15th Nordic Workshop on Statistical Physics: Biological, Complex and Non-Equilibrium Systems

25 Feb 2026, 09:00 → 27 Feb 2026, 19:00 Europe/Stockholm

Albano 3: 4205 - SU Conference Room (40 seats) (Albano Building 3)

Astrid de Wijn (Norwegian University of Science and Technology), Ralf Eichhorn (Stockholm University, Nordita)

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Venue

Nordita, Stockholm, Sweden

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Scope

This workshop series provides a forum where scientists in the Nordic countries working in the area of Statistical Physics can meet regularly. The meeting brings together experts interested in the broad spectrum of timely problems in Statistical Physics, ranging from fundamental aspects in the theory of non-equilibrium processes to modern applications in biophysics. Topics covered include diffusion problems, non-equilibrium transport, work relations and fluctuation theorems, large deviations, resetting, inference methods, soft condensed matter (colloids, liquid crystals etc.), self-assembly, population dynamics, physics of DNA and bio-molecules, single-molecule kinetics, neuronal networks, quantum thermodynamics and many more.

The workshop will start on Wednesday morning at around 9.00 with registration and coffee/cake. It will end on Friday (early) afternoon. There will be a conference dinner on Thursday evening.

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Invited speakers

Antonio Ciarlo (University of Gothenburg)	Bernhard Mehlig (Gothenburg University)
Matthew de Courcy-Ireland (Nordita, Stockholm)	Juliette Monsel (Chalmers University)
Amin Doostmohammadi (NBI, Copenhagen)	Pijush Patra (Nordita, Stockholm)
Nils Gustafsson (Lund University)	Navdeep Rana (University of Oslo)
Mogens Hogh Jensen (Niels Bohr Institute, Copenhagen)	Maria Sammalkorpi (Aalto University)
Supriya Krishnamurthy (Stockholm University)	Alberto Scacchi (University of Turku)
Sreekanth Manikandan (Gothenburg University)	Sigurdur Örn Stefansson (University of Iceland)
	Joakim Stenhammar (Lund University)

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Registration

If you want to participate in the workshop, please fill in the registration form.

Registration deadline: Feb 15, 2026

There is no registration fee.

There is a (very) limited number of travel grants available for PhD students and young Postdoc fellows from the Nordic countries. If you are interested in such a grant, please contact the organizers via email, and provide a rough estimate of your expenses (travel and/or accommodation).

For administrative reasons you have to register before February 8, if you want to apply for such a travel grant.

Depending on interest and time constraints we *might* set up a session dedicated to short talks by junior researchers (PhD students, young Postdocs). During registration you have the possibility to indicate if you are interested in contributing such a short talk (likely around 5-10 min).

 

Please be aware that scammers sometimes approach participants claiming to be able to provide accommodation and asking for credit card details. Do not give this information to them! If you are in any doubt about the legitimacy of an approach, please get in contact with the organizers.

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Sponsored by:

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Wednesday 25 February

09:00 → 10:25 Registration & Breakfast

10:25 → 10:30 Opening

Speakers: Astrid de Wijn (Norwegian University of Science and Technology), Ralf Eichhorn (Stockholm University, Nordita)

10:30 → 11:15 Phase Separation, Entrainment and Genetic Resonance in Cell Dynamics

When cells are damaged or stressed, they often respond by oscillating protein densities. We show that liquid-liquid phase separations lead to condensates of repair proteins around damage sites which occur in an oscillating fashion thus preventing Oswald ripening. The period of oscillations provides an optimal time scale for the repair mechanism [1]. By applying an external periodic protein signal, the internal oscillation can lock to the external signal and thus controls the genes [2]. The locking occurs when the ratio between the two frequencies is a rational number leading to Arnold tongues. If tongues overlap, chaotic dynamics may appear [2]. When the cells are not stressed and again applying an external periodic protein signal, we obtain non-linear resonance phenomena in the genetic response [3]. The findings are supported by experimental data from our collaborative groups at Harvard Medical School and Taipei.
[1] M.S. Heltberg, A. Lucchetti, F.-S. Hsieh, D.P.M. Nguyen, S.-h.Chen and Mogens H. Jensen, "Enhanced DNA repair through droplet formation and p53 oscillations", Cell 185, 4394–4408 (2022).
[2] A. Jimenez, A. Lucchetti, M.S. Heltberg, L. Moretto, C. Sanchez, A. Jambhekar, G. Lahav and M.H. Jensen, “Entrainment and multi-stability of the p53 oscillator in human cells”, Cell Systems 15, 956-968 (2024).
[3] M.S. Heltberg, A. Jimenez, G. Lahav and M.H. Jensen, "Genetic Resonance in the p53 Signaling Network", Cell Systems, March (2026).

Speaker: Mogens Hogh Jensen (Niels Bohr Institute)

11:15 → 12:00 How molecular motors work: Protein engineering as a tool to probe nonequilibrium energy conversion in molecular motors

Motor proteins are molecular machines that operate outside equilibrium to produce directed motion from chemical energy. Our understanding of how motor proteins transduce energy at the molecular scale is obscured by the complexity of natural motors. We attempt to use protein engineering and single-molecule biophysics to create minimal systems that allow us to test principles of nonequilibrium energy conversion. We recently developed Tumbleweed (TW), an artificial clocked protein walker and demonstrated it was capable of directional movement along a short DNA track.
TW takes up to 11 consecutive 17 nm steps with a 7 second step time dictated by our microfluidics. TW operates as a Brownian ratchet where steps are accomplished by diffusion and then rectified by the controlling ligands. To model how the observed behavior on a short track translates to long-range stepping we used Master equations governing the kinetics between the TW feet and the track. We predict that a TW moves at a speed of about 0.5 track periods per solution cycle, or ∼1.2 nm/s using the 21 s experimental cycle time.
We plan to analyse the stepping behaviour of TW using the framework of stochastic thermodynamics, which provides quantitative bounds linking efficiency, energy use, and fluctuations. To achieve this, we design DNA origami-based tracks that allow the performance of TW in terms of speed, accuracy, processivity to be measured at the single molecule level on a stiff extended linear track. The ambition is to directly compare these measured parameters to predictions Thermodynamic Uncertainty Relations, to establish fundamental bounds on motor performance.

Speaker: Nils Gustafsson (Lund University)

12:00 → 14:00 Lunch

14:00 → 14:45 Thermodynamic cost of finite-time (recurrent) erasure

What is the work cost of recurrently erasing information in a finite time duration? For Markovian processes, many results are known in the context of the so-called "finite-time Landauer erasure principle". Two optimization problems that are typically studied in this context are: 1) Designing optimal protocols that transition between two specified distributions within finite time and 2) designing optimum protocols that minimize the cost needed to shift between two different potential energy landscapes, often harmonic, in finite time. In both cases this optimization problem can be used to place very general bounds on the least amount of work cost necessary to implement information erasure in finite time.
In this talk I will talk about some results (including our own) in this topic.

Speaker: Supriya Krishnamurthy (Stockholm University)

14:45 → 15:30 Autonomous demon exploiting heat and information: stochastic trajectories and current fluctuations

Nanoscale devices have access not only to heat, like usual heat engines, but also to other resources, such as information, like in Maxwell demon-based engines, or nonthermal distributions. Furthermore, since fluctuations can be sizeable at the nanoscale, precision, namely how much the noise of the output power is suppressed, is a key performance quantifier for such devices. In this talk, I will present a refrigerator-type device exploiting the thermoelectric effect but fed by a nonthermal resource. The device generates a heat flow from cold to hot in the working substance in the absence of any average particle or energy flow from the resource region,
thereby acting as a “demon”.
Specifically, the device consists of three capacitively coupled quantum dots, one of which is tunnel-coupled to two electronic reservoirs at different temperatures (the working substance) while the other two dots are respectively in contact with a hot and a cold reservoir (the demonic resource).
In such a setup, a finite cooling power can be obtained in the working substance, while the energy exchange with the resource region exactly cancels out on average. At the same time, information is always exchanged, even on average, due to the capacitive coupling between the working substance and the resource region. The proposed system therefore, implements an autonomous demon with fully vanishing heat extraction from the resource.
I will give a comprehensive description of the thermodynamic performance of the proposed autonomous demon by using two complementary approaches: stochastic trajectories and full counting statistics. I will first show that the precision of the cooling power strongly depends on the operation principle of the device. More precisely, the interplay of information flow and counter-balancing heat flows at the trajectory level dramatically impacts the trade-off between cooling power, efficiency, and precision [1]. I will then provide further insights on the operation of the device by analyzing the noise in the input heat flow and cross-correlations between heat currents, evidencing in particular that the output noise – namely cooling power fluctuations – can be made much smaller than the input noise [2].
These results are of relevance for guiding the design of energy-conversion processes exploiting nonthermal resources.

[1] J. Monsel, M. Acciai, R. Sánchez, and J. Splettstoesser, Autonomous
demon exploiting heat and information at the trajectory level,
Phys. Rev. B 111, 045419 (2025).
[2] J. Monsel, M. Acciai, N. Chiabrando, R. Sánchez, and J. Splettstoesser,
Precision of an autonomous demon exploiting heat and information,
arXiv:2510.14578.

Speaker: Juliette Monsel (Chalmers)

15:30 → 16:00 Coffee Break

16:00 → 16:45 Limits of tree-like random graphs

A finite graph embedded in the plane is called a series--parallel map if it can be obtained from a finite tree by repeatedly subdividing and doubling edges. We study the large-scale geometry of random two-connected series--parallel maps with $n$ edges. Our main result shows that, when graph distances are rescaled by a factor $n^{-1/2}$, these maps converge to a constant multiple of Aldous' continuum random tree (CRT). This identifies the CRT as the universal scaling limit governing the macroscopic metric structure of this model.
The proof relies on a bijection between series--parallel maps with $n$ edges and a class of trees with $n$ leaves. This correspondence allows us to compare geodesics in the maps with paths in the associated trees which enables us to transfer metric information from trees to maps and thereby establish convergence to the continuum limit.

Speaker: Sigurdur Örn Stefansson (University of Iceland)

16:45 → 17:30 Room for one more? Saturation probability of random lattice sphere packings

This talk is based on joint work with Anders Södergren, motivated by the question of whether the densest sphere packings in high dimensions are ordered or disordered. A strong form of translational order is the structure of a lattice (i.e. Bravais lattice), where the packing is just a single sphere per fundamental cell repeated periodically. In high dimensions, there are many possibilities for the shape of the cell, leading to a rich space of lattices. A natural way to explore this space is to choose a lattice at random according to the invariant measure with respect to the special linear group.
We show that, with high probability as the dimension of space grows, there is enough room to insert additional spheres into the packing given by a random lattice. In this sense, most lattices fail quite badly to give dense packings.

Speaker: Matthew de Courcy-Ireland (Nordita and SU Department of Mathematics)

Thursday 26 February

10:00 → 10:45 Anomalous geometry and topology of active fluids

I will present experimental evidence of universal geometry in diverse active fluids, from dog kidney cells, and human breast cancer cells, to pathogenic bacteria. I will discuss how this universal geometry is encoded in conformal invariance of vorticity contours, which, surprisingly, show statistics consistent with critical percolation in all the systems. I will then show how this universality and conformal symmetry can become broken or restored upon molecular perturbations of cellular systems. I will then present results from modeling and experiments on reconstituted systems and swimming bacteria that put forward the notion of conformal phase transition in active fluids. Finally, I will discuss topological signatures of this phase transition and end with introducing topological strings in the context of an active fluid that is subject to external aligning field.

Speaker: Amin Doostmohammadi (Niels Bohr Institute)

10:45 → 11:30 Pattern formation in non-reciprocal mixtures

I will present our recent findings on pattern formation in non-reciprocal mixtures. First, I will discuss a disorder-to-order transition and new kind of defect interactions in the Nonreciprocal Cahn-Hilliard model. I will then highlight the role of hydrodynamics and demonstrate how nonreciprocity couples with nonlinearities to stabilize fluctuating polar order against linear Stokesian instabilities.

[1] Giulia Pisegna, Navdeep Rana, Ramin Golestanian, and Suropriya Saha. PRL 135, 108301 (2025)
[2] Navdeep Rana and Ramin Golestanian. PRL 133, 078301 (2024)
[3] Navdeep Rana and Ramin Golestanian. NJP 26, 123008 (2024)

Speaker: Navdeep Rana (University of Oslo)

11:30 → 12:15 Fluctuations, collective motion, and hydrodynamic instabilities in microswimmer suspensions

The collective dynamics of swimming microorganisms is often dictated by long-ranged hydrodynamic interactions, making them an archetypical example of fluid-dominated, “wet” active matter. One example is the collective motion of swimming bacteria that interact through their long-ranged dipolar flow fields to create a stateof so-called “bacterial turbulence” with chaotic, collective swimming with long-ranged orientation correlations. In this talk, I will address several properties of this collective motion, in bulk as well as near interfaces. In 3-dimensional bulk suspensions, I will discuss how enhanced, “giant”, number fluctuations (GNFs), which are a hallmark property of dry active matter systems, become altered in the presence of fluid flows, shedding new light on previous experimental observations of GNFs in bacterial suspensions. In the second part, I will discuss a set of hydrodynamic instabilities arising in microswimmers confined to a 2d plane by a solid or liquid interface. These instabilities correspond to qualitatively novel forms of surface-induced collective motion and microswimmer clustering, in accordance with previous experimental observations.

Speaker: Joakim Stenhammar (Lund University)

12:15 → 13:30 Lunch

13:30 → 14:15 SmartTrap: Autonomous Optical Tweezers for Statistical Physics of Non-Equilibrium Systems

Optical tweezers enable the direct measurement of forces, work, and fluctuations in single-particle and single-molecule systems. They are a vital experimental tool in non-equilibrium statistical physics, ranging from biomolecular folding to soft matter dynamics. However, manual operation limits throughput and hinders the systematic probing of rare events and heterogeneous dynamics.
We present SmartTrap, a fully autonomous optical tweezers platform designed for high-throughput studies of non-equilibrium processes. SmartTrap integrates real-time, deep learning–based 3D particle tracking, adaptive feedback control, and automated microfluidic handling. These features enable the system to execute complete force spectroscopy protocols without human intervention. Once initialized, the system operates continuously, performing trapping, molecular attachment, force manipulation, and bead replacement autonomously.
We demonstrate its capabilities using DNA pulling experiments on λ-DNA, which enable high-throughput force-extension curve and folding-unfolding kinetics experiments. Beyond biomolecules, SmartTrap can be used to study colloidal interactions and single-cell experiments. By providing high-throughput access to microscopic fluctuations, SmartTrap creates new opportunities for conducting quantitative tests of non-equilibrium statistical physics in complex systems.

Speaker: Antonio Ciarlo (Gothenburg University)

14:15 → 15:00 Localising Entropy Production and Maximally Dissipative Coordinates from Experimental Data

Identifying whether a process is in equilibrium, quantifying how far it lies from equilibrium, and determining optimal reduced descriptions of non-equilibrium processes remain challenging open problems. Here, we discuss how novel data-driven techniques grounded in stochastic thermodynamics can be used to efficiently learn these features directly from experimental data. In particular, we show how entropy production can be localized in space and time, and how maximally dissipative coordinates can be consistently inferred as effective low-dimensional descriptions of non-equilibrium processes. We further discuss applications to experimental biophysical systems and outline key challenges and limitations.

Speaker: Sreekanth Manikandan (Gothenburg University)

15:00 → 15:30 Coffee Break

15:30 → 15:45 Temporal resolution in the analysis of single-molecule trajectories

Speaker: Erik Clarkson (Lund University)

15:45 → 16:00 Rotational Brownian Motion in Magnetization Experiments

Speaker: Felix Hartmann (University of Potsdam)

16:00 → 16:15 Pareto-optimal protocols for active particles in moving traps

Speaker: Jonas Berx (Niels Bohr Institute)

16:15 → 16:30 On the effect of class unbalance in diffusion model

Speaker: Flavio Nicoletti (Chalmers)

16:30 → 16:45 Coffee Break

16:45 → 17:00 Anomalous underscreening: could ionic aggregates be the culprit?

Speaker: David Ribar (Lund University)

17:00 → 17:15 Electroferrofluid instabilities via non-variationally coupled Swift-Hohenberg equations

Speaker: Emil Stråka (Aalto University)

17:15 → 17:30 Signatures of coherent initial ensembles on all work moments

Standard treatments of quantum work using projective energy measurements erase initial coherence and alter the dynamics, thereby failing to capture the thermodynamic effects of coherent superpositions of energy eigenstates in an ensemble of initial states. In this article, we use an operational work definition that is non-intrusive, applying it to the case of a driven dissipative qubit, where the qubit's initial preparation comprises coherent superposition states, while the driving is coherence-less. We derive an evolution equation for the moment generating function for this work, faithfully capturing the thermodynamic signature of coherent superpositions in the initial ensemble. We demonstrate that different initial ensembles that correspond to the same density matrix upon ensemble average, while having the same average work, display different work fluctuations. For monotonic driving, we show that fluctuations are maximum for coherence-less initial ensembles. As an application, we consider quantum bit-erasure in finite time and demonstrate significantly different work statistics for erasing a classical bit of information versus a Haar random initial ensemble. Our results indicate that coherence in the initial ensemble can be utilized as a resource for thermodynamic precision without incurring additional dissipative work costs. We also obtain a generalized fluctuation theorem that establishes a new quantum lower bound on the mean dissipated work. This bound, counterintuitively, is also applicable to a "classical" initial ensemble with the same initial density matrix and is connected to quantum absolute irreversibility.

Speaker: Pranay Nayak (Stockholm University)

18:30 → 20:30 Conference Dinner

Friday 27 February

09:30 → 10:15 Droplet evaporation at the cloud edge

The reflectance, lifetime, and spatial extent of atmospheric clouds – and thus their impact on Earth’s climate and weather – are strongly influenced by how turbulence mixes dry and cloudy air at the cloud edge. This mixing generates small-scale heterogeneities in droplet numbers and sizes across multiple length scales. Here we report on theoretical analysis of in-situ observations of shallow cumulus cloud edges on scales from 1 mm to 10 m, performed by G. Bagheri and E. Bodenschatz. We find that there is significant variability in the underlying microscopic processes under similar atmospheric conditions: some cloud edges expand by entrainment, where relatively moist environmental air dilutes the cloud and droplet evaporation is negligible. In other cases, however, droplet evaporation dominates over dilution. The theory demonstrates that this variability arises from significant differences in turbulent mixing times for different observations. The theory also explains how fluctuations and variability depend on the spatial resolution of the observations. State-of-the-art weather and climate models assume that  clouds are instantaneously mixed and therefore spatially uniform at small scales. But our results imply that one must consider time-dependent local turbulent mixing and the resulting inhomogeneities to explain droplet populations at the cloud edge. Mean-field models assuming a global equilibrium must fail. This talk is based on work carried out with F. Hoffmann, G. Bagheri, and E. Bodenschatz.

Speaker: Bernhard Mehlig (University of Gothenburg)

10:15 → 11:00 Droplet growth in clouds: the role of electrostatic interactions

Rain formation in clouds begins with collisions and coalescence among small droplets, which govern the evolution of the droplet size distribution and the onset of precipitation. Because cloud droplets often carry electric charges and experience atmospheric electric fields—from weak fair-weather fields to intense thundercloud fields—electrostatic forces can modify their collision dynamics. In this study, we examine how droplet charges and external electric fields alter pairwise trajectories and collision rates for droplets settling under gravity or interacting in laminar background flows. Our analysis accounts for exact hydrodynamic interactions, electrostatic forces, and van der Waals forces. Furthermore, we incorporate these effects within a Smoluchowski framework to predict the evolution of the droplet size distribution. We show that electrostatic interactions can substantially enhance collision rates, promoting faster droplet growth and potentially accelerating precipitation initiation, with important implications for cloud microphysics parameterizations and weather prediction models.

Speaker: Pijush Patra (Stockholm University)

11:00 → 11:30 Coffee Break

11:30 → 12:15 Computational modelling and phase diagrams in understanding biomacromolecular materials

Biologically in yeast and bacterial cultures synthesized proteins offer a scalable, environmentally sustainable means to self-assembling biomacromolecular materials
with, e.g. adaptive mechanical properties, adhesive characteristics, and biointeractions as advanced functionalities. We have used computational particle simulations and thermodynamics based phase diagram considerations to study both equilibrium and non-equilibrium mechanism for the molecular assembly structure. We extract dependencies on the block composition and, e.g. protein length and domains on the assembly response, allowing deducing resulting materials dependencies on the composition and conditions [1-4].  I discuss in this talk our modelling findings in respect to designing self-organization of block protein systems and achieving tunable materials properties.

[1] D. Tolmachev, I. Tunn, A. L. Harmat, N. B. Möttönen, A. Scacchi, M. B. Linder, M. Sammalkorpi, “Temperature and time induced assembly phase changes of engineered
spidroin protein solutions” International Journal of Biological Macromolecules 329, 147712 (2025). https://doi.org/10.1016/j.ijbiomac.2025.147712
[2] D. Fedorov, F.-E. Sammalisto, A. L. Harmat*, M. Ahlberg, S. Koskela, M. P. Haataja, A. Scacchi, M. Sammalkorpi, M. B. Linder, “Metastable liquid–liquid phase separation and aging lead to strong processing path dependence in mini‐spidroin solutions”, Advanced Functional Materials 2410421 (2024). https://doi.org/10.1002/adfm.202410421
[3] D. Tolmachev, M. Malkamäki, M. B. Linder, M. Sammalkorpi, “Spidroins under the Influence of Alcohol: Effect of Ethanol on Secondary Structure
and Molecular Level Solvation of Silk-Like Proteins”, Biomacromolecules 24 (12),
5638-5653 (2023). https://doi.org/10.1021/acs.biomac.3c00637
[4] D. Fedorov, N. Roas‐Escalona,D. Tolmachev, A. L. Harmat, A. Scacchi, M. Sammalkorpi, A. S. Aranko, M. B. Linder, “Triblock Proteins with Weakly Dimerizing Terminal Blocks and an Intrinsically Disordered Region for Rational Design of Condensate Properties”, Small 2306817 (2023). https://doi.org/10.1002/smll.202306817

Speaker: Maria Sammalkorpi (Aalto University)

12:15 → 13:00 From Particle Simulations to Classical Density Functional Theory: Partitioning in Polymeric Mixtures

Partitioning of (bio)materials in polymer mixtures underlies processes ranging from cellular organization to industrial separation technologies. Despite its importance, the physical mechanisms governing phase coexistence and interfacial structure are not yet fully understood.
As a controllable model system, we first investigate a demixing mixture of coarse-grained polymers containing magnetic nanoparticles using particle-based simulations [1]. An external magnetic field enables controlled modulation of the interface, providing a tunable platform to quantify interfacial properties such as surface tension and to analyze how particle size and interactions influence partitioning across coexisting phases. Throughout, the model parameters are chosen to ensure qualitative and semi-quantitative consistency with experimental behavior.
To generalize these insights, we develop an improved classical density functional theory (DFT) framework with refined free-energy functionals and an algorithm capable of resolving phase coexistence in mixtures containing n polymers and m colloidal components across multiple phases [2]. While particle-based simulations become computationally prohibitive for spanning the large parameter space, the DFT approach provides a scalable description of multicomponent systems and is quantitatively benchmarked against simulations, showing very good agreement.

[1] A. Scacchi, C. Rigoni, M. Haataja, J. V. I. Timonen, M. Sammalkorpi, "A corase-grained model for aqueous two-phase systems: Application to ferrofluids", Journal of Colloid and Interface Science 686, (2025).
[2] V. A. Varma & A. Scacchi, "General approach for partitioning and phase separation in macromolecular coexisting phases", arXiv preprint arXiv:2509.14392, (2025).

Speaker: Alberto Scacchi (University of Turku)

13:00 → 14:30 Light Lunch

14:30 → 17:00 Self-organized Discussions