To explore the intriguing new possibilities offered by hybrid mechanical-atomic systems, we built a membrane optomechanics setup in a cryostat and an ultracold atom setup. Our setup allows to engineer light-mediated interactions in a very flexible way, coupling the mechanical oscillator either to the motion of the atoms or to their collective spin, realizing unidirectional or bidirectional interactions, and in particular also interactions where the two systems are connected in a loop geometry. In parallel, we developed a rigorous theoretical framework for describing the light-mediated Hamiltonian interactions that can be generated between the two systems over long distances [1].
With our experimental setup, and guided by our theoretical work, we obtained a number of exciting new results. Initial experiments focused on coupling of the mechanical oscillator to the atomic motion, demonstrating cooling of the mechanical vibrations and a range of further interesting phenomena [2,3]. A breakthrough was the observation of light-mediated strong coupling between the mechanical oscillator and the atomic spins across a distance of 1 meter [4]. This first demonstration of strong Hamiltonian coupling at a distance represents a major breakthrough of the project. The power and flexibility of the approach were demonstrated by realizing different dynamical regimes, observing normal mode splitting and coherent state swaps between the atoms and the membrane, two-mode squeezing dynamics, as well as dissipative interactions and exceptional points [4]. In a next step, we explored the light-mediated strong coupling for a demonstration of feedback cooling of the mechanical oscillator using the atomic spins as a coherent controller [5].
In the final stage of the project, we switched our attention to a new and unexpected possibility that emerged from our theoretical analysis of light-mediated interactions in loop geometries. In our optomechanics setup we realized an optical coherent feedback loop that allows us to control the vibrations of the nanomechanical membrane. By adjusting the phase and time delay of the feedback, we were able to demonstrate coherent feedback cooling of the membrane, which we demonstrated to overcome the fundamental limits of standard cavity optomechanical cooling and control techniques in the unresolved sideband regime [6].
The results of the project were published in leading peer-review journals and presented at numerous conferences in the field.
[1] T. M. Karg, B. Gouraud, P. Treutlein, and K. Hammerer, Remote Hamiltonian interactions mediated by light, Phys. Rev. A 99, 063829 (2019).
[2] A. Jöckel, A. Faber, T. Kampschulte, M. Korppi, M. T. Rakher, and P. Treutlein, Sympathetic cooling of a membrane oscillator in a hybrid mechanical-atomic system, Nature Nanotechnology 10, 55-59 (2015).
[3] A. Vochezer, T. Kampschulte, K. Hammerer, and P. Treutlein, Light-Mediated Collective Atomic Motion in an Optical Lattice Coupled to a Membrane, Phys. Rev. Lett. 120, 073602 (2018).
[4] T. M. Karg, B. Gouraud, C. T. Ngai, G.-L. Schmid, K. Hammerer, and P. Treutlein, Light-mediated strong coupling between a mechanical oscillator and atomic spins one meter apart, Science 369, 174 (2020).
[5] G.-L. Schmid, C. T. Ngai, M. Ernzer, M. Bosch Aguilera, T. M. Karg, and P. Treutlein, Coherent feedback cooling of a nanomechanical membrane with atomic spins, Phys. Rev. X 12, 011020 (2022).
[6] M. Ernzer, M. Bosch Aguilera, M. Brunelli, G.-L. Schmid, C. Bruder, P. P. Potts, and P. Treutlein, Optical coherent feedback control of a mechanical oscillator, preprint arXiv:2210.07674
