By Guillermo Arregui, from the Laboratory of Photonics and Quantum Measurements (Swiss Federal Institute of Technology Lausanne (EPFL), CH-1015 Lausanne, Switzerland).
Hosted by IMB-CNM researchers Mar Álvarez and Carlos Domínguez.
About the talk
Tensile-stressed silicon nitride nanomechanical resonators are among the most coherent mechanical oscillators available: dissipation dilution and soft clamping push their quality factors beyond 109 at room temperature, making them exquisite transducers of force, mass and heat [1]. Turning that coherence into sensitivity requires a displacement readout whose imprecision lies far below the thermal motion of the resonator, which cavity-enhanced optical interferometry delivers. Conventionally the cavity is assembled from bulk optics, aligned and mode-matched device by device. Photonic integration replaces it by the near field of a waveguide or microresonator patterned a few hundred nanometres away, giving an alignment-free, lithographically defined and scalable readout at the price of a far closer material environment.
In this talk I will present two sensing experiments that expose either side of that trade-off. In the first, the measured perturbation is an unwanted one: the dielectric that must sit a few hundred nanometres from an ultracoherent resonator in order to read it out introduces non-contact friction, degrading the mechanical coherence. With thermal force noise below 1 aN/√Hz, beyond the reach of the best scanning-probe cantilevers, these resonators resolve that friction at separations two to three orders of magnitude larger than the nanometre-scale tip-sample distances at which it had previously been observed - an intrinsic limit on integrated readout that doubles as a uniquely sensitive probe of dissipation [2]. In the second, the perturbation is the signal and the same friction is harmless: its 1/Ωm scaling places it well below the detection fl oor of the higher-frequency, moderate-Q resonators used here, so that proximity becomes a pure asset. In a photonic-integrated mid-infrared detector covering 2.5-14 µm, a trampoline resonator coated with an impedance-matched ultrathin platinum absorber is read out by an on-chip microring, reaching a noise-equivalent power of 3.35pW/√Hz for a broadband thermal source [3]. I will close on the scaling argument that motivates integration in the first place: many resonators sharing one photonic bus, turning single devices into multiplexed sensor arrays at no additional fabrication complexity.
References
[1] N. J. Engelsen, A. Beccari and T. J. Kippenberg, Ultrahigh-quality-factor micro- and nanomechanical resonators using dissipation dilution, Nature Nanotechnology 19, 725 (2024).
[2] A. Arabmoheghi, A. Zicoschi, G. Arregui, M. J. Bereyhi, Y. Xia, N. J. Engelsen and T. J. Kippenberg, Non-contact friction in ultracoherent nanomechanical resonators near dielectric materials, Nature Physics (2026).
[3] G. Arregui, A. Arabmoheghi, A. Zicoschi, X. Ji, S. Umesh Hulyal, S. Kenning, Y. Xia, S. Bhave and T. J. Kippenberg, A broadband mid-infrared detector based on photonic integrated circuits and trampoline mechanical resonators, Proceedings of SPIE 14086, 1408629 (2026).
