57 research outputs found
Quantum bath refrigeration towards absolute zero: unattainability principle challenged
A minimal model of a quantum refrigerator (QR), i.e. a periodically
phase-flipped two-level system permanently coupled to a finite-capacity bath
(cold bath) and an infinite heat dump (hot bath), is introduced and used to
investigate the cooling of the cold bath towards the absolute zero (T=0).
Remarkably, the temperature scaling of the cold-bath cooling rate reveals that
it does not vanish as T->0 for certain realistic quantized baths, e.g. phonons
in strongly disordered media (fractons) or quantized spin-waves in ferromagnets
(magnons). This result challenges Nernst's third-law formulation known as the
unattainability principle
Thermodynamic principles and implementations of quantum machines
The efficiency of cyclic heat engines is limited by the Carnot bound. This
bound follows from the second law of thermodynamics and is attained by engines
that operate between two thermal baths under the reversibility condition
whereby the total entropy does not increase. By contrast, the efficiency of
engines powered by quantum non-thermal baths has been claimed to surpass the
thermodynamic Carnot bound. The key to understanding the performance of such
engines is a proper division of the energy supplied by the bath to the system
into heat and work, depending on the associated change in the system entropy
and ergotropy. Due to their hybrid character, the efficiency bound for quantum
engines powered by a non-thermal bath does not solely follow from the laws of
thermodynamics. Hence, the thermodynamic Carnot bound is inapplicable to such
hybrid engines. Yet, they do not violate the principles of thermodynamics.
An alternative means of boosting machine performance is the concept of
heat-to-work conversion catalysis by quantum non-linear (squeezed) pumping of
the piston mode. This enhancement is due to the increased ability of the
squeezed piston to store ergotropy. Since the catalyzed machine is fueled by
thermal baths, it adheres to the Carnot bound.
We conclude by arguing that it is not quantumness per se that improves the
machine performance, but rather the properties of the baths, the working fluid
and the piston that boost the ergotropy and minimize the wasted heat in both
the input and the output.Comment: As a chapter of: F. Binder, L. A. Correa, C. Gogolin, J. Anders, and
G. Adesso (eds.), "Thermodynamics in the quantum regime - Recent Progress and
Outlook", (Springer International Publishing
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Perspectives on weak interactions in complex materials at different length scales
Nanocomposite materials consist of nanometer-sized quantum objects such as atoms, molecules, voids or nanoparticles embedded in a host material. These quantum objects can be exploited as a super-structure, which can be designed to create material properties targeted for specific applications. For electromagnetism, such targeted properties include field enhancements around the bandgap of a semiconductor used for solar cells, directional decay in topological insulators, high kinetic inductance in superconducting circuits, and many more. Despite very different application areas, all of these properties are united by the common aim of exploiting collective interaction effects between quantum objects. The literature on the topic spreads over very many different disciplines and scientific communities. In this review, we present a cross-disciplinary overview of different approaches for the creation, analysis and theoretical description of nanocomposites with applications related to electromagnetic properties
Perspectives on weak interactions in complex materials at different length scales
Nanocomposite materials consist of nanometer-sized quantum objects such as atoms, molecules, voids or nanoparticles embedded in a host material. These quantum objects can be exploited as a super-structure, which can be designed to create material properties targeted for specific applications. For electromagnetism, such targeted properties include field enhancements around the bandgap of a semiconductor used for solar cells, directional decay in topological insulators, high kinetic inductance in superconducting circuits, and many more. Despite very different application areas, all of these properties are united by the common aim of exploiting collective interaction effects between quantum objects. The literature on the topic spreads over very many different disciplines and scientific communities. In this review, we present a cross-disciplinary overview of different approaches for the creation, analysis and theoretical description of nanocomposites with applications related to electromagnetic properties
Hierarchical Equations of Motion Approach to Quantum Thermodynamics
We present a theoretical framework to investigate quantum thermodynamic
processes under non-Markovian system-bath interactions on the basis of the
hierarchical equations of motion (HEOM) approach, which is convenient to carry
out numerically "exact" calculations. This formalism is valuable because it can
be used to treat not only strong system-bath coupling but also system-bath
correlation or entanglement, which will be essential to characterize the heat
transport between the system and quantum heat baths. Using this formalism, we
demonstrated an importance of the thermodynamic effect from the tri-partite
correlations (TPC) for a two-level heat transfer model and a three-level
autonomous heat engine model under the conditions that the conventional quantum
master equation approaches are failed. Our numerical calculations show that TPC
contributions, which distinguish the heat current from the energy current, have
to be take into account to satisfy the thermodynamic laws.Comment: 9 pages, 4 figures. As a chapter of: F. Binder, L. A. Correa, C.
Gogolin, J. Anders, and G. Adesso (eds.), "Thermodynamics in the quantum
regime - Recent Progress and Outlook", (Springer International Publishing
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