My comment: The article explains that the boost to energy storage rapidly
descreases as the number of entangled particles in a system increases, but
what counts as a system? If a nucleus or an atom is a system of small
number of particles perhaps they are capable of storing more energy under
the right circumstances than was previously thought possible.

Synopsis: Putting Quantum Systems to Work

October 22, 2015

Quantum effects such as coherence and entanglement increase a system’s
ability to store energy.

Engines in cars and airplanes are thermal machines that are capable of
doing work. Scientists have recently demonstrated the existence of
so-called quantum thermal machines, tiny versions of engines and
refrigerators consisting of only a few quantum-mechanical units. When
calculating how much work such microscopic systems can accomplish, quantum
effects such as coherence and entanglement must be taken into account. Now,
researchers have shown that systems in which quantum effects are pronounced
can store more energy than systems that are purely classical.

Antonio Acín at the Institute of Photonic Sciences, Spain, and co-workers
studied how isolated ensembles of nnquantum particles could optimally store
usable energy. The researchers imagined a set of correlated particles at
the same temperature. These particles are useless individually—one cannot,
for example, run a thermal machine without a temperature gradient—but
correlations among them can be exploited for extracting work. Acín and his
colleagues theoretically demonstrated that entangled states can store more
energy than nonentangled states. However, this advantage vanishes as the
number of particles increases. For example, small ensembles of entangled
particles (n=2n=2) stored 100% more energy than purely classical particles;
for n=50n=50 the quantum advantage reduced to only 2%. This finding
supports the hypothesis that thermodynamics on a macroscopic scale is
insensitive to the underlying microscopic mechanics. The team now plans to
study how different kinds of entanglement affect energy storage.

This research is published in Physical Review X.

–Katherine Kornei



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