Quantum Entanglement in Quantum Computing Systems

Quantum entanglement describes a quantum mechanical phenomenon by which two or more particles share a single, inseparable quantum state. Within quantum computing systems, it underpins capabilities ranging from error correction to the execution of algorithms that outperform classical counterparts. In multipartite settings, entanglement may assume various structures—such as Bell pairs, Greenberger–Horne–Zeilinger states or graph states—each tailored to specific computational or communicational tasks. The coherent manipulation of entangled qubits enables secure communication protocols, quantum teleportation and enhanced sensing, while also serving as a resource in algorithmic speed-ups such as Shor’s and Grover’s algorithms. Achieving high-fidelity entanglement across many qubits remains a central challenge due to decoherence, gate errors and readout noise. Progress in physical platforms—encompassing superconducting circuits, trapped ions, spin qubits and photonic systems—has led to demonstrations of genuine multipartite entanglement on ever-larger registers. Concurrent advances in circuit compilation, noise modelling and entanglement witnessing refine our ability to benchmark device performance, inform architecture design and guide the development of fault-tolerant schemes. As research converges towards error-corrected quantum processors, entanglement not only functions as a performance metric but also as the essential enabler of quantum advantage, with global efforts focusing on scalable methods for its generation, verification and preservation.

Research from Nature Portfolio

Recent work has demonstrated genuine entanglement across twenty superconducting qubits configured in a linear graph state. By performing full quantum state tomography on overlapping four-qubit subchains and applying multipartite entanglement witnesses, researchers established that every adjacent pair of qubits was inseparable and that genuine three-qubit entanglement pervaded the system. This milestone represents one of the largest solid-state entangled registers to date and provides a benchmark for hardware connectivity, coherence times and calibration techniques. The methodology highlights the interplay between graph-based state preparation, noise mitigation through error-detection circuits and systematic fidelity analysis, setting a practical standard for scaling up entangled resources in near-term devices.

Research from all publishers

Innovations in quantum data compression have emerged through the development of quantum autoencoders that employ mixed reference states. By optimising a cost function combining encoding fidelity and quantum mutual information, these devices compress high-entropy states more effectively than pure-state encoders, with successful implementations on cloud-accessible superconducting processors. In parallel, the preparation and verification of Greenberger–Horne–Zeilinger states on twenty-seven qubits in a superconducting architecture has demonstrated genuine multipartite entanglement with fidelity exceeding 0.5, enabled by readout-error mitigation and parity-verification error-detection. Another significant advance reports full bipartite entanglement graphs spanning sixty-five superconducting qubits; through native-graph state construction and readout-error mitigation, connected entangled pairs were detected across the entire devices, reflecting the scaling potential of noisy intermediate-scale quantum platforms. Together, these studies illustrate progress in entanglement generation, structure detection and resource optimisation across diverse hardware, offering complementary strategies for robust multi-qubit control and benchmarking.

Quantum Entanglement in Quantum Computing Systems publication trend

The graph below shows the total number of articles in quantum entanglement in quantum computing systems across all publications each year (not limited to Nature Index journals).

Technical terms

Qubit: The fundamental two-level quantum unit of information, analogous to a classical bit but capable of superposition.

Quantum entanglement: A correlation between quantum systems whereby the joint state cannot be expressed as a product of individual states.

Multipartite entanglement: Entanglement shared among three or more quantum systems, exhibiting complex correlation structures.

Greenberger–Horne–Zeilinger (GHZ) state: A maximally entangled state of three or more qubits used for fundamental tests and error diagnosis.

Entanglement witness: An observable whose measured value certifies the presence of entanglement in a quantum state.

References

1. Entanglement in a 20-Qubit Superconducting Quantum Computer. Scientific Reports (2019).
2. Quantum autoencoders using mixed reference states. npj Quantum Information (2024).
3. Generation and verification of 27-qubit Greenberger-Horne-Zeilinger states in a superconducting quantum computer. Journal of Physics Communications (2021).
4. Whole‐Device Entanglement in a 65‐Qubit Superconducting Quantum Computer. Advanced Quantum Technologies (2021).