**Motivation**

Thermodynamics constitutes one of the pillars of natural sciences, describing diverse concepts from the arrow of time to the efficiency of engines and motors. Above all, thermodynamics is a pragmatic theory: it offers clear and simple guidelines on which process can or cannot happen. However, in order to accomplish this, it relies on a few very strong assumptions. Most importantly is the notion of emergent phenomena, that take place when dealing with a macroscopically large number of particles. In essence, thermodynamics describes systems which are so unbearably complicated that they actually become simple; while a system of 50 particles may rely on all its degrees of freedom to be described, a system with 10^(23) relies only on a handful, such as energy, pressure and entropy.

In view of its simplicity and success, it becomes natural to ask whether the laws of thermodynamics can also be extended to other scenarios. That is, whether there exists systems that lie beyond the standard thermodynamic paradigm but which nonetheless enjoy a similarly simple and powerful set of rules. In the last four decades this question has been partially addressed in the micro- and mesoscopic regime. Initially it was believed that microscopic systems were simply not thermodynamic. However, it is now known that a consistent theoretical framework can be built, provided one interprets thermodynamic quantities such as heat and work as random variables, subject to fluctuations that are inherent of small systems. This field is called stochastic thermodynamics and has been remarkably successful in describing a diverse set of systems and processes, from biological engines to nanoscale junctions.

Small systems should also be subject to the rules of quantum mechanics. However, due to the phe- nomena of decoherence, most quantum phenomena never manifest themselves in practice. Effects such as entanglement and superposition are fragile, being quickly lost due to the contact between the system and its surroundings. This has been the main motivation behind the so-called quantum coherent platforms: systems in which the effects of the environment can be controlled to shield it from decoherence. Examples include superconducting circuits, optomechanical devices, trapped ions, ultra-cold atoms and so on. In such systems, classical effects such as heat flow can be combined with quantum effects, such as entanglement, to produce exciting new phenomena.

The remarkable progress in quantum coherent experiments is the main drive behind the field of quantum thermodynamics. The laws developed in stochastic thermodynamics now have to be updated to include such novel features. Quantities such as entanglement now play the role of an informational resource, which in this regime can be combined with standard energetic resources such as heat and work. Such resources can be consumed to perform thermodynamic tasks or interconverted from one another. In addition, the backaction from quantum measurements (“wavefunction collapse”) also plays a central role. This backac- tion makes quantum thermodynamics extrinsic; i.e., dependent not only on the process itself, but also on the way the experimenter chooses the probe that process.

Absolutely central to thermodynamics is the second law and the concept of entropy production. Entropy does not satisfy a continuity equation, in the sense that the entropy leaving one system does not have to equal the entropy entering another. In addition to possible entropy flows, there may also be some entropy which is irreversibly produced during the process. Since entropy can only flow or be created, the net entropy is always an increasing function of time. Since this imposes constraints on which kinds of processes may occur, it has both a foundational significance, concerning the arrow of time, as well a practical one, providing guidelines on how to design better devices.

**Goals**

The overarching goal of my research is to formulate a set of operationally useful laws of thermody- namics in the quantum regime. These should contemplate informational and energetic resources on equal footing and also account for the measurement backaction. Moreover, it should also recover stochastic ther- modynamics in the classical limit. My research has revolved, in particular, around the question of how to formulate the second law in the quantum regime. To date, the most prolific approach has been to connect entropy production with information-theoretic quantities. Information theory views probabilities and quan- tum states as descriptions of the amount of information one has about a system, as well as the amount of information shared between two or more systems. Entropy production can then viewed as a measure of how much information the system shares with its surroundings. And irreversibility emerges from the fact that this information is seldom retrievable, specially when the environment is large.

Viewing the second law in this way opens up many exciting perspectives. First, it allows for a unified description of heat and information engines (such as Maxwell’s demons or Szilard engines). Second, it places Landauer’s principle on information erasure on equal footing as work extraction or related tasks that are common in e.g. biological systems. Third, it naturally encompasses the effect of the measurement backaction, which disturbs the information shared between system and environment.

In light of this, some of the questions that I have recently addressed and which I plan to continue examining in the near future, include:

• Thermodynamic Uncertainty Relations.

• Continuously monitored quantum systems.

• Thermometry at the quantum regime.

• Collisional models.

• Fully quantum fluctuation theorems.

• Thermodynamics in quantum phase space.

• Entropy production at criticality.

You can also browse through our list of publications or click here for accessing the research project of each student in the group.

RECENT COLLABORATORS (in alphabetical order)

- Albert Schliesser, Neils Bohr Institute.

- André Timpanaro, UFABC, Santo André.

- Cecília Cormick, NUC, Cordoba.

- Domingos Salazar, UFRPE, Brazil.

- Dragi Karevski, Université de Lorraine, Nancy.

- Eduardo Duzzioni, UFSC, Florianópolis.

- Eric Lutz, Stuttgart University.

- Fernando Semião, UFABC, Santo André.

- Frederico Brito, IFSC-USP, São Carlos.

- Gabriele de Chiara, Queens University in Belfast.

- Giacomo Guarnieri, Trinity College Dublin.

- Gerardo Adesso, University of Nottingham.

- John Goold, Trinity College Dublin.

- Lucas Céleri, UFG, Goiânia.

- Luis Correa, University of Exeter.

- Malte Henkel, Université de Lorraine, Nancy.

- Mauro Paternostro, Queens University in Belfast.

- Paulo Henrique Souto Ribeiro, UFSC, Florianópolis.

- Raphael Drummond, UFMG, Belo Horizonte.

- Roberto Serra, UFABC, Santo André.

- Sascha Wald, SISSA Trieste.

- Stefan Nimmrichter, Max Planck Erlangen.

- Stephen Clark, Bristol University.

- Valerio Scarani, CQT Singapore.

ACTIVE RESEARCH PROJECTS

- Fapesp regular research project (2018/12813-0).

- Fapesp-Queens SPRINT collaboration with Prof. Mauro Paternostro (2017/50304-7).

- Fapesp-Nottingham-Birmingham joint collaboration with Profs. Gerardo Adesso and Vincent Boyer (2017/07973-5).

- INCT Quantum Information network (465469/2014-0).