Palestrante
Descrição
Quantum thermodynamics (QT) is an emerging field of research (1) that aims to investigate how the laws of thermodynamics and quantum mechanics merge together in small quantum systems. With advances at the necessary technology to control and measure those small physical systems this field has acquired even more importance, not only in the sense that it can be tested, which is a good feature for basic research, but that new applications could be implemented at these scales, so a better comprehension of the limitations imposed by quantum thermodynamics turns out to be of a crucial importance for these goals, which forces theoreticians to produce experimentally relevant versions of these new concepts. Another important aspect present at those systems is that part of them work in a regime where its constituents are described by non-thermal states, in particular in non-thermal steady states, which brings to light a different thermodynamic description. One of the related subtopics that physicists deal with in QT and can possibly involve non-thermal stationary states is the physics of heat engines at the quantum domain, and one of the main features that this new regime could possibly allow, is the use of quantum resources as a way to overcome classical limitations imposed on its performance, like to attain efficiencies higher than Carnot's. This has generated a wave of ecstasy in the scientific community although it might be too soon to claim that these new features are true considering that people came up with results that apparently contradict it other. For instance, when dealing with non-thermal states, there is one result that tells us that the Carnot's efficiency cannot be overcomed (2) if we consider that part of the energy absorbed by the quantum working substance, known as housekeeping heat, is used maintain its non-thermal stationary state. Another approach towards this issue is the distinction of the "heat" absorbed from the environment in two different types of energy, the variation in passive energy which is the part responsible for the changes in entropy, and variation in ergotropy, that is a work-like energy that can be later extracted by means of a suitable unitary transformation. And in this case again, the irreversibility criterion to obtain the upper bound efficiency is different, because the ergotropy does not cause any entropy change. So in order to clarify the underlying physics of those systems in a non-thermal regime, any experimentally well suited content is more than welcome. So keeping that in mind we devised a experimentally relevant (3) thermodynamic cycle for a transmon qubit working substance (WS) interacting with a non-thermal environment composed by two subsystems, a externally excited cavity and a classical heat bath with temperature T. The WS undergoes a non-conventional cycle (different from Otto, Carnot, etc.) through a succession of non-thermal stationary states obtained by slowly varying its bare frequency and the amplitude of the field applied on the cavity. We calculate the the efficiency of this engine, obtaining its maximum value up to 47%. As a next step in this research we are studying what the presence of coherence in the WS can do to the efficiency of the engine and what order of coherence are the most important when it comes to change the behavior of the engine.
Referências
1 BINDER, F. et al. (Eds) Thermodynamics in the quantum regime: fundamental aspects and new directions. Switzerland: Sringer Nature, 2018. (Fundamental theories of physics,v.195)
2 GARDAS, B.; DEFFNER, S. Thermodynamic universality of quantum Carnot engines. Pysical Review E, v. 92, n. 4, p. 042126-1-042126-6, 2015.
3 ROUXINOL, F. et. al. Measurements of nanoresonator-qubit interactions in a hybrid quantum electromechanical system. Nanotechnology, v. 27, n.36, p.364003-1-364003,2016.
| Subárea | Teoria da Informação Quântica |
|---|---|
| Apresentação do trabalho acadêmico para o público geral | Não |
