How to measure macroscopic entanglement

Macroscopic entanglement

If macroscopic objects become entangled, how can we tell? The usual way to measure entanglement on the microscopic level is to carry out a Bell experiment, in which the quantum states of two particles are measured.  If the results of these measurements fall within certain bounds, the particles are considered to be entangled.

These kinds of quantum measurements are not possible with macroscopic bodies but recent work suggests there may be other ways to spot entanglement. Vlatko Vedral  at the University of Leeds and pals outline one of these on the arXiv.

Their idea is based on the third law of thermodynamics which states that the entropy at absolute zero is dependent only on the degeneracy of the ground state. This in turn implies that the specific heat capacity of a material must asymptotically approach zero as the temperature gets closer to absolute zero. But if particles within the material were entangled, Vedral and pals say this would not be the case.

That kind of thinking suggests a straightforward experiment: simply measure the heat capacity of a material as its temperature drops to zero. If it doesn’t asymptotically approach zero, then you’ve got some entanglement on your hands.

Best of all, measuring heat capacity is standard technique so there’s no reason this can’t be done pronto.

Ref: Heat Capacity as A Witness of Entanglement

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