We will discuss the behavior of one or more elementary quantum system (atom, molecules, quantum dot, …) interacting with a stationary, simple and rich electromagnetic environment out of thermal equilibrium: The electromagnetic field is produced by a simple configuration of macroscopic objects held at thermal equilibrium at different temperatures. We will show how the internal atomic dynamics can be deeply affected by the non equilibrium configuration leading to unexpected phenomena like a spontaneous inversion of population, new cooling mechanisms obtained by heating the system, and the possibility to create and protect entanglement in a stationary and robust way. Finally, we will discuss how this system may directly allow the realization of atomic quantum thermal machines, with high efficiency and a genuine quantum behavior.
We will discuss the behavior of one or more elementary quantum system (atom, molecules, quantum dot, …) interacting with a stationary, simple and rich electromagnetic environment out of thermal equilibrium: The electromagnetic field is produced by a simple configuration of macroscopic objects held at thermal equilibrium at different temperatures. We will show how the internal atomic dynamics can be deeply affected by the non equilibrium configuration leading to unexpected phenomena like a spontaneous inversion of population, new cooling mechanisms obtained by heating the system, and the possibility to create and protect entanglement in a stationary and robust way. Finally, we will discuss how this system may directly allow the realization of atomic quantum thermal machines, with high efficiency and a genuine quantum behavior.
We will discuss the behavior of an elementary quantum system (atom, quantum dot, …) interacting with an environment out of thermal equilibrium. We show how the internal atomic dynamics can be deeply affected by the non equilibrium configuration leading to unexpected phenomena like a spontaneous inversion of population, new cooling mechanisms obtained by heating the system, and the possibility to create and protect entanglement in a stationary and robust way [1,2,3].----------------References: [1] B. Bellomo, R. Messina, and M. Antezza, Europhys. Lett. 100, 20006 (2012); Phys. Rev. A 87, 012101 (2013).[2] B. Bellomo and M. Antezza, New Journal of Physics 15, 113052 (2013); Europhys. Lett. 104, 10006 (2013).[3] R. Messina and M. Antezza, Europhys. Lett. 95, 61002 (2011); Phys. Rev. A 84, 042102 (2011); Phys. Rev. A in press, arXiv:1402.2506 (2014).
We study the internal dynamics, the quantum thermalization and the entanglementof elementary quantum systems (one or two atoms) placed close to a body held at atemperature different from that of the surrounding radiation.Concerning the single atom dynamics [1,2], we derive general expressions for lifetimeand density matrix valid for bodies of arbitrary geometry and dielectric permittivity.Out of equilibrium, the thermalization process and steady states become both qualitativelyand quantitatively significantly different from the case of radiation at thermalequilibrium. For the case of a three-level atom close to a slab of finite thickness, wepredict the occurrence of population inversion and an efficient cooling mechanism forthe quantum system, whose effective internal temperature can be driven to values muchlower than both involved temperatures. Our results show that non-equilibrium configurationsprovide new promising ways to control the state of an atomic system.We also consider two two-level atomic quantum systems (qubits) [3]. While at thermalequilibrium the two-qubit dynamics is characterized by not entangled steady thermalstates, we show that absence of thermal equilibrium may bring to the generationof entangled steady states. Remarkably, this entanglement emerges from the two-qubitdissipative dynamic itself, without any further external action on the two qubits, suggestinga new protocol to produce and protect entanglement which is intrinsically robustto environmental effects.======================[1] Bruno Bellomo, Riccardo Messina, and Mauro Antezza, Europhys. Lett. 100, 20006(2012).[2] Bruno Bellomo, Riccardo Messina, Didier Felbacq, and Mauro Antezza, Phys. Rev.A 87, 012101 (2013).[3] Bruno Bellomo, and Mauro Antezza, arXiv:1304.2864 (2013).
We study the functioning of a three-level thermal machine when acting on a many-qubit system, the entire system being placed in an electromagnetic field in a stationary out-of-thermal-equilibrium configuration. This realistic setup stands between the two so-far-explored cases of single-qubit and macroscopic object targets, providing information on the scaling with system size of purely quantum properties in thermodynamic contexts. We show that, thanks to the presence of robust correlations among the qubits induced by the field, thermodynamic tasks can be delivered by the machine both locally to each qubit and collectively to the many-qubit system: This allows a task to be delivered also on systems much bigger than the machine size.
Quantum thermodynamics (QT) is an emerging field of research 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 thing 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 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, and in particular non-thermal steady states, which brings to light a different thermodynamic description, usually called steady-state thermodynamics, therefore one of the goals that we are willing to achieve with this thesis is to give an introduction to QT of systems out-of-equilibrium.One of the related subtopics that physicists deal with in QT and the one that we will be focusing on this work are the use of non-thermal stationary states to build heat engines in the quantum domain, and the analyses of the features that this new regime could possibly allow, like the use of quantum resources as a way to overcome classical limitations imposed on its performance, like to attain efficiencies higher than Carnot's or operate in certain regimes unattainable using only classical resources.Therefore, 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 an experimentally relevant thermodynamic cycle for a transmon qubit WS interacting with a non-thermal environment composed by two subsystems, an 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.The efficiency of this engine obtains a maximum value up to 47% in the regime of operation used.We also wanted to look for the role played by the different types of coherences, present at the WS, on the behavior of the engine and its efficiency.By different types of coherence we mean the so called modes of coherence, whose definition is based on how they respond to symmetry transformations.We did that for the trivial case of the qubit, that only contains the modes 1 and -1, and that has shown to be extremely important for the efficiency of the machine.The same procedure was repeated for a 3-level system WS.The modes 1 and -1 was again very important, not only to the absolute value of the engine's efficiency but to the regime of operation of the machine.The additional modes, 2 and -2, had a negative impact on the efficiency, reducing its absolute value.This result appears to show some evidences that quantumness won't necessarily bring improvements to the operation of those machines.
Abstract. We investigate the creation of entanglement between two quantum emitters interacting with a realistic common stationary electromagnetic field out of thermal equilibrium. In the case of two qubits we show that the absence of equilibrium allows the generation of steady entangled states, which is inaccessible at thermal equilibrium and is realized without any further external action on the two qubits. We first give a simple physical interpretation of the phenomenon in a specific case and then we report a detailed investigation on the dependence of the entanglement dynamics on the various physical parameters involved. Sub- and super-radiant effects are discussed, and qualitative differences in the dynamics concerning both creation and protection of entanglement according to the initial two-qubit state are pointed out.