Low-Latency Digital Signal Processing for Feedback and Feedforward in Quantum Computing and Communication
Yves Salathé, Philipp Kurpiers, Thomas Karg, Christian Lang, Christian Kraglund Andersen, Abdulkadir Akin, Sebastian Krinner, Christopher Eichler, Andreas Wallraff · Physical Review Applied · 2018
Feedback is a main component of many algorithms for quantum computing and communication. A key requirement for any quantum feedback scheme is that the $l\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}y$ of the feedback loop ($i.e.$ the time between beginning to measure a state and the end of feedback action on the state) must be significantly shorter than the coherence time of the system. In this work a superconducting qubit is initialized in its ground state by active feedback, using a field-programmable gate array (FPGA) with very short latency. This in-depth discussion of the FPGA-based processing unit provides a useful reference for future development of feedback electronics for quantum systems.