2024/12/27 by Ahn, Seongjin, Park, Kichan, Cho, Daehee +3
#FOS: Physical sciences #Quantum Physics (quant-ph)
paper · doi:10.48550/arxiv.2412.19561
Quantum information processing comprises physical processes, which obey the quantum speed limit (QSL): high speed requires strong driving. Single-qubit gates using Rabi oscillation, which is based on the rotating wave approximation (RWA), satisfy this bound in the form that the gate time T is inversely proportional to the Rabi frequency Ω, characterizing the driving strength. However, if the gate time is comparable or shorter than the qubit period T0 ≡ 2π/ ω0, the RWA actually breaks down since the Rabi frequency has to be large compared to the qubit frequency ω0 due to the QSL, which is given as T \gtrsim π/Ω. We show that it is possible to construct a universal set of single-qubit gates at this strong-coupling and ultrafast regime, by adjusting the central frequency ω and the Rabi frequency Ω of the driving pulse. We observe a transition in the scaling behavior of the central frequency from the long-gate time regime (T ≫ T0) to the short-gate time (T ≪ T0) regime. In the former, the central frequency is nearly resonant to the qubit, i.e., ω≃ ω0, whereas in the latter, the central frequency is inversely proportional to the gate time, i.e., ω∼ π/T. We identify the transition gate time at which the scaling exponent n of the optimal central frequency ω∼ Tn changes from n=0 to n=-1.