Quantum Optomechanics at the Standard Quantum Limit

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This award supports research in relativity and relativistic astrophysics, and it addresses the priority areas of NSF's "Windows on the Universe" Big Idea. The direct detection of gravitational waves (GW) was made possible by decades of work developing the physics and experimental expertise needed to construct the interferometers that made the detections. GW detectors are now limited in their sensitivity by quantum noise in the forms of shot noise, associated with counting error in the number of photons detected, and backaction in the form of radiation pressure noise. This project will explore the interplay of these quantum noises in a prototype system that uses micromechanical mirror oscillators in a cryogenic system. The project will explore techniques to mitigate the effects of these noises in a small system so that they may be applied to large GW detectors in the future. The award will support and mentor students and encourage participants from non-traditional backgrounds and traditionally underrepresented groups. Participants in the research play a strong role in disseminating exciting physics research, including in the areas of quantum mechanics and GWs, through research talks, public talks, and lab tours.The Standard Quantum Limit (SQL) limits any continuous position measurement in which the measurement imprecision (shot noise) is uncorrelated with the quantum backaction (radiation pressure noise). The SQL may be breached, in principle, by correlating the two noises. In the proposed research, this will be experimentally demonstrated by using the optical spring effect in a detuned cavity with a movable 50 nanogram mirror. This system was previously used to observe quantum backaction at room temperature, and here will be cooled to 20 degrees Kelvin to reach the required sensitivity. Other methods to surpass the SQL, including the variational readout, will also be explored. The results of these experiments will inform the design of future GW detectors. The micromirror oscillators, with Brownian thermal noise below the SQL, are also candidates for unstable optomechanical filter cavities. The project will also develop techniques to measure the thermal noise at a level below the SQL.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.