The platform

The experiment couples a single neutral strontium-88 atom, held in an optical tweezer, to a suspended Si₃N₄ photonic-crystal defect cavity resonant with the narrow 689 nm ¹S₀ → ³P₁ intercombination transition. The cavity hosts a co-localised nanomechanical mode of the same membrane, giving us a three-way interface between the atom, the optical mode, and a macroscopic mechanical oscillator.

Strontium is a convenient platform here for three reasons. Its singlet–triplet level structure provides both a broad 461 nm transition for laser cooling and a narrow 7.5 kHz 689 nm transition for high-cooperativity coupling to the photonic-crystal cavity. The bosonic ⁸⁸Sr isotope has zero nuclear spin, so the level structure stays simple. 

Why it matters

A coherent atom–phonon interface is one of the cleaner routes to preparing macroscopic mechanical objects in non-classical states. The atom is a well-understood, low-noise quantum emitter; the membrane is a gram-scale-by-comparison mechanical object that, if entangled with the atom, would sit firmly in the regime where quantum mechanics and classical mechanics meet. Beyond the fundamental physics, the same platform is a testbed for cavity-mediated quantum networks, optically cooled mechanical sensors, and hybrid quantum memories.

For the full research context, see the group website.