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arXiv 2104.12072cond-mat.stat-mech
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记忆的时间对称性决定热力学效率

Time Symmetries of Memory Determine Thermodynamic Efficiency

Alexander B. Boyd, Paul M. Riechers, Gregory W. Wimsatt, James P. Crutchfield, Mile Gu

摘要:

虽然兰道尔原理为计算所需的工作设定了下限,但该工作对于有效计算是可恢复的。然而,实用的物理计算机,例如现代数字计算机或生化系统,受到限制,使它们效率低下--不可逆转地消耗大量能量。最近的研究结果表明,在这样的系统中的耗散是有界的嵌入式计算的非互易性。我们调查的后果,这种绑定不同类型的内存,显示不同的内存设备更适合不同的计算。这种对应关系来自记忆的时间反转对称性,这取决于信息是以位置方式存储还是以磁性方式存储。这表明,记忆装置的时间对称性在决定能量学方面起着重要作用。时间对称性的能量后果在几乎确定性的计算中特别明显,其中计算成本偏离误差率的负对数。我们将这种发散的系数确定为耗散发散。我们发现,耗散发散可能是零的计算时,在一种类型的存储器中实现,而它的最大时,与另一种实现。考虑到存储器类型的灵活性,耗散发散在计算的平均状态压缩下有界。此外,我们展示了如何显式地构建内存,以实现这种最小的耗散。因此,我们发现逻辑可逆计算确实是高效的,但逻辑不可逆性的代价比以前预期的要高得多。

英文摘要:

While Landauer's Principle sets a lower bound for the work required for a computation, that work is recoverable for efficient computations. However, practical physical computers, such as modern digital computers or biochemical systems, are subject to constraints that make them inefficient -- irreversibly dissipating significant energy. Recent results show that the dissipation in such systems is bounded by the nonreciprocity of the embedded computation. We investigate the consequences of this bound for different types of memory, showing that different memory devices are better suited for different computations. This correspondence comes from the time-reversal symmetries of the memory, which depend on whether information is stored positionally or magnetically. This establishes that the time symmetries of the memory device play an essential roll in determining energetics. The energetic consequences of time symmetries are particularly pronounced in nearly deterministic computations, where the cost of computing diverges as minus log of the error rate. We identify the coefficient of that divergence as the dissipation divergence. We find that the dissipation divergence may be zero for a computation when implemented in one type of memory while it's maximal when implemented with another. Given flexibility in the type of memory, the dissipation divergence is bounded below by the average state compression of the computation. Moreover, we show how to explicitly construct the memory to achieve this minimal dissipation. As a result, we find that logically reversible computations are indeed thermodynamically efficient, but logical irreversibility comes at a much higher cost than previously anticipated.

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