Journal
NATURE COMMUNICATIONS
Volume 13, Issue 1, Pages -Publisher
NATURE PORTFOLIO
DOI: 10.1038/s41467-022-32610-8
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Funding
- German Science Foundation (DFG) [SPP1601, FOR2724]
- European Research Council (ASTERIQS, SMel, ERC grant) [742610]
- Max Planck Society
- project QC4BW
- QTBW
- Hong Kong Research Grants Council General Research Fund Project [143000119]
- European Research Council (ERC) [742610] Funding Source: European Research Council (ERC)
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Conventional nonlinear spectroscopy can only access a limited set of correlations in a quantum system, while quantum nonlinear spectroscopy can extract arbitrary types and orders of correlations. The authors used quantum nonlinear spectroscopy to measure fourth-order correlations and identified Gaussian noises, random-phased AC fields, and quantum spins.
Conventional nonlinear spectroscopy, which use classical probes, can only access a limited set of correlations in a quantum system. Here we demonstrate that quantum nonlinear spectroscopy, in which a quantum sensor and a quantum object are first entangled and the sensor is measured along a chosen basis, can extract arbitrary types and orders of correlations in a quantum system. We measured fourth-order correlations of single nuclear spins that cannot be measured in conventional nonlinear spectroscopy, using sequential weak measurement via a nitrogen-vacancy center in diamond. The quantum nonlinear spectroscopy provides fingerprint features to identify different types of objects, such as Gaussian noises, random-phased AC fields, and quantum spins, which would be indistinguishable in second-order correlations. This work constitutes an initial step toward the application of higher-order correlations to quantum sensing, to examining the quantum foundation (by, e.g., higher-order Leggett-Garg inequality), and to studying quantum many-body physics. Signals that look the same from their low-order correlations can often be distinguished by looking at higher-order ones. Here, the authors exploit the sensitivity of quantum nonlinear spectroscopy to fourth-order correlations to identify Gaussian noises, random-phased AC fields, and quantum spins.
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