Presentation
The main motivations for that meeting are to present and to discuss relevant and recent issues in the field of quantum thermodynamics.
Invited Speakers
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Luis A. CORREA (Nottingham University, UK)
Title:
Quantum-coherent weakly driven thermal machines can be simulated classically
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Abstract: The performance enhancements recently observed in various models of continuous quantum thermal ma-chines have been linked to the buildup of coherences in a preferred basis. But, is this connection an evidence of ''quantum supremacy''? By force of example, we show that this is not necessarily the case. In particular,we compare a power-driven three-level quantum refrigerator with a four-level combined cycle, partly driven by power and partly by heat. We focus on the weak driving regime and find the four-level model to be superior since it can operate in parameter regimes in which the three-level model cannot, it may exhibit a larger cooling rate, and, simultaneously, a better coefficient of performance. Furthermore, we observe that the improvement in the cooling rate matches the increase in the stationary quantum coherences exactly. Crucially, though, we also show that the thermodynamic variables for both models follow from a classical representation based on graph theory. This implies that we can always build incoherent stochastic-thermodynamic analogues with the same steady-state operation; or, in short, that both coherent refrigerators can be simulated classically. We prove this rigorously for any N-level weakly driven model with a ''cyclic'' pattern of transitions. Hence, observing performance improvements in thermal machines is not, in itself, a conclusive indication of quantumness.
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Geneviève FLEURY (SPEC, CEA, France)
Title:
Simulating time dependent thermoelectric transport with the t-Kwant software
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Abstract: Recent theoretical works suggest that the thermoelectric efficiency of a nanodevice could be greatly
enhanced if it is suddenly pushed out of equilibrium with the use of an external time-dependent
parameter [1-3]. In those studies, quantum dot models were considered and the thermoelectric
properties were calculated analytically with a non equilibrium Green's function (NEGF) approach. In
the Group of Modelisation and Theory at SPEC, CEA Saclay, we are developing an extension to the t-Kwant software [4] which will enable us to study numerically time-dependent thermoelectric
transport in arbitrary (non-interacting) tight-binding models. It is based on a wave function approach,
equivalent to the NEGF approach but drastically more efficient from a numerical point of view.
I will first give an introduction to the t-Kwant software developed at INAC, CEA Grenoble for the study of electronic quantum transport in the time domain. Then I will discuss its generalization to thermoelectric transport and the fundamental questions which are raised when defining time-dependent heat currents. As a validity check of our code, I will show that we reproduce previous results derived in the literature within the NEGF formalism for the resonant level model [1,5]. Finally, I will discuss the possibility offered by t-Kwant of investigating dynamic thermoelectric transport in more complicated nanodevices.
[1] A. Crepieux, F. Simkovic, B. Cambon, and F. Michelini, Phys. Rev. B 83, 153417 (2014). [2] H. Zhou, J. Thingna, P. Hanggi, J.-S. Wang and B. Li, Scientific Reports 5, 14870 (2015).
[3] A.-M. Dare and P. Lombardo, Phys. Rev. B 93, 035303 (2016). [4] B. Gaury, J. Weston, M. Santin, M. Houzet, C. Groth and X. Waintal, Physics Reports 534, 1 (2014). [5] F. Covito, F. G. Eich, R. Tuovinen, M. A. Sentef and A. Rubio, J. Chem. Theory Comput. 14, 2495 (2018).
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Bayan KARIMI (Pico, Espoo, Finland)
Title:
Measuring heat current and its fluctuations in superconducting quantum circuits
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Abstract: I present recent work of the PICO group on thermodynamics of quantum systems. Superconducting circuit QED (Quantum Electro-Dynamics) presents a prominent platform for this purpose. Here, we investigate a superconducting qubit coupled between two nominally identical coplanar waveguide (CPW) resonators, each terminated by a normal-metal
mesoscopic resistor as a heat bath. We observe tunable photonic heat transport through
the resonator-qubit-resonator assembly when the temperatures of the two heat baths are
unequal. Using a theoretical model here developed, we are able to reproduce experimental data. The reservoir-to-reservoir heat flux depends on the interplay between the qubit-resonator and the resonator-reservoir couplings, yielding qualitatively dissimilar results
in different coupling regimes [1].
Importantly, in order to detect noise of the heat current and single microwave quanta, one
needs fast and sensitive nanocalorimetry [2]. We present non-invasive rf-thermometry
based on proximitized tunnel contact between normal metal and a superconductor [3]. We
expect theoretically [4] and test experimentally heat current noise both under equilibrium
and non-equilibrium conditions. In the talk I present preliminary experimental results.
Acknowledgements: This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant
agreement No 766025. We acknowledge the facilities and technical support of Otaniemi
research infrastructure for Micro and Nanotechnologies (OtaNano).
[1] Alberto Ronzani, Bayan Karimi, Jorden Senior, Yu-Cheng Chang, Joonas Peltonen, ChiiDong Cheng, and Jukka P. Pekola, Realization of a quantum heat valve, [arXiv:1801.09312], Nature Physics (2018).
[2] S. Gasparinetti, K. L. Viisanen, O.-P. Saira, T. Faivre, M. Arzeo, M. Meschke, J.
P. Pekola, Fast electron thermometry towards ultra-sensitive calorimetric detection,
[arXiv:1405.7568], Physical Review Applied 3, 014007 (2015).
[3] Bayan Karimi, Jukka P. Pekola, Non-invasive thermometer based on proximity superconductor for ultra-sensitive calorimetry, [arXiv:1807.08962] (2018).
[4] F. Brange, P. Samuelsson, B. Karimi, J. P. Pekola, Realization of a quantum heat
valve, Nanoscale Quantum Calorimetry with Electronic Temperature Fluctuations,
[arXiv:1805.02728] (2018).
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Tomas MANCAL (Charles University, Czech Republic)
Title:
Excitation energy transfer in photosynthetic pigment-protein complexes
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Abstract:Light-energy harvesting antennae of plants and bacteria represent some of the
most intricate and diverse photo-reactive machinery occurring in nature.
Primary steps of the light harvesting process in these organisms exhibit high
quantum efficiency, and they are often discussed as a possible inspiration for
improvements in the design of photo-voltaics and artificial photo-synthesis of
fuels. Often it is stated that the remarkable efficiency of light-to-chemical-energy
conversion rests upon the quantum nature of the photosynthetic energy transfer.
In this presentation we will briefly introduce the basic principles of the physical
model of natural light harvesting antennae. We will discuss which aspects of the
photosynthetic excitation energy transfer should be considered to be of quantum
nature. By considering in parallel the classical and the quantum models of
photosynthetic antennae, we will identify coherent energy transfer as a process
easily mapped on well-motivated classical models of photosynthesis. The
thermodynamic behavior of the excited state quasi-equilibrium, on the other
hand, will be found out of reach of the same classical models. Using the ideas
from decoherence theory, we will show that the thermodynamic behavior of the
excited state quasi-equilibrium in a photosynthetic antenna is conditioned by the
existence of the system-bath entanglement, and constitutes thus a uniquely
quantum effect. It is therefore not only the excitons in photosynthetic antennae
that exhibit quantum properties. Inevitably, also the protein environment must
show quantum behavior in order for the whole pigment-protein complex to
behave as observed in some of the simplest spectroscopic experiments.
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Rosa LOPEZ (IFISC, Mallorca, Spain)
Title:
Anomalous Joule law in the adiabatic dynamics of a
quantum dot in contact with normal-metal and
superconducting reservoirs
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Abstract: We formulate a general theory to study the time-dependent charge and energy
transport of an adiabatically driven quantum dot in contact with normal and
superconducting reservoirs at T= 0. This setup is a generalization of a quantum RC
circuit, with capacitive components due to Andreev processes and induced pairing
fluctuations, in addition to the conventional normal charge fluctuations. The
dynamics for the dissipation of energy is ruled by a Joule law for four channels in
parallel with the universal Büttiker resistance R0=h/e^2 per channel. Two
transport channels are associated with the two spin components of the usual charge
fluctuations, while the other two are associated with electrons and holes due to
pairing fluctuations. The latter leads to an ''anomalous'' component of the Joule law
and takes place with a vanishing net current due to the opposite flows of electrons.
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Samy MERABIA (ILM, Lyon, France)
Title:
Interfacial heat transfer at the nano-scale: from Kapitza resistance to ultra near-field energy transfer
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Abstract: Thermal boundary conductance is basically dictated by phonon transmission at interfaces [1], and an
accurate prediction at nanoscale is of a great importance for many applications where thermal management is
a vital issue. In microelectronics there is a strong need to know how energy can be exchanged across small
vacuum gaps having separation distances of few nanometers. A key yet unsolved question concerns the
relative contribution of phonon/phonon or electron/phonon scattering at the interface between a
semiconductor, e.g. silicon and a metal [2].
Recent experimental studies found giant heat flux transfer between gold and silica at nanometer
separation distance [3]. Theoretically, it is expected that at such nanometer distances, heat is exchanged
primarily by acoustic waves [4], while radiative heat transfer dominates when the gap is larger than a few
nanometers [5].
We have developed a new computational method to probe phonon scattering at interfaces between
FCC or diamond like structure materials. The idea is to combine lattice dynamics calculations with inputs from
ab-initio calculations. Lattice dynamics has been already successfully applied to describe interfacial thermal
conductance, but it relies on semi-empirical potentials and lacks the accuracy to describe phonon dispersion
curves of bulk materials. Coupling lattice dynamics with interatomic force constants calculated using ab initio
calculations opens the way to an accurate description of phonon transmission at interfaces.
We performed lattice dynamics calculations at silicon/germanium and across nanoscale vacuum gaps
using ab initio interatomic force constants [5]. This analysis allows us to predict the interfacial phonon
transmission coefficient as a function of both the phonon wavevector and the frequency. Our simulations
show that, quite generally a large contribution of the transmitted energy flux corresponds to small scattered
angles, close to the direction normal to the interface.
We used these calculations to probe heat transfer across nanoscale vacuum gaps. We first characterize
the thermal conductance due to phonons for silicon/vacuum/silicon and gold/vacuum/gold interfaces. We
characterize the probability for phonons to be transmitted across the gap, and show that the cone of
transmission is very narrow and corresponds to a scattered direction normal to the interface. Moreover, we
demonstrate the major role played by phonon scattering as compared with electron/phonon processes at
interfaces [2]. Finally, we compare our ab-initio lattice dynamics results with simplified acoustic mismatch
models [4,5]. We clearly demonstrate that these models fail by several orders of magnitude to describe the
thermal conductance across nanoscale gaps. We show that these discrepancies originate from the contribution
of intermediate phonon frequencies which are not accurately described by acoustic models.
[1] S. Merabia and K. Termentzidis, Phys. Rev. B 86, 094303 (2012).
[2] J. Lombard, F. Detcheverry and S. Merabia, J. Phys. Cond. Mat. 27, 015007 (2015).
[3] Konstantin Kloppstech et al., Nat. Comm. 8, 144505 (2017).
[4] V. Chiloyan, J. Garg, K. Esfarjani and G. Chen, Nat. Comm. 6, 6755 (2015), B. V. Budaev and D. B. Bogy, Appl.
Phys. Lett. 99, 053109 (2011).
[5] A. Alkurdi, S. Pailhes, S. Merabia, Appl. Phys. Lett. 111, 093101 (2017).
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David SANCHEZ (IFISC, Mallorca, Spain)
Title:
Thermoelectrics and heat in hybrid superconductor-quantum dot junctions
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Abstract: We discuss the thermoelectric and heat properties of a quantum dot
coupled to ferromagnetic and superconducting electrodes. The combination
of spin polarized tunneling at the ferromagnetic-quantum dot interface
and the application of an external magnetic field that Zeeman splits the
dot energy level leads to large values of the thermopower (Seebeck
coefficient). Importantly, the thermopower can be tuned with an external
gate voltage connected to the dot. We compute the heat conductance and
thereby the thermoelectric figure of merit, which is found to attain
high values. We analyze the different contributions from Andreev
reflection processes and quasiparticle tunneling into and out of the
superconducting contact. Furthermore, we obtain dramatic variations of
both the magnetothermopower and the spin Seebeck effect, which suggest
that in our device spin currents can be controlled with temperature
gradients only. Finally, we discuss diode-like effects that occur in the
nonlinear regime of thermal transport.
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Nathalie VAST (IRAMIS, CEA, France)
Title:
Hydrodynamic heat transport regime in bismuth: a theoretical viewpoint
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Abstract: Currently, a lot of attention is devoted to the study of phonon-based heat transport regimes in
nanostructures. Of particular interest is the hydrodynamic regime, in which a number of
fascinating phenomena such as Poiseuille's phonon flow and second sound occur, and
where temperature fluctuations are predicted to propagate as a true temperature wave of the
form exp(i(kr-wt)). Together with solid helium and NaF, bismuth is one of the rare materials in
which second sound has been experimentally observed, and regimes of heat transport vary
with the increase of the (yet cryogenic) temperature: from heat transport via ballistic phonons,
to the regime of Poiseuille's flow with second sound, to the diffusive (Fourier) propagation [1].
In this work [2,3], a major advance consists of accounting for the phonon repopulation by the
normal phonon-phonon processes in the framework of the exact variational solution of the
Boltzmann transport equation (BTE), coupled to the ab initio description of anharmonicity:
three-phonon collisions turn out to be particularly strong at low temperatures and lead to the
creation of new phonons in the direction of the heat flow (normal processes), which enhance
the heat transport. This induces time and length scales over which heat carriers behave
collectively and form a hydrodynamic flow that cannot be described by independent phonons
with their own energy and lifetime.
Our exact calculations predict the occurrence of this Poiseuille phonon flow between =1.5
and =3.5 K, in a sample size of 3.86 and 9.06 mm, consistent with the experimental
observations. Hydrodynamic heat flow characteristics are given for any temperature: heat
wave propagation length, drift velocity, and Knudsen number. I will discuss a Gedanken
experiment allowing us to assess the presence of a hydrodynamic regime in any isotopically
pure bulk material.
Furthermore, for the study of thermoelectricity, we have combined BTEs for electrons and
phonons and computed the effect of electron-phonon interaction on the Seebeck coefficient,
known as the phonon-drag contribution to the Seebeck coefficient. I will show the influence of
the nanostructure size and shape on the phonon-drag contribution of the thermoelectric
coefficient of silicon.
Support from the Chaire Energie of the Ecole Polytechnique, the program NEEDS Materiaux, and
from ANR-10-LABX-0039-PALM (Project Femtonic) is gratefully acknowledged. Computer time was
granted by Ecole Polytechnique through the LLR-LSI Project and by GENCI.
[1] V. Narayanamurti and R. Dynes. Observation of Second Sound in Bismuth, Phys. Rev. Lett. 28,
1461 (1972).
[2] M. Markov, J. Sjakste, G. Barbarino, G. Fugallo, L. Paulatto, M. Lazzeri, F. Mauri, and N. Vast.
Same title as above, Phys. Rev. Lett., 120, 075901 (2018).
[3] M. Markov, J. Sjakste, G. Fugallo, L. Paulatto, M. Lazzeri, F. Mauri and N. Vast. Nanoscale
mechanisms for the reduction of heat transport in bismuth, Phys. Rev. B 93, 064301 (2016).
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Robert WHITNEY (LPMMC, Grenoble, France)
Title:
A non-equilibrium system as a demon
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Abstract: Maxwell demons are imaginary creatures able to extract work from a system or to cool a system without adding any energy to the system. Conventionally, the demon's action consists in measuring microscopic quantities (such as the position and velocity of individual particles) and performing feedback. Here we show that using a non-equilibrium distribution as a resource can lead to similar effects, without any measurement-feedback loop. It seemingly break the second law of thermodynamics, when the demon part of the setup is disregarded, but including the demon's entropy resorts the second law. We discuss proposals both for an electronic and for an optical implementation of this phenomenon.
Announcement
Flyer
Program
Click here to download the program (updated: 13th November)
List of posters
Registration
If you want to attend this mini-workshop (no registration fees/no deadline), please register by sending an e-mail to F. Michelini
Past Editions
2014 : Perspectives in quantum thermolectricity: time-dependent systems, correlations and measurements - Marseille (France)
2011 : Charge and heat dynamics in nano-systems - Orsay (France)
2009 : Frequency- and time-resolved electron transport in nano-circuits - Marseille (France)
Place
FRUMAM, Campus Saint-Charles,
Aix-Marseille University, France
Map from Marseille's train station to FRUMAM
Organizers
F. Michelini, IM2NP, Marseille
A.-M. Daré, IM2NP, Marseille
A. Crépieux, CPT, Marseille
Funded by