January 17, 2025 -- Researchers at AIST, in collaboration with Tokyo Denki University, have identified the origin of long-period electrical instability in silicon qubit devices for the first time. It is well known that the electrical characteristic of qubits, which are the basic elements of quantum computers, is not always kept constant and it changes over periods of a few tens of seconds or hours.

Indeed, such long-period electrical instability has been observed in commercially available quantum computers. Since the electrical instability induces errors in quantum calculation, a calibration procedure to tune the state of qubits is necessary. The calibration procedure often takes several hours, limiting the available time of the quantum computer. Long-period electrical instability is also observed in silicon qubit devices, but the cause of electrical instability has not yet been clarified. In this research, we have identified that the electron trapping phenomenon at the oxide/semiconductor interface is the origin of the electrical instability in fin-type qubit devices, which is one of the promising hosts for spin qubits to realize highly integrated quantum computers. This achievement provides a guideline for developing qubit manufacturing technology toward the stable operation of silicon quantum computers.

AIST is engaged in the research and development of silicon qubits and cryo-CMOS circuits and devices as the control/readout electronics of qubits for the realization of highly integrated quantum computers. In recent years, AIST has achieved world-leading research on cryo-CMOS devices clarifying the performance limiting factors in cryogenic operations such as on-current, switching characteristics, and noise performance.

Semiconductor Frontier Research Center in AIST has been conducting research on device technology for silicon quantum computers and has identified the origin of the long-period electrical instability in silicon fin-type qubits by utilizing the CMOS characterization techniques.