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Do the classical definitions of work, heat and entropy, and the laws of thermodynamics apply at the quantum scale? The foundations of Quantum Thermodynamics (QTD) emerged from the need to formalize these concepts in the quantum realm. This exciting field has been challenging our understanding of how energy transforms in the quantum world. Would you ever imagine that putting together a hot and a cold body in contact, the hot would get hotter and the cold would get colder instead of thermalizing? QTD explains how this is possible!
At an applied level, just think about quantum computing: the cooling needed to operate superconductor architectures, the level of control needed to perform quantum operations in time scales enabling quantum algorithms to run, strategies to suppress errors from the external environment. The QTD community has been very creative in addressing these questions!
At an applied level, just think about quantum computing: the cooling needed to operate superconductor architectures, the level of control needed to perform quantum operations in time scales enabling quantum algorithms to run, strategies to suppress errors from the external environment. The QTD community has been very creative in addressing these questions!
I first became fascinated with QTD at the time I was a graduate student and one of my colleagues was involved in the first experiments with NMR at the Federal University of ABC. Since then, I have been obsessed with the idea that entanglement can be considered a thermodynamic resource. Since entanglement is the key ingredient in many-body phenomena, my passion naturally led me to explore the role of many-body effects in thermodynamic processes, especially those involving extraction of work.
Below, I share some of my (modest) contributions to this field.
Quantum work distribution and irreversibility
Quantum Thermodynamics emerged as a sub-field of quantum information, driven by the need to define the laws of statistical mechanics to systems at the nanoscale and interpret them from an informational perspective. For atoms, molecules and devices away from the thermodynamical limit, the conventional definitions of work, heat and entropy no longer apply due to a constraint in the number of degrees of freedom. Moreover, these thermodynamical quantities are not associated with an observable, but instead with distributions. The statistics allow us to quantify average values and their fluctuations.
Since its foundation, quantum thermodynamics has been rapidly evolving, and promising applications are trending. Quantum heat engines built from many-particle systems as working medium are an elegant example of a problem to exploit quantum advantage. To run efficient thermal cycles requires operating them at finite-time to mitigating errors due to decoherence. Efforts in this direction are still in their infancy. A good starting point is to characterize the energetics of complex systems and gain insights to develop quantum control strategies. We then started investigating the work statistics of systems driven across a phase transition in finite time. We showed that the skewness of the distribution witnesses the transition and provides an indirect measurement for irreversibility . We later proposed the use of the skewness and negentropy as of metrics for the non-Gaussianity of the work distribution. Deviations from non-Gaussianity allow to identify time scales at which the sudden quench and adiabatic approximations hold.
Another interesting line we have been working on aims to approximate the quantum thermodynamics of complicated many-body systems using Density Functional Theory. Future directions include proposals of novel models for thermal machines, optimization of thermal cycles at finite-time, and improvement over the DFT-inspired approximations.
Papers
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I co-authored an article in a recent issue of the Roadmap on Quantum Thermodynamics discussing theoretical and experimental challenges in studying complex many-body systems for real-world applications of quantum thermodynamics.
The quantum Mpemba effect
Historically, the Mpemba effect refers to the anomalous cooling of water, a phenomenon where initially hot configurations can cool faster than cold ones.
The quantum Mpemba effect gained popularity in 2024, with a variety of theoretical works studying its manifestation in microscopic systems, regarded as a speedup in relaxation processes. Its occurrence refers to a situation in which the larger the distance between the initial configuration and the stationary state, the faster it reaches stationarity. This holds in isolated many-body systems in dynamics restoring symmetries. In open quantum systems, it has been understood that this acceleration can occur whenever the degrees of freedom that slow the dynamics are suppressed, the initial state and spectral properties of the Liouvillian being central ingredients.
Our work filled a fundamental gap in understanding the effect from thermodynamic principles. We identified the central thermodynamic quantity: the non-equilibrium free energy. Additionally, we proposed a generic protocol to activate the effect in a system that would not necessarily manifest it for an accessible initial state. Our protocol works by eliminating the slow modes' contributions, which increases the non-equilibrium energy and guides the system to a metastable state that reaches the fixed point more quickly.
Papers
Transport in boundary driven quantum systems
The minimal model to describe the out-of-equilibrium dynamics of a quantum transistor considers a quantum system coupled at the boundaries to two external reservoirs. By carefully engineering the interactions between system and reservoirs in such a way to allow for some excitations to flow through the device, one can control the transport of heat, energy and particles.
A natural question that emerges is how resilient are the transport properties to an additional reservoir with the role of spoiling the quantum features: noise. Noise is well known for corrupting information processing in quantum computers. However, contrary to the expectations, interactions with the environment are not always detrimental.
Recently, we showed that in systems exhibiting Wannier-Stark localization, a many-body phenomena, the environment can suppress the effects hindering the flow of particles and energy.
Papers
Dephasing-assisted transport in a tight-binding chain with a linear potential