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The Physics of Maxwell's demon and information
Maxwell's demon was born in 1867 and still thrives in modern physics. He
plays important roles in clarifying the connections between two theories:
thermodynamics and information. Here, we present the history of the demon and a
variety of interesting consequences of the second law of thermodynamics, mainly
in quantum mechanics, but also in the theory of gravity. We also highlight some
of the recent work that explores the role of information, illuminated by
Maxwell's demon, in the arena of quantum information theory.Comment: 24 pages, 13 figures. v2: some refs added, figs improve
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Burnt to memory: Data extraction from heat damaged mobile phones
Data is retained in SIM card devices that are subjected to temperatures which exceed those likely to be experienced in house fires. In some cases the data is retrievable by rebuilding severed connections; however, in the majority of instances, chips will suffer additional damage to the top surface or circuitry, or experience some mechanical damage. In these cases, although the data is retained in the memory, it cannot be read by conventional methods, and an alternative technique, such as direct probing of the stored charge, needs to be employed to access the retained data
Curry-style type Isomorphisms and Game Semantics
Curry-style system F, ie. system F with no explicit types in terms, can be
seen as a core presentation of polymorphism from the point of view of
programming languages. This paper gives a characterisation of type isomorphisms
for this language, by using a game model whose intuitions come both from the
syntax and from the game semantics universe. The model is composed of: an
untyped part to interpret terms, a notion of game to interpret types, and a
typed part to express the fact that an untyped strategy plays on a game. By
analysing isomorphisms in the model, we prove that the equational system
corresponding to type isomorphisms for Curry-style system F is the extension of
the equational system for Church-style isomorphisms with a new, non-trivial
equation: forall X.A = A[forall Y.Y/X] if X appears only positively in A.Comment: Accept\'e \`a Mathematical Structures for Computer Science, Special
Issue on Type Isomorphism
DEMONIC programming: a computational language for single-particle equilibrium thermodynamics, and its formal semantics
Maxwell's Demon, 'a being whose faculties are so sharpened that he can follow
every molecule in its course', has been the centre of much debate about its
abilities to violate the second law of thermodynamics. Landauer's hypothesis,
that the Demon must erase its memory and incur a thermodynamic cost, has become
the standard response to Maxwell's dilemma, and its implications for the
thermodynamics of computation reach into many areas of quantum and classical
computing. It remains, however, still a hypothesis. Debate has often centred
around simple toy models of a single particle in a box. Despite their
simplicity, the ability of these systems to accurately represent thermodynamics
(specifically to satisfy the second law) and whether or not they display
Landauer Erasure, has been a matter of ongoing argument. The recent
Norton-Ladyman controversy is one such example.
In this paper we introduce a programming language to describe these simple
thermodynamic processes, and give a formal operational semantics and program
logic as a basis for formal reasoning about thermodynamic systems. We formalise
the basic single-particle operations as statements in the language, and then
show that the second law must be satisfied by any composition of these basic
operations. This is done by finding a computational invariant of the system. We
show, furthermore, that this invariant requires an erasure cost to exist within
the system, equal to kTln2 for a bit of information: Landauer Erasure becomes a
theorem of the formal system. The Norton-Ladyman controversy can therefore be
resolved in a rigorous fashion, and moreover the formalism we introduce gives a
set of reasoning tools for further analysis of Landauer erasure, which are
provably consistent with the second law of thermodynamics.Comment: In Proceedings QPL 2015, arXiv:1511.01181. Dominic Horsman published
previously as Clare Horsma
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