Feedback Levitation on an Inverted Potential: A new tool for macroscopic quantum physics, sensing and information thermodynamics

Project Information

FLIP

Grant agreement ID: 101106514

DOI

10.3030/101106514

Project closed

EC signature date 29 March 2023

Start date 1 May 2023

End date 30 June 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 183 600,96

Coordinated by

UNIVERSITAT WIEN
Austria

Periodic Reporting for period 1 - FLIP (Feedback Levitation on an Inverted Potential: A new tool for macroscopic quantum physics, sensing and information thermodynamics)

Reporting period: 2023-05-01 to 2025-06-30

Summary of the context and overall objectives of the project

Controlling mesoscopic objects in the quantum regime is essential for advancing sensing, thermodynamics, and macroscopic quantum physics. Optical levitation has enabled key progress but remains limited by heating due to light absorption. This restricts the use of many materials and prevents certain quantum experiments.

The FLIP (Feedback Levitation on an Inverted Potential) project introduces a new approach that avoids optical confinement. By combining dark-field detection with active feedback control, it enables stable levitation and cooling without absorption. This makes it possible to control absorbing particles in high vacuum, such as those containing internal quantum degrees of freedom.

The project builds on recent advances in feedback-based ground-state cooling and aims to establish a new class of quantum control using dark and therefore unstable optical potentials for detection. It will allow quantum experiments with internally cold particles in free fall, enable sensing in non-conservative potentials, and make it possible to use absorbing particles like NV-doped nanodiamonds in levitated setups.

FLIP expands the range of systems that can be controlled in the quantum regime and provides new experimental platforms to study quantum states beyond the standard harmonic potential framework.

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

The FLIP project aimed to implement levitation and control of mesoscopic particles using an inverted optical potential combined with active feedback, eliminating the need for trapping forces and therefore overcoming the absorption limitation in standard optical trapping. The primary technical objective was to demonstrate stable feedback-based confinement of a particle at the top of an unstable (anti-trapping) potential — a novel configuration enabling absorption-free control.

This goal was achieved during the project, culminating in the experimental demonstration of levitation on an inverted optical potential, as reported in a first publication. The study showed that a single nanoparticle can be stabilized and cooled in real time using measurement-based feedback alone, without relying on any conservative trapping potential.

This result represents a key milestone toward the full implementation of FLIP that would combine this stabilization scheme and a 'dark' detection in the intensity minimum in a higher gaussian mode light beam.

Additional technical developments during the project included upgrades to FPGA-based feedback systems to adapt to the experimental challenges of differentiating slow motion of the particle rolling down the inverted potential from other experimental drifts.
The project also participated in improving detection strategies under dark-field illumination, with the long term goal of detecting the particle motion in an intensity minimum to further mitigate the absorption.

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)

The main outcome of the project is the successful demonstration of feedback-based stabilization in an inverted optical potential, proving the core concept of the FLIP approach. This establishes a new regime for levitation, free from optical confinement and associated absorption, and opens the door to quantum experiments with a wider range of particle types and internal structures.

The next critical step is to demonstrate efficient optical detection in the intensity minimum of a higher-order optical mode, enabling position readout without absorption. Combining this with inverted-potential feedback in high vacuum will allow cooling to the quantum ground state in the FLIP configuration.

Further research is required to optimize the signal-to-noise ratio of the detection in the dark-field conditions and to ensure stable operation at ultra-low pressures. Long-term, this platform could support applications in quantum sensing, spin-mechanics, and foundational tests of quantum physics. Uptake of these results will depend on continued access to advanced optomechanical infrastructure, and collaborative research across experimental and theoretical groups.

Schematic representation of the FLIP experiment