the clique cover model. This framework provides the most efficient and experimentally feasible measurement schemes to date, significantly reducing the measurement costs. Our approach is also applicable to determining RDMs with different topological structures. Moreover, we experimentally validate the feasibility of our schemes on practical nuclear spin processor using average measurements and further apply our method to noisy data from a superconducting quantum processor employing projection measurements. The results highlight the strong power of overlapping tomography, paving the way for advanced quantum system characterization and state property learning in the future.