The R&D Item is responsible for overseeing the entire project and organising the quantum computer as a system and is working on three specific R&D tasks (#1, #2 and #3) in the diagram below.
The first is research on the development of a two-dimensional qubit array of qubits, which is a milestone in the process of scaling up silicon quantum computers. The second is the development of qubit high-precision control and high-sensitivity readout circuits, which are necessary to control this qubit array with high precision and read out quantum information with high sensitivity. The third is to develop the system architecture for operating the entire system as a computer. Through these efforts, we aim to realise a large-scale integrated silicon quantum computing system that utilises the features of silicon semiconductor technology.

In a study on two-dimensional qubit arraying, spin manipulation of one and two qubits was carried out through prototyping and evaluation of array structures. Spin manipulation sequences that further improve coherence in spin manipulation were investigated. In spin qubits, a qubit manipulation technique (Concatenated Continuous Driving: CCD) was developed to reduce external noise and extend the coherence time. CROT (Controlled-Rotation) spectra reflecting the entangled state of the two-qubit were observed, and a CROT-based two-qubit manipulation was successfully achieved.

In the research on qubit high-precision control and high-sensitivity readout circuits, the detailed design of a microwave generator circuit chip applying the Polar modulation method, a phase reduction method, was completed for further high-precision control of qubits, and power efficiency was improved by operating the amplitude modulation intermittently and the LO (Local Oscillator) block for phase modulation. The sampling PLL (Phase-Lock-Loop) method was adopted for the LO block for phase modulation to reduce the phase. As a result of the study, the jitter, which is a phase error component, was expected to be reduced from 137 fsec to 80 fsec.
In the system architecture study, the quantum operating system was extended to assist the experimentalist and a one-click qubit measurement system was developed to automate single-qubit Rabi oscillation measurements. Methods to automate the analysis process were investigated and the implementation of an automated calibration library was completed. Demonstration tests using natural silicon devices confirmed that automatic calibration can reduce the measurement time by 81%, as well as ensuring traceability of the operating state and confirming the automatic calibration functionality against temperature and device characteristic fluctuations.