[extropy-chat] Macroscale entanglement

Damien Broderick thespike at satx.rr.com
Sat Apr 2 21:24:32 UTC 2005

Has this been mentioned here before?

"Crucial Role of Quantum Entanglement in Bulk Properties of Solids"


Authors: Caslav Brukner, Vlatko Vedral, Anton Zeilinger
Comments: 4 pages, 2 figures

We demonstrate that the magnetic susceptibility of strongly alternating 
antiferromagnetic spin-1/2 chains is an entanglement witness. Specifically, 
magnetic susceptibility of copper nitrate (CN) measured in 1963 (Berger et 
al., Phys. Rev. 132, 1057 (1963)) cannot be described without presence of 
entanglement. A detailed analysis of the spin correlations in CN as 
obtained from neutron scattering experiments (Xu et al., Phys. Rev. Lett. 
84, 4465 (2000)) provides microscopic support for this interpretation. We 
present a quantitative analysis resulting in the critical temperature of 5K 
in both, completely independent, experiments below which entanglement exists.

an extract:

"The usual arguments against seeing entanglement on macroscopic scales is 
that large objects contain large number of degrees of freedom that can 
interact with environment thus inducing decoherence that ultimately lead to 
a quantum-to-classical transition. Remarkably, macroscopic entanglement in 
solids, that is, entanglement in the thermodynamical limit of infinite 
large number of constituents of solids, was theoretically predicted to 
exist even at moderately high temperatures [11, 12, 13, 14, 15]. Recently, 
it was demonstrated that entanglement can even affect macroscopic 
thermodynamical properties of solids [13, 16, 17, 18, 19, 20], such as its 
magnetic susceptibility or heat capacity, albeit at very low temperature 
(few milikelvin) and only for a special material system - the insulating 
magnetic salt LiHoxY1Å|xF4 [20]. This extraordinary result shows that 
entanglement can have significant macroscopic effects. Here ... we analyse 
experimental results of neutron scattering measurement of CN obtained in 
2000 [2] and show that they provide, for the first time, a direct 
experimental demonstration of macroscopic entanglement in solids."

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