arXiv subjects

Jong-Min Park

Publications and source records attributed to Jong-Min Park.

22 records · Page 2Linked to original sources

arXiv2019

Quantum mechanical bound for efficiency of quantum Otto heat engine

The second law of thermodynamics constrains that the efficiency of heat engines, classical or quantum, cannot be greater than the universal Carnot efficiency. We discover another bound for the efficiency of a quantum Otto heat engine consisting of a harmonic oscillator. Dynamics of the engine is governed by the Lindblad equation for the density matrix, which is mapped to the Fokker-Planck equation for the quasi-probability distribution. Applying stochastic thermodynamics to the Fokker-Planck equation system, we obtain the $\hbar$-dependent quantum mechanical bound for the efficiency. It turns out that the bound is tighter than the Carnot efficiency. The engine achieves the bound in the low temperature limit where quantum effects dominate. Our work demonstrates that quantum nature could suppress the performance of heat engines in terms of efficiency bound, work and power output.

cond-mat.stat-mech↗

arXiv2017

Tricritical behavior of nonequilibrium Ising spins in fluctuating environments

We investigate the phase transitions in a coupled system of Ising spins and a fluctuating network. Each spin interacts with $q$ neighbors through links of the rewiring network. The Ising spins and the network are in thermal contact with the heat baths at temperatures $T_S$ and $T_L$, respectively, so that the whole system is driven out of equilibrium for $T_S \neq T_L$. The model is a generalization of the $q$-neighbor Ising model, which corresponds to the limiting case of $T_L=\infty$. Despite the mean field nature of the interaction, the $q$-neighbor Ising model was shown to display a discontinuous phase transition for $q\geq 4$. Setting up the rate equations for the magnetization and the energy density, we obtain the phase diagram in the $T_S$-$T_L$ parameter space. The phase diagram consists of a ferromagnetic phase and a paramagnetic phase. The two phases are separated by a continuous phase transition belonging to the mean field universality class or by a discontinuous phase transition with an intervening coexistence phase. The equilibrium system with $T_S=T_L$ falls into the former case while the $q$-neighbor Ising model falls into the latter case. At the tricritical point, the system exhibits the mean field tricritical behavior. Our model demonstrates a possibility that a continuous phase transition turns into a discontinuous transition by a nonequilibrium driving. Heat flow induced by the temperature difference between two heat baths is also studied.

cond-mat.stat-mech↗

arXiv2016

Efficiency at maximum power and efficiency fluctuations in a linear Brownian heat engine model

We investigate stochastic thermodynamics of a two-particles Langevin system. Each particle is in contact with a heat bath at different temperatures $T_1$ and $T_2~(<T_1)$, respectively. Particles are trapped by a harmonic potential and driven by a linear external force. The system can act as an autonomous heat engine performing work against the external driving force. Linearity of the system enables us to examine thermodynamic properties of the engine analytically. We find that the efficiency of the engine at maximum power $η_{MP}$ is given by $η_{MP} = 1-\sqrt{T_2/T_1}$. This universal form has been known as a characteristic of endoreversible heat engines. Our result extends the universal behavior of $η_{MP}$ to non-endoreversible engines. We also obtain the large deviation function of the probability distribution for the stochastic efficiency in the overdamped limit. The large deviation function takes the minimum value at mean efficiency $η= \barη$ and increases monotonically until it reaches plateaus when $η\leq η_L$ and $η\geq η_R$ with model dependent parameters $η_{R,L}$. It has been known for heat engines with a finite number of microscopic configurations with time-symmetric protocol that the probability of achieving the Carnot efficiency is minimum. Our result reveals that the least likeliness of the Carnot efficiency is not the generic property of heat engines.

cond-mat.stat-mech↗

arXiv2012

Fluctuation Relation for Heat

We present a fluctuation relation for heat dissipation in a nonequilibrium system. A nonequilibrium work is known to obey the fluctuation theorem in any time interval $t$. A heat, which differs from a work by an energy change, is shown to satisfy a modified fluctuation relation. Modification is brought by correlation between a heat and an energy change during nonequilibrium processes whose effect may not be negligible even in the $t\to\infty$ limit. The fluctuation relation is derived for overdamped Langevin equation systems, and tested in a linear diffusion system.

cond-mat.stat-mech↗