Integrated Calendar

Quantum thermodynamics deals with thermodynamic effects and thermodynamic constraints (e.g. the 2nd law) that emerge in out-of-equilibrium microscopic open quantum systems, and in microscopic heat machines. Presently, the technology developed for quantum computing is sufficient for exploring quantum thermodynamic experimentally (new experimental results will be shown). On top of the second law, thermodynamic resource theory predicts additional mathematical constraints on thermal transformation of microscopic systems. Unlike the second law, these constraints cannot be related to thermodynamic observables. Consequently, they are useful for some theoretical purposes, but not for making concrete predictions on realistic scenarios. In this talk I will present a new formalism that yields additional “seconds laws” that follow the logic and structure of the standard 2nd law. While the 2nd law deals with the first moment of the energy (average heat, average work), the observables in the new laws are higher moments of the energy. I will show several scenarios where these laws provide concrete answers to “blind spots” that are not addressed by the standard 2nd law. In other cases tighter bounds are obtained compared to the standard 2nd law. Potentially, this formalism can significantly extend the thermodynamic framework, and put additional practical bounds on thermal transformations and microscopic heat machines. Finally, I will discuss the connection to quantum coherence measures and list several research directions.

Electrical and thermal transport in unconventional materials such as "bad metals” continues to pose tough challenges for theory. I will argue that a promising approach to understanding the properties of these materials is through the notion of fundamental quantum bounds on certain observables, that can apply independently of the microscopic dynamics. Some evidence for such bounds has come from the study of black holes, which have been argued to be the “most extreme” of all physical systems in various senses that I will discuss. In particular, the diffusion of energy across a black hole event horizon shares important features in common with the transport of energy and change in a bad metal.

The self-consistent phonons (SCP) method is a practical approach for computing structural and dynamical properties of a general quantum or classical many-body system while incorporating anharmonic effects. In SCP one finds an effective temperature-dependent harmonic Hamiltonian that provides the “best fit” for the physical Hamiltonian, the “best fit” being defined as the one that optimizes the Helmholtz free energy at a fixed temperature. The numerical bottleneck of the method is the evaluation of Gaussian averages of the potential energy and its derivatives. Several algorithmic ideas/tricks are introduced to reduce the cost of such integration by orders of magnitude, e.g., relative to that of the previous implementation of the SCP approach by Calvo et al.
[J. Chem. Phys. 133, 074303 (2010)]. One such algorithmic improvement is the replacement of standard Monte Carlo integration by quasi-Monte Carlo integration utilizing low-discrepancy sequences. SCP has been used to study the equilibrium properties and the structural transitions in small and large Lennard-Jones clusters. The method was also applied to computations of vibrational spectra of water clusters.