Decocherence of Levitated Microscopic Particles in Extreme Isolation

Project Information

DecoXtreme

Grant agreement ID: 101103589

DOI

10.3030/101103589

Project terminated on 31 March 2025

EC signature date 6 July 2023

Start date 1 August 2023

End date 31 July 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 199 440,96

Coordinated by

OESTERREICHISCHE AKADEMIE DER WISSENSCHAFTEN
Austria

Periodic Reporting for period 1 - DecoXtreme (Decocherence of Levitated Microscopic Particles in Extreme Isolation)

Reporting period: 2023-08-01 to 2025-07-31

Summary of the context and overall objectives of the project

At the heart of quantum mechanics lies the superposition principle: if a system can exist in two different states, it can also exist in both at once. This means that, in principle, a particle can be in two places at the same time. While this counterintuitive idea has been confirmed in experiments with electrons, atoms, and even complex molecules, testing it at larger mass and length scales remains one of the great challenges in modern physics.
Levitated nanoparticles offer a promising route to explore quantum superpositions at unprecedented scales. In 2020, researchers succeeded in cooling the motion of such a nanoparticle to a highly pure quantum state—an important step toward observing macroscopic quantum behavior. However, due to their large mass, quantum effects in these systems occur at extremely small scales—on the order of picometers—requiring exceptional isolation from environmental noise and decoherence to be observable.
This project aims to advance our understanding of noise and decoherence in levitated systems, particularly beyond standard models. By refining the theoretical framework and proposing experimental strategies to control and certify quantum behavior in these challenging conditions, we aim to theoretically support efforts to test the limits of quantum mechanics at the macroscopic scale.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the Action, we have contributed to the theoretical understanding of the quantum dynamics of levitated particles. In particular, we have:
- Developed a theoretical framework to describe the quantum dynamics of a levitated nanoparticle's center-of-mass motion in nonlinear potentials, incorporating the effects of noise and decoherence.
- Provided theoretical support for a cutting-edge experiment that achieved a coherent spatial delocalization of the nanoparticle’s center-of-mass state beyond its zero-point fluctuations.
- Contributed to a proof-of-concept experiment exploring the exponentially fast expansion of a nanoparticle’s wavefunction using an unstable potential, offering a novel route to amplify quantum signatures.
- Conducted a rigorous analysis of quantum certification for macroscopic particles, focusing on regimes where classical and quantum predictions are difficult to distinguish experimentally.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Our research has pushed forward the state of the art in several ways. First, we developed a novel theoretical method to calculate the nonlinear open dynamics of a levitated nanoparticle's center-of-mass motion. While approximate, this method has broad applicability in massive systems that are first delocalized and then exposed to a wide nonlinear potential. Importantly, the method provides an analytical expression for the quantum state, enabling a detailed exploration of how key experimental parameters—such as the initial temperature of the particle and the length scale of the potential—affect the system’s behavior.
Second, the experiments we supported theoretically represent a significant technological advancement in levitated nanoparticle systems. These experiments demonstrate on the one hand the largest coherent delocalization of a nanoparticle state to date and, on the other, the successful proof-of-concept of using an unstable potentials to delocalize the system's wavefunction exponentially fast.
Finally, our study on quantum certification reveals that by exploiting subtle global differences between classical and quantum mechanical predictions for measurement outcomes, it is possible to certify quantum behavior even in the absence of observable interference patterns. This opens new avenues for verifying quantum mechanics under challenging experimental conditions.

Decoherence Sketch