Showing 1–13 of 13 results for author: Betz, T

Time reversal breaking of colloidal particles in cells

Authors: Gabriel Knotz, Till M. Muenker, Timo Betz, Matthias Krüger

Abstract: We investigate signatures of broken time reversal symmetry in stochastic trajectory data, employing the previously introduced three point correlation called mean back relaxation. We specifically investigate data from a simple driven model, as well as from colloidal particles within living or passivated biological cells. Both in the model as well as in cell data, MBR detects broken time reversal sy… ▽ More We investigate signatures of broken time reversal symmetry in stochastic trajectory data, employing the previously introduced three point correlation called mean back relaxation. We specifically investigate data from a simple driven model, as well as from colloidal particles within living or passivated biological cells. Both in the model as well as in cell data, MBR detects broken time reversal symmetry, and furthermore, allows to determine relevant time and length scales of activity. For the cells, we show, by applying various drugs, that it is predominantly the presence of microtubules which is needed for a time reversal symmetry breaking. We employ a bound for entropy production, finding that it is in striking relation to previously determined active energies that quantify violation of the fluctuation dissipation theorem. △ Less

Submitted 17 March, 2026; originally announced March 2026.

Comments: 12 pages, 11 figures

Evaluating non-equilibrium trajectories via mean back relaxation: Dependence on length and time scales

Authors: Gabriel Knotz, Till M. Muenker, Timo Betz, Matthias Krüger

Abstract: The mean back relaxation (MBR) relates the value of a stochastic process at three different time points. It has been shown to detect broken detailed balance under certain conditions. For experiments of probe particles in living and passivated cells, MBR was found to be related to the so called effective energy, which quantifies the violation of the fluctuation dissipation theorem. In this manuscri… ▽ More The mean back relaxation (MBR) relates the value of a stochastic process at three different time points. It has been shown to detect broken detailed balance under certain conditions. For experiments of probe particles in living and passivated cells, MBR was found to be related to the so called effective energy, which quantifies the violation of the fluctuation dissipation theorem. In this manuscript, we discuss the dependence on the length and time parameters that enter MBR, both for cells as well as for a model system, finding qualitative agreement between the two. For the cell data, we extend the phenomenological relation between MBR and effective energy to a larger range of time parameters compared to previous work, allowing to test it in systems with limited resolution. We analyze the variance of back relaxation (VBR) in dependence of the mentioned parameters, relevant for the statistical error in MBR evaluation. For Gaussian systems, the variance is found analytically in terms of the mean squared displacement, and we determine its absolute minimum as a function of the length and time parameters. Comparing VBR from cell data to a Gaussian prediction demonstrates a non-Gaussian process. △ Less

Submitted 11 September, 2025; v1 submitted 8 July, 2025; originally announced July 2025.

Comments: 19 pages, 10 figures, accepted version

Variance Sum Rule for Entropy Production

Authors: I. Di Terlizzi, M. Gironella, D. Herraez-Aguilar, T. Betz, F. Monroy, M. Baiesi, F. Ritort

Abstract: Entropy production is the hallmark of nonequilibrium physics, quantifying irreversibility, dissipation, and the efficiency of energy transduction processes. Despite many efforts, its measurement at the nanoscale remains challenging. We introduce a variance sum rule for displacement and force variances that permits us to measure the entropy production rate $σ$ in nonequilibrium steady states. We fi… ▽ More Entropy production is the hallmark of nonequilibrium physics, quantifying irreversibility, dissipation, and the efficiency of energy transduction processes. Despite many efforts, its measurement at the nanoscale remains challenging. We introduce a variance sum rule for displacement and force variances that permits us to measure the entropy production rate $σ$ in nonequilibrium steady states. We first illustrate it for directly measurable forces, such as an active Brownian particle in an optical trap. We then apply the variance sum rule to flickering experiments in human red blood cells. We find that $σ$ is spatially heterogeneous with a finite correlation length and its average value agrees with calorimetry measurements. The VSR paves the way to derive $σ$ using force spectroscopy and time-resolved imaging in living and active matter. △ Less

Submitted 6 March, 2024; v1 submitted 16 February, 2023; originally announced February 2023.

Comments: 5 pages and 4 figures. It also contains Supp. Info. with 6 additional figures and 4 tables

MSC Class: 82A02

Journal ref: Science, 383, 971-976 (2024)

Entropy bound for time reversal markers

Authors: Gabriel Knotz, Till M. Muenker, Timo Betz, Matthias Krüger

Abstract: We derive a bound for entropy production in terms of the mean of normalizable path-antisymmetric observables. The optimal observable for this bound is shown to be the signum of entropy production, which is often easier determined or estimated than entropy production itself. It can be preserved under coarse graining by use of a simple path grouping algorithm. We demonstrate this relation and its pr… ▽ More We derive a bound for entropy production in terms of the mean of normalizable path-antisymmetric observables. The optimal observable for this bound is shown to be the signum of entropy production, which is often easier determined or estimated than entropy production itself. It can be preserved under coarse graining by use of a simple path grouping algorithm. We demonstrate this relation and its properties using a driven network on a ring, for which the bound saturates for short times for any driving strength. This work can open a way to systematic coarse graining of entropy production. △ Less

Submitted 13 November, 2023; v1 submitted 15 February, 2023; originally announced February 2023.

Comments: 5 pages, 2 figures

Roadmap for Optical Tweezers

Authors: Giovanni Volpe, Onofrio M. Maragò, Halina Rubinzstein-Dunlop, Giuseppe Pesce, Alexander B. Stilgoe, Giorgio Volpe, Georgiy Tkachenko, Viet Giang Truong, Síle Nic Chormaic, Fatemeh Kalantarifard, Parviz Elahi, Mikael Käll, Agnese Callegari, Manuel I. Marqués, Antonio A. R. Neves, Wendel L. Moreira, Adriana Fontes, Carlos L. Cesar, Rosalba Saija, Abir Saidi, Paul Beck, Jörg S. Eismann, Peter Banzer, Thales F. D. Fernandes, Francesco Pedaci , et al. (58 additional authors not shown)

Abstract: Optical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in life sciences, physics, and engineering. These include accurate force… ▽ More Optical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in life sciences, physics, and engineering. These include accurate force and torque measurement at the femtonewton level, microrheology of complex fluids, single micro- and nanoparticle spectroscopy, single-cell analysis, and statistical-physics experiments. This roadmap provides insights into current investigations involving optical forces and optical tweezers from their theoretical foundations to designs and setups. It also offers perspectives for applications to a wide range of research fields, from biophysics to space exploration. △ Less

Submitted 28 June, 2022; originally announced June 2022.

Comments: 181 pages, 61 figures

Nonequilibrium dissipation in living oocytes

Authors: Étienne Fodor, Wylie W. Ahmed, Maria Almonacid, Matthias Bussonnier, Nir S. Gov, Marie-Hélène Verlhac, Timo Betz, Paolo Visco, Frédéric van Wijland

Abstract: Living organisms are inherently out-of-equilibrium systems. We employ new developments in stochastic energetics and rely on a minimal microscopic model to predict the amount of mechanical energy dissipated by such dynamics. Our model includes complex rheological effects and nonequilibrium stochastic forces. By performing active microrheology and tracking micron-sized vesicles in the cytoplasm of l… ▽ More Living organisms are inherently out-of-equilibrium systems. We employ new developments in stochastic energetics and rely on a minimal microscopic model to predict the amount of mechanical energy dissipated by such dynamics. Our model includes complex rheological effects and nonequilibrium stochastic forces. By performing active microrheology and tracking micron-sized vesicles in the cytoplasm of living oocytes, we provide unprecedented measurements of the spectrum of dissipated energy. We show that our model is fully consistent with the experimental data, and we use it to offer predictions for the injection and dissipation energy scales involved in active fluctuations. △ Less

Submitted 22 December, 2016; v1 submitted 3 November, 2015; originally announced November 2015.

Comments: 5 pages, 2 figures

Journal ref: EPL 116, 30008 (2016)

Active mechanics reveal molecular-scale force kinetics in living oocytes

Authors: Wylie W. Ahmed, Etienne Fodor, Maria Almonacid, Matthias Bussonnier, Marie-Helene Verlhac, Nir S. Gov, Paolo Visco, Frederic van Wijland, Timo Betz

Abstract: Active diffusion of intracellular components is emerging as an important process in cell biology. This process is mediated by complex assemblies of molecular motors and cytoskeletal filaments that drive force generation in the cytoplasm and facilitate enhanced motion. The kinetics of molecular motors have been precisely characterized in-vitro by single molecule approaches, however, their in-vivo b… ▽ More Active diffusion of intracellular components is emerging as an important process in cell biology. This process is mediated by complex assemblies of molecular motors and cytoskeletal filaments that drive force generation in the cytoplasm and facilitate enhanced motion. The kinetics of molecular motors have been precisely characterized in-vitro by single molecule approaches, however, their in-vivo behavior remains elusive. Here, we study the active diffusion of vesicles in mouse oocytes, where this process plays a key role in nuclear positioning during development, and combine an experimental and theoretical framework to extract molecular-scale force kinetics (force, power-stroke, and velocity) of the in-vivo active process. Assuming a single dominant process, we find that the nonequilibrium activity induces rapid kicks of duration $τ\sim$ 300 $μ$s resulting in an average force of $F \sim$ 0.4 pN on vesicles in in-vivo oocytes, remarkably similar to the kinetics of in-vitro myosin-V. Our results reveal that measuring in-vivo active fluctuations allows extraction of the molecular-scale activity in agreement with single-molecule studies and demonstrates a mesoscopic framework to access force kinetics. △ Less

Submitted 8 February, 2018; v1 submitted 28 October, 2015; originally announced October 2015.

Comments: 20 pages, 4 figures, see ancillary files for Supplementary Materials, * equally contributing authors

Journal ref: Biophysical Journal 114,7, 1667(2018)

Dynamics of parametric matter wave amplification

Authors: Robert Bücker, Ulrich Hohenester, Tarik Berrada, Sandrine van Frank, Aurélien Perrin, Stephanie Manz, Thomas Betz, Julian Grond, Thorsten Schumm, Jörg Schmiedmayer

Abstract: We develop a model for parametric amplification, based on a density matrix approach, which naturally accounts for the peculiarities arising for matter waves: significant depletion and explicit time-dependence of the source state population, long interaction times, and spatial dynamics of the amplified modes. We apply our model to explain the details in an experimental study on twin-atom beam emiss… ▽ More We develop a model for parametric amplification, based on a density matrix approach, which naturally accounts for the peculiarities arising for matter waves: significant depletion and explicit time-dependence of the source state population, long interaction times, and spatial dynamics of the amplified modes. We apply our model to explain the details in an experimental study on twin-atom beam emission from a one-dimensional degenerate Bose gas. △ Less

Submitted 26 September, 2012; v1 submitted 23 March, 2012; originally announced March 2012.

Comments: 10 pages, 8 figures

Journal ref: Phys. Rev. A 86, 013638 (2012)

Shapiro effect in atomchip-based bosonic Josephson junctions

Authors: Julian Grond, Thomas Betz, Ulrich Hohenester, Norbert J. Mauser, Joerg Schmiedmayer, Thorsten Schumm

Abstract: We analyze the emergence of Shapiro resonances in tunnel-coupled Bose-Einstein condensates, realizing a bosonic Josephson junction. Our analysis is based on an experimentally relevant implementation using magnetic double well potentials on an atomchip. In this configuration the potential bias (implementing the junction voltage) and the potential barrier (realizing the Josephson link) are intrinsic… ▽ More We analyze the emergence of Shapiro resonances in tunnel-coupled Bose-Einstein condensates, realizing a bosonic Josephson junction. Our analysis is based on an experimentally relevant implementation using magnetic double well potentials on an atomchip. In this configuration the potential bias (implementing the junction voltage) and the potential barrier (realizing the Josephson link) are intrinsically coupled. We show that the dynamically driven system exhibits significantly enhanced Shapiro resonances which will facilitate experimental observation. To describe the systems response to the dynamic drive we compare a single-mode Gross-Pitaevskii (GP) description, an improved two-mode (TM) model and the self-consistent multi-configurational time dependent Hartree for Bosons (MCTDHB) method. We show that in the case of significant atom-atom interactions or strong driving, the spatial dynamics of the involved modes have to be taken into account, and only the MCTDHB method allows reliable predictions. △ Less

Submitted 7 February, 2011; originally announced February 2011.

Comments: 16 pages, 4 figures

Journal ref: New J. Phys. 13 065026 (2011)

Hanbury Brown and Twiss correlations across the Bose-Einstein condensation threshold

Authors: Aurélien Perrin, Robert Bücker, Stephanie manz, Thomas Betz, Christian Koller, Thomas Plisson, Thorsten Schumm, Jörg Schmiedmayer

Abstract: Hanbury Brown and Twiss (HBT) correlations, i.e. correlations in far-field intensity fluctuations, yield fundamental information on the quantum statistics of light sources, as highlighted after the discovery of photon bunching. Drawing on the analogy between photons and atoms, similar measurements have been performed for matter-wave sources, probing density fluctuations of expanding ultracold Bose… ▽ More Hanbury Brown and Twiss (HBT) correlations, i.e. correlations in far-field intensity fluctuations, yield fundamental information on the quantum statistics of light sources, as highlighted after the discovery of photon bunching. Drawing on the analogy between photons and atoms, similar measurements have been performed for matter-wave sources, probing density fluctuations of expanding ultracold Bose gases. Here we use two-point density correlations to study how coherence is gradually established when crossing the Bose-Einstein condensation (BEC) threshold. Our experiments reveal a persistent multimode character of the emerging matter-wave as seen in the non-trivial spatial shape of the correlation functions for all probed source geometries from nearly isotropic to quasi-one-dimensional (quasi-1D), and for all probed temperatures. The qualitative features of our observations are captured by ideal Bose gas theory, the quantitative differences illustrate the role of particle interactions. △ Less

Submitted 26 September, 2012; v1 submitted 23 December, 2010; originally announced December 2010.

Journal ref: Nat. Phys. 8, 195 (2012)

Twin-atom beams

Authors: Robert Bücker, Julian Grond, Stephanie Manz, Tarik Berrada, Thomas Betz, Christian Koller, Ulrich Hohenester, Thorsten Schumm, Aurélien Perrin, Jörg Schmiedmayer

Abstract: We present highly efficient emission of twin-atom beams into a single transversal mode of a waveguide potential. The source is a one-dimensional degenerate Bose gas in the first radially excited state. We directly measure a suppression of fluctuations in the atom number difference between the beams to 0.37(3) with respect to the classical expectation, equivalent to 0.11(2) after correcting for det… ▽ More We present highly efficient emission of twin-atom beams into a single transversal mode of a waveguide potential. The source is a one-dimensional degenerate Bose gas in the first radially excited state. We directly measure a suppression of fluctuations in the atom number difference between the beams to 0.37(3) with respect to the classical expectation, equivalent to 0.11(2) after correcting for detection noise. Our results underline the high potential of ultracold atomic gases as sources for quantum matter wave optics and will enable the implementation of schemes previously unattainable with massive particles △ Less

Submitted 27 September, 2012; v1 submitted 10 December, 2010; originally announced December 2010.

Comments: 7 pages (including supplementary material), 5 figures

Journal ref: Nature Physics 7, 608 (2011)

Two-point phase correlations of a one-dimensional bosonic Josephson junction

Authors: Thomas Betz, Stephanie Manz, Robert Bücker, Tarik Berrada, Christian Koller, Georgy Kazakov, Igor E. Mazets, Hans-Peter Stimming, Aurelien Perrin, Thorsten Schumm, Jörg Schmiedmayer

Abstract: We realize a one-dimensional Josephson junction using quantum degenerate Bose gases in a tunable double well potential on an atom chip. Matter wave interferometry gives direct access to the relative phase field, which reflects the interplay of thermally driven fluctuations and phase locking due to tunneling. The thermal equilibrium state is characterized by probing the full statistical distributio… ▽ More We realize a one-dimensional Josephson junction using quantum degenerate Bose gases in a tunable double well potential on an atom chip. Matter wave interferometry gives direct access to the relative phase field, which reflects the interplay of thermally driven fluctuations and phase locking due to tunneling. The thermal equilibrium state is characterized by probing the full statistical distribution function of the two-point phase correlation. Comparison to a stochastic model allows to measure the coupling strength and temperature and hence a full characterization of the system. △ Less

Submitted 29 March, 2011; v1 submitted 28 October, 2010; originally announced October 2010.

Journal ref: Phys. Rev. Lett. 106, 020407 (2011)

Two-point density correlations of quasicondensates in free expansion

Authors: S. Manz, R. Bücker, T. Betz, Ch. Koller, S. Hofferberth, I. E. Mazets, A. Imambekov, E. Demler, A. Perrin, J. Schmiedmayer, T. Schumm

Abstract: We measure the two-point density correlation function of freely expanding quasicondensates in the weakly interacting quasi-one-dimensional (1D) regime. While initially suppressed in the trap, density fluctuations emerge gradually during expansion as a result of initial phase fluctuations present in the trapped quasicondensate. Asymptotically, they are governed by the thermal coherence length of th… ▽ More We measure the two-point density correlation function of freely expanding quasicondensates in the weakly interacting quasi-one-dimensional (1D) regime. While initially suppressed in the trap, density fluctuations emerge gradually during expansion as a result of initial phase fluctuations present in the trapped quasicondensate. Asymptotically, they are governed by the thermal coherence length of the system. Our measurements take place in an intermediate regime where density correlations are related to near-field diffraction effects and anomalous correlations play an important role. Comparison with a recent theoretical approach described by Imambekov et al. yields good agreement with our experimental results and shows that density correlations can be used for thermometry of quasicondensates. △ Less

Submitted 28 March, 2010; v1 submitted 12 November, 2009; originally announced November 2009.

Comments: 4 pages, 4 figures, minor changes

Journal ref: Phys. Rev. A 81, 031610(R) (2010)