We will discuss the behavior of one or more elementary quantum systems (atoms, molecules, quantum dots,etc) interacting with a stationary, simple and rich electromagnetic environment out of thermal equilibrium. Particularattention will be devoted to the new features that this system offers toward the possibility to manipulatecollective atomic states and leading to improved performances in: creation and protection of entanglement,quantum thermal machines, transport of excitations.
We will discuss the behavior of one or more elementary quantum systems (atoms, molecules, quantum dots,etc) interacting with a stationary, simple and rich electromagnetic environment out of thermal equilibrium. Particularattention will be devoted to the new features that this system offers toward the possibility to manipulatecollective atomic states and leading to improved performances in: creation and protection of entanglement,quantum thermal machines, transport of excitations.
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).
Among the few lessons that Physics teaches us on a daily basis, one in particular is hard to miss: thermalization processes are ubiquitous. With the same degree of certainty, one can predict an apple to fall onto the ground if its stalk is cut, or a cup of tea to be found cold if left on the table for too long. In this respect, generic classical and quantum mechanical systems seem to behave in the same way. This is also one of the main difficulties in the experimental observation of the bizarre effects predicted from the quantum theory, as several of these are known to disappear at finite temperatures. It has been known for a long time that thermalization is associated with “chaotic” behavior at the microscopic level, but recently systematic efforts, both theoretical and experimental, have allowed us to understand its mechanisms at an unprecedented level of accuracy. Indeed, it has been realized that thermalization generally occurs also in isolated systems, where the absence of interactions with the environment allows for first principle theoretical investigations1. In this case thermalization takes place locally, as the whole system acts as a thermal bath for its own subsystems. Theoretical research has been motivated and paralleled by exciting experimental progress in cold-atom physics, which has provided robust, nearly ideal realizations of several theoretical models2. As an established piece of knowledge, recent research has now confirmed that two outstanding exceptions actually exist in the quantum realm, where thermalization is prevented to occur. These are many-body localized systems3, where disorder plays a crucial role, and integrable ones, which are protected by the existence of higher conservation laws. By their own nature, these systems display exceptional non-equilibrium features, which are not washed out by the onset of thermalization as relaxation occurs. At the core of the present thesis lie the remarkable properties of integrable systems out of equilibrium, with a special attention to physical effects which could be observed in cold-atom realizations. The work collected here is part of a large theoretical effort4 which in the past decade has focused on the study of relatively simple protocols to bring a quantum system out of equilibrium, such as the so-called quantum quench. In these “theoretical laboratories” it has been possible to provide quantitative predictions which helped us to develop an intuition on general questions regarding non-equilibrium and thermalization processes. Furthermore, in some cases these studies have highlighted interesting physical effects which could be directly probed experimentally within cold-atom settings. The contribution of the present thesis is two-fold. On the one hand, we have developed new technical tools for the study of integrable systems out of equilibrium, and for the computation of measurable physical quantities such as correlation functions. The techniques employed are mainly analytical and rooted within the mathematical structures of integrability. On the other hand, we have singled out physically relevant nonequilibrium situations where exotic, non-thermal states of matter emerge after relaxation occurs, and provided quantitative analytical predictions in these cases. A comprehensive discussion of the motivations and results of our work will be presented in Chapter 1, where we provide a complete overview of this thesis and discuss the organization of its content.
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 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.
Quantum systems exhibit unique behavior, often defying classical expectations. Their dynamics are profoundly shaped by the interplay of quantum and thermal fluctuations, making precise predictions challenging. This paper explores the non-equilibrium thermodynamics of quantum systems, focusing on the development of a novel framework to address this challenge. We propose a 'quantum-thermal coupling' algorithm, designed to capture the complex dynamics of these systems, offering a paradigm shift in our understanding of quantum phenomena in a dynamically changing environment. The core claim is to provide a robust and adaptable approach for modeling and predicting the behavior of quantum systems in non-equilibrium conditions, considering the intricate interplay of quantum and thermal effects. This work builds upon existing research in quantum mechanics and thermodynamics, addressing limitations in current models and establishing a foundational step towards a more complete understanding of these systems.