Strong Interaction Between the Light Field and an Ultra-Coherent Mechanical Oscillator

The search for quantum phenomena in macroscopic objects has accelerated in the past decade. Precise experiments that strongly measure large objects can shed light into the measurement problem and help study the dynamics of open quantum systems. Engineered ultracoherent mechanical resonators with low-masses but micrometer dimensions are at the forefront of this endeavor. Due to the plethora of systems that can couple to mechanical motion, low dissipation resonators can also be used as transducers of quantum information or as long-lived quantum memories.
The advances in ultra-low dissipation rate mechanical resonators have allowed the observation of true quantum effects at room-temperature. Experiments that were previously only possible at cryogenic temperatures have started to translate to room temperature. Light, with its persistent quantum nature, is the tool that allows measurement and control at the needed precision.
In this work, we have designed and implemented a 126μm-long optical micro-cavity to enhance the interaction of light with a mechanical resonator placed in its center. We have fabricated mirrors that are shielded from vibrations. Using phononic crystal patterns, we have suppressed the motion of the mirrors’ surface in a frequency span between 1MHz and 1.5MHz. The motion of the mirror at these frequencies is measured to be at least three orders of magnitude smaller than outside the region. The cavity is specifically designed to house our mechanical resonator, a silicon-nitride membrane. Our system is passively aligned and it allows the cavity to exceed 60000 finesse when loaded with the membrane, all while keeping the resonator’s quality factor intact, which is close to 108.
Our room-temperature system is capable of reaching quantum cooperativities around 0.32,
where values above 1 indicate that the system is dominated by quantum fluctuations. In theory, this interaction strength cools our oscillator to an occupation of 32 phonons, equivalent to a temperature of 1.4mK.
We identify laser phase noise as the limiting factor of our setup. Without it, we predict that our platform will be able to prepare the resonator in its ground state through feedback cooling. Furthermore, we expect a reduction of the fluctuations of light below vacuum fluctuations through optomechanical squeezing.