Entropy Dynamics in the System of Interacting Qubits

Abstract

The classical Second Law of Thermodynamics demands that an isolated system evolves with a nondiminishing entropy. This holds as well in quantum mechanics if the evolution of the energy-isolated system can be described by a unital quantum channel. At the same time, the entropy of a system evolving via a non-unital channel can, in principle, decrease. Here, we analyze the behavior of the entropy in the context of the H-theorem. As exemplary phenomena, we discuss the action of a Maxwell demon (MD) operating a qubit and the processes of heating and cooling in a two-qubit system. We further discuss how small initial correlations between a quantum system and a reservoir affect the increase in the entropy under the evolution of the quantum system.

H-Theorem for Systems with an Interaction Invariant Distribution Function

“…Moreover, for an energetically isolated quantum system this criteria can identify a non-unital channels preserving the energy of the system and which can lower its entropy without heat exchange with the reservoir. Such a situation corresponds to an action of a quantum Maxwell demon [15] and was demonstrated in the system of interacting qubits [16]. In this article we prove a new unitality criteria which is expressed in terms of invariance of the diagonal density matrix elements i.e.…”

Quantum entanglement in the anisotropic Heisenberg model with multicomponent DM and KSEA interactions

“…If in the model with P 23 -symmetry, Eq. ( 28), the external field is uniform, then in the other three systems the field is parallel for one spin component and antiparallel for the other two components [see Eqs (30), (32), and (34)]. Further, in all models, only three components (out of six possible D x , D y , D z , Γ x , Γ y , and Γ z ) of DM-KSEA interactions can be present in total.…”

“…According to classical thermodynamics, heat engines cyclically operating at a single temperature are not possible, the maximum efficiency of any heat engine is limited by the Carnot bound, etc. In contrast, in quantum thermodynamics, engines that operate at a single temperature are proposed [22,23,24], entangled thermal systems that can be more efficient in extracting work than the systems without quantum correlations are considered [25,26,27], emergence of the second law of thermodynamics is discussed [28,29,30,31].…”

Boosting quantum key distribution via the end-to-end physical control

“…As was shown in Refs. [4][5][6][7], even to construct an operation reversing a simplest specific scattering event and, consequently, to harvest information, Eve already has to have an a priori information about the scattered signal. And if a single scattering occurs once per a wavelength, then to handle scattering in a 1 km-long channel, Eve would need to build a billion quantum Maxwell demon-like devices, each reversing the entropy dynamics of losses from the corresponding individual scattering center.…”