Distributed Learning of Quantum State Tomography Robust to Readout Errors

TL;DR

This paper presents a unified distributed framework for quantum state tomography that jointly estimates states and readout errors, improving scalability and robustness in large multiqubit systems.

Contribution

It introduces a structured bilinear optimization approach with a distributed ADMM-based algorithm and provides analytical guarantees for convergence and identifiability.

Findings

Joint estimation outperforms fixed-readout methods in simulations.

The approach recovers a significant portion of oracle performance.

There is a tradeoff between estimation accuracy, communication, and computation.

Abstract

Scalable estimation of quantum states with readout errors is a central challenge in large multiqubit systems. Existing overlapping-tomography methods improve scalability by working with local subsystems, but they usually assume known or separately calibrated measurements. At the same time, readout-estimation methods model measurement errors without enforcing consistency among overlapping regional states. In this context, the present paper introduces a unified framework for joint regional quantum state tomography with readout errors. A multiqubit system is partitioned in overlapping regions, each region is assigned to a local density operator and a local confusion matrix, and neighboring regions are coupled through reduced-state consistency on shared subsystems. This leads to a structured bilinear optimization problem. To solve it, a distributed alternating method is developed in which the state-update step is handled by the alternating direction method of multipliers (ADMM), while the confusion-matrix updates are carried out locally in parallel. Analytical guarantees are also established, including a sufficient condition for local identifiability, local quadratic growth of the population misfit, and convergence of the inner state-update procedure. Simulations on Ring, Ladder, Torus, and Hub graph geometries show that joint estimation improves state recovery over fixed-readout reconstruction, recovers a substantial portion of oracle performance, and reveals a clear tradeoff between state estimation performance, communication, and computation.