# Hornberger group - Welcome

## Welcome to our website

We are exploring the complex dynamics of open nanoscale quantum systems, partly in collaboration with leading experimentalists.

Current projects focus on the study of coherence and entanglement phenomena in nanomechanical systems and molecular matter waves, and on the microscopic mechanisms that effect their quantum-to-classical transition.

## October 25, 2019

## Dr. Marduk Bolaños Puchet

Habemus etiam doctorem! Marduk Bolaños received a Ph.D. from the Faculty of Physics for his dissertation on the *Decoherence of non-relativistic bosonic quantum fields*.

Congrats, Marduk!

## September 24, 2019

## Björn Schrinski, Ph.D.

Habemus doctorem! Björn Schrinski received a Ph.D. from the Faculty of Physics for his dissertation on *Assessing the macroscopicity of quantum mechanical superposition tests via hypothesis falsification*.

Congrats, Björn!

## September 16, 2019

## Schrödinger's cat put on the scale

We establish an objective scheme to determine the degree of macroscopicity reached in quantum mechanical superposition tests, i.e. the size of an experimentally realized Schrödinger's cat. Based on the Bayesian falsification of macrorealistic modifications, it uses the raw data of an experiment, taking into account all measurement uncertainties.

## 29 Jul - 1 Aug 2019

## Workshop on Levitated Optomechanics

A WE-Heraeus seminar on Levitated Optomechanicswas held at Physikzentrum Bad Honnef, Germany on 29 Jul - 1 Aug 2019 (organized by K. Hornberger, J. Millen, and M. Arndt).

The seminar brought together leading scientists and young researchers working on the control of nanoparticles suspended in vacuum by optical or electric forces. The most recent advances were discussed of cooling untethered nano-mechanical systems into the quantum regime and of observing their rotranslational motion in the quantum-classical borderlands, as well as the perspectives of harnessing their coherent quantum dynamics for fundamental experiments and technological applications.

## June 27, 2019

## Decoherence of quantum fields

We present a generic description of the quantum-to-classical transition of non-relativistic bosonic fields.

## November 20, 2018

## Coherence of molecular superrotors

Decoherence theory explains the surprising stability of the alignment of rapidly rotating molecules, in excellent quantitative agreement with the experimental observation.

## October 29, 2018

## Orientational quantum superpositions of nanoscale rotors

In a recent preprint, we propose an experimentally viable scheme to probe orientational quantum revivals with nanoscale particles, an interference effect of the rotational degrees of freedom testifying a superposition of all orientations. This opens the door to tests of rotational quantum physics with submicron objects and to quantum gyroscopic torque sensors.

New Journal of Physics **20,** 122001 (2018) (Fast Track Communication)

## September 17, 2018

## Conformer-selection by matter-wave interference

In almost all larger molecules, the spatial arrangement of the atoms can show up in different geometries, even with all binding links equal. We show that such conformers can be selected from a mixture using a matter-wave interferometer.

## July 3, 2018

## Best Talk Award for Björn Schrinski

At the Bayesian Young Statisticians Meeting (BAYSM 2018) in Warwick (UK) Björn Schrinski gave a lecture entitled "Towards Bayesian hypothesis testing of macrorealistic modifications of quantum mechanics", and he duly received a Best Talk Award for his presentation.

Congrats, Björn!

## June 15, 2018

## Rotational friction and diffusion of quantum rotors

We present the general quantum description of friction, diffusion, decoherence, and thermalization in the rotational motion of rigid bodies. In the semiclassical limit, one obtains the classical Fokker-Planck equation for the rotational dynamics of a top.

## June 15, 2018

## Thesis Award for Lukas Martinetz

Lukas Martinetz was awarded the prize for the best master thesis from the Faculty of Physics. The award certificate was presented by the Rector of the University of Duisburg-Essen, Prof. Ulrich Radtke, during the Dies Academicus ceremony.

Congrats, Lukas!

## May 11, 2018

## Gas-induced friction and diffusion of classical rigid rotors

The impact of a rarefid gas on the coupled rotational and translational motion of arbitrarily shaped particles can be predicted microscopically from the Boltzmann equation, yielding the associated friction and diffusion tensors.

Phys. Rev. E 97, 052112 (2018)

This article was designated as an Editor's Suggestion by *Physical Review E. *

## December 7, 2017

## Quantum Angular Momentum Diffusion of Nanoparticles

The rotational quantum dynamics of an arbitrarily shaped nanoparticle exhibits angular momentum diffusion due to the interaction with environmental gases and background fields.

New Journal of Physics 19 (2017) 122001 (Fast Track Communication)

This article was designated as Highlight 2017 by *New Journal of Physics.*

## November 22, 2017

## A nanoscale clock with precise dials

Suitably modulated laser beams imprint the precision of an electronic clock onto the intrinsically chaotic angular motion of a levitated nanoscale dial.

## March 13, 2017

## Optical Control of Levitated Nanorods

The ro-translational motion of silicon nanorods can be detected and manipulated by laser light in an optical cavity.

## November 4, 2016

## Kai Walter, Ph.D.

Habemus doctorem! Kai Walter received a Ph.D. from the Faculty of Physics for his dissertation on *Coherence and Decoherence in High-mass Matter-wave Interferometry*.

Congrats, Kai!

おめでとう

## October 14, 2016

## Rotranslational Cavity Cooling of Dielectric Rods and Disks

Nonspherical nanoparticles can be cooled to the quantum regime of their center-of-mass and rotational motion.

Phys. Rev. A**94**, 033818 (2016)

## October 10, 2016

## Lutz Sörgel, Ph.D.

Habemus doctorem! Lutz Sörgel received a Ph.D. from the Faculty of Physics for his dissertation on *Pointer state dynamics of dissipative quantum systems*.

Congrats, Lutz!

## September 10, 2016

## Björn Schrinski Receives Poster Award

Björn Schrinski presented his poster entitled *Interference of Bose-Einstein Condensates under the Influence of Decoherence *at the Conference *Frontiers in Matter Wave Optics* (*FOMF2016*) in Arcachon, France, and he received a poster award for his contribution.

Congrats, Björn!

## July 4, 2016

## Attending Bill Phillips' Master Class

Benjamin Stickler attended this year's *Lindau Nobel Laureate Meeting *at Lake Constance, and presented his research results in Bill Phillips' master class. Benjamin was also one of the few young researchers selected to present their work on a poster for all participants.

Congrats, Benjamin!

## June 11, 2015

## Coherent photoabsorption in a molecule interferometer

The absorption of individual photons by large molecules gives rise to surprising coherence effects which can be observed in a matter wave interferometer.

## December 4, 2014

## Stefan Nimmrichter receives Award of Excellence 2014

Stefan Nimmrichter was granted the Award of Excellence by the Federal Minister for Science, Research, and Commerce of the Republic of Austria.

Congrats Stefan!

## September 2, 2014

## Near-field interferometry of a free-falling nanoparticle from a point-like source

Our proposal for a near-field interference scheme for 10^{6} amu silicon particles based on the single-source Talbot effect appeared in *Nature Communications*. It would allow testing the quantum superposition principle at unrivaled scales.

## August 6, 2014

## Felix Lucas, Ph.D.

Habemus doctorem! Felix Lucas received a Ph.D. from the Faculty of Physics for his dissertation on *Adaptive Resummation of Markovian Quantum Dynamics*.

Congrats, Felix!

## August 5, 2014

## Incoherent Control of the Retinal Isomerization

The back-action of quantum measurements can provide a handle for controling relatively complex quantum systems. This is demonstrated by means of an important bio-chemical reaction, the photo-induced isomerization of retinal in the protein rhodopsin.

Phys. Rev. Lett. **113**, 058301 (2014)

## Optomechanical sensing of spontaneous wave-function collapse

Hypothetical modifications of the Schrödinger equation, which serve to destroy superpositions on macroscopic scales, can be sensed by monitoring a test mass. Surprisingly, this mass should not be much greater than a few picogramms.

Phys. Rev. Lett. **113**, 020405 (2014)

## April 29, 2014

## Timo Fischer, Ph.D.

Habemus doctorem! Timo Fischer received a Ph.D. from the Faculty of Physics for his dissertation *Decoherence of the Orientation State*.

Congrats, Timo!

## April 1, 2014

## Testing the limits of quantum mechanical superpositions

A review article on tests of the quantum superposition principle in increasingly macroscopic systems appeared in *Nature Physics*.

Nature Phys. **10**, 271-277 (2014)

This is part of a dedicated issue, a *Nature Physics Insight*, on the foundations of quantum mechanics.

## January 15, 2014

## Adaptive Resummation of Markovian Quantum Dynamics

Our method for deriving analytic approximations for the dynamics of open quantum systems appeared in *Physical Review Letters*.

Phys. Rev. Lett **110**, 240401 (2013)

A more detailled article discusses the convergence properties and the numerical implementation of the resummation: Phys. Rev. A **89**, 012112 (2014)

## Dezember 30, 2013

## Quantum mechanics in curved phase spaces

Our consistent extension of the Wigner-Weyl-Moyal phase-space formulation of quantum mechanics to general curved configuration spaces appeared in *Physical Review A*.

## October 29, 2013

## Stefan Nimmrichter, Ph.D.

Habemus doctorem! Stefan Nimmrichter received a Ph.D. from the University of Vienna for his dissertation on *Macroscopic matter wave interferometry*.

The work was awarded a *Springer Thesis Prize*,and it will be published as a *Springer Thesis* — 'Recognizing Outstanding Ph.D. Research'.

Congrats, Stefan!

## July 9, 2013

## Nonlocal Young tests with Einstein-Podolsky-Rosen-correlated particle pairs

Nonlocal interference based on EPR-correlated particles allows one to detect entanglement and non-classical particle behavior using simple position measurements.

## June 7, 2013

## Wigner function for the orientation state

Our extension of the Wigner-Weyl phase space representation to the rotation dynamics of solid quantum objects appeared in *New Journal of Physics*.

## April 18, 2013

## Macroscopicity of mechanical quantum superposition states

Our proposal for an experimentally accessible, objective, and universal measure for the macroscopicity of superposition states in material quantum systems appeared in *Physical Review Letters*.

Phys. Rev. Lett.** 110**, 160403 (2013)

Feature articles on this work can be found in New Scientist (*Quantum effects get a weirdness scale*), in Physics World (*How fat is Schrödinger’s cat?*) and in Physics (*Quantumness put on the scale*). See also phys.org (*Physicists propose measure of macroscopicity*) und phsycs.com (*Physicists introduce magnitude of macroscopicity*).

## May 12th - 17th, 2013

## Summer school on tests of the quantum superposition principle

A summer school on **Exploring the quantum superposition principle** took place at the Physikzentrum Bad Honnef (near Bonn/Germany) on May 12th-17th, 2013. Further information is available at the school website.

Organizers: M. Arndt (U Vienna), K. Hornberger (U Duisburg-Essen)

Generous funding is provided by the Wilhem & Else Heraeus Foundation

## February 7th, 2013

## Kickoff meeting of NANOQUESTFIT collaboration

The kickoff meeting of the NANOQUESTFIT collaboration took place at Campus Duisburg, MG 465 on February 7th and 8th. A goal of this EU research project (ICT FET Open STREP) is to use matter wave interferometry of large molecules and clusters to probe the limits of the quantum superposition principle.

## Feb 8, 2012

## Quantum interference of clusters and molecules

Our review article on matter wave interferometry of complex organic molecules and inorganic clusters appeared in *Reviews of Modern Physics*.

It has been reviewed by Mark Buchanan in *Nature Physics*.