Researchers Achieve 90% Fidelity in Measurement-based Quantum Computation with 4-qubit Clusters

Generating entanglement remains a central challenge in the development of measurement-based quantum computation, a promising approach to building powerful quantum computers. Rahul Dev Sharma from Shahjalal University of Science and Technology and Md Sakibul Islam from CECS University of Central Florida, along with their colleagues, investigate the creation of a fundamental building block for this type of computation: the one-dimensional cluster state. Their work focuses on a four-qubit system, analytically deriving and numerically validating methods for generating these entangled states, and crucially, assessing how different types of noise impact their stability. The results demonstrate that energy relaxation causes a relatively modest fidelity loss, maintaining 90% fidelity, while dephasing significantly degrades the cluster state, and highlight the importance of prioritising error mitigation strategies for practical quantum computers.

Decoherence Limits Cluster-State Quantum Computing

Quantum computing promises computational capabilities far beyond those of classical computers, leveraging the principles of superposition and entanglement. Unlike classical bits, quantum bits, or qubits, explore a vastly larger computational space, potentially revolutionising fields like drug discovery and materials science. However, realising this potential requires overcoming significant challenges, particularly the fragility of quantum states and their susceptibility to environmental noise, which degrades the information stored within qubits. Researchers are actively investigating methods to combat these challenges and build practical quantum computers. One promising approach is measurement-based quantum computing, which relies on preparing a highly entangled state, known as a cluster state, and then performing computations through a series of measurements. This differs from the traditional circuit model and offers a streamlined path towards quantum computation.

Superconducting Cluster States for Measurement-Based Computation

Researchers designed a comprehensive study of measurement-based quantum computing, focusing on the generation and properties of cluster states, essential resources for this computational approach. The team investigated how these states, built upon the principle of quantum entanglement, can drive computations through a series of single-qubit measurements. This method streamlines computation by preparing a highly entangled state and then consuming qubits via projective measurements, with each measurement basis adapting based on prior outcomes to ensure deterministic execution of algorithms. To explore the feasibility of this approach, scientists focused on superconducting quantum circuits, a leading platform for quantum computing. The study recreates and expands upon previous work demonstrating a method for generating large cluster states, leveraging brief activation of interqubit coupling to create states robust to parameter variations, ideal for solid-state quantum computing.

High Fidelity Cluster States With Decoherence

Researchers have made significant advances in measurement-based quantum computing by meticulously investigating the creation and stability of cluster states. The team focused on a four-qubit cluster state, providing detailed analytical derivations and numerical validations to enhance understanding of its properties and potential applications. Experiments reveal that incorporating energy relaxation yields a remarkably high fidelity, demonstrating the potential for robust performance even with some degree of noise. However, the study also highlights the detrimental effects of decoherence, showing that pure dephasing causes a significant decay in the quality of the cluster state, while combined noise further reduces fidelity over time. The findings demonstrate that cluster state fidelity is particularly sensitive to dephasing, emphasising the critical need for targeted error-mitigation strategies in near-term MBQC implementations.

Cluster State Fidelity Limits with Decoherence

This study investigates the generation of multi-qubit cluster states, essential resources for measurement-based quantum computing. Researchers successfully verified the formation of these states, demonstrating high fidelity under ideal conditions. However, simulations incorporating realistic noise, specifically decoherence based on current superconducting qubit technology, revealed a significant degradation in fidelity over time. The results indicate that the detrimental effects of decoherence, particularly dephasing, limit the coherence of the cluster state and necessitate rapid operations for successful quantum computation. These findings highlight the sensitivity of cluster state preparation to noise and underscore the importance of mitigating these effects in near-term quantum devices. The authors acknowledge that this decay in fidelity is a key challenge for practical implementation and suggest future work could focus on engineering hardware to improve resilience to noise and enhance the stability of cluster states.