Reservoir computing is a powerful machine learning paradigm for online time series processing. It has reached state-of-the-art performance in tasks such as chaotic time series prediction and continuous speech recognition thanks to its unique combination of high computational power and low training cost which sets it aside from alternatives such as traditionally trained recurrent neural networks, and furthermore is amenable to implementations in dedicated hardware, potentially leading to extremely compact and efficient reservoir computers. Recently the use of random quantum systems has been proposed, leveraging the complexity of quantum dynamics for classical time series processing. Extracting the output from a quantum system without disturbing its state too much is problematic however, and can be expected to become a bottleneck in such approaches. Here we propose a reservoir computing inspired approach to online processing of time series consisting of quantum information, sidestepping the measurement problem. We illustrate its power by generalizing two paradigmatic benchmark tasks from classical reservoir computing to quantum information and introducing a task without a classical analogue where a random system is trained to both create and distribute entanglement between systems that never directly interact. Finally, we discuss partial generalizations where only the input or only the output time series is quantum.
Oscillator-qubit generalized quantum signal processing for vibronic models: a case study of uracil cation
SKKU Advanced Institute of Nano Technology (SAINT), Sungkyunkwan University（成均馆大学 SKKU 纳米技术高级研究所 (SAINT)）；Ulsan National Institute of Science and Technology（蔚山科学技术院）；Yonsei University（延世大学）
Measurement-enabled online quantum processing with amplitude encoding
ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology（光子科学研究所，巴塞罗那科学与技术研究院）；Instituut-Lorentz, Universiteit Leiden（洛伦兹研究所，莱顿大学）；Applied Quantum Algorithms, Leiden University（莱顿大学应用量子算法）；Donostia International Physics Center（圣塞巴斯蒂安国际物理中心）
Direct estimation of arbitrary observables of an oscillator
National University of Singapore（新加坡国立大学）；Centre for Quantum Technologies, National University of Singapore（新加坡国立大学量子技术中心）；Horizon Quantum Computing, Singapore（新加坡地平线量子计算）；Palacký University（帕拉茨基大学）；Department of Optics, Palacký University（帕拉茨基大学光学系）；Department of Physics, National University of Singapore（新加坡国立大学物理系）
