Researchers from the Quantum Hardware group at CIC nanoGUNE, in collaboration with the British company Quantum Motion, have demonstrated an advanced readout sensor for spin qubits that, while being more compact that previous designs, can reach the level of readout precision needed to implement quantum error correction protocols. The study has been published in the journal Nature Sensors.

One of the greatest challenges facing quantum computing is increasing the number of interconnected qubits that can be integrated onto a single chip while maintaining the ability to control and read them precisely. The study involved advancing a new type of sensor called a single-electron box (SEB) whose smaller footprint enables fitting on a chip more interacted qubits while retaining the capability to read them. Besides, the invention has been integrated in a silicon chip fabricated using the industry standard metal–oxide–semiconductor (MOS) process, the most widely used in modern digital and analogue electronics. Despite being physically more compact than previous models, the new sensor achieves a spin readout fidelity comparable to that of the most advanced state-of-the-art devices.

According to the research team, “the results show that it is possible to reduce the physical footprint of these sensors without sacrificing performance.” This improvement is particularly significant because it frees up space inside the quantum processor, enabling a greater number of interconnected qubits to be integrated on the same surface. As a result, “it paves the way for the development of more powerful and scalable quantum processors,” they add.

Beyond quantum computing, SEB sensors offer a wide range of applications in advanced electronics. These include nanoscale thermometry, high-resolution energy spectroscopy, and electrical signal processing in the frequency domain. These capabilities enable parametric quantum-limited amplification or frequency mixing, which are key technologies for developing high-precision electronic systems.