Exceptional sensitivity near the bistable transition point of a hybrid quantum system

Nature Physics (2026)Cite this article Phase transitions can dramatically alter system dynamics, potentially improving device performance. Exceptional points, in which the eigenvalues and corresponding eigenvectors of a coupled linear system coalesce, are particularly relevant for sensing applications because they can increase sensor response to external perturbations. However, the coalescence of eigenstates at linear exceptional points amplifies noise, negating the signal-to-noise-ratio enhancement. Here we overcame this limitation using nonlinearity that produces an exceptionally high signal-to-noise ratio around a bistable transition point. We coupled a diamond nitrogen-vacancy quantum sensor to a nonlinear van der Pol oscillator, forming a self-oscillating hybrid system that exhibits both single-valued and bistable phases. The boundaries between these phases are marked by both adiabatic and deterministic non-adiabatic transitions that enable chiral state switching and state coalescence at the bistable transition point. Nitrogen-vacancy magnetometry performed near the bistable transition point exhibited a 17-fold enhancement in the signal-to-noise ratio. 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TrusheimDepartment of Physics, University of Massachusetts Boston, Boston, MA, USAKurt JacobsSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarH.W. and M.E.T. created the set-up and conducted the experiments. H.W., K.J. and M.E.T. developed the theory. D.F. and M.E.T. conducted the preliminary experiment. H.W. and M.E.T. prepared the paper. Y.H. assisted with the time-domain measurements. All authors discussed the results and revised the paper. M.E.T. and D.R.E. supervised the project.Correspondence to Hanfeng Wang or Matthew E. Trusheim.The authors declare no competing interests.Nature Physics thanks Dmitry Budker, Jingyan Xu, Chong Zu and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.a, The experimental setup for the NV-VdP system, we use a microwave cavity and two coupling loops to form a loop oscillator, we use a directional coupler to direct the signal out, this signal is then directed to a heterodyne measurement, where an external signal generator is used to move the microwave signal to an intermediate frequency with a frequency of several MHz. We use a series of amplifiers and attenuators to reach a low microwave input to the system so that the spin is not saturated for the NV-cQED system. b, COMSOL simulation for the dielectric resonator. Our dielectric resonator contains two cylinder with outer diameter: 0.669 inch; inner diameter: 0.236 inch; Thickness: 0.314 inch. c, The cavity measurement with critical coupling.Source dataSupplementary Figs. 1–7.Source data for Fig. 1.Source data for Fig. 2.Source data for Fig. 3.Source data for Fig. 4.Source data for Extended Data Fig. 1.Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.Reprints and permissionsWang, H., Jacobs, K., Fahey, D. et al. Exceptional sensitivity near the bistable transition point of a hybrid quantum system. Nat. Phys. (2026). https://doi.org/10.1038/s41567-026-03217-3Download citationReceived: 09 June 2025Accepted: 12 February 2026Published: 20 March 2026Version of record: 20 March 2026DOI: https://doi.org/10.1038/s41567-026-03217-3Anyone you share the following link with will be able to read this content:Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative