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Mesoscopic Physics Group


group picture

In the Mesoscopic Physics Group, we are working towards a better understanding of nanoscale systems, where phase coherence meets fluctuations. Our goal thereby is to accelerate and contribute to the development of quantum technologies which make use of intriguing quantum features such as coherence and entanglement.
Read more about our research here.



Reaching the ultimate energy resolution of a quantum detector

Sketch of the setup for measuring temperature fluctuations

Nat. Commun. 11, 367 (2020)

Quantum calorimetry, the thermal measurement of quanta, is a method of choice for ultrasensitive radiation detection ranging from microwaves to gamma rays. The fundamental temperature fluctuations of the calorimeter, dictated by the coupling of it to the heat bath, set the ultimate lower bound of its energy resolution. Here we reach this limit of fundamental equilibrium fluctuations of temperature in a nanoscale electron calorimeter, exchanging energy with the phonon bath at very low temperatures.

Certifying Nonclassical Behavior for Negative Keldysh Quasiprobabilities

Title page of the Journal Physical Review Letters

Phys. Rev. Lett. 122, 110401 (2019)
Measurements in quantum mechanics induce an unavoidable backaction on the system. As a consequence, multiple observables can in general not be described by a positive probability distribution. Here we provide an experimentally accessible inequality which serves as a test to certify if a description in terms of positive probabilities is possible. The inequality rests on a few natural assumptions on the measurement apparatus. This research was featured on the cover of Phys. Rev. Lett.


Detailed Fluctuation Relation for Arbitrary Measurement and Feedback

Graphic representation of Detailed Fluctuation Relation for Arbitrary Measurement and Feedback Schemes

Phys. Rev. Lett. 121, 210603 (2018)
Fluctuation relations relate probabilities of forward experiments to probabilities of backward experiments. While the backward experiment is usually determined by time-reversal of the forward experiment, the presence of measurement and feedback introduces a certain freedom in choosing the backward experiment. Using this freedom, we provide a recipe for obtaining different fluctuation relations. We then use this recipe to find a particularly useful relation which overcomes problems encountered in previous approaches.


Supremacy of the quantum many-body Szilard engine with attractive bosons

Model of a manybody szilard engine

Phys. Rev. Lett. 120, 100601 (2018)
We show that the work output of a Szilard engine containing a quantum gas of attractive bosons is superior to that generated by an engine containing non-interacting particles and that this supremacy increases significantly with particle number. Our work demonstrates an intricate interplay between quantum mechanics, thermodynamics and information theory and sheds light on a hitherto unexplored fundamental question that is relevant for a wide range of many-body quantum systems where interactions are important.

Optimal quantum interference thermoelectric heat engine with edge states

Model of a of a close-to-optimal heat engine is proposed in an electronic Mach-Zehnder interferometer with a mesoscopic capacitor coupled to one arm

Phys. Rev. Lett. 118, 256801 (2017)
We show theoretically that a thermoelectric heat engine, operating exclusively due to quantum-mechanical interference, can reach optimal linear-response performance. A chiral edge state implementation of a close-to-optimal heat engine is proposed in an electronic Mach-Zehnder interferometer with a mesoscopic capacitor coupled to one arm. We demonstrate that the maximum power and corresponding efficiency can reach 90% and 83%, respectively, of the theoretical maximum. The proposed heat engine can be realized with existing experimental techniques and has a performance robust against moderate dephasing.

Minimal Entanglement Witness From Electrical Current Correlations

Model how to witness entanglement that minimizes the number of measurements required

Phys. Rev. Lett. 118, 036804 (2017)
Over the past few decades, several different methods for entanglement detection, including Bell inequalities, quantum state tomography and entanglement witnesses, have been proposed based on zero-frequency current cross correlations, the experimentally accessible quantities in solid state conductors. However, limited control of detector settings and low detector efficiencies make entanglement detection in solid state conductors experimentally highly challenging. In this Letter, we address these challenges by investigating a witness that minimizes the number of measurements required. We show that two correlation measurements are sufficient to detect entanglement and that detection is possible even for arbitrarily low (nonzero) efficiencies. Furthermore, we show that all entangled pure states can be detected with two measurements, except the maximally entangled, which require three.

Former Members

Fredrik Brange, PhD Student until 2019
PhD Thesis: Quantum Correlations and Temperature Fluctuations in Nanoscale Systems

Sara Kheradsoud, PhD Student until 2019
PhD Thesis: Thermoelectric Effects and Single Electron Sources in Mesoscopic Transport; a Scattering Approach

Tineke van den Berg, Postdoc, 2013-2016.

Ognjen Malkoc, PhD Student until 2016
PhD Thesis: Entanglement detection schemes and coherent manipulation of spin in quantum dots

Christian Bergenfeldt, PhD Student until 2014
PhD-thesis: Transport effects in hybrid circuit QED structures

Francesca Battista, PhD Student until 2013
PhD-thesis: Scattering approach to time-dependent charge and energy transport in mesoscopic conductors

Open Positions

Presently, we are looking for a Postdoc working on quantum thermodynamics, click here for more information. Additionally, motivated applicants for a PhD or Postdoc position are always welcome to peter [dot] samuelsson [at] teorfys [dot] lu [dot] se (contact me). Please include a CV, a list of publications, and a motivation letter in your application.