arXiv subjects

Parth Kumar

Publications and source records attributed to Parth Kumar.

4 recordsLinked to original sources

arXiv2025

Entropy Flow at the Quantum Limit

Thermal management is a key challenge, both globally and microscopically in integrated circuits and quantum technologies. The associated heat flow $I_Q$ has been understood since the advent of thermodynamics by a process of elimination, $I_Q{=}I_E{-}\mu I_N$, subtracting from the energy flow $I_E$ its convective contribution. However, in the quantum limit, this formula implies the paradoxical result that the entropy entrained by heat flow is unbounded even though the entropy itself tends to zero. We resolve this conundrum by recognizing that the traditional formula for heat is missing a quantum term. The correct quantum formula predicts that the heat produced in quantum processes is vastly smaller than previously believed, with correspondingly beneficial consequences for the efficiency of quantum machines.

quant-ph↗

arXiv2024

Thermodynamics of a Quantum Subsystem

Several prior attempts to formulate the Laws of Thermodynamics for a small region within a larger quantum system have led to inconsistencies and unexplained infinities. The entropy and external work, in particular, require careful analysis when partitioning over the various subsystems. In this work, we analyze the thermodynamics of a quantum subsystem driven quasi-statically by external forces. We show that the thermodynamic functions of a quantum subsystem can be defined dynamically in terms of its local spectrum. The external work is found to be intrinsically nonlocal due to the nonlocal character of the underlying quantum states. This nonlocal quantum work can be harnessed in a "quantum lever" to provide up to 100% amplification of the local work done on a quantum subsystem.

quant-ph↗

arXiv2024

Work Sum Rule for Open Quantum Systems

A key question in the thermodynamics of open quantum systems is how to partition thermodynamic quantities such as entropy, work, and internal energy between the system and its environment. We show that the only partition under which entropy is nonsingular is based on a partition of Hilbert space, which assigns half the system-environment coupling to the system and half to the environment. However, quantum work partitions nontrivially under Hilbert-space partition, and we derive a work sum rule that accounts for quantum work at a distance. All state functions of the system are shown to be path independent once this nonlocal quantum work is properly accounted for. Our results are illustrated with application to a driven resonant level strongly coupled to a reservoir.

quant-ph↗

arXiv2022

On the First Law of Thermodynamics in Time-Dependent Open Quantum Systems

How to rigorously define thermodynamic quantities such as heat, work, and internal energy in open quantum systems driven far from equilibrium remains a significant open question in quantum thermodynamics. Heat is a quantity whose fundamental definition applies only to processes in systems infinitesimally perturbed from equilibrium, and as such, must be accounted for carefully in strongly-driven systems. A key insight from Mesoscopics is that infinitely far from the local driving and coupling of an open quantum system, reservoirs are indeed only infinitesimally perturbed, thereby allowing the heat dissipated to be defined. The resulting partition of the entropy necessitates a Hilbert-space partition of the energetics, leading to an unambiguous operator for the internal energy of an interacting time-dependent open quantum system. Fully general expressions for the heat current and the power delivered by various agents to the system are derived using the formalism of nonequilibrium Green's functions, establishing an experimentally meaningful and quantum mechanically consistent division of the energy of the system under consideration into Heat flowing out of and Work done on the system. The spatio-temporal distribution of internal energy in a strongly-driven open quantum system is also analyzed. This formalism is applied to analyze the thermodynamic performance of a model quantum machine: a driven two-level quantum system strongly coupled to two metallic reservoirs, which can operate in several configurations--as a chemical pump/engine or a heat pump/engine.

cond-mat.mes-hall↗