Speaker
Description
We report a multimode optomechanical system with quantum cooperativity 𝐶_q = 4𝑔^2/𝜅𝛾 ≫ 1
already at moderate cryogenic temperature T~10 K [1]. Here, 𝛾 = 𝑘B𝑇/ℏ𝑄 is the quantum decoherence
rate of the mechanical system, and Q~10^7 the mechanical quality factor. In this regime, the quantum
backaction of the optical measurement dominates over the thermal Langevin noise. As a consequence,
optical measurements create quantum correlations between the optical and mechanical degrees of
freedom, which are measured as ponderomotive squeezing (-2.4 dB) of the light emerging from the
cavity. In the multimode setting investigated here, we observe optically-induced hybridisation of
mechanical modes, and the generation of squeezed light by hybrid modes [1].
Furthermore, we have implemented a hybrid system by combining this optomechanical system with
a room-temperature atomic ensemble [2]. A light beam probes the spin state through Faraday
interaction, and subsequently the motion of the nanomechanical membrane. We show that it is possible
to cancel part of the measurement’s quantum backaction by appropriately tailoring the light-spin, and
subsequent light-mechanical interaction.
Finally, we report on the development of a novel type of membrane and string resonators with
dramatically reduced decoherence [3]. By patterning a phononic crystal directly into a stressed SiN
membrane we realise a “soft clamp” for a localised defect mode. Its engineered mode shape exhibits
reduced curvature and therefore dissipation, reaching room-temperature Qf-products in excess of
10^{14} Hz—the highest reported to date—as well as Q~10^9 at T~4 K. The corresponding room
temperature coherence time approaches that of optically trapped dielectric particles, and for cryogenic
operation becomes comparable (~1 ms) to that of trapped ions. Extensive characterisation through
laser-based imaging of mode shapes [3] and stress distribution [4] confirms a model that quantitatively
predicts the quality factors over a wide parameter range.
References
[1] W. H. P. Nielsen, Y. Tsaturyan, C. B. Møller, E. S. Polzik, and A. Schliesser, PNAS 114, 62 (2017).
[2] C. B. Møller, R. A. Thomas, G. Vasilakis, E. Zeuthen, Y. Tsaturyan, K. Jensen, A. Schliesser, K. Hammerer and E. S. Polzik, arXiv:1608.03613
[3] Y. Tsaturyan, A. Barg, E. S. Polzik, and A. Schliesser, arXiv:1608.00937
[4] A. Barg, Y. Tsaturyan, E. Belhage, H. P. W. Nielsen, C. B. Møller, and A. Schliesser, Applied Physics B 123, 8 (2017).
[5] T. Capelle, Y. Tsaturyan, A. Barg, and A. Schliesser, in preparation.
