Entangled Quantum States of Magnetic Dipoles

TL;DR

This paper demonstrates that entanglement and level splitting in insulating magnetic salts lead to a power-law magnetic response, highlighting the fundamental role of quantum mechanics in simple magnetic systems.

Contribution

It shows that quantum entanglement and level splitting are essential for understanding power-law magnetic behavior in insulating salts, a novel insight into quantum effects in such materials.

Findings

Power-law magnetization observed in insulating salts.

Quantum entanglement influences magnetic properties at small tunnelling.

Numerical simulations confirm quantum mechanics' role in the phenomena.

Abstract

Free magnetic moments usually manifest themselves in Curie Laws, where weak external magnetic fields produce magnetizations diverging as the reciprocal 1/T of the temperature. for a variety of materials that do not disply static magnetism, including doped semiconductors and certain rare earth intermetallics, the 1/T law is changed to a power law T^-a with a<1. We report here that a considerably simpler material, namely an insulating magneticsalt can also display such a power law, and show via comparison to specific heat data and numerical simulations that quantum mechanics is crucial for its formation. Two quantum mechanical phenomena are needed, namely level splitting - which affects the spectrum of excited states - and entanglement - where the wavefunction of a system with several degrees of freedom cannot be written as a product of wavefunctions for each degree of freedom. Entanglement effects become visible for remarkably small tunnelling terms, and are turned on well before tunnelling has visible effects on the spectrum. Our work is significant because it illustrates that entanglement is at the very heart of a very simple experimental observation for an insulating quantum spin system.