Like a candle in the wind: flicker noise in nano-optomechanical systems

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The frequency stability level of mechanical systems, including nanoelectromechanical systems (NEMS) and nano-optomechanical systems (NOMS), is of paramount importance to their performance, both as ultrasensitive sensors, and as reference oscillators. Recent work in our field has shown that this performance is almost never limited by the fundamental noise source of thermomechanical noise, as one would desire, but rather is almost always limited by frequency flicker noise. A recent breakthrough [Roy, Sauer, Westwood-Bachman, Venkatasubramanian, Hiebert (2018) Science 360, eaar5220] established the surprising result that precision mechanical resonator performance can be maintained and even improved by reducing quality factor (increasing damping). The improvement in frequency stability with damping seems to be related to suppression of this ubiquitous flicker noise through the thermal conduction of surrounding (damping) air. Following on from this breakthrough work, we seek to explore the realm of flicker noise contribution to NEMS and NOMS frequency stability. Using tuning knobs of: air damping, device dimension, device temperature coefficient (tunable through internal stress), optomechanical spring tuning, optomechanical coupling, and temperature, we will thoroughly explore and understand the source of flicker noise in NOMS devices, identifying which of two competing models explain the noise throughout this parameter space. Once well-understood, we will design devices to minimize and eliminate this noise in order to reach the fundamental noise level, and ultimate frequency stability limit, of NOMS systems. Combining air damping and its flicker mitigation channel with high-finesse optomechanics will allow self-oscillation of NOMS devices even in highly-damped conditions. Ultimate limit frequency stability in such NOMS oscillators that operate in ambient air will ultimately lead to profound advancements in sensor technology, such as single-Da mass spectrometry in air.