RIKEN and IBM Researchers Advance Precision Control in Quantum Processors
New breakthroughs in silicon spin qubit accuracy and real-time error correction bring the industry closer to stable, large-scale quantum computing hardware.
< h2> Overcoming Simultaneous Operation Errors in Silicon Qubits
Silicon spin qubits have long been favored as a pathway to practical quantum hardware because they can be produced using the same semiconductor manufacturing methods that power today’s computer chips. However, researchers have faced a significant hurdle: when multiple qubits are controlled at the same time, their operations tend to become less accurate. Building practical, large quantum computers will require scientists to control many qubits simultaneously while keeping errors to a minimum.
Researchers at the RIKEN Center for Emergent Matter Science and their collaborators have now made important progress toward solving this problem. In a study published in Nature Physics, the team demonstrated highly accurate control of several silicon spin qubits operating simultaneously. Their experiments used an array of five qubits connected to a shared microwave control line. By identifying a major cause of errors during simultaneous operation, the scientists developed a technique to reduce those errors and maintain precision.
The team traced much of this problem to a phenomenon called the AC Stark shift. This effect occurs when microwave control signals alter a qubit’s effective energy levels, producing changes in the phase of its quantum state. Those phase shifts can disrupt the intended operation of individual qubits, particularly when several are being controlled at once. To counteract the problem, the team created a calibration method that compensates for these unwanted shifts. Rather than separately calibrating every possible combination of qubits, the technique relies on calibrations performed between individual qubits and the shared control line, offering a more efficient path to scaling up processor arrays.
< h2> The Role of AC Stark Shift in Quantum Interference
Unlike conventional computers, which store information as bits representing either 0 or 1, quantum computers use quantum bits, or qubits, that can exist in combinations of both states. Silicon spin qubits store this information using the spin of individual electrons confined within silicon. Performing reliable quantum calculations requires extremely precise control over these electron spins. Microwave signals provide that control, but operating multiple qubits simultaneously can create unwanted effects that interfere with their accuracy.
The researchers identified the AC Stark shift as a primary source of simultaneous operation errors. This effect occurs when microwave control signals alter a qubit’s effective energy levels, producing changes in the phase of its quantum state. Those phase shifts can disrupt the intended operation of individual qubits, particularly when several are being controlled at once. The team’s new calibration method compensates for phase shifts caused by microwave interference between qubits, allowing the system to maintain an accuracy of approximately 99.9% even when all five qubits were running at once.
Leon Camenzind, a RIKEN research scientist and co-first author who supervised the experiments, explained the significance of the results: “This shows that high-fidelity control can be maintained even when several qubits are operated at the same time and represents an important step toward scaling up silicon-based quantum processors.”
< h2> Implementing Real-Time Error Correction for Fault Tolerance
Fault tolerance remains one of the most formidable challenges in quantum computing. Classical computers can rely on redundancy and simple checksums to detect and correct errors, but quantum systems are far more delicate. Quantum decoherence occurs when qubits are not sufficiently isolated from environmental noise, introducing errors into calculations. Global government investment in quantum computing reached $10 billion by April 2025, underscoring the strategic importance of overcoming these hardware limitations.
A study using an IBM Quantum Heron processor demonstrated real-time error correction across 156 qubits. The experiment involved nearly 5,000 qubit operations, alternating between scrambling (spreading chaos through the system) and controlling (resetting qubits where needed). The system was configured with two alternating tasks designed to both introduce chaos and then correct for it, which is the same basic mechanism that will be needed for fault tolerance.
To test their new approach, the researchers used a 156-qubit IBM Quantum Heron processor, connecting together as many as 100 qubits at once. Across nearly 5,000 qubit operations and almost 5,000 checks and resets, order was resumed when the checks and resets made up more than half of the operations overall. As more qubits were added, the tipping point became more well defined in the data—evidence that this is a true quantum effect and a phase transition, like water turning into ice in a unified way. The agreement between the experiment and the theory showed that this was not an accidental feature of a small circuit; it was collective behavior emerging across the quantum system.
< h2> Scaling From Experimental Prototypes to Stable Processors
The RIKEN breakthrough addresses the immediate problem of controlling multiple qubits simultaneously, while the IBM study tackles the longer-term requirement of fault tolerance. Together, these advances represent parallel progress in the two fronts necessary for stable, large-scale quantum computing: precise control of quantum states and the ability to maintain those states during computation.
Quantum computers use qubits that exist in a superposition of states, unlike classical bits. Quantum decoherence occurs when qubits are not sufficiently isolated from environmental noise. Large-scale quantum computers have the theoretical potential to break widely used encryption schemes, which has driven significant investment from governments and industry. The new calibration method for silicon spin qubits and the real-time error correction demonstrated on the IBM Heron processor bring the industry closer to hardware that can support practical, fault-tolerant quantum computation.
Future implications for cryptographic security remain a key consideration. As quantum hardware matures, the ability to perform reliable calculations with an increasing number of qubits will determine whether these machines transition from experimental milestones to tools for specialized tasks such as physical simulations and optimization problems. The progress reported by RIKEN and IBM suggests that the technical barriers to scaling are being addressed, one calibration and one error-correction cycle at a time.
Sources
- Quantum computing
- Scientists overcome a hidden obstacle to more powerful quantum computers
- We're a Step Closer to Quantum Computers That Can Correct Their Own Mistakes
Photo: Department for Science, Innovation & Technology (CC BY 2.0)
