Nanoparticles Cooled to Quantum Ground-State in Two Motional Dimensions

Abstract Cold Energy Particle Physics

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Physicists are learning glass nanoparticles trapped by lasers in a vacuum to discover the boundaries of the quantum world and decide when classical physics now not applies. This is a part of the ERC-Synergy mission Q-Xtreme, the place a crew is working in direction of reaching the quantum ground-state by lowering the vitality saved within the nanoparticle’s movement as a lot as doable.

Glass nanoparticles trapped by lasers in excessive vacuum are thought-about a promising platform for exploring the boundaries of the quantum world. Since the arrival of quantum principle, the query at which sizes an object begins being described by the legal guidelines of quantum physics relatively than the foundations of classical physics has remained unanswered.

A crew fashioned by Lukas Novotny (ETH Zurich), Markus Aspelmeyer (University of Vienna), Oriol Romero-Isart (University of Innsbruck), and Romain Quidant (Zurich) is trying to reply exactly this query throughout the ERC-Synergy mission Q-Xtreme. An important step on the best way to this purpose is to scale back the vitality saved within the movement of the nanoparticle as a lot as doable, i.e. to chill the particle right down to the so-called quantum ground-state.

Control over all dimensions of motion

The Q-Xtreme crew has been working collectively on ground-state cooling of nanoparticles for a very long time. Several experiments in Zurich and Vienna, supported by theoretical calculations by Dr. Gonzalez-Ballestero and Prof. Romero-Isart on the University of Innsbruck, have led to the primary demonstrations of such ground-state cooling of a nanoparticle, both by dampening the particle movement utilizing digital management (energetic suggestions) or by putting the particle between two mirrors (cavity-based cooling). So far in experiments, the bottom state has been achieved solely alongside one of many three instructions of particle movement, leaving the movement alongside the opposite two instructions “hot.”

Experimental Setup to Levitate Particle

The vacuum chamber with the experimental setup to levitate a particle within a cavity. The cavity consists of two mirrors coated to be extraordinarily reflective for infrared gentle. The cylindrical half within the middle holds a lens at its tip to focus the infrared laser down to some extent at which the particle is trapped. Credit: Johannes Piotrowski

“Achieving ground-state cooling along more than one direction is key for exploring novel quantum physics,” emphasizes Gonzalez-Ballestero of the Institute for Quantum Optics and Quantum Information on the Austrian Academy of Sciences and the Department of Theoretical Physics on the University of Innsbruck. “But so far this achievement remained elusive as it was challenging to make the mirrors between which the particle is positioned interact efficiently with the motion along some of the three directions” The so-called “Dark Mode Effect” prevented cooling to the complete floor state.

With totally different frequencies towards the purpose

Now, the analysis on the Photonics Laboratory of ETH Zurich has succeeded for the primary time in ground-state cooling of a nanoparticle alongside two instructions of movement. A glass sphere, a couple of thousand occasions smaller than a grain of sand, is totally remoted from its surroundings in a excessive vacuum and held by a strongly centered laser beam whereas concurrently being cooled to close absolute zero. Based on theoretical predictions from the Innsbruck team, the Swiss physicists were able to circumvent the dark-state problem. “To do so, we designed the frequencies at which the particle oscillates in the two directions differently and carefully adjusted the polarization of the laser light,” says Lukas Novotny of ETH Zurich.

The work, published in Nature Physics, demonstrates that it is possible to reach the minimum energy state for the three motional directions. It also allows the creation of fragile quantum states in two directions, which could be used to create ultrasensitive gyroscopes and sensors.

Reference: “Simultaneous ground-state cooling of two mechanical modes of a levitated nanoparticle. Johannes Piotrowski, Dominik Windey, Jayadev Vijayan, Carlos Gonzalez-Ballestero, Andrés de los Ríos Sommer, Nadine Meyer, Romain Quidant, Oriol Romero-Isart, René Reimann and Lukas Novotny” 6 March 2023, Nature Physics.
DOI: 10.1038/s41567-023-01956-1

The research was financially supported by the European Research Council ERC and the European Union, among others.