Researchers have made significant strides in improving the reliability of quantum computers by developing new techniques for quantum error correction. This advancement is crucial for the future of quantum computing, as it aims to create more robust algorithms capable of handling complex computations.
Understanding Quantum Error Correction
At the heart of this development are quantum error correction codes, which protect quantum information from decoherence and quantum noise. One notable example is the five-qubit error correction code, the minimum number of qubits necessary to correct single-qubit errors. This code employs five physical qubits—fundamental units of quantum information—to safeguard one logical qubit, which is a collection of these physical qubits arranged to rectify errors.
Despite this framework, imperfections in hardware can still induce quantum errors, necessitating more effective verification methods. One such method is known as self-testing, a powerful approach that verifies quantum properties using only input-output statistics, treating quantum devices as black boxes. This technique has evolved from examining bipartite systems, which consist of two quantum subsystems, to multipartite entanglement involving three or more subsystems. The latest advancements focus on genuinely entangled subspaces, where every state is fully entangled across all subsystems, offering a higher level of reliability.
Self-Testing Techniques in Quantum Computing
In recent research, self-testing techniques were employed to certify genuinely entangled logical subspaces within the five-qubit code on both photonic and superconducting platforms. Researchers prepared informationally complete logical states that span the entire logical space, ensuring the set is comprehensive enough to fully characterize the behavior of the system.
To simulate real-world noise, the team intentionally introduced basic quantum errors by applying Pauli errors to the physical qubit. They then utilized mathematical tests known as Bell inequalities, tailored to the quantum error correction framework, to evaluate whether the system remained within the initial logical subspaces after these errors were introduced.
The research yielded encouraging results, with extractability measures indicating how closely the tested quantum system aligns with the ideal target state. An extractability measure of 1 signifies a perfect match. The certification achieved scores of at least 0.828 ± 0.006 for the photonic systems and 0.621 ± 0.007 for the superconducting systems. Notably, the photonic platform demonstrated a high extractability score, indicating that its logical subspace was very close to the ideal state. The superconducting platform, while achieving a lower score, still exhibited meaningful entanglement.
These findings confirm the effectiveness of the self-testing method in practice and provide evidence of strong entanglement within the five-qubit code across both platforms. The research not only advances the field of quantum technologies but also introduces robust methods for verifying and characterizing complex quantum structures, essential for developing reliable and scalable quantum systems.
Furthermore, this study illustrates that device-independent certification can extend beyond quantum states and measurements to encompass more general quantum structures, paving the way for future innovations in quantum computing.
The full research article, titled “Certification of genuinely entangled subspaces of the five-qubit code via robust self-testing,” was published by Yu Guo et al. in 2025 in the journal Reports on Progress in Physics.
