Abstract
In force sensing, optomechanics, and quantum motion experiments, it is typically advantageous to create lightweight, compliant mechanical elements with the lowest possible force noise. Here we report wafer-scale batch fabrication and characterization of high-aspect-ratio, nanogram-scale Si$_3$N$_4$ "trampolines" having quality factors above $4 \times 10^7$ and ringdown times exceeding five minutes (1 mHz linewidth). We measure a thermally limited force noise sensitivity of 16.2$\pm$0.8 aN/Hz$^{1/2}$ at room temperature, with a spring constant ($\sim$1 N/m) 2-5 orders of magnitude larger than those of competing technologies. We also characterize the suitability of these devices for high-finesse cavity readout and optomechanics applications, finding no evidence of surface or bulk optical losses from the processed nitride in a cavity achieving finesse 40,000. These parameters provide access to a single-photon cooperativity $C_0 \sim 8$ in the resolved-sideband limit, wherein a variety of outstanding optomechanics goals become feasible.
Highlights
Advances in nanofabrication over the past decades have enabled the growth and patterning of pristine materials, and the creation of mechanical force sensors of extraordinary quality
Cantilevers sensitive to attonewton forces at room temperature have been fabricated from silicon (50 aN=Hz1=2 [1]) and diamond (26 aN=Hz1=2 [2]) using “top-down” techniques, while at cryogenic temperatures, “bottom-up-fabricated” devices have achieved 1 zN=Hz1=2 [3]
Top-down devices are currently not as sensitive at low temperatures but outperform at higher temperatures; they are compatible with a wide variety of probes and naturally integrate with other on-chip systems
Summary
Advances in nanofabrication over the past decades have enabled the growth and patterning of pristine materials, and the creation of mechanical force sensors of extraordinary quality. Cantilevers sensitive to attonewton forces at room temperature have been fabricated from silicon (50 aN=Hz1=2 [1]) and diamond (26 aN=Hz1=2 [2]) using “top-down” techniques, while at cryogenic temperatures, “bottom-up-fabricated” devices (e.g., carbon nanotubes) have achieved 1 zN=Hz1=2 [3] These complementary approaches carry with them an important trade-off: Whereas bottom-up techniques can assemble a small number of atoms to produce exquisite low-temperature sensors, the technology is comparatively young, and it is difficult to incorporate additional structures and/or probes. [16] (submitted simultaneously), has an intrinsic force noise below 20 aN=Hz1=2 at room temperature (293 K), which is the lowest among solid mechanical force sensors This is accompanied by spring constants Keff ∼ 1 N=m that are 2–4 orders of magnitude higher than existing devices of comparable sensitivity [1,2]. Consistent with recent simulations [19], we find that the majority of this “clipped” light is, in many cases, recovered by the cavity
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