Nanohertz Pendulum toward Macroscopic Entanglement under Structural Damping

2026/08/03 by Azusa Sawada, Hina Nakano, Kanta Watanabe +3
Physics and Astronomy · #quant-ph #physics.ins-det

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arxiv created 2026/08/03 · arxiv updated 2026/08/04

Abstract

Pendulums are attractive for macroscopic quantum control because gravity dilution reduces mechanical loss, while the 1/f force-noise spectrum associated with structural damping allows nearly lossless trapping to suppress the thermal noise sampled at an upward-shifted resonance. The same 1/f spectrum, however, produces a low-frequency tail that penalizes entanglement. With 10% detection loss, we find that this tail raises the required back-action-to-thermal force-noise ratio by about 50%, corresponding to a required suspension gain G_{\rm req}=1.49. To overcome this structural-noise penalty, we realize a 7-mg pendulum suspended by a stepped fused-silica fiber, with an energy-decay rate Γ/2π=361(39) nHz (Q≡ω₀/Γ=7.3(8)×10⁶) at ω₀/2π=2.63 Hz. The reduction in ω₀Γ yields a measured gain G_q≃2.5 relative to the previous monolithic device, exceeding the requirement.

Citations

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