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Hendrik Ulbricht

Publications and source records attributed to Hendrik Ulbricht.

At least 91 records · Page 5Linked to original sources
arXiv2014

On the Existence of Low-Mass Dark Matter and its Direct Detection

Dark Matter (DM) is an elusive form of matter which has been postulated to explain astronomical observations through its gravitational effects on stars and galaxies, gravitational lensing of light around these, and through its imprint on the Cosmic Microwave Background (CMB). This indirect evidence implies that DM accounts for as much as 84.5% of all matter in our Universe, yet it has so far evaded all attempts at direct detection, leaving such confirmation and the consequent discovery of its nature as one of the biggest challenges in modern physics. Here we present a novel form of low-mass DM $χ$ that would have been missed by all experiments so far. While its large interaction strength might at first seem unlikely, neither constraints from particle physics nor cosmological/astronomical observations are sufficient to rule out this type of DM, and it motivates our proposal for direct detection by optomechanics technology which should soon be within reach, namely, through the precise position measurement of a levitated mesoscopic particle which will be perturbed by elastic collisions with $χ$ particles. We show that a recently proposed nanoparticle matter-wave interferometer, originally conceived for tests of the quantum superposition principle, is sensitive to these collisions, too.

hep-ph↗
arXiv2014

Influence of conformational molecular dynamics on matter wave interferometry

We investigate the influence of thermally activated internal molecular dynamics on the phase shifts of matter waves inside a molecule interferometer. While de Broglie physics generally describes only the center-of-mass motion of a quantum object, our experiment demonstrates that the translational quantum phase is sensitive to dynamic conformational state changes inside the diffracted molecules. The structural flexibility of tailor-made hot organic particles is sufficient to admit a mixture of strongly fluctuating dipole moments. These modify the electric susceptibility and through this the quantum interference pattern in the presence of an external electric field. Detailed molecular dynamics simulations combined with density functional theory allow us to quantify the time-dependent structural reconfigurations and to predict the ensemble-averaged square of the dipole moment which is found to be in good agreement with the interferometric result. The experiment thus opens a new perspective on matter wave interferometry as it demonstrates for the first time that it is possible to collect structural information about molecules even if they are delocalized over more than hundred times their own diameter.

quant-ph↗
arXiv2014

Extended Wigner function formalism for the spatial propagation of particles with internal degrees of freedom

An extended Wigner function formalism is introduced for describing the quantum dynamics of particles with internal degrees of freedom in the presence of spatially inhomogeneous fields. The approach is used for quantitative simulations of molecular beam experiments involving space-spin entanglement, such as the Stern-Gerlach and the Rabi experiment. The formalism allows a graphical visualization of entanglement and decoherence processes.

quant-ph↗
arXiv2013

Optomechanical interface for probing matter-wave coherence

We combine matter-wave interferometry and cavity optomechanics to propose a coherent matter--light interface based on mechanical motion at the quantum level. We demonstrate a mechanism that is able to transfer non-classical features imprinted on the state of a matter-wave system to an optomechanical device, transducing them into distinctive interference fringes. This provides a reliable tool for the inference of quantum coherence in the particle beam. Moreover, we discuss how our system allows for intriguing perspectives, paving the way to the construction of a device for the encoding of quantum information in matter-wave systems. Our proposal, which highlights previously unforeseen possibilities for the synergetic exploitation of these two experimental platforms, is explicitly based on existing technology, available and widely used in current cutting-edge experiments.

quant-ph↗
arXiv2013

Testing the quantum superposition principle in the frequency domain

New technological developments allow to explore the quantum properties of very complex systems, bringing the question of whether also macroscopic systems share such features, within experimental reach. The interest in this question is increased by the fact that, on the theory side, many suggest that the quantum superposition principle is not exact, departures from it being the larger, the more macroscopic the system. Here we propose a novel way to test the possible violation of the superposition principle, by analyzing its effect on the spectral properties of a generic two-level system. We will show that spectral lines shapes are modified, if the superposition principle is violated, and we quantify the magnitude of the violation. We show how this effect can be distinguished from that of standard environmental noises. We argue that accurate enough spectroscopic experiments are within reach, with current technology.

quant-ph↗
arXiv2013

Manipulation of a continuous beam of molecules by light pulses

We experimentally observe the action of multiple light pulses on the transverse motion of a continuous beam of fullerenes. The light potential is generated by non-resonant ultra-short laser pulses in perpendicular spatial overlap with the molecule beam. We observe a small but clear enhancement of the number of molecules in the center fraction of the molecular beam. Relatively low light intensity and short laser pulse duration prevent the molecule from fragmentation and ionization. Experimental results are confirmed by Monte Carlo trajectory simulations.

physics.atm-clus↗
arXiv2012

Models of Wave-function Collapse, Underlying Theories, and Experimental Tests

Quantum mechanics is an extremely successful theory that agrees with every experiment. However, the principle of linear superposition, a central tenet of the theory, apparently contradicts a commonplace observation: macroscopic objects are never found in a linear superposition of position states. Moreover, the theory does not really explain as to why during a quantum measurement, deterministic evolution is replaced by probabilistic evolution, whose random outcomes obey the Born probability rule. In this article we review an experimentally falsifiable phenomenological proposal, known as Continuous Spontaneous Collapse: a stochastic non-linear modification of the Schrödinger equation, which resolves these problems, while giving the same experimental results as quantum theory in the microscopic regime. Two underlying theories for this phenomenology are reviewed: Trace Dynamics, and gravity induced collapse. As one approaches the macroscopic scale, the predictions of this proposal begin to differ appreciably from those of quantum theory, and are being confronted by ongoing laboratory experiments that include molecular interferometry and optomechanics. These experiments, which essentially test the validity of linear superposition for large systems, are reviewed here, and their technical challenges, current results, and future prospects summarized. We conclude that it is likely that over the next two decades or so, these experiments can verify or rule out the proposed stochastic modification of quantum theory.

quant-ph↗
arXiv2012

Is quantum linear superposition an exact principle of nature?

The principle of linear superposition is a hallmark of quantum theory. It has been confirmed experimentally for photons, electrons, neutrons, atoms, for molecules having masses up to ten thousand amu, and also in collective states such as SQUIDs and Bose-Einstein condensates. However, the principle does not seem to hold for positions of large objects! Why for instance, a table is never found to be in two places at the same time? One possible explanation for the absence of macroscopic superpositions is that quantum theory is an approximation to a stochastic nonlinear theory. This hypothesis may have its fundamental origins in gravitational physics, and is being put to test by modern ongoing experiments on matter wave interferometry.

quant-ph↗
arXiv2010

Wave and Particle in Molecular Interference Lithography

The wave-particle duality of massive objects is a cornerstone of quantum physics and a key property of many modern tools such as electron microscopy, neutron diffraction or atom interferometry. Here we report on the first experimental demonstration of quantum interference lithography with complex molecules. Molecular matter-wave interference patterns are deposited onto a reconstructed Si(111) 7x7 surface and imaged using scanning tunneling microscopy. Thereby both the particle and the quantum wave character of the molecules can be visualized in one and the same image. This new approach to nanolithography therefore also represents a sensitive new detection scheme for quantum interference experiments.

quant-ph↗
arXiv2009

Theory and experimental verification of Kapitza-Dirac-Talbot-Lau interferometry

Kapitza-Dirac-Talbot-Lau interferometry (KDTLI) has recently been established for demonstrating the quantum wave nature of large molecules. A phase space treatment permits us to derive closed equations for the near-field interference pattern, as well as for the Moire-type pattern that would arise if the molecules were to be treated as classical particles. The model provides a simple and elegant way to account for the molecular phase shifts related to the optical dipole potential as well as for the incoherent effect of photon absorption at the second grating. We present experimental results for different molecular masses, polarizabilities and absorption cross sections using fullerenes and fluorofullerenes and discuss the alignment requirements. Our results with C60 and C70, C60F36 and C60F48 verify the theoretical description to a high degree of precision.

quant-ph↗
arXiv2008

Absolute absorption spectroscopy based on molecule interferometry

We propose a new method to measure the absolute photon absorption cross section of neutral molecules in a molecular beam. It is independent of our knowledge of the particle beam density, nor does it rely on photo-induced fragmentation or ionization. The method is based on resolving the recoil resulting from photon absorption by means of near-field matter-wave interference, and it thus applies even to very dilute beams with low optical densities. Our discussion includes the possibility of internal state conversion as well as fluorescence. We assess the influence of various experimental uncertainties and show that the measurement of absolute absorption cross sections is conceivable with high precision and using existing technologies.

quant-ph↗
arXiv2008

A Kapitza-Dirac-Talbot-Lau interferometer for highly polarizable molecules

Research on matter waves is a thriving field of quantum physics and has recently stimulated many investigations with electrons, neutrons, atoms, Bose-condensed ensembles, cold clusters and hot molecules. Coherence experiments with complex objects are of interest for exploring the transition to classical physics, for measuring molecular properties and they have even been proposed for testing new models of space-time. For matter-wave experiments with complex molecules, the strongly dispersive effect of the interaction between the diffracted molecule and the grating wall is a major challenge because it imposes enormous constraints on the velocity selection of the molecular beam. We here describe the first experimental realization of a new interferometer that solves this problem by combining the advantages of a Talbot-Lau setup with the benefits of an optical phase grating and we show quantum interference with new large molecules.

quant-ph↗
arXiv2007

Optical polarizabilities of large molecules measured in near-field interferometry

We discuss a novel application of matter wave interferometry to characterize the scalar optical polarizability of molecules at 532 nm. The interferometer presented here consists of two material absorptive gratings and one central optical phase grating. The interaction of the molecules with the standing light wave is determined by the optical dipole force and is therefore directly dependent on the molecular polarizability at the wavelength of the diffracting laser light. By comparing the observed matter-wave interference contrast with a theoretical model for several intensities of the standing light wave and molecular velocities we can infer the polarizability in this first proof-of-principle experiment for the fullerenes C60 and C70 and we find a good agreement with literature values.

quant-ph↗
arXiv2007

Gas phase sorting of nanoparticles

We discuss Stark deflectometry of micro-modulated molecular beams for the enrichment of biomolecular isomers as well as single-wall carbon nanotubes and we demonstrate the working principle of this idea with fullerenes. The sorting is based on the species-dependent polarizability-to-mass ratio $α/m$. The device is compatible with a high molecular throughput, and the spatial micro-modulation of the beam permits to obtain a fine spatial resolution and a high sorting sensitivity.

quant-ph↗
arXiv2007

Slow beams of massive molecules

Slow beams of neutral molecules are of great interest for a wide range of applications, from cold chemistry through precision measurements to tests of the foundations of quantum mechanics. We report on the quantitative observation of thermal beams of perfluorinated macromolecules with masses up to 6000 amu, reaching velocities down to 11 m/s. Such slow, heavy and neutral molecular beams are of importance for a new class of experiments in matter-wave interferometry and we also discuss the requirements for further manipulation and cooling schemes with molecules in this unprecedented mass range.

quant-ph↗
arXiv2003

The interlayer cohesive energy of graphite from thermal desorption of polyaromatic hydrocarbons

We have studied the interaction of polyaromatic hydrocarbons (PAHs) with the basal plane of graphite using thermal desorption spectroscopy. Desorption kinetics of benzene, naphthalene, coronene and ovalene at sub-monolayer coverages yield activation energies of 0.50 eV, 0.85 eV, 1.40 eV and 2.1 eV, respectively. Benzene and naphthalene follow simple first order desorption kinetics while coronene and ovalene exhibit fractional order kinetics owing to the stability of 2-D adsorbate islands up to the desorption temperature. Pre-exponential frequency factors are found to be in the range $10^{14}$-$10^{21} s^{-1}$ as obtained from both Falconer--Madix (isothermal desorption) analysis and Antoine's fit to vapour pressure data. The resulting binding energy per carbon atom of the PAH is $52\pm$5 meV and can be identified with the interlayer cohesive energy of graphite. The resulting cleavage energy of graphite is $61\pm5$~meV/atom which is considerably larger than previously reported experimental values.

cond-mat.mtrl-sci↗
arXiv2002

Physisorption of molecular oxygen on single-wall carbon nanotube bundles and graphite

We present a study on the kinetics of oxygen adsorption and desorption from single-wall carbon nanotube (SWNT) and highly oriented pyrolytic graphite (HOPG) samples. Thermal desorption spectra for SWNT samples show a broad desorption feature peaked at 62 K which is shifted to significantly higher temperature than the low-coverage desorption feature on HOPG. The low-coverage O2 binding energy on SWNT bundles, 18.5 kJ/mol, is 55% higher than that for adsorption on HOPG, 12.0 kJ/mol. In combination with molecular mechanics calculations we show that the observed binding energies for both systems can be attributed to van der Waals interactions, i.e. physisorption. The experiments provide no evidence for a more strongly bound chemisorbed species or for dissociative oxygen adsorption.

cond-mat.mtrl-sci↗