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IN RETROSPECT

60 years of Landauer’s principle

Nature Reviews Physics volume 3, page 770 (2021)Cite this article

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Maxwell’s demon — the imaginary being that can apparently defy the second law of thermodynamics — has been haunting physicists for the past 150 years. In 1929, Leo Szilard made a first breakthrough  in solving the Maxwell’s demon paradox by linking its actions to information. Then, sixty years ago, Rolf Landauer put the last nail in the demon’s coffin.

In 1961, Landauer showed that there is an absolute minimum thermodynamic cost associated with erasing one bit of information: kBTln2. Landauer observed that “logical irreversibility in turn implies physical irreversibility, and the latter is accompanied by dissipative effects”. Logical irreversibility means that an operation has multiple inputs, but a single output, a many-to-one map like an OR or AND. “Computation is inevitably done with real physical degrees of freedom, obeying the laws of physics,” Landauer later wrote in 1991. Thinking in terms of physical states, a logically irreversible operation will reduce the number of degrees of freedom and in so doing decrease entropy at the price of dissipating heat to the environment. So the reason why Maxwell’s demon cannot evade the second law of thermodynamics is not because of the measurement itself, but because the erasure of the information in the memory (to enable the next measurement to be recorded) is logically irreversible, as Charles Bennett pointed out in 1982.

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References

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  1. Nature Reviews Physics https://www.nature.com/natrevphys/

    Iulia Georgescu

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  1. Iulia Georgescu
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Correspondence to Iulia Georgescu.

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Georgescu, I. 60 years of Landauer’s principle. Nat Rev Phys 3, 770 (2021). https://doi.org/10.1038/s42254-021-00400-8

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