160 research outputs found
Pulse Width Modulation for Speeding Up Quantum Optimal Control Design
This paper focuses on accelerating quantum optimal control design for complex
quantum systems. Based on our previous work [{arXiv:1607.04054}], we combine
Pulse Width Modulation (PWM) and gradient descent algorithm into solving
quantum optimal control problems, which shows distinct improvement of
computational efficiency in various cases. To further apply this algorithm to
potential experiments, we also propose the smooth realization of the optimized
control solution, e.g. using Gaussian pulse train to replace rectangular
pulses. Based on the experimental data of the D-Norleucine molecule, we
numerically find optimal control functions in -qubit and -qubit systems,
and demonstrate its efficiency advantage compared with basic GRAPE algorithm
Experimental exploration over a quantum control landscape through nuclear magnetic resonance
The growing successes in performing quantum control experiments motivated the
development of control landscape analysis as a basis to explain these
findings.When a quantum system is controlled by an electromagnetic field, the
observable as a functional of the control field forms a landscape. Theoretical
analyses have revealed many properties of control landscapes, especially
regarding their slopes, curvatures, and topologies. A full experimental
assessment of the landscape predictions is important for future consideration
of controlling quantum phenomena. Nuclear magnetic resonance (NMR) is exploited
here as an ideal laboratory setting for quantitative testing of the landscape
principles. The experiments are performed on a simple two-level proton system
in a HO-DO sample. We report a variety of NMR experiments roving over
the control landscape based on estimation of the gradient and Hessian,
including ascent or descent of the landscape, level set exploration, and an
assessment of the theoretical predictions on the structure of the Hessian. The
experimental results are fully consistent with the theoretical predictions. The
procedures employed in this study provide the basis for future multispin
control landscape exploration where additional features are predicted to exist
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