Active-feedback quantum control of an integrated, low-frequency mechanical resonator

Kavli Affiliate: Simon Groblacher

| First 5 Authors: Jingkun Guo, Jin Chang, Xiong Yao, Simon Gröblacher,

| Summary:

Preparing a massive mechanical resonator in a state where its motional energy
is limited by quantum mechanics provides a promising platform for studying
fundamental physics with macroscopic systems and allows to realize a variety of
applications, including precise sensing. While over the past decade several
demonstrations of such ground-state cooled systems have been achieved, in
particular in sideband-resolved cavity optomechanics, for many systems
overcoming the heating rate from the thermal bath remains a major challenge. In
contrast, optomechanical systems in the sideband-unresolved limit are much
easier to realize due to the relaxed requirements on the optical properties of
the system. For such a system, a measurement based real-time control scheme can
be implemented to reduce its motional energy, and the achievable energy is
ultimately limited by the correlation between the measurement precision and the
back-action due to the measurement. Here, we demonstrate measurement-based
feedback cooling on a fully integrated optomechanical device fabricated using a
pick-and-place method, operating deep in the sideband-unresolved limit. With
the large optomechanical interaction and a low thermal decoherence rate, we
achieve a minimal average phonon occupation of 0.76 when pre-cooled with liquid
helium and 3.5 in a liquid nitrogen environment. Significant sideband asymmetry
for all bath temperatures verifies the quantum character of the mechanical
motion. Our method and device are ideally suited for sensing applications
directly operating at the quantum limit and greatly simplifies the operation of
an optomechanical system in this regime.

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