arXiv subjects

Nikhil Gupt

Publications and source records attributed to Nikhil Gupt.

7 recordsLinked to original sources

arXiv2024

Fluctuations and optimal control in a Floquet Quantum Thermal Transistor

We use Full Counting Statistics to study fluctuations and optimal control in a three-terminal Floquet quantum thermal transistor. We model the setup using three qubits (termed as the emitter, collector and base) coupled to three thermal baths. As shown in Phys. Rev. E 106, 024110 (2022), one can achieve significant change in the emitter and collector currents through a small change in the base current, thereby achieving a thermal transistor operation. Using sinusoidal and pi-flip modulations of the base qubit frequency, we show that the variance of the base current is much less compared to those of the emitter and collector currents, while the opposite is true in case of the Fano factor. We then apply optimal control through the Chopped Random Basis optimization protocol, in order to significantly enhance the amplification obtained in the transistor. In contrast, a reduction in the Fano factor of the setup through optimal control is associated with a large base current, thereby suggesting a trade-off between precision and base current. We expect our results will be relevant for developing heat modulation devices in near-term quantum technologies.

quant-ph↗

arXiv2024

Inverse Current in Coupled Transport: A Quantum Thermodynamic Model

The recent discovery of inverse current in coupled transport (ICC) in classical systems~\textcolor{blue}{[\textbf{Phys. Rev. Lett.} \textbf{124}, 110607 (2020)]} -- where an induced current flows opposite to two mutually parallel thermodynamic forces, yet remains consistent with the second law of thermodynamics -- reveals a striking and counterintuitive transport phenomenon. Using an exactly solvable model of strongly coupled quantum dots, we develop a thermodynamic framework to describe the ICC phenomenon at the quantum level. By systematically connecting the microscopic and macroscopic formulations of the entropy production rate in terms of appropriate entropic biases and entropic fluxes, our analysis identifies the conditions under which a \textit{genuine} ICC effect can arise in quantum thermal transport and highlights potential applications in autonomous quantum engines and refrigerators.

quant-ph↗

arXiv2023

Graph theoretic analysis of three-terminal quantum dot thermocouples: Onsager relations and spin-thermoelectric effects

We introduce a simplified model for a three-terminal quantum thermocouple consisting of two strongly-coupled quantum dots. To elucidate spin-dependent Seebeck and Peltier effects, we employ a microscopic Hamiltonian and map the Lindblad master equation onto a quantum transition network, capturing the key working principles for both reciprocal effects. Our analysis reveals quantum thermodynamic networks encompassing both Coulomb interaction and spin-flipping processes, lead to the emergence of spin-thermolectric effects. Using algebraic graph theory, we recover the phenomenological law of irreversible thermodynamics from the stochastic version of the entropy production rate expressed in terms of cycle flux and cycle forces. Remarkably, Onsager reciprocity and Kelvin relation for transport coefficients find their premises in the properties of cycle flux trajectories within the quantum transition network. This underscores the universal generality of thermodynamic principles across classical and quantum realms, despite their fundamentally different basis from classical laws of irreversible thermodynamics relying on local equilibrium assumptions.

cond-mat.mes-hall↗

arXiv2023

Top-Ranked Cycle Flux Network Analysis of Molecular Photocells

We introduce a top-ranked cycle flux ranking scheme of network analysis to assess the performance of molecular junction solar cells. By mapping the Lindblad master equation to the quantum-transition network, we propose a microscopic Hamiltonian description underpinning the rate equations commonly used to characterize molecular photocells. Our approach elucidates the paramount significance of edge flux and unveils two pertinent electron transfer pathways that play equally important roles in robust photocurrent generation. Furthermore, we demonstrate that non-radiative loss processes impede the maximum power efficiency of photocells, which may otherwise be above the Curzon-Ahlborn limit. These findings shed light on the intricate functionalities that govern molecular photovoltaics and offer a comprehensive approach to address them in a systematic way.

cond-mat.mes-hall↗

arXiv2022

Universal behaviour of Coulomb coupled Fermionic thermal diode

We propose a minimal model of a Coulomb coupled fermionic quantum dot thermal diode that can act as an efficient thermal switch and exhibit complete rectification behaviour, even in presence of a small temperature gradient. Using two well defined dimensionless system parameters, universal characteristics of the optimal heat current condition are identified. It is shown to be independent of any system parameter and is obtained only at the mean transitions point "$-0.5$", associated with the equilibrium distribution of the two fermionic reservoirs, tacitly referred to as "$\textit{universal magic mean}$".

quant-ph↗

arXiv2022

Floquet Quantum Thermal Transistor

We apply periodic control to realize a quantum thermal transistor, which we term as the Floquet Quantum thermal Transistor. Periodic modulation allows us to control the heat flows and achieve large amplification factors even for fixed bath temperatures. Importantly, this transistor effect persists in the cut-off region, where traditional quantum thermal transistors operating in absence of periodic modulation, fail to act as viable heat modulation devices.

quant-ph↗

arXiv2021

Statistical Generalization of Regenerative Bosonic and Fermionic Stirling Cycles

We have constructed a unified framework for generalizing the finite-time thermodynamic behavior of statistically distinct bosonic and fermionic Stirling cycles with regenerative characteristics. In our formalism, working fluid consisting of particles obeying Fermi-Dirac and Bose-Einstein statistics are treated under equal footing and modelled as a collection of non-interacting harmonic and fermionic oscillators. In terms of frequency and population of the two oscillators, we have provided an interesting generalization for the definitions of heat and work that are valid for classical as well as non-classical working fluids. Based on a generic setting under finite time relaxation dynamics, novel results on low and high temperature heat transfer rates are derived. Characterized by equal power, efficiency, entropy production, cycle time and coefficient of performance, thermodynamic equivalence between two types of Stirling cycles is established in the low temperature "quantum" regime.

quant-ph↗