Non-thermal pathways to non-equilibrium control of correlated quantum materials

Miroslav Hopjan, Claudio Verdozzi

Jincheng Zhang

Quantum noise poses a significant challenge to the reliable operation of quantum technologies, particularly in quantum computing and quantum information processing. Traditional noise mitigation techniques often rely on cryogenic cooling and shielding, which can be resource-intensive and may not fully address the underlying noise mechanisms. This paper proposes a novel approach to quantum noise suppression based on precise control of the non-equilibrium thermodynamic relationship between a quantum system and its environment. The core idea is to utilize micro-heat sources and micro-cold sources to apply non-equilibrium thermal driving to the quantum system, effectively tuning its energy distribution and thereby reducing the density of noise energy. This approach leverages fundamental principles of thermodynamics to actively manage and mitigate quantum noise. The theoretical framework presented demonstrates a pathway to significantly extending coherence times in quantum bits (qubits) through this tailored non-equilibrium control. We explore the mathematical formalism underpinning this approach, highlighting the key equations governing the system's energy state and noise correlation. The efficacy of this strategy is discussed in terms of controlling the system's temperature and its impact on the quantum noise.

K. Berrada

Adolfo del Campo, Luis Pedro García-Pintos, Diego Tielas +1 more

Jiajun Li, Hugo U. R. Strand, Philipp Werner +1 more

Photo-induced hidden phases are often observed in materials with intertwined orders. Understanding the formation of these non-thermal phases is challenging and requires a resolution of the cooperative interplay between different orders on the ultra-short timescale. In this work, we demonstrate that non-equilibrium photo-excitations can induce a state with spin-orbital orders entirely different from the equilibrium state in the three-quarter-filled two-band Hubbard model. We identify a general mechanism governing the transition to the hidden state, which relies on a non-thermal partial melting of the intertwined orders mediated by photoinduced charge excitations in the presence of strong spin-orbital exchange interactions. Our study theoretically confirms the crucial role played by orbital degrees of freedom in the light-induced dynamics of strongly correlated materials and it shows that the switching to hidden states can be controlled already on the fs timescale of the electron dynamics.

Jonathan Lux

This purely theoretical thesis covers aspects of two contemporary research fields: the non-equilibrium dynamics in quantum systems \nand the electronic properties of three-dimensional topological insulators. \n \nIn the first part we investigate the non-equilibrium dynamics in closed quantum systems. Thanks to recent technologies, especially from the field \nof ultracold quantum gases, it is possible to realize such systems in the laboratory. The focus is on the influence of hydrodynamic slow \nmodes on the thermalization process. \nGeneric systems in equilibrium, either classical or quantum, in equilibrium are described by thermodynamics. \nThis is characterized by an ensemble of maximal entropy, but constrained by macroscopically conserved quantities. We will show that these \nconservation laws slow down thermalization and the final equilibrium state can be approached only algebraically in time. \nWhen the conservation laws are violated thermalization takes place exponential in time. \nIn a different study we calculate probability distributions of projective quantum measurements. \nNewly developed quantum microscopes provide the opportunity to realize new measurement protocols which go far beyond the conventional \nmeasurements of correlation functions. \n \nThe second part of this thesis is dedicated to a new class of materials known as three-dimensional topological insulators. \nAlso here new experimental techniques have made it possible to fabricate these materials to a high enough quality that their topological nature is revealed. \nHowever, their transport properties are not fully understood yet. Motivated by unusual experimental results in the optical conductivity \nwe have investigated the formation and thermal destruction of spatially localized electron- and hole-doped regions. \nThese are caused by charged impurities which are introduced into the material in order to make the bulk insulating. \nOur theoretical results are in agreement with the experiment and can explain the results semi-quantitatively. \nFurthermore, we study emergent lengthscales in the bulk as well as close to the conducting surface.