Quantum computing stands at the frontier of scientific innovation, promising transformative capabilities beyond the reach of classical computers. However, this promising technology faces profound obstacles related to qubit stability, chiefly stemming from decoherence and the resultant errors known as bit flips and phase flips. These errors abruptly alter a qubit’s state from ‘0’ to ‘1’ or invert the relative phase in a superposition, posing formidable challenges to reliable information processing.
To mitigate such errors, the concept of logical qubits—constructed from ensembles of multiple physical qubits—has become central. By deploying continuous error correction protocols, these logical qubits maintain quantum information integrity over time despite pervasive noise. Nonetheless, the technology must transcend mere data preservation and facilitate quantum gate operations, the fundamental building blocks for quantum algorithms, while actively correcting errors as computations unfold.
A groundbreaking experimental leap has been achieved by the team led by Professor Andreas Wallraff at ETH Zurich, in collaboration with researchers from the Paul Scherrer Institute and theoretical physicists at RWTH Aachen University and Forschungszentrum Jülich. Their study, recently published in Nature Physics, demonstrates a pioneering approach to performing quantum logical operations on superconducting qubits with concurrent error correction—a feat that addresses a critical bottleneck in realizing functional quantum processors.
Quantum error correction diverges starkly from its classical counterpart. Classical error correction relies on creating multiple identical copies of bits and employing majority voting to detect and rectify bit flips. Such cloning techniques, however, are infeasible in quantum mechanics due to the no-cloning theorem. Instead, quantum information is safeguarded by encoding it into entangled states distributed across many physical qubits. This entanglement-based framework must also correct phase-flip errors, unique to quantum computation, alongside bit flips, exponentially complicating error management.
Surface codes have emerged as one of the most promising architectures for quantum error correction. In this scheme, a logical qubit’s state is embedded within many physical ‘data qubits.’ Error correction hinges on the measurement of ‘stabilizers’—special qubits linked to data qubits designed to detect deviations in bit and phase values without collapsing the stored quantum information. Specifically, Z-type stabilizers signal bit-flip errors, while X-type stabilizers detect phase flips. The data qubits themselves remain unmeasured and hence preserve the encoded logical state.
Crucially, executing logical operations such as the controlled-NOT gate between two logical qubits requires even more nuanced control since errors can manifest during the gate operation itself. Ideally, qubits would be spatially movable, allowing arbitrary interactions. Yet, in superconducting qubit arrays arranged on fixed two-dimensional lattices, connectivity is constrained by physical proximity—only adjacent qubits can interact directly. This spatial limitation necessitates inventive strategies to perform fault-tolerant logical gates.
The breakthrough comes through the realization of ‘lattice surgery,’ a method that reconciles these spatial constraints. In their experiment, the researchers encoded a single logical qubit using 17 physical qubits arranged roughly in a square lattice. By cyclically reading the stabilizers every 1.66 microseconds, they implemented ongoing correction of both bit-flip and phase-flip errors, ensuring robust logical qubit stability.
When time progressed to performing the operation termed ‘surgery,’ the team selectively read out three data qubits centered in the square, effectively splitting the surface code into two distinct halves. Concurrently, they suspended the measurement of X-type stabilizers. This deft manipulation produced two logically entangled qubits—an essential stepping stone towards complex quantum gate operations. Throughout this lattice surgery, bit-flip errors were continuously corrected and subsequently the error correction process resumed independently on both resulting halves.
While this initial lattice surgery operation is not a complete controlled-NOT gate, it forms the foundational building block for such gates. Through a sequence of lattice surgery splits and merges, it becomes possible to compose the full range of fault-tolerant quantum logic operations. Researcher Michael Kerschbaum elucidates that performing such logical operations fault-tolerantly under fixed spatial constraints would be straightforward if qubit repositioning were possible; lattice surgery ingeniously bypasses this limit.
This demonstration constitutes the first realization of lattice surgery on superconducting qubits—a milestone that significantly advances the field’s pursuit of scalable, error-resilient quantum computing. Nevertheless, challenges remain: to fully stabilize the splitting operation against phase-flip errors, the system would require scaling to at least 41 physical qubits per logical qubit. Despite these hurdles, this achievement demonstrates the feasibility of complex logical manipulations in current hardware platforms.
The implications of incorporating lattice surgery into superconducting qubit architectures are profound. By enabling fault-tolerant logical gates within the physical constraints of planar qubit arrays, this technique paves a crucial path toward quantum devices composed of thousands, or even millions, of qubits. These larger quantum processors could handle significantly more intricate algorithms and error rates, bringing practical quantum computing closer than ever before.
Furthermore, the ability to perform quantum operations while dynamically correcting errors heralds a new era in quantum control precision and architectural design. The meticulous interplay of stabilizer measurements, selective readouts, and lattice surgery processes highlights how intricate quantum engineering must be to actualize reliable information processing beyond classical limits.
In summary, the Wallraff team’s experimental success at ETH Zurich and their collaborators represents a landmark step in the ongoing quest for usable quantum computers. Their lattice surgery approach cleverly navigates the spatial limitations inherent in superconducting qubits, effectively balancing quantum coherence and fault tolerance. As the technology matures and qubit numbers grow, such innovations will underpin the quantum revolution poised to transform computation, simulation, and encryption paradigms worldwide.
Subject of Research: Quantum error correction and fault-tolerant quantum operations in superconducting qubits
Article Title: Realizing lattice surgery on two distance-three repetition codes with superconducting qubits
News Publication Date: 30-Jan-2026
Web References:
DOI:10.1038/s41567-025-03090-6
Press release by Forschungszentrum Jülich (in German)
References:
Besedin, I., Kerschbaum, M. et al. Realizing lattice surgery on two distance-three repetition codes with superconducting qubits. Nat. Phys. (2026).
Image Credits: Quantum Device Lab / ETH Zurich
Keywords
Quantum computing, error correction, superconducting qubits, logical qubits, lattice surgery, surface codes, fault-tolerant quantum gates, bit-flip errors, phase-flip errors, quantum algorithms, quantum entanglement, quantum decoherence
