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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 required to operate superconductor architectures, the level of control needed to perform quantum operations in time scales that allow quantum algorithms to run, and strategies to suppress errors caused by interactions with 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 required to operate superconductor architectures, the level of control needed to perform quantum operations in time scales that allow quantum algorithms to run, and strategies to suppress errors caused by interactions with 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. I remember that the click occurred thanks to one of my colleagues who was involved in early QTD experiments with NMR at the Federal University of ABC. One of these experiments explored the role of entanglement in thermodynamic processes and showcased very curious consequences. I learned that entanglement can be considered a thermodynamic resource and there was a resource theory to make the most of it.
It was very appealing to me because I was obsessed by entanglement in many-body phenomena. My reasoning to start playing around with QTD was: " In strongly correlated systems entanglement is sovereign . Entanglement has interesting thermodynamical consequences. Whats the role of many-body effects to thermodynamic processes?" The temptation ... question naturally tempted me to explore the topic of many-body quantum thermodynamics. Nice colleagues and advisors encouraged me to jumping into this. It did not take long for me to start finding problems. The beginning was very focused on the extraction of work at criticality. Then, the quantum Mpemba effect popped up. Now, optimization protocols for many-body heat engines based on variational quantum algorithms.
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 for systems at the nanoscale and reinterpret them from an informational-theoretic perspective. For atoms, molecules and devices away from the thermodynamical limit, the conventional definitions of work, heat and entropy no longer apply due to the limited 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 emerging. Quantum heat engines built from many-particle systems as working medium are an elegant example of a problem to exploit quantum advantage. Running 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 metrics for the non-Gaussianity of the work distribution. Deviations from non-Gaussianity allow us 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. It occurs when the larger the distance between the initial configuration and the stationary state, the faster the system relaxes toward 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 contributions of slow modes, 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
A minimal model describing the out-of-equilibrium dynamics of a quantum transistor considers a quantum system coupled at its 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 the transport properties are 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 phenomenon, 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