Efficient and robust certification of genuine multipartite entanglement in noisy quantum error correction circuits

TL;DR

This paper presents a noise-robust, efficient method for certifying genuine multipartite entanglement in quantum error correction circuits, crucial for fault-tolerant quantum computing.

Contribution

It introduces a scalable witnessing technique that detects GME efficiently and robustly against noise, improving over previous methods and applicable to experimental setups.

Findings

The method detects GME with linearly many measurements and bipartitions.

It outperforms standard fidelity tests in noisy conditions.

The approach is adaptable to trapped-ion quantum hardware.

Abstract

Ensuring the correct functioning of quantum error correction (QEC) circuits is crucial to achieve fault tolerance in realistic quantum processors subjected to noise. The first checkpoint for a fully operational QEC circuit is to create genuine multipartite entanglement across all subsystems of physical qubits. We introduce a conditional witnessing technique to certify genuine multipartite entanglement (GME) that is efficient in the number of subsystems and, importantly, robust against experimental noise and imperfections. Specifically, we prove that the detection of entanglement in a linear number of bipartitions by a number of measurements that also scales linearly, suffices to certify GME. Moreover, our method goes beyond the standard procedure of separating the state from the convex hull of biseparable states, yielding an improved finesse and robustness compared to previous techniques. We apply our method to the noisy readout of stabilizer operators of the distance-three topological color code and its flag-based fault-tolerant version. In particular, we subject the circuits to combinations of three types of noise, namely, uniform depolarizing noise, two-qubit gate depolarizing noise, and bit-flip measurement noise. We numerically compare our method with the standard, yet generally inefficient, fidelity test and to a pair of efficient witnesses, verifying the increased robustness of our method. Last but not least, we provide the full translation of our analysis to a trapped-ion native gate set that makes it suitable for experimental applications.