In a landmark achievement that promises to reshape the landscape of quantum computing, researchers at the Quantum Control Laboratory within the University of Sydney Nano Institute have realized an experimental breakthrough in quantum logic gates, drastically reducing the physical qubit overhead traditionally needed for scalable quantum systems. This advancement centers on the utilization of Gottesman-Kitaev-Preskill (GKP) codes—often hailed as the ‘Rosetta stone’ of quantum information science—for encoding error-correctable logical qubits within a single trapped ion. By harnessing the subtle quantum oscillations intrinsic to a charged ytterbium atom confined in a Paul trap, the team has for the first time demonstrated the entanglement of these encoded qubits, marking a critical step toward large-scale, fault-tolerant quantum computation.
Quantum bits, or qubits, are notoriously fragile, susceptible to spontaneous errors that have long posed a barrier to the practical realization of reliable quantum machines. While error correction codes help mitigate this problem by encoding a single logical qubit into multiple physical qubits, the exponential increase in physical qubit resources—termed hardware overhead—has remained a daunting engineering challenge. The GKP codes present a theoretical framework to significantly alleviate this overhead by encoding logical qubits in continuous quantum variables, effectively translating the analog nature of quantum states into discrete, digital-like patterns that facilitate error detection and correction.
Until now, GKP codes have existed largely as a theoretical promise rather than an experimentally viable solution. The team led by Dr. Tingrei Tan has not only materialized these codes in the lab but has also engineered a universal set of quantum gates acting on GKP-encoded qubits. This universal set is fundamental because it means researchers can perform any quantum operation necessary for computation using qubits stored within the same physical quantum system. Their approach leverages exquisite control over the harmonic oscillations of a single trapped ytterbium ion, manipulating its motion in quantized vibrational modes to represent two logical qubits simultaneously.
Achieving entanglement between these logical qubits was a pivotal milestone. Entanglement, a uniquely quantum phenomenon where the state of one qubit instantaneously correlates with another regardless of distance, underpins the enhanced computational capabilities of quantum computers. Here, rather than entangling separate physical qubits, the researchers ingeniously entangled two distinct quantum vibrational modes—akin to quantized oscillations—within a single atom. This “quantum plumbing” not only conserves physical resources but also simplifies the traditionally complex architecture of quantum processors.
The logic gate constructed operates by precisely tuning the trapped ion’s quantum vibrations using advanced quantum control software developed by Q-CTRL, a spin-off from the laboratory itself. This control software employs physics-based models to minimize deleterious distortions to the delicate GKP code states throughout quantum operations. Maintaining the GKP code’s intricate structure during gate execution is paramount, as any degradation could negate the error-correcting advantages these codes provide. The experimental fidelity achieved in these control protocols demonstrates a crucial proof of concept for high-quality logical qubit manipulation within a practicable physical system.
A central experimental tool in this research is the Paul trap, a sophisticated device that confines charged ions using oscillating electric fields generated by precisely arranged electrodes. Unlike many quantum platforms requiring ultracold conditions, this trap operates at room temperature while maintaining stable control over the ion’s complex vibrational dynamics in three dimensions. By isolating and manipulating two specific motional modes of the ytterbium ion, the team effectively harnessed the continuous quantum variables necessary for GKP encoding, merging the mechanical quantum properties of the ion with state-of-the-art quantum error correction techniques.
This accomplishment represents more than a novel method; it acts as a blueprint for dramatically scaling quantum computers while overcoming one of their most formidable limitations: the physical qubit resource overhead. By embedding two error-correctable logical qubits within a single atom and demonstrating entanglement gates between them, the researchers have significantly lowered the barrier to hardware-efficient quantum computation. This efficiency is critical as the quantum computing community races to build devices with millions of logical qubits, which until now required unimaginably complex arrays of physical qubits.
The implications extend beyond mere hardware efficiency. The logical gates realized in this work establish a path toward more robust quantum information processing that leverages continuous-variable quantum systems. Unlike conventional qubits, which are two-state systems, continuous-variable qubits stored in harmonic oscillators enable richer encoding schemes and naturally integrate with quantum error correction protocols such as the GKP code. This hybrid approach effectively combines the benefits of discrete and continuous quantum systems, broadening the technological toolbox for quantum engineers.
Collaborator and lead author Vassili Matsos emphasizes the collaboration between theoretical and experimental quantum control, highlighting how the precisely engineered gate designs were made possible by integrating quantum control algorithms with physical modeling of GKP states. This synergy not only realized the first universal logical gate set for GKP qubits but also points toward a future in which complex quantum algorithms can be executed with unprecedented fidelity using these codes, reducing error rates that have historically limited the scale and reliability of quantum processors.
Looking forward, the researchers aim to expand their methods to entangle multiple logical qubits and integrate these gates into larger quantum circuits, laying foundational work for scalable, fault-tolerant quantum computers. As quantum devices continue to grow in both size and complexity, innovations like this will be instrumental in overcoming the resource bottleneck. They bring the theoretical promises of quantum error correction and continuous-variable qubits into tangible, programmable architectures, accelerating the timeline for quantum technologies capable of transformative applications in cryptography, materials science, and beyond.
This breakthrough, published in Nature Physics, not only validates longstanding theoretical models but raises compelling questions about the future architectures of quantum machines. By turning the abstract mathematical symmetries of the GKP code into a practical engineering reality, the University of Sydney researchers demonstrate how fundamental physics insights can revolutionize computing paradigms. Their achievement underscores the intricate dance between quantum theory, precision engineering, and control algorithms necessary to unlock quantum computing’s full potential.
The team acknowledges the critical role of international and interdisciplinary support, including funding from the Australian Research Council, the US Office of Naval Research, the US Army Research Office, the US Air Force Office of Scientific Research, Lockheed Martin, Sydney Quantum Academy, and private benefactors. Such collaboration and resources are essential as quantum research ventures deeper into uncharted scientific and technological territory, where each milestone requires the convergence of expertise and innovation at the highest level.
Media enquiries regarding this research can be directed to Marcus Strom at the University of Sydney. The detailed paper titled “Universal quantum gate set for Gottesman-Kitaev-Preskill logical qubits” offers comprehensive experimental data and technical discourse for those wishing to dive deeper into the mechanisms underpinning this advance.
Subject of Research: Not applicable
Article Title: Universal quantum gate set for Gottesman-Kitaev-Preskill logical qubits
News Publication Date: 21-Aug-2025
Web References:
– Quantum Control Laboratory: https://quantum.sydney.edu.au/research/quantum-control-laboratory/
– University of Sydney Nano Institute: https://www.sydney.edu.au/nano/
– Original article: https://www.nature.com/nphys/
References:
Matsos, V. et al ‘Universal quantum gate set for Gottesman-Kitaev-Preskill logical qubits’ (Nature Physics 2025) DOI: 10.1038/s41567-025-03002-8
Image Credits: Fiona Wolf/University of Sydney
Keywords
Quantum computing, quantum error correction, Gottesman-Kitaev-Preskill (GKP) code, logical qubits, trapped ion, quantum entanglement, Paul trap, quantum logic gates, harmonic oscillations, quantum control, continuous-variable quantum systems, scalable quantum computing
