arXiv subjects

Markus Arndt

Publications and source records attributed to Markus Arndt.

At least 19 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↗

arXiv2025

Probing quantum mechanics using nanoparticle Schr\"odinger cats

The quantum superposition principle is a cornerstone of physics and at the heart of many quantum technologies. Yet, it is still often regarded counterintuitive because we do not observe its key features on the macroscopic scales of our daily lives. It is therefore intriguing to ask how quantum properties persist or change as we increase the size and complexity of objects. A paradigmatic test for this question can be realized by matter-wave interferometry, where the motion of individual massive particles becomes delocalized and needs to be described by a wave function that spans regions far larger than the particle itself. Here we present an experimental platform extending matter-wave interference to a qualitatively new class of materials that can vary widely in mass and size. We specifically demonstrate quantum interference of sodium nanoparticles, which can each contain more than 7'000 atoms at masses greater than 170'000 dalton. They propagate in a Schr\"odinger cat state with a macroscopicity of $\mu$ = 15.5, surpassing all previous experiments by an order of magnitude and providing the most stringent exclusion limit for generic macrorealistic modifications of the Schr\"odinger equation to date.

quant-ph↗

arXiv2024

Diffracting molecular matter-waves at deep-ultraviolet standing-light waves

Matter-wave interferometry with molecules is intriguing both because it demonstrates a fundamental quantum phenomenon and because it opens avenues to quantum-enhanced measurements in physical chemistry. One great challenge in such experiments is to establish matter-wave beam splitting mechanisms that are efficient and applicable to a wide range of particles. In the past, continuous standing light waves in the visible spectral range were used predominantly as phase gratings, while pulsed vacuum ultraviolet light found applications in photo-ionisation gratings. Here, we explore the regime of continuous, intense deep-ultraviolet ($\rm >1 MW/cm^2$, $\rm 266\,nm$) light masks, where a rich variety of photo-physical and photo-chemical phenomena and relaxation pathways must be considered. The improved understanding of the mechanisms in this interaction opens new potential pathways to protein interferometry and to matter-wave enhanced sensing of molecular properties.

quant-ph↗

arXiv2024

Probing molecular photophysics in a matter-wave interferometer

We show that matter-wave diffraction off a single standing laser wave can be used as an accurate measurement scheme for photophysical molecular parameters. These include state-dependent optical polarizabilities and photon-absorption cross sections, the relaxation rates for fluorescence, internal conversion, and intersystem crossing, as well as ionization or cleavage probabilities. We discuss how the different photophysical processes manifest as features of the interference pattern, and we determine the accuracy of molecular parameters estimated from a realistic measurement with finite particle numbers. The analysis is based on an analytic calculation in Wigner representation, which accounts for the laser-induced coherent and incoherent dynamics, for the finite longitudinal and transverse coherence in the matter-wave beam, the gravitational and Coriolis acceleration, and an imperfect standing laser wave.

physics.atom-ph↗

arXiv2024

Requirements for probing chiral Casimir-Polder forces in a molecular Talbot-Lau interferometer

We theoretically investigate the influence of chiral Casimir-Polder (CP) forces in Talbot-Lau interferometry, based on three nanomechanical gratings. We study scenarios where the second grating is either directly written into a chiral material or where the nanomask is coated with chiral substances. We show requirements for probing enantiospecific effects in matter-wave interferometry in the transmission signal and the interference fringe visibility, which depend on the de Broglie wavelength and the molecular chirality. The proposed setup is particularly sensitive to CP forces in the non-retarded regime where chiral effects can be comparable in magnitude to their electric and magnetic counterparts. While the first and third gratings do not change the phase of the matter wave, applying a coating of chiral substances to them enhances the instrument's chiral selectivity.

quant-ph↗

arXiv2024

Impact of molecular properties on diffraction at nanomasks with low charge density

The quantum wave nature of matter is a cornerstone of modern physics, which has been demonstrated for a wide range of fundamental and composite particles. While diffraction at nanomechanical masks is usually regarded to be independent of atomic or molecular internal states, the particles' polarisabilities and dipole moments lead to dispersive interactions with the grating surface. In prior experiments, such forces largely prevented matter-wave experiments with polar molecules, as they led to dephasing of the matter wave in the presence of randomly distributed charges incorporated into the grating. Here we show that ion-beam milling using neon facilitates the fabrication of lowly-charged nanomasks in gold-capped silicon nitride membranes. This allows us to observe the diffraction of polar molecules with a four times larger electric dipole moment than in previous experiments. This new capability opens a path to the assessment of the structure of polar molecules in matter-wave diffraction experiments.

quant-ph↗

arXiv2023

Experimental challenges for high-mass matter-wave interference with nanoparticles

We discuss recent advances towards matter-wave interference experiments with free beams of metallic and dielectric nanoparticles. They require a brilliant source, an efficient detection scheme and a coherent method to divide the de Broglie waves associated with these clusters: We describe an approach based on a magnetron sputtering source which ejects an intense cluster beam with a wide mass dispersion but a small velocity spread of 10%. The source is universal as it can be used with all conducting and many semiconducting or even insulating materials. Here we focus on metals and dielectrics with a low work function of the bulk and thus a low cluster ionization energy. This allows us to realize photoionization gratings as coherent matter-wave beam splitters and also to realize an efficient ionization detection scheme. These new methods are now combined in an upgraded Talbot-Lau interferometer with three 266 nm depletion gratings. We here describe the experimental boundary conditions and how to realize them in the lab. This next generation of near-field interferometers shall allow us to soon push the limits of matter-wave interference to masses up to 10 megadaltons.

quant-ph↗

arXiv2022

Nanoscale magnetism probed in a matter-wave interferometer

We explore a wide range of fundamental magnetic phenomena by measuring the dephasing of matter-wave interference fringes upon application of a variable magnetic gradient. The versatility of our interferometric Stern-Gerlach technique enables us to study alkali atoms, organic radicals and fullerenes in the same device, with magnetic moments ranging from a Bohr magneton to less than a nuclear magneton. We find evidence for magnetization of a supersonic beam of organic radicals and, most notably, observe a strong magnetic response of a thermal C$_{60}$ beam consistent with high-temperature atom-like deflection of rotational magnetic moments.

quant-ph↗

arXiv2022

MAQRO -- BPS 2023 Research Campaign Whitepaper

The objective of the proposed MAQRO mission is to harness space for achieving long free-fall times, extreme vacuum, nano-gravity, and cryogenic temperatures to test the foundations of physics in macroscopic quantum experiments. This will result in the development of novel quantum sensors and a means to probe the foundations of quantum physics at the interface with gravity. Earlier studies showed that the proposal is feasible but that several critical challenges remain, and key technologies need to be developed. These new technologies will open up the potential for achieving additional science objectives. The proposed research campaign aims to advance the state of the art and to perform the first macroscopic quantum experiments in space. Experiments on the ground, in micro-gravity, and in space will drive the proposed research campaign during the current decade to enable the implementation of MAQRO within the subsequent decade.

quant-ph↗

arXiv2021

Single-, double-, and triple-slit diffraction of molecular matter-waves

Even 100 years after its introduction by Louis de Broglie, the wave-nature of matter is often regarded as a mind-boggling phenomenon. To give an intuitive introduction to this field, we here discuss the diffraction of massive molecules through a single, double, and triple slit, as well as a nanomechanical grating. While the experiments are in good agreement with undergraduate textbook predictions, we also observe pronounced differences resulting from the molecules' mass and internal complexity. The molecules' polarizability causes an attractive van der Waals interaction with the slit walls, which can be modified by rotating the nanomechanical mask with respect to the molecular beam. The text is meant to introduce students and teachers to the concepts of molecule diffraction, supported by problems and solutions that can be discussed in class.

quant-ph↗

arXiv2021

Kapitza-Dirac blockade: A universal tool for the deterministic preparation of non-Gaussian oscillator states

Harmonic oscillators count among the most fundamental quantum systems with important applications in molecular physics, nanoparticle trapping, and quantum information processing. Their equidistant energy level spacing is often a desired feature, but at the same time a challenge if the goal is to deterministically populate specific eigenstates. Here, we show how interference in the transition amplitudes in a bichromatic laser field can suppress the sequential climbing of harmonic oscillator states (Kapitza-Dirac blockade) and achieve selective excitation of energy eigenstates, Schrödinger cats and other non-Gaussian states. This technique can transform the harmonic oscillator into a coherent two-level system or be used to build a large-momentum-transfer beam splitter for matter-waves. To illustrate the universality of the concept, we discuss feasible experiments that cover many orders of magnitude in mass, from single electrons over large molecules to dielectric nanoparticles.

quant-ph↗

arXiv2021

High finesse microcavities in the optical telecom O-band

Optical microcavities allow to strongly confine light in small mode volumes and with long photon lifetimes. This confinement significantly enhances the interaction between light and matter inside the cavity, with applications such as optical trapping and cooling of nanoparticles, single-photon emission enhancement, quantum information processing, and sensing. For many applications, open resonators with direct access to the mode volume are necessary. Here we report on a scalable, open-access optical microcavity platform with mode volumes < 30 $λ^3$ and finesse approaching $5x10^5$. This result significantly exceeds the highest optical enhancement factors achieved to date for Fabry-Pérot cavities. The platform provides a building block for high-performance quantum devices relying on strong light-matter interaction.

quant-ph↗

arXiv2021

Experimental decoherence in molecule interferometry

Complex molecules are intriguing objects at the interface between quantum and classical phenomena. Compared to the electrons, neutrons, or atoms studied in earlier matter-wave experiments, they feature a much more complicated internal structure, but can still behave as quantum objects in their center-of-mass motion. Molecules may involve a large number of vibrational modes and highly excited rotational states, they can emit thermal photons, electrons, or even atoms, and they exhibit large cross sections for collisional interactions with residual background gases. This makes them ideal candidates for decoherence experiments which we review in this contribution.

quant-ph↗

arXiv2020

Bragg diffraction of large organic molecules

We demonstrate Bragg diffraction of the antibiotic ciprofloxacin and the dye molecule phthalocyanine at a thick optical grating. The observed patterns show a single dominant diffraction order with the expected dependence on the incidence angle as well as oscillating population transfer between the undiffracted and diffracted beams. We achieve an equal-amplitude splitting of $14 \hbar k$ (photon momenta) and maximum momentum transfer of $18 \hbar k$. This paves the way for efficient, large-momentum beam splitters and mirrors for hot and complex molecules.

physics.optics↗

arXiv2020

A fiber-based beam profiler for high-power laser beams in confined spaces and ultra-high vacuum

Laser beam profilometry is an important scientific task with well-established solutions for beams propagating in air. It has, however, remained an open challenge to measure beam profiles of high-power lasers in ultra-high vacuum and in tightly confined spaces. Here we present a novel scheme that uses a single multi-mode fiber to scatter light and guide it to a detector. The method competes well with commercial systems in position resolution, can reach through apertures smaller than $500\times 500$~$μ$m$^2$ and is compatible with ultra-high vacuum conditions. The scheme is simple, compact, reliable and can withstand laser intensities beyond 2~MW/cm$^2$.

physics.ins-det↗

arXiv2019

Matter-wave interference of a native polypeptide

The de Broglie wave nature of matter is a paradigmatic example of fundamental quantum physics and enables precise measurements of forces, fundamental constants and even material properties. However, even though matter-wave interferometry is nowadays routinely realized in many laboratories, this feat has remained an outstanding challenge for the vast class of native polypeptides, the building blocks of life, which are ubiquitous in biology but fragile and difficult to handle. Here, we demonstrate the quantum wave nature of gramicidin, a natural antibiotic composed of 15 amino acids. Femtosecond laser desorption of a thin biomolecular film with intensities up to 1~TW/cm$^2$ transfers these molecules into a cold noble gas jet. Even though the peptide's de Broglie wavelength is as tiny as 350~fm, the molecular coherence is delocalized over more than 20 times the molecular size in our all-optical time-domain Talbot-Lau interferometer. We compare the observed interference fringes for two different interference orders with a model that includes both a rigorous treatment of the peptide's quantum wave nature as well as a quantum chemical assessment of its optical properties to distinguish our result from classical predictions. The successful realization of quantum optics with this polypeptide as a prototypical biomolecule paves the way for quantum-assisted molecule metrology and in particular the optical spectroscopy of a large class of biologically relevant molecules.

quant-ph↗

arXiv2018

Probing Macroscopic Quantum Superpositions with Nanorotors

Whether quantum physics is universally valid is an open question with far-reaching implications. Intense research is therefore invested into testing the quantum superposition principle with ever heavier and more complex objects. Here we propose a radically new, experimentally viable route towards studies at the quantum-to-classical borderline by probing the orientational quantum revivals of a nanoscale rigid rotor. The proposed interference experiment testifies a macroscopic superposition of all possible orientations. It requires no diffraction grating, uses only a single levitated particle, and works with moderate motional temperatures under realistic environmental conditions. The first exploitation of quantum rotations of a massive object opens the door to new tests of quantum physics with submicron particles and to quantum gyroscopic torque sensors, holding the potential to improve state-of-the art devices by many orders of magnitude.

quant-ph↗

arXiv2018

Conformer-selection by matter-wave interference

We establish that matter-wave interference at near-resonant ultraviolet optical gratings can be used to spatially separate individual conformers of complex molecules. Our calculations show that the conformational purity of the prepared beam can be close to 100% and that all molecules remain in their electronic ground state. The proposed technique is independent of the dipole moment and the spin of the molecule and thus paves the way for structure-sensitive experiments with hydrocarbons and biomolecules, such as neurotransmitters and hormones, which evaded conformer-pure isolation so far

physics.chem-ph↗