QDev Seminar: Jun Yoneda
Quantum Functional System Research Group Center for Emergent Matter Science, RIKEN Hirosawa, Japan
Microwave engineering for high fidelity spin qubit control in the presence of a self-induced frequency shift
Spins confined in silicon quantum dots are an attractive solid-state qubit system, especially in terms of foundry compatibility. As the qubit quality factor increases (with a gate time orders of magnitude shorter than the coherence time), the control fidelity can be easily degraded by small unitary errors, necessitating precise characterization and compensation of their influence. In this talk, we first show that the precession frequency of Si/SiGe electron spin qubits [1,2] will shift appreciably during a microwave burst, which would limit the electric-dipole spin resonance control fidelity below 99.8% when only conventional, amplitude-modulated pulses are used. Part of the observed shift may be explained by the heating effect, but the overall physical origin remains unknown and will require further investigation. Notwithstanding, we present a way to improve the fidelity by introducing a quadrature control method  inspired by techniques used in superconducting qubits . We validate this approach experimentally by demonstrating gate fidelities > 99.9%. Our finding facilitates high fidelity manipulations of spin qubits in quantum dots subject to systematic phase errors.
 Takeda, K. et al. A fault-tolerant addressable spin qubit in a natural silicon quantum dot. Sci. Adv. 2, e1600694 (2016).
 Yoneda, J. et al. A quantum-dot spin qubit with coherence limited by charge noise and fidelity higher than 99.9%, Nat. Nanotechnol. 13, 102–106 (2018).
 Takeda, K., Yoneda, J. et al. submitted.
 Lucero, E. et al. Reduced phase error through optimized control of a superconducting qubit. Phys. Rev. A 82, 042339 (2010).