Particle physics research

Research offers new use for optical cavities as mechanical quantum presses

Advances in quantum physics offer new opportunities to dramatically improve the accuracy of sensors and thus enable new technologies. A team led by Oriol Romero-Isart from the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences and the Department of Theoretical Physics at the University of Innsbruck and a team led by Romain Quidant from the ETH Zurich are now offering a new concept for a high-precision quantum sensor.

The researchers suggest that the motion fluctuations of a nanoparticle trapped in a microscopic optical resonator could be significantly reduced below the zero-point motion, exploiting the fast and unstable dynamics of the system.

Particle stuck between mirrors

Quantum mechanical compression reduces the uncertainty of motion fluctuations below zero point motion, and this has been demonstrated experimentally in the past with micromechanical resonators in the quantum regime. The researchers now propose a new approach, specially adapted to levitating mechanical systems. “We demonstrate that a properly designed optical cavity can be used to rapidly and strongly compress the motion of a levitating nanoparticle.” says Katja Kustura of Oriol Romero-Isart’s team in Innsbruck. In an optical resonator, light is reflected between mirrors and interacts with the levitating nanoparticle. Such an interaction can give rise to dynamic instabilities, which are often considered undesirable. Researchers are now showing how they can instead be used as a resource.

“In the present work, we show how, by properly controlling these instabilities, the resulting unstable dynamics of a mechanical oscillator inside an optical cavity leads to mechanical compression”, Kustura said. The new protocol is robust in the presence of dissipation, which makes it particularly feasible in levitating optomechanics. In the article published in the journal Physical Review Letters, the researchers apply this approach to a silica nanoparticle coupled to a microcavity by coherent diffusion.

“This example shows that we can compress the particle by orders of magnitude below zero-point motion, even though we are starting from an initial thermal state,” Oriol Romero-Isart is happy to say.

The work provides a new use for optical cavities as mechanical quantum presses and suggests a viable new path in levitating optomechanics beyond ground-state quantum cooling. Micro-resonators thus offer an interesting new platform for the design of quantum sensors, which could be used, for example, in satellite missions, autonomous cars and in seismology. The research in Innsbruck and Zurich was financially supported by the European Union.