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arXiv 1906.09369cond-mat.stat-mech
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随机协议下热力学量和功涨落定理的收敛性

Convergence of thermodynamic quantities and work fluctuation theorems in presence of random protocols

Rahul Marathe, Sourabh Lahiri

摘要:

近年来,对于任意偏离平衡点的系统,人们发现了许多结果,即涨落定理。其中许多关系已经过实验测试。所考虑的系统通常是由一个外部的时间依赖的参数,遵循一个特定的{\it协议}驱动的平衡。为了找到统计相关的结果,需要对同一实验进行多次迭代。由于系统是微观的,波动占主导地位。研究相关热力学量与实现次数的收敛性也很重要,因为它给出了一个需要执行的迭代次数的粗略估计。在每次迭代中,协议遵循预定的{\it相同/固定}形式。然而,协议本身可能易于波动。在这项工作中,我们有兴趣在一个简单的非平衡系统,即布朗粒子被困在一个谐波势。然后根据协议拖动陷阱的中心。不过,我们取消了固定协议的条件。在我们的例子中,每个实现中的协议是不同的。我们认为协议的参数之一是随机变量,从一些已知的分布。我们研究系统的分析以及数值。我们具体研究了平均功和自由能差随实现次数的收敛性。有趣的是,在几种情况下,与固定的协议结果相比,协议中的随机性似乎不会影响收敛。我们研究对称函数。对双势阱中的布朗粒子进行了数值研究。我们相信我们的结果可以得到实验验证。

英文摘要:

Recently many results namely the Fluctuation theorems (FT), have been discovered for systems arbitrarily away from equilibrium. Many of these relations have been experimentally tested. The system under consideration is usually driven out of equilibrium by an external time-dependent parameter which follows a particular {\it protocol}. One needs to perform several iterations of the same experiment in order to find statistically relevant results. Since the systems are microscopic, fluctuations dominate. Studying the convergence of relevant thermodynamics quantities with number of realizations is also important as it gives a rough estimate of number of iterations one needs to perform. In each iteration the protocol follows a predetermined {\it identical/fixed} form. However, the protocol itself may be prone to fluctuations. In this work we are interested in looking at a simple non-equilibrium system namely a Brownian particle trapped in a harmonic potential. The center of the trap is then dragged according to a protocol. We however lift the condition of fixed protocol. In our case the protocol in each realization is different. We consider one of the parameters of the protocol as a random variable, chosen from some known distribution. We study the systems analytically as well as numerically. We specifically study the convergence of the average work and free energy difference with number of realizations. Interestingly, in several cases, randomness in the protocol does not seem to affect the convergence when compared to fixed protocol results. We study symmetry functions. A Brownian particle in a double well potential is also studied numerically. We believe that our results can be experimentally verified.

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