High-Q Nanomechanical Resonators as Force Sensors and Synthetic Two Level Systems

Deividas Sabonis
ETH Zürich, Switzerland

In the first half of this contribution [1], we demonstrate that soft-clamped silicon nitride strings with large aspect ratio can be operated at mK temperatures. The quality factors (Q) show consistent dependency on the cryostat temperature, with soft clamped mechanical modes reaching Q > 10^9 at 80 mK. For low optical readout power, Q is found to saturate, indicating good thermalization between the sample and the stage it is mounted on. Our best device exhibits a force sensitivity of 12.6 zN/√Hz and a thermal decoherence time of 0.22 s which bode well for future applications such as nanomechanical force sensing and beyond. We also elaborate on potential next steps on performing force sensing using high-Q perimeter mode resonators with integrated optical cavities. In the second half [2], we study the Kerr Parametric Oscillator as an approximation to a synthetic two-level system. In the presence of strong noise, the system switches between two states via a fluctuating trajectory in phase space, instead of following a straight path. The presence of such fluctuating trajectories makes it hard to establish a precise count, or even a useful definition, of the ``lifetime'' of the state. Addressing this issue, we compare several rate counting methods that allow to estimate a lifetime for the levels. In particular, we establish that a peak in the Allan variance of fluctuations can also be used to determine the levels' lifetime. Our work provides a basis for characterizing KPO networks for simulated annealing where an accurate determination of the state lifetime is of fundamental importance.

References:
[1] arXiv:2112.03730
[2] arXiv:2112.03357