Offset-Charge-Tunable Transmon Qubit

99.37% Charge-Parity Detection Fidelity

Achieves high-fidelity mapping of charge-parity states onto qubit states via controllable coupling to offset charge, enabling ultra-low energy particle detection.

Yao-Yao, Jiang · Su, Tang · Yuxiang, Liu · Yi-Ming, Guo · Yidong, Song · Yu-Long, Li · Zeng, Y. · Xue, Guangming · Weijie, Sun · Mei-Ling, Li · Jin, Yirong · Wang, Junhua · Xuegang, Li · Yu, Haifeng

Science China: Physics, Mechanics and Astronomy 2026

Specifications

Single-qubit gate fidelity

{'zh': '99.96', 'en': '99.96'} %

Charge-parity mapping fidelity

{'zh': '99.37', 'en': '99.37'} %

Continuous monitoring fidelity

{'zh': '93.4', 'en': '93.4'} %

Advantages

Detection fidelity reaches 99.37%

By combining a net-zero pulse and a spin-echo sequence, the charge-parity state is precisely mapped onto the qubit state, achieving high detection fidelity.

Single-qubit gate fidelity of 99.96%

By applying a gate control line to tune the offset charge, a single-qubit gate fidelity up to 99.96% is achieved, providing a basis for high-precision quantum operations.

Continuous monitoring fidelity exceeds 93.4%

Continuous monitoring of the charge-parity state is performed at a 4-microsecond sampling interval with a fidelity of over 93.4%, suitable for long-term observation.

Applications

• Quantum Precision Measurement：High-fidelity mapping of charge-parity states onto qubits offers a new tool for precision measurement.
• Particle Detection：Enables detection of ultra-low energy particles for rare event searches.
• Superconducting Quantum Circuits：This offset-charge-tunable transmon can be directly integrated into existing superconducting quantum circuits.