arXiv subjects

Henning Rudolph

Publications and source records attributed to Henning Rudolph.

9 recordsLinked to original sources

arXiv2025

Quantum ground-state cooling of two librational modes of a nanorotor

Controlling the motion of nanoscale objects at the quantum limit promises new tests of quantum mechanics and advanced sensors. Rotational motion is of particular interest, as it follows nonlinear dynamics in a compact, closed configuration space, which opens up a plethora of phenomena and applications beyond the possibilities of free or trapped linear motion. A prerequisite for such experiments is the capability to trap nanorotors and initialize them in a quantum ground state of libration. Here, we demonstrate the reliable, repetitive laser-induced loading of silica nanodimers and trimers into an optical tweezer. Coherent scattering in a high-finesse cavity allows us to cool two different librational modes to the quantum ground state with occupation numbers as low as $n_{\beta}=0.54\pm0.32$ and $n_{\alpha}=0.21\pm0.03$. By simultaneously cooling both degrees of freedom ($n_\beta=0.73\pm0.22$, $n_\alpha=1.02\pm0.08$) we align nanorotors to a space-fixed axis with precision better than 20$\,\mu$rad, close to the zero-point amplitude of librations.

quant-ph↗

arXiv2024

Quantum Optical Binding of Nanoscale Particles

Optical binding refers to the light-induced interaction between two or more objects illuminated by laser fields. The high tunability of the strength, sign, and reciprocity of this interaction renders it highly attractive for controlling nanoscale mechanical motion. Here, we discuss the quantum theory of optical binding and identify unique signatures of this interaction in the quantum regime. We show that these signatures are observable in near-future experiments with levitated nanoparticles. In addition, we prove the impossibility of entanglement induced by far-field optical binding in free space and identify strategies to circumvent this no-go theorem.

quant-ph↗

arXiv2023

Non-Hermitian dynamics and nonreciprocity of optically coupled nanoparticles

Non-Hermitian dynamics, as observed in photonic, atomic, electrical, and optomechanical platforms, holds great potential for sensing applications and signal processing. Recently, fully tunable nonreciprocal optical interaction has been demonstrated between levitated nanoparticles. Here, we use this tunability to investigate the collective non-Hermitian dynamics of two nonreciprocally and nonlinearly interacting nanoparticles. We observe parity-time symmetry breaking and, for sufficiently strong coupling, a collective mechanical lasing transition, where the particles move along stable limit cycles. This work opens up a research avenue of nonequilibrium multi-particle collective effects, tailored by the dynamic control of individual sites in a tweezer array.

physics.optics↗

arXiv2023

Quantum theory of non-Hermitian optical binding between nanoparticles

Recent experiments demonstrate highly tunable nonreciprocal coupling between levitated nanoparticles due to optical binding [Rieser et al., Science 377, 987 (2022)]. In view of recent experiments cooling nanoparticles to the quantum regime, we here develop the quantum theory of small dielectric objects interacting via the forces and torques induced by scattered tweezer photons. The interaction is fundamentally non-Hermitian and accompanied by correlated quantum noise. We present the corresponding Markovian quantum master equation and show how to reach nonreciprocal and unidirectional coupling. Our work provides the theoretical tools for exploring and exploiting the rich quantum physics of nonreciprocally coupled nanoparticle arrays.

quant-ph↗

arXiv2023

Force-Gradient Sensing and Entanglement via Feedback Cooling of Interacting Nanoparticles

We show theoretically that feedback-cooling of two levitated, interacting nanoparticles enables differential sensing of forces and the observation of stationary entanglement. The feedback drives the two particles into a stationary, non-thermal state which is susceptible to inhomogeneous force fields and which exhibits entanglement for sufficiently strong inter-particle couplings. We predict that force-gradient sensing at the zepto-Newton per micron range is feasible and that entanglement due to the Coulomb interaction between charged particles can be realistically observed in state-of-the-art setups.

quant-ph↗

arXiv2022

Observation of strong and tunable light-induced dipole-dipole interactions between optically levitated nanoparticles

Arrays of optically trapped nanoparticles have emerged as a promising platform for the study of complex non-equilibrium phenomena. Analogous to atomic many-body systems, one of the crucial ingredients is the ability to precisely control the interactions between particles. However, the optical interactions studied thus far only provide conservative optical binding forces of limited tunability. Here we demonstrate a coupling mechanism that is orders of magnitude stronger and has new qualitative features. These effects arise from the previously unexplored phase coherence between the optical fields that drive the light-induced dipole-dipole interaction. In addition, polarization control allows us to observe electrostatic coupling between charged particles in the array. Our results pave the way for a fully programmable many-body system of interacting nanoparticles with tunable dissipative and nonreciprocal interactions, which are instrumental for exploring entanglement and topological phases in arrays of levitated nanoparticles.

physics.optics↗

arXiv2021

Theory of nanoparticle cooling by elliptic coherent scattering

Coherent scattering of an elliptically polarised tweezer into a cavity mode provides a promising platform for cooling levitated nanoparticles into their combined rotational and translational quantum regime [Phys. Rev. Lett. 126, 163603 (2021)]. This article presents the theory of how aspherical nanoparticles are affected by elliptically polarised laser beams, how two orthogonal cavity modes enable rotational and translational cooling, and how the resulting power spectra contain signatures of rotational non-linearities. We provide analytic expressions for the resulting trapping frequencies, opto-mechanical coupling strengths, cooling rates, and steady-state occupations and we study their dependence on the tweezer ellipticity.

quant-ph↗

arXiv2021

Cooling nanorotors by elliptic coherent scattering

Simultaneously cooling the rotational and translational motion of nanoscale dielectrics into the quantum regime is an open task of great importance for sensing applications and quantum superposition tests. Here, we show that the six-dimensional ground state can be reached by coherent-scattering cooling with an elliptically polarized and shaped optical tweezer. We determine the cooling rates and steady-state occupations in a realistic setup and discuss applications for mechanical sensing and fundamental experiments.

quant-ph↗

arXiv2020

Entangling levitated nanoparticles by coherent scattering

We show how entanglement between two optically levitated nanoparticles can be generated and detected by coherent scattering of tweezer photons into a single cavity mode. Triggered by the detection of a Stokes photon, the tweezer detuning is switched from the blue to the red; entanglement is then verified by the conditioned anti-Stokes photon flux, which oscillates with the mechanical beat frequency. The proposed setup is realizable with near-future technology and opens the door to the first experimental observation of non-classical center-of-mass correlations between two or more levitated nanoscale objects.

quant-ph↗