Researchers at RIKEN, Japan’s largest research institute, have taken a step towards building larger quantum processors with silicon spin qubits, the same material used in ordinary chips. The study was published in Nature Physics.
The team used a five-qubit array controlled through a single shared microwave line. The problem is that control signals shift the phase of neighbouring qubits and reduce precision when several work at the same time. The researchers created a pairwise calibration protocol that compensates for these shifts without calibrating every possible combination.
With qubits operated one at a time, gate fidelity was above 99.99%, with the best close to 99.999%. With up to three qubits operating simultaneously it stayed above 99.99%, and with all five in parallel it was about 99.9%.
The loss of coherence caused by the higher microwave power needed for parallel operation still has to be solved. The team wants to improve the device design, with the long-term goal of building a fault-tolerant silicon-based quantum computer.
