QPOS

Quantum Phenomena in Optomechanical Systems

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 Obiettivo del progetto (Objective)

'Cavity optomechanics is a flourishing research field concerned with the study of macroscopic objects in a regime where quantum mechanical effects become apparent. A strong interaction between the optical field and the mechanical motion of optomechanical resonators, usually mediated by radiation pressure, enables both new photonic technologies as well as fundamental experiments that are at the heart of quantum mechanics. This proposal aims to study micro- and nano-optomechanical systems cooled close to their ground state of motion to advance both fundamental and applied concepts in quantum optomechanics. A first aim is to study a recently developed optomechanical device based on a 2D photonic crystal defect cavity. In particular, we aim to cool this device down to its ground state of motion by embedding it in a Helium-3 cryostat and using radiation pressure induced laser cooling to reach its ground state of motion. The high optomechanical coupling strength measured on these devices promises to allow ground state cooling with moderate efforts. A second objective is to implement the technique of motional side-band spectroscopy, adapted from ion trapping experiments, to characterize the degree of occupancy of the ground state of motion of optomechanical resonators, providing a definite quantum-mechanical signature in these macroscopic objects. Finally, we will use the recently observed effect of optomechanically-induced transparency (OMIT) in microresonators, in which the optomechanical coupling induces a very narrow transparency window accompanied by a strong group velocity reduction, for storing and stopping light pulses in optomechanical modes. This proposal will allow the applicant, a physicist recently graduated with distinction from the Institute of Photonic Sciences (ICFO) in Barcelona, to join the Laboratory of Photonics and Quantum Measurements in the Federal Institute of Technology in Lausanne (EPFL), a group with high recognition in this field of research.'

Introduzione (Teaser)

Cavity optomechanics is an area of research exploring the interactions between light and matter at the boundary between the classical and quantum mechanical regimes. Novel setups and experimental protocols have made exciting new experiments possible.

Descrizione progetto (Article)

Heralded as a Nature Milestone, cavity optomechanics exploits the interaction between photons and mirrors in table-top experiments. It enables macroscopic objects to be studied in the regime where quantum effects become apparent. It also has exciting practical applications in fields such as sensing and silicon photonics.

A common experimental protocol exploits a tiny optical cavity that confines light in all directions, coupled to a mechanical oscillator. Radiation pressure, the pressure exerted on any surface exposed to electromagnetic radiation, can be used to cool a mechanical resonator toward the quantum ground state of motion. This system was the focus of the EU-funded project 'Quantum phenomena in optomechanical systems' (QPOS).

All experiments combined passive cryogenic cooling with optical cooling. The team developed a new setup consisting of a silicon nitride nanobeam electromagnetically or, more specifically, evanescently coupled to a silica microdisk resonator. It demonstrated an unprecedented high cooperativity, a measure of coupling strength, which makes possible a number of different experiments.

Exploiting this system, the team conducted a long study related to feedback cooling. This is a technique that uses the displacement of the oscillator to apply a force related to it to the oscillator in a feedback loop. Scientists successfully cooled the fundamental mechanical mode of a nanostring to five to 10 phonons, a measure of collective oscillations in condensed matter. The result is currently being prepared as a manuscript.

In other experiments, the team demonstrated the significant heating due to optical absorption that must be reduced for a cleaner protocol. They also developed a setup and theoretical calculations to study another source of mechanical losses, phonon scattering and adsorption. It consists of a high-frequency optomechanical resonator with low clamping losses. It will soon be implemented in low-temperature experiments.

QPOS had great success in developing innovative setups to investigate optomechanical interactions at the transition from the classical to the quantum regime. Implementation of some of those has already borne fruit with results upcoming in several publications.