Quantum Breakthrough Brings Fault‑Tolerant Computing Closer * Science and Technology Times

Researchers at ETH Zurich have demonstrated a new method for performing quantum operations while correcting errors continuously, addressing one of the biggest obstacles in building practical quantum computers.
Their experiment uses a technique called lattice surgery to split a protected qubit into two entangled ones without losing stability.
The work represents a significant step toward scalable, fault‑tolerant quantum machines.

A New Approach to Quantum Stability

Quantum computers promise major advances in fields such as materials science and cryptography, yet they remain extremely difficult to operate due to the fragility of qubits. These quantum units are highly sensitive to disturbances, especially during calculations, where even a single error can derail an entire operation. Errors typically appear as bit flips or phase flips, each capable of altering stored information in unpredictable ways. Preventing such disruptions has long been one of the central engineering challenges in quantum computing.

To preserve information, researchers often combine many physical qubits into a single logical qubit. This structure allows continuous error correction, making long‑term storage more reliable. Running algorithms, however, requires manipulating qubits through quantum gates, and performing these operations without introducing new errors has proven far more difficult. The need to compute while maintaining protection has been a major barrier to scaling quantum systems.

A team at ETH Zurich has now demonstrated a method that addresses this problem directly. Their approach allows quantum operations to proceed while error correction remains active. The results show that protected qubits can be manipulated without sacrificing stability, bringing practical quantum computing a step closer.

Lattice Surgery Enables Mid‑Operation Error Correction

The experiment, led by Professor Andreas Wallraff in collaboration with researchers from the Paul Scherrer Institute and theorists at RWTH Aachen University and Forschungszentrum Jülich, demonstrates how lattice surgery can be used to manipulate superconducting logical qubits. Their findings, published in Nature Physics, show that operations can be performed while correcting errors continuously. This marks an important advance toward fault‑tolerant quantum computing.

Classical error correction relies on copying information, but quantum data cannot be cloned. Instead, information must be distributed across entangled qubits, which makes the process more complex. Quantum systems also suffer from phase flip errors, which have no classical equivalent and require specialized correction techniques. These challenges make mid‑operation error correction particularly difficult.

Surface codes offer one solution by spreading a logical qubit’s information across multiple physical qubits. Stabilizers monitor the system for bit and phase flips without directly measuring the data qubits. This structure allows errors to be detected and corrected repeatedly. Performing logical operations, however, introduces new opportunities for errors, especially in systems where qubits cannot be moved and only interact with neighbors.

To overcome these constraints, the ETH Zurich team used lattice surgery. They began with a logical qubit encoded across seventeen physical qubits arranged in a square pattern. Stabilizers were measured every 1.66 microseconds to correct errors. At a key moment, three central data qubits were measured, effectively splitting the logical qubit into two entangled halves. Bit flip correction continued throughout the process, and afterward each half resumed independent error correction.

A First for Superconducting Qubits

The researchers note that lattice surgery can serve as a foundational operation from which more complex gates, such as controlled‑NOT operations, can be constructed. This demonstration is the first time lattice surgery has been performed on superconducting qubits, marking a milestone for the field. While the current setup corrects bit flips during the split, stabilizing the process against phase flips would require a larger system of around forty‑one physical qubits.

Despite these limitations, the experiment represents a significant step toward building quantum computers capable of running long, complex algorithms without being overwhelmed by errors. The ability to manipulate logical qubits while maintaining protection is essential for scaling systems to thousands of qubits. Researchers view this as a key requirement for achieving practical, fault‑tolerant quantum computing.

The work also highlights the importance of combining theoretical insights with experimental advances. Lattice surgery has been studied conceptually for years, but implementing it on real hardware required precise control over superconducting qubits and stabilizer measurements. The success of this experiment demonstrates that such techniques are becoming feasible in laboratory settings.

Future research will focus on expanding the method to larger qubit arrays and integrating additional error‑correction layers. Achieving full fault tolerance will require protecting against both bit and phase flips during all operations. The ETH Zurich team’s results suggest that this goal is increasingly within reach.