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Description
Excitation of trapped-ion hyperfine qubits with fast optical Raman pulses enables faster-than-trap-period entangling gates with qubits of long coherence time for practical quantum computation. Achieving high-fidelity fast two-qubit gates requires high-quality spin-dependent kicks (SDKs), which form their fundamental building blocks for spin–motion coupling: a spin flip is accompanied by a momentum change whose sign depends on the spin state.
In precursory studies, the ideal parameter regimes needed to create SDKs with pulsed protocols were derived under three approximations: high-pulse number trains, instantaneous pulses and negligible ion motion [1, 2], which limit the fidelities achievable under realistic experimental conditions [3].
This work achieves theoretical characterization of all relevant control parameters that maximize the performance of single-ion SDKs for protocols compatible with experimental implementations involving a small number of fast pulses: Raman frequency difference, repetition time between pulses, Lamb–Dicke parameter, temperature, pulse duration and gate time. We show that low infidelity—below $10^{-3}$ for protocols with $\gtrsim10$ fixed-amplitude, equally-spaced, picosecond pulses—is attainable in gate times of a few nanoseconds, with a power-law decay as the number of pulses becomes larger. We demonstrate through analytical methods and numerical simulations that, within the model commonly used for infidelity optimization, pulse duration plays a crucial role, whereas ion secular motion has a negligible impact for nanosecond-scale protocols, with an error of the order of $10^{-5}$. This work lays the foundation for sub-microsecond trapped-ion quantum computing.
[1] J. Mizrahi, et al. Phys. Rev. Lett. 110, 203001 (2013).
[2] J. Mizrahi, et al. Appl. Phys. B 114, 45–61 (2014).
[3] J. D. Wong-Campos, et al. Phys. Rev. Lett. 119, 230501 (2017).
| Academic level | PhD student |
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