Characterization of entanglement on superconducting quantum computers of up to 414 qubits

TL;DR

This paper investigates large-scale entanglement on IBM superconducting quantum devices, demonstrating multipartite and bipartite entanglement, and explores how dynamical decoupling improves coherence and noise suppression, serving as a device benchmark.

Contribution

It provides the first large-scale characterization of entanglement on up to 414 qubits, introducing methods for entanglement benchmarking and noise analysis on superconducting quantum computers.

Findings

Achieved 32-qubit GHZ state with fidelity 0.519, certifying GME.

Observed linear decoherence rate trend up to 15 qubits, confirming absence of superdecoherence.

Demonstrated entanglement oscillations and noise suppression in 2-qubit states.

Abstract

As quantum technology advances and the size of quantum computers grow, it becomes increasingly important to understand the extent of quality in the devices. As large-scale entanglement is a quantum resource crucial for achieving quantum advantage, the challenge in its generation makes it a valuable benchmark for measuring the performance of universal quantum devices. In this work, we study entanglement in Greenberger-Horne-Zeilinger (GHZ) and graph states prepared on the range of IBM Quantum devices. We generate GHZ states and investigate their coherence times with respect to state size and dynamical decoupling techniques. A GHZ fidelity of $0.519 \pm 0.014$ is measured on a 32-qubit GHZ state, certifying its genuine multipartite entanglement (GME). We show a substantial improvement in GHZ decoherence rates for a 7-qubit GHZ state after implementing dynamical decoupling, and observe a linear trend in the decoherence rate of $\alpha=(7.13N+5.54)10^{-3}\mu s^{-1}$ for up to $N=15$ qubits, confirming the absence of superdecoherence. Additionally, we prepare and characterize fully bipartite entangled native graph states on 22 superconducting quantum devices with qubit counts as high as 414 qubits, all active qubits of the 433-qubit IBM Osprey device. Analysis of the decay of 2-qubit entanglement within the prepared states shows suppression of coherent noise signals with the implementation of dynamical decoupling techniques. Additionally, we observe that the entanglement in some qubit pairs oscillates over time, which is likely caused by residual ZZ-interactions. Characterizing entanglement in native graph states, along with detecting entanglement oscillations, can be an effective approach to low-level device benchmarking that encapsulates 2-qubit error rates along with additional sources of noise, with possible applications to quantum circuit compilation.