AQP Seminar: From gravitational-wave detection to quantum optomechanics

From gravitational-wave detection to quantum optomechanics

Pierre-François Cohadon (Laboratoire Kastler Brossel, Ecole Normale Supérieure and CNRS, Paris)
 

Abstract: Detecting gravitational waves required four decades of experimental effort to achieve a sensitivity on the order of h ≃ 10⁻²¹, corresponding to mirror displacements of less than 10⁻¹⁸ m. Apart from the classical noises (seismic noise, thermal noise, etc.) that had to be overcome, Carlton Caves identified, as early as the 1980s, the two noises related to the quantum nature of light that limit the sensitivity of these interferometers and demonstrated the existence of the Standard Quantum Limit (SQL), the smallest observable displacement with a laser beam in a coherent state. Doing so, he gave a new status to the interferometer mirrors: from simple devices for reflecting light, they became true physical objects that respond to quantum radiation pressure fluctuations of the meter laser beam. No one knows it yet, and no one calls it that, but optomechanics was born. The existence of the SQL has been be a driving force behind the first squeezing experiments in the mid-1980s. I will present the various avenues explored to go beyond the SQL, from the first experimental demonstrations on suspended interferometers or tabletop experiments, to the now routine operation of squeezing to improve the sensitivity of high-frequency gravitational interferometers. I will also explain how the tremendous recent progress in microfabrication has enabled the emergence of a new field, quantum optomechanics, which consists of coupling mechanical micro- or nanoresonators to light, in the optical or microwave domain. The focus can be on the quantum state of the fields or on that of the resonator, which can, for example, be cooled by radiation pressure close to its ground quantum state. This field is very promising for the study of the foundations of quantum mechanics, for the study of quantum states and the decoherence of macroscopic mechanical resonators or for quantum information processing. I will present a very recent experiment where we managed to resonantly couple a MHz vibration of a SiN membrane to a low-frequency fluxonium qubit.