TITLE: Proximity, for better and for worse: photonic-integrated readout of strained silicon nitride nanomechanical resonators
AUTHOR: Guillermo Arregui - Laboratory of Photonics and Quantum Measurements, EPFL
INVITED BY: Pedro David García, ICMM-CSIC
WHEN: September, 2nd – 12PM
WHERE: Sala de Seminarios, ICMM
ABSTRACT: Guillermo will present recent work on the photonic-integrated readout of silicon nitride nanomechanical resonators, including non-contact friction in ultracoherent resonators and photonic-integrated mid-infrared detection, as well as the prospects for scalable and multiplexed nanomechanical sensor arrays.
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. Turning that coherence into sensitivity requires a displacement readout whose imprecision lies far below the thermal motion of theresonator, 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√n on 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. In the second, the perturbation is the signal and the same friction is harmless: its 1/Ωm scaling places it well below the detection floor 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 3.35 pW/ Hz for a broadband thermal source. 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.
