Research

At the interface between levitated solid-state objects and atomic physics

Cavity QED

Mock-up of a levitated nanoparticle (donut-shaped radiation pattern) inside of an optical cavity

Experimental setup for motional ground state cooling (reproduced from Science 367, 892)

Optically levitated nanoparticles are driven dipoles and as such they radiate light in phase with the driving laser. Optical cavities can be used to enhance their dipole radiation into the desired cavity mode, the so-called Purcell enhancement. For a properly chosen detuning of the driving field with respect to the cavity resonance, the Stokes and anti-Stokes scattering photons (inelastic scattering of the driving laser) can be employed for optomechanical interaction: cavity cooling or entanglement.

In our work, we strive to push the optomechanical interaction into the regime of ultrastrong and deep strong coupling regime by maximizing the overlap of the dipole radiation with the cavity field.

Read our work on cavity optomechanics:

K. Dare, J. J. Hansen, I. Coroli, A. Johnson, M. Aspelmeyer, U. Delić, Linear Ultrastrong Optomechanical Interaction

arXiv: 2305.16226 (2023), accepted for publication in Phys. Rev. Research

M. Toroš, U. Delić, F. Hales, T. Monteiro

Coherent scattering 2D cooling in levitated cavity optomechanics

Phys. Rev. Research 3, 023071 (2021), arXiv: 2012.15822

U. Delić, M. Reisenbauer, K. Dare, D. Grass, V. Vuletić, N. Kiesel, M. Aspelmeyer, Cooling of a levitated nanoparticle to the motional quantum ground state

Science 367, 892 (2020), arXiv: 1911.04406

U. Delić, D. Grass, M. Reisenbauer, T. Damm, M. Weitz, N. Kiesel, M. Aspelmeyer, Levitated cavity optomechanics in high vacuum

Quantum Sci. Technol. 5, 025006 (2020), arXiv: 1902.06605

U. Delić, M.Reisenbauer, D. Grass, N. Kiesel, V. Vuletić, M. Aspelmeyer, Cavity cooling of a levitated nanosphere by coherent scattering

Phys. Rev. Lett. 122, 123602 (2019) arXiv: 1812.09358

This research is supported by the Austrian Academy of Sciences (ÖAW) with the ESQ Discovery Grant "Ultrastrong Cavity Optomechanics".

Collective quantum effects

Experimental setup to generate a 2D array of trapped nanoparticles with acousto-optical deflectors. Upper-right corner: Image of 4 nanoparticles trapped in a 2x2 array of optical tweezers (© Livia Egyed)

Illustration of the emergence of limit cycle orbits through nonreciprocal interactions © Equinox Graphics Ltd.

Optically levitated nanoparticles are able to interact directly in different ways. Recently, we have shown that the interaction through the scattered light, the so-called "light-induced dipole-dipole interaction", is inherently non-reciprocal for two particles trapped in distinct optical tweezers.

Inspired by "More is different", we aim to build a large trap array of nanoparticles and exploit the unique opportunities offered by levitated systems for collective quantum effects.

For more insight, read our recent work:

M. Reisenbauer, H. Rudolph, L. Egyed, K. Hornberger, A. V. Zasedatelev, M. Abuzarli, B. A. Stickler, U. Delić

Non-Hermitian dynamics and nonreciprocity of optically coupled nanoparticles

Nature Physics (2024)

https://doi.org/10.1038/s41567-024-02589-8

arXiV: 2310.02610

H. Xu, U. Delić, G. Wang, C. Li, P. Cappellaro, J. Li

Exponentially Enhanced non-Hermitian Cooling

Phys. Rev. Lett. 132, 110402 (2024), arXiv: 2309.07731

C. Jakubec, P. Solano, U. Delić, K. Sinha

Fluctuation-induced forces on nanospheres in external fields

Physical Review A 109 (5), 052807 (2024), arXiv: 2311.10496

H. Rudolph, U. Delić, K. Hornberger, B. A. Stickler

Quantum theory of non-hermitian optical binding between nanoparticles

arXiv: 2306.11893 (2023)

J. Rieser, M. A. Ciampini, H. Rudolph, N. Kiesel, K. Hornberger, B. A. Stickler, M. Aspelmeyer, U. Delić, Tunable light-induced dipole-dipole interactions between optically levitated nanoparticles

Science 377, 987 (2022), arXiv: 2203.04198

This research is supported by the Austrian Science Fund (FWF) (Grant number: I 5111) and the John Templeton Foundation.

Quantum and classical sensing

Optically levitated nanoparticles are excellent force sensors due to their exceptional isolation from the thermal environment and susceptibility to various external forces.

We ask the following questions:

Is it possible to enhance force sensitivity by going beyond linear harmonic oscillators?

Can we optimize a particular sensing scheme by using entangled states of motion?

Can interacting arrays of particles provide novel sensing schemes?

For our recent work see:

H. Rudolph, U. Delić, M. Aspelmeyer, K. Hornberger, B. A. Stickler, Force-gradient sensing and entanglement via feedback cooling of interacting nanoparticles

Phys. Rev. Lett. 129, 193602 (2022), arXiv: 2204.13684