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arXiv:2209.09869 · Physical Review Applied

Quantum optimal control without arbitrary waveform generators

Qiming Chen, HERSCHEL A. RABITZ, Re-Bing Wu

Published Dec 8, 2023• 3 citations
arXivHTMLPDF

Abstract

Simple, precise, and robust control is demanded for qubit operations on large quantum information processors. However, existing routes to high-fidelity quantum control heavily rely on arbitrary waveform generators that are difficult to scale up. Here, we show that the arbitrary control of a quantum system can be achieved by simply turning the control fields on and off in a proper sequence. The switching instances can be designed using conventional quantum optimal control algorithms, while the required computational resources for matrix exponentials can be substantially reduced. We demonstrate the flexibility and robustness of the resulting control protocol, and illustrate it in the context of superconducting quantum circuits. We expect this proposal to be achievable with current semiconductor and superconductor technologies, which offers a significant step towards scalable quantum computing.

DOI
10.1103/physrevapplied.20.064016

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Simple, precise, and robust control is demanded for qubit operations on large quantum information processors. However, existing routes to high-fidelity quantum control heavily rely on arbitrary waveform generators that are difficult to scale up. Here, we show that the arbitrary control of a quantum system can be achieved by simply turning the control fields on and off in a proper sequence. The switching instances can be designed using conventional quantum optimal control algorithms, while the required computational resources for matrix exponentials can be substantially reduced. We demonstrate the flexibility and robustness of the resulting control protocol, and illustrate it in the context of superconducting quantum circuits. We expect this proposal to be achievable with current semiconductor and superconductor technologies, which offers a significant step towards scalable quantum computing.
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Signal generators for qubit control and measure-ments play a key role in quantum computers in terms of latency and scalability. Typically, the control pulses are generated by arbitrary waveform generators (AWGs) via preloaded lookup tables. However, this method lacks the flexibility to adjust phase and frequency in complicated programs, such as variational quantum eigensolvers (VAE) or pulse shape optimization al-gorithms. Therefore, we propose a quantum control system composed of a quantum control processor (QCP) and a run-time waveform-configurable signal generator in this work. For the signal generator, we developed a parallelized direct digital synthesis (DDS) structure to adaptively generate waveforms without requiring the entire waveform to be preloaded. The QCP, based on HiSEP-Q, is optimized with a deeper pipelined architecture to increase frequency and match the high bandwidth of signal generators. Additionally, we introduce a synchronization architecture in the QCP to manage uneven delays among different generation threads. Validated on the ZCU216 platform, our system achieves flexible signal generation with an average latency of 20 ns and reduces memory usage by more than 50%.