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Strong single-photon radiation-pressure coupling for quantum optomechanics

Periodic Reporting for period 4 - STRONG-Q (Strong single-photon radiation-pressure coupling for quantum optomechanics)

Reporting period: 2020-09-01 to 2021-02-28

While quantum physics is one of the most successful theories in modern science, it remains a puzzle why we do not observe quantum effects in our macroscopic every-day life. Quantum theory in fact does not pose an inherent limit on the size and mass of a quantum system. The field of optomechanics has been established with the explicit goal of testing massive, macroscopic quantum states. Here, the radiation-pressure force is used to bring a mechanical oscillator into a quantum state by coupling it to light. Most current experiments are however limited by either the optical or mechanical quality of the mechanical system, which so far have prevented a true breakthrough. In this project we develop mechanical oscillators with state-of-the-art quality that will allow us to realize experiments for probing quantum physics with large objects at room temperature. The understanding of these effects will have a profound impact on the fundamental physics that governs our every day lives and will lead to novel technologies in sensing applications.

The project has brought the enticing goal of observing quantum effects in macroscopic systems at room temperature much closer to reality, by creating a new approach to high-quality mechanical oscillators with unprecedented low dissipation rates. This has allowed us to increase the optomechanical coupling through arrays of mechanical elements and observe new multi-mode effects.
We have developed novel mechanical systems of unprecedented mechanical quality. We have also made these devices highly reflective by patterning a photonic crystal in their center, which allows for efficient coupling to a laser. The devices feature the best force-sensitivity on-chip at room temperature, which will allow for novel force sensing applications, while at the same time functioning as a building block for fundamentally new quantum technologies. Recently, we have developed an integrated way of building arrays of several of these mechanical devices, and have demonstrated an increase in the opto-mechanical coupling strength, potentially opening up the possibilities for experiments in the so-called strong coupling regime. These new kind of optomechanical systems, has further allowed us to observe a competition in the coupling rates of macroscopic mechanical systems, as well as realize a new way of cancelling mechanical noise.

In particular, the most important achievements were disseminated through publications:

Ultra-high quality mechanical resonators: R. A. Norte et al., Phys. Rev. Lett. 116, 147202 (2016)

Array of high-reflectivity membranes with enhanced coupling: C. Gärtner et al., Nano Lett. 18, 7171 (2018)

Cooperativity competition and noise cancellation: M.H.J. de Jong et al., arXiv:2012.11733 (2020)
The quality and sensitivity of devices developed are well beyond the state-of-the-art and has allowed us to fabricate some of the largest high-aspect ration high-reflectivity mirrors in the world. In addition, we have demonstrated the first integrated two-device array of high-reflectivity mirrors, which forms the direct basis for future quantum experiments with mechanical systems at room temperature. Decisive steps have been taken to realize such experiments by demonstrating a coupling enhancement and the suppression of noise in mechanical spectra through coherent coupling.
An artist’s impression of a high-quality SiN membrane coupled to a laser beam. The periodic pattern