Peng Xinhua’s research group at the Key Laboratory of Microscopic Magnetic Resonance of the Chinese Academy of Sciences at the University of Science and Technology of China and Liu Renbao’s research group at the Chinese University of Hong Kong have made important progress in the high-precision measurement of timing correlations in open quantum many-body systems. Using quantum channels synthesized by controllable physical processes, they proposed a theoretical scheme for selectively measuring any type of timing correlations in open quantum many-body systems, and successfully detected fourth-order quantum timing correlations in nuclear spin systems for the first time. The relevant research results were published online on May 16, 2024 in the international academic journal Physical Review Letters under the title “Selective Detection of Dynamics-Complete Set of Correlations via Quantum Channels” [ Phys. Rev. Lett. 132 , 200802 (2024)].
The correlation between physical quantities is crucial for the understanding of many-body systems and for the development of quantum technologies. In order to comprehensively describe the dynamics of a physical system, all temporal correlation information in the system is required, that is, a dynamically complete set of temporal correlations. For quantum many-body systems, the non-commutability of physical quantities (operators) brings various complex inequivalent forms to quantum correlations. However, current measurement schemes can only extract a few special forms of timing correlation information, and so far there is no systematic and feasible scheme to extract all types of timing correlation information in a dynamically complete set. In 2019, Professor Liu Renbao of the Chinese University of Hong Kong proposed an arbitrary quantum timing correlation measurement scheme based on continuous weak measurements [ Phys. Rev. Lett. 123 , 050603 (2019)]. However, as the number of measurements increases with the continuous weak measurement method, the signal-to-noise ratio of high-order quantum correlation signals drops sharply, making its experimental implementation very difficult. Therefore, how to systematically and selectively measure dynamically complete arbitrary quantum timing correlations has always been a challenging scientific problem.
Figure: (a) The dynamic evolution of quantum many-body systems derives various forms of quantum timing correlations. (b) Quantum circuit for selective measurement of arbitrary N-order quantum timing correlation. (c) Experimental measurement of fourth-order quantum correlation. (d) Numerical simulation of quantum optimization control based on high-order quantum timing correlation.
In order to solve the above challenges, Peng Xinhua’s research group and Liu Renbao’s research group collaborated to innovatively propose any type of quantum timing correlation selective measurement protocol based on controllable physical process synthesis of quantum channels, see Figures (a) and (b). This protocol not only greatly improves the measurement signal-to-noise ratio of high-order quantum correlations and reduces the difficulty of experimental implementation, but is also applicable to a wider range of experimental systems, including single spin and ensemble quantum systems. Using high-precision quantum control of nuclear magnetic resonance, this work experimentally verified the feasibility of the measurement protocol on a multi-spin system, and successfully measured the fourth-order quantum timing correlation in a quantum multi-body system for the first time, as shown in Figure (c). Furthermore, this work applies the high-order quantum correlation information obtained experimentally to high-precision quantum optimization control tasks. The numerical simulation results shown in Figure (d) show that for single-spin quantum gates (such as Pauli-X gates), compared with previous optimization methods that only use second-order quantum correlation information, when the fourth-order quantum correlation is considered in the optimization control After correction, the quantum gate fidelity can be improved from 99.987% to 99.99996%.
This work has potential application value in the fields of quantum information and quantum many-body physics. On the one hand, the complete extraction of all quantum timing correlation information in the quantum thermal library provides a method to completely characterize quantum noise, which is very important for quantum information technology (such as quantum control and quantum precision measurement). On the other hand, since the dynamic behavior of a quantum many-body system can be decomposed into a superposition of various quantum timing correlations step by step, accurate measurement of any quantum timing correlation can help us better characterize and understand the non-linear behavior of quantum many-body systems. Equilibrium properties. Future directions plan to further improve the signal-to-noise ratio and spectral resolution of measuring quantum timing correlations by mitigating decoherence effects and utilizing quantum resources (such as entanglement and compression). The reviewer spoke highly of this work: ” It’s a significant addition to the field of quantum metrology, offering insights into quantum systems dynamics. ” ).
Oregonstate News Blog 