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<p id="d12971480e181">The second law of thermodynamics states that the total entropy
of an isolated system
is constant or increasing. This constrains the laws of physics, ruling out perpetual-motion
machines that convert heat to work without any side effect. At its heart, the second
law is a statement about entropy, yet entropy is an elusive concept: To date, it has
not been directly measured but is rather inferred from other quantities, such as the
integral of the specific heat over temperature. Here, by measuring the work required
to erase a fraction of a bit of information, we isolate directly the change in entropy,
showing that it is compatible with the functional form proposed by Shannon, demonstrating
its physical meaning in this context.
</p><p class="first" id="d12971480e184">Stochastic thermodynamics extends classical
thermodynamics to small systems in contact
with one or more heat baths. It can account for the effects of thermal fluctuations
and describe systems far from thermodynamic equilibrium. A basic assumption is that
the expression for Shannon entropy is the appropriate description for the entropy
of a nonequilibrium system in such a setting. Here we measure experimentally this
function in a system that is in local but not global equilibrium. Our system is a
micron-scale colloidal particle in water, in a virtual double-well potential created
by a feedback trap. We measure the work to erase a fraction of a bit of information
and show that it is bounded by the Shannon entropy for a two-state system. Further,
by measuring directly the reversibility of slow protocols, we can distinguish unambiguously
between protocols that can and cannot reach the expected thermodynamic bounds.
</p>

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C Jarzynski (1996)

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Udo Seifert (2012)

- Record: found
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- Article: found

D Collin, C Bustamante, I Tinoco … (2005)

Proceedings of the National Academy of Sciences

0027-8424

1091-6490

10.1073/pnas.1708689114

5651767

29073017

Self URI (article page):
http://www.pnas.org/lookup/doi/10.1073/pnas.1708689114