Compact parallel-plate capacitor for quantum sensors
Researchers in Austria have reportedly achieved ‘world-record’ thinness in a capacitor.
The reduced 32nm gap between a capacitor’s movable aluminium membrane and fixed electrode is part of wider quantum sensing hardware developments.
Conventional optomechanical experiments use light to read the motion of tiny mechanical structures, but non-optical set-ups could enable more compact sensors.
The 32nm capacitor uses an electrical resonant circuit in place of optical oscillations, while in other experiments, the researchers use purely mechanical resonators whose vibrations can be deliberately coupled to one another.
‘The vibrations of our nanomembrane are influenced by various parameters,’ explains Daniel Platz from Vienna University of Technology.
He continues, ‘Our aluminium membrane forms a tiny capacitor together with an electrode. Combined with an inductor, this creates a resonant circuit whose resonance is extremely sensitive to any change in the mechanical vibration.’
The coupling of membrane motion and electrical resonant circuit enables measurement of extremely small vibrations, which are normally affected by noise, without relying on optical components.
This technology could be useful for atomic force microscopes, where measurement of tiny interactions between atoms and a thin tip yields a precise image on the surface.
With a different structure, the team has also demonstrated that purely mechanical systems integrated on a chip can be used instead.
Platz says, ‘Many existing quantum sensing experiments only work near absolute zero’, but this development avoids that problem.
‘Even at room temperature, the vibrations of a purely micromechanical system can be coupled over a GHz frequency range without thermal noise overwhelming the coupling effects,’ he adds.
The experiments seek to refine mechanical and electromechanical nanostructures to the point where they could enable quantum-level measurements and make quantum sensing easier to use, more robust and more versatile.
