Aykut Argun defended his PhD Thesis in Physics on 14 June 2021. Congrats!

(Image by Aykut Argun)
Aykut Argun defended his Ph.D. thesis on June 14, 2021, at 2 pm CEST. Congrats!

The details of the presentation can be found below. The link to the webinar is announced on the faculty website.

Title: Thermodynamics of microscopic environments: From anomalous diffusion to heat engines.

Unlike their macroscopic counterparts, microscopic systems do not evolve deterministically due to the thermal noise becoming prominent. Such systems are subject to fluctuations that can only be studied within the framework of stochastic thermodynamics. Within the last few decades, the development of stochastic thermodynamics has lead to microscopic heat engines, nonequilibrium relations and the study of anomalous diffusion and active Brownian motion. In this thesis, I experimentally show that the non-Boltzmann statistics emerge in systems that are coupled to an active bath. These non-Boltzmann statistics that result from correlated active noise also disturb the nonequilibrium relations. Nevertheless, I show that these relations can be recovered using an effective potential approach. Next, I demonstrate an experimental realization of a microscopic heat engine. This engine is referred to as the Brownian gyrator, which is coupled to two different heat baths along perpendicular directions. I show that when confined into an elliptical trap that is not aligned with the temperature anisotropy, the Brownian particle is subject to a torque due to the symmetry breaking. This torque creates an autonomous engine whose direction and amplitude can be controlled by tuning the alignment of the elliptical trap. Then, I show that the force fields acting on Brownian particles can be calibrated using a data-driven method that outperforms the existing calibration methods. More importantly, I show that this method, named DeepCalib, can calibrate non-conservative and time-varying force fields that no standard calibration methods exist. Finally, I show that a similar machine-learning-based approach can be used to characterize anomalous diffusion from single trajectories. This method, named RANDI, is very versatile and performs very well in various tasks including classification, inference and segmentation of anomalous diffusion. The work presented in this thesis presents novel experiments that advance microscopic thermodynamics as well as newly developed methods that open up new possibilities in analyzing stochastic trajectories. These findings increased the scientific knowledge at the nexus between microscopic thermodynamics, anomalous diffusion, active matter and machine learning.

Supervisor: Giovanni Volpe
Co-supervisors: Joakim Stenhammar, Mattias Goksör
Examiner: Bernhard Mehlig
Opponent: Juan M. R. Parrondo
Committee: Monika Ritsch-Marte, Sabine H. L. Klapp, Édgar Roldán

Screenshots from Aykut Argun’s PhD Thesis defense.

PhD Thesis Committee, Supervisor, Co-Supervisor, Opponent, and GU Physics Department Chair.
PhD Thesis Committee, Supervisor, Opponent, and GU Physics Department Chair.
PhD Opponent presentation.
PhD Thesis presentation starts.
PhD Thesis front slide.
PhD Thesis content slide.
PhD Thesis final acknowledgment slide.
PhD Thesis final acknowledgment slide.

Seminar by R. Ganapathy at Soft Matter Lab, 7 April 2021

On Wednesday, 7 April 2021, Rajesh Ganapathy will give a seminar at the Soft Matter Lab and the Department of Physics, University of Gothenburg. He will speak on how energy can be harvested in microscopic environments making use of active baths.

Tuning the performance of a micron-sized Stirling engine by ‘active’ noise
Rajesh Ganapathy
Time: 07 April, 2021, 11:00
Place: Online via Zoom (link to be shared)

Abstract: Mesoscale heat engines, wherein a single atom or a micron-sized colloidal particle is the working substance, are paradigmatic models to elucidate the conversion of heat into work in a noisy environment. While stochastic thermodynamics provides a precise framework for quantifying the performance of these engines when operating between thermal baths, how energy transduction occurs when the reservoirs themselves are out-of-equilibrium, life for instance for a biological motor carrying cargo inside a cell, remains largely unclear. In the first part of my talk, I will describe the design, construction, and quantification of a colloidal Stirling geat engine operating, in the quasistatic limit, between bacterial baths characterized by different levels of activity. We will show that due to ‘active noise’ the performance of the Stirling engine even surpasses a thermal Stirling engine operating between reservoirs with an infinite temperature difference. In the second part of my talk, we will outline a reservoir engineering approach that allowed us to operate the ‘active’ Stirling engine not only in the quasi-static-limit but also at finite cycle durations. Armed with this capability, we will show that the performance of a micron-sized Stirling engine can be tuned by altering only the nature of the reservoir noise statistics.

Presentation by A. Argun at OSA Life Sciences Conference, Tucson, 14-17 April 2019

Statistics of Brownian particles held in non-harmonic potentials in an active bath

Aykut Argun and Giovanni Volpe
OSA Life Sciences Conference,
Tucson, 14-17 April 2019


Active systems are subject to persistent noise that arise from biological media or artificial activity like self-propelled particles. Therefore, these systems are  intrinsically out of equilibrium and can only be studied within the framework of non-equilibrium physics. So far, steady-state behavior and dynamical fluctuations of Brownian particles in active baths have been investigated both theoretically and experimentally. While some of the equilibrium properties can be retained by using an effective temperature, for most systems this generalization is not possible. Here, we extend the existing studies to non-harmonic potential cases, where other qualitative distinctions of the active matter emerge.

Talk on optical tweezers by Aykut Argun at Gothenburg PhD Pub. 17 Oct 2018

Aykut Argun will present a popular science talk on the principles and applications of optical tweezers at a PhD-student event called Gothenburg Ph.D. Pub.

Title: Optical tweezers and applications

Abstract: Can objects be moved contact-free only by the power of light?
The answer which deserved a Nobel Prize in Physics last week is yes.
Aykut Argun from GU Physics will present how in the next Ph.D. Pub.

Place: Haket – Bar å sånt, Första långgatan 32, 413 27 Gothenburg
Time: Wednesday, October 17, 2018 at 7 PM – 10 PM

Talk by A. Argun at IONS Scandinavia 2018, Copenhagen, 5-9 Jun 2018

Experimental realization of a minimal microscopic heat engine
Aykut Argun, Jalpa Soni, Lennart Dabelow, Stefano Bo, Giuseppe Pesce,
Ralf Eichborn & Giovanni Volpe
IONS Scandinavia 2018, Copenhagen, Denmark
5-9 June 2018

Abstract:  Microscopic heat engines are microscale systems that convert energy flows between heat reservoirs into work or systematic motion. We have experimentally realized a minimal microscopic heat engine. It consists of a colloidal Brownian particle optically trapped in an elliptical potential well and simultaneously coupled to two heat baths at different temperatures acting along perpendicular directions. For a generic arrangement of the principal directions of the baths and the potential, the symmetry of the system is broken, such that the heat flow drives a systematic gyrating motion of the particle around the potential minimum. Using the experimentally measured trajectories, we quantify the gyrating motion of the particle, the resulting torque that it exerts on the potential, and the associated heat flow between the heat baths. We find excellent agreement between the experimental results and the theoretical predictions. 

Reference: Argun et al. Experimental realization of a minimal microscopic heat engine. Physical Review E 96(5), 052106 (2017)