Optimal Control of Spin Qudits Subject to Decoherence Using Amplitude-and-Frequency-Constrained Pulses
arxiv(2024)
摘要
Quantum optimal control theory (QOCT) can be used to design the shape of
electromagnetic pulses that implement operations on quantum devices. By using
non-trivially shaped waveforms, gates can be made significantly faster than
those built by concatenating monochromatic pulses. Recently, we applied this
technique to the control of molecular spin qudits modelled with Schrödinger's
equation and showed it can speed up operations, helping mitigate the effects of
decoherence [Phys. Rev. Appl. 17, 064028 (2022)]. However, short gate
times result in large optimal pulse amplitudes, which may not be experimentally
accessible. Introducing bounds to the amplitudes then unavoidably leads to
longer operation times, for which decoherence can no longer be neglected. Here,
we study how to improve this procedure by applying QOCT on top of Lindblad's
equation, to design control pulses accounting for decoherence already in the
optimization process. In addition, we introduce a formulation that allows us to
bound the maximum amplitude and frequency of the signals, which are the typical
limitations of waveform generators. The pulses we obtain consistently enhance
operation fidelities compared to those achieved with Schrödinger's equation
across various target gates and durations, demonstrating the flexibility and
robustness of our method. The improvement is larger the shorter the spin
coherence time T_2.
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